the following five criteria have been successfully applied sequentially to optimize selection for a bioimaging model : specific embodiments can be created from lines of mice transgenically manipulated with either the 5k or 10k vectors according to the following process . results described below are from one such selection process that started with 35 transgenic lines . fig5 graphically summarizes this process . from generated transgenic lines , one selects lines in which in vivo whole animal , e . g ., mouse , imaging at the peak of postnatal myelination ( e . g ., 3 - 5 weeks g1 mice ) shows cns specific imaging . six out of the selected 35 lines were advanced to the next selection stage . next lines in which ex vivo imaging confirms luciferase transgene expression mainly in the white matter region of brain were selected . five of the 6 lines from step 1 were advanced to the next stage . then lines in which the luciferase image intensity highly correlated with changes in demyelination and remyelination induced in , in this example , a cuprizone demyelination model was selected . three of the 5 lines from step 2 were advanced to the next stage . next lines which showed clear histological demyelination in the above cuprizone model were selected . two of the 3 from step 3 were selected as preferred lines . as a final proof of concept we selected one line , in which the efficacy of a003398711 , a pparδ selective agonist , was optimally detectable in the bioimaging model . an exemplary line designated line 171 ( b6c3 strain , heterozygous ) was selected using the above five criteria and used as a preferred model . amore detailed description of this process is described in examples below . as used herein unless indicated otherwise terms have meanings as generally used in the science parlance which may differ from colloquial common usage . a gene should be interpreted broadly to include transcribed as well as non - transcribed regions . compound is interpreted broadly to include chemical compounds , e . g ., organic chemical entities , biologic compounds , e . g ., antibodies and antigen recognizing fragments and constructs , nucleic acids , e . g ., rnai , etc . transgenic mice that expressed firefly luciferase were generated . in these animals , the reporter gene , luciferase , was linked to an mbp promoter , thus driving expression of luciferase in cells of white matter ( myelinated ) region e . g ., of the cns when mbp expression was turned on . systemic injection of the substrate luciferin ( iv , ip , sc ) generates a detectable and quantifiable light signal from a living mouse &# 39 ; s head . by applying a cuprizone demyelination model to select mbp - luci lines and injecting these animals with luciferin repetitively , one can serially monitor and quantify demyelination and remyelination through noninvasive bio - luminescence imaging longitudinally , for example , over a two month period . this model successfully quantitatively monitored a cuprizone - induced demyelination and a pparδ compound - induced remyelination . advances in detector technology have led to substantial improvement in sensitivity and image quality . photons are now detected by specialized charge coupled device ( ccd ) cameras that convert photons into electrons as photons strike silicon wafers . ccd cameras spatially encode the intensity of incident photons into electrical charge patterns which are then processed to generate an image . the noise is reduced by super - cooling the ccd camera and mounting the camera in a light - tight box . these cameras are generally controlled by a computer during image acquisition and analysis . second - generation camera systems that are much smaller and therefore can be accommodated on laboratory bench tops made the technology feasible and practical for day - to - day experimentation . xenogene company has commercialized bioimaging technology . of the imaging modalities available , optical techniques based on bioluminescence or fluorescence have emerged as the most accessible and easily manipulated . bioluminescent imaging ( bli ) is characterized by remarkable sensitivity , as background luminescence ( noise ) from tissues is exceedingly low . to date , bli has been successfully used to monitor biological processes such as cell movement , tumor progression , gene expression , and viral infection in a variety of animal models . firefly luciferase requires intracellular cofactors such as atp for activity . this limited its use to cells that were genetically engineered to express the enzyme . as a result , many useful imaging applications , such as , monitoring distribution of circulating factors , detecting extracellular antigen expression , and labeling endogenous cells are not amenable to firefly luciferase imaging . an additional drawback of firefly luciferase is the lack of alternative substrates for detecting it in fixed cells and tissue samples . this has made it difficult to correlate in vivo imaging with microscopic analysis . sensitivity of detecting light emitted from internal organs depends on several factors , including the level of luciferase expression , the depth of labeled cells within the body ( the distance that the photons must travel through tissue ), and the sensitivity of the detection system . the monitoring of expression of luciferase reporter expression cassettes using non - invasive whole animal imaging has been described ( contag , c ., u . s . pat . no . 5 , 650 , 135 , jul . 22 , 1997 , herein incorporated by reference ; contag , p ., et al , nature medicine 4 ( 2 ): 245 - 247 , 1998 ; contag , c ., et al , osa tops on biomedical optical spectroscopy and diagnostics 3 : 220 - 224 , 1996 ; contag , c . h ., photochemistry and photobiology 66 ( 4 ): 523 - 531 , 1997 ; contag , c . h ., al , molecular microbiology 18 ( 4 ): 593 - 603 , 1995 ). such imaging typically uses at least one photo detector device element , for example , a charge - coupled device ( ccd ) camera . myelin basic proteins ( mbps ) are a family of polypeptides that are predominantly expressed in the nervous system where they play a major role in myelination . expression of mbp , for example in differentiating oligodendrocytes is mainly regulated at the transcriptional level . in the journal of neuroscience , farhadi et al . described a new regulatory combinatorial element that temporally controls expression of the mbp gene . farhadi et al showed that glia use different combinations of regulatory sequences to control expression of mbp at various stages during and after the onset of myelination . myelin basic protein ( mbp ) is required for normal myelin compaction and is implicated in both experimental and human demyelinating diseases , like ms . in order to further advance understanding of myelin biology and test myelin enhancement compound in living animals . the present invention used the mbp promoter qualities and the most sensitive luciferase reporter technology to generate the present mbp - luci model . the model now permits sensitive in vivo measurements of myelin gene transcriptional responses in living animals . the 129svev bac library ( cell & amp ; molecular technologies ) was screened with a probe located in mbp promoter m3 region . the probe was 507 bps and was generated with primer pair ( 5 ′- actccttaccacacttcttgcagg - 3 ′ 5 ′- tctattgggtgatgtgtgccatc - 3 ). ( seq id nos . 1 and 2 ) mbp bac was confirmed with the same probe through southern analysis ( 7 . 6k fragment digested using ecori and / or 13 . 8k digested with bamhi ). “ long ” mbp promoter containing m1 through m4 ( 10k ) amplified by high fidelity pcr with primer set ( mbp - l - sp2 5 - gggggatccacctgggacgtagcttttgctg and mbp - ap1 5 - ggggtttaaactccggaagctgctgtggg ) ( seq id nos . 3 and 4 ) was cloned into invitrogen &# 39 ; s xl - topo vector to produce an intermediate vector ( topo mbp10k vector ). then mbp 10k promoter ( bamhi and pmei fragment ) was inserted into pgl3 hygro neo vector ( bglii and pmei sites ). the final 10k vector was called pgl3 - hygro - long mbp - luci ( see e . g ., fig4 ). “ short ” mbp promoter containing m1 to m3 ( 5k ) amplified by high fidelity pcr with primer set ( mbp - s - sp2 5 - gggggatccatccctggatgcctcagaagag and mbp - ap1 5 - ggggtttaaactccggaagctgctgtggg ) ( seq id nos . 5 and 6 ) was cloned into invitrogen &# 39 ; s p2 . 1 - top ( ) vector to produce an intermediate vector ( topo mbp5k vector ). then mbp 5k promoter ( bamhi and pmei fragment ) was inserted into pgl3 hygro neo vector ( bglii and pmei sites ). the final 5k vector was called pgl3 - hygro - short mbp - luci . ( see e . g ., fig3 ). dna sequences from both pgl3 - hygo - mbp plasmids confirmed m1 , m2 , m3 and m4 reading . in addition , transient transfection of these plasmids into 293t cells gave detectable luciferase activity . all animal work was performed in accordance with federal guidelines . three different strains of mice ( fvb , b6c3 and c57 bl / 6 ) have been used . imaging was performed under inhalation anesthesia with isoflurane ( baxter , deerfield , ill . ); mice were observed until fully recovered . transgenic mice were generated as follows : either pgl3 - hygro - mbp10k - luci or pgl3 - hygro - mbp5k - luci plasmid was digested with noti and bamhi enzymes . a fragment containing the mbp promoter , luciferase and polyadenylation signal was then gel purified . transgenic mice were generated by standard pronuclear injection into fvb , b6c3 or c57bl / 6 embryos . in brief , during pronuclear microinjection , the mbp - luci gene cassette dna is introduced directly into the mouse egg just after fertilization . using a fine needle , the dna is injected into the large male pronucleus , which is derived from the sperm . the dna tends to integrate as many tandem arranged copies at a random position in the genome , often after one or two cell divisions have occurred . therefore , the resulting mouse is only partially transgenic . if the transgenic cells contribute to the germ line , then some transgenic eggs or sperm will be produced and the next generation of mice will be fully transgenic . transgenic founders and their tg + g1 offspring were identified by polymerase chain reaction ( pcr ) of tail biopsy dna using primers specific for the firefly luciferase gene ( pcr primers : 5 ′ gaaatgtccgttcggttggcagaagc - 3 ′, and 5 ′ ccaaaaccgtgatggaatggaacaaca - 3 ′) ( seq id nos . 7 and 8 ) offspring of 25 positive founders were imaged using the in vivo imaging system ( ivis 100 ; xenogen , alameda , calif . ), and six transgenic lines were identified with brain imaging signal ( two fvb lines and four b6c3hf1 lines ). since no brain imaging positive c57 bl / 6 founder was generated in this exercise , one fvb line was backcrossed to c57bl / 6 mice to achieve a c57 bl6 strain . b6c3 line 171 mice were subsequently propagated by intercrossing to achieve homozygous transgenic mating pairs . b6c3f1 line 171 was also backcrossed to c57 albino line . in vivo bioluminescence imaging was used to screen select mbp - luci lines . g1 mice were anesthetized with isoflurane , and a dose of 250 mg / kg luciferin was injected through the tail vein or s . c . eight minutes after the luciferin injection , mice were imaged . six lines were identified with brain imaging signal ( fig5 , two fvb strain lines : 58 and 121 and four b6c3 strain line : 12 , 23 , 85 and 171 ). except line 58 the other five lines showed ex vivo luciferase imaging signal at white matter region of brain . table 1 shows data from 35 transgenic dna positive founder mice identified shortly after birth through tail biopsies pcr genotype . fifteen dna positive founder lines generated mbp - 10k luci and twenty dna positive founder lines generated mbp - 5k luci . throughout this application , the transgene and the transgenic mouse are abbreviated as mbp - luci . ex vivo luciferase imaging of isolated organs was performed immediately after euthanasia of the animals by co 2 , 10 min after sc injection of luciferin ( 250 mg / kg ). dissected organs were placed on a black paper covered with plastic sheet and imaged by ivis ; strong bioluminescent signals remained detectable within 20 to 30 min after dissection . image analysis and bioluminescent quantification was performed using living image software ( xenogen corp .). tissue samples were placed in lysis buffer with inhibitors ( passive lysis buffer [ promega ] and complete mini protease inhibitor cocktail [ roche , indianapolis , ind .]). the tissues were homogenized using a tissue homogenizer . tissues were further homogenized by brief sonication . tissue homogenates were centrifuged and clarified lysates were used for luminometer assays . for the luminometer assays , luciferase assay substrate ( luciferase assay system , promega ) was prepared as indicated by the manufacturer . tissue homogenates ( 20 μl ) and substrate ( 100 μl ) were mixed and measurements were taken in a luminometer . background luminescence readings were obtained and the background readings were subtracted from the luminescent data . protein concentrations were determined using the bca protein assay kit ( pierce , rockford , ill .) following the manufacturer &# 39 ; s protocols . the luminescence for each of the protein lysates was calculated as arbitrary units of light per microgram of protein . administration of cuprizone to mice over a period of four weeks resulted in extensive demyelination of the corpus callosum . cuprizone - induced demyelination is associated with significant microgliosis and macrophage recruitment ( bakker and ludwin , j neurol sci 78 : 125 - 37 , 1987 ; hiremath et al ., j neuroimmunol 92 : 38 - 49 , 1998 ; mcmahon et al ., j neuroimmunol 130 : 32 - 45 , 2002 ), but does have minimal t - cell responses ( matsushima and morell , brain pathol 11 : 107 - 16 , 2001 ). the consistent and predictable nature of the site of myelin injury in this model results in easily quantifiable change in corpus callosum myelination . these changes might result from the de - novo myelination by oligodendrocytes progenitor cells , however , prevention of terminal demyelination by immunomodulatory mechanisms ( pluchino et al ., nature 436 : 266 - 71 , 2005 ), might be a viable alternative explanation . as outlined above , multiple strains of mbp - luciferase transgenic ( mbp - luci tg ) mice were evaluated for in vivo assessment of cuprizone - induced demyelination / remyelination events . expression of the myelin basic protein ( mbp ) promoter driven luciferase ( luci ) allowed in vivo bioimaging quantification of myelin in the brain of a transgenic ( tg ) mammal expressing the mbp protein . the model , for example , can use wild type c57 / bl6 mice fed 0 . 2 % cuprizone in their diet . previous models required terminal sacrifice at multiple time points for assessment of myelin after various compound treatments . since multiple animals were required inter - animal variability was a factor requiring additional subjects ( higher ns ) to achieve significance . the mbp 5k - luci line 171 ( b6c3 ) mice showed prominent and significant demyelination in the corpus callosum of the brain as assessed by luxol fast blue ( lfb ) histochemical staining on 0 . 2 % cuprizone in the diet for four weeks . this demyelination was further correlated with a drop in the bioimaging in vivo luciferase signal . the fvb strain , however , of mbp 10 - luci line 121 mice has not shown comparable demyelination . additional studies were conducted in the fvb mouse in an attempt to identify a potential regimen of varying amounts of cuprizone in the diet and varying time periods of cuprizone treatment that might result in significant demyelination . the results showed only moderate amounts demyelination by lfb assessments in the corpus callosum . accordingly , line 171 was preferentially developed . transgenic mice have frequently been created using the fvb / nj ( fvb ) strain due to its high fecundity . fvb strain mice are also extensively used for transgenic bioimaging model due to their white relatively non - light absorbing fur color . removal of hair , such as by shaving can also be used to reduce signal loss due to absorbance or scattering by hair or fur in fvb or other strains . because interstrain differences were observed for the cuprizone model , selection of strain may affect results . selection of an optimal strain for a particular purpose is considered routine optimization dependent , for example , on selected assay and equipment . however , creating the transgenic mammal is not considered a limiting factor ; rather the susceptibility of the particular strain and transgenic line to , e . g ., a myelination affecting condition is used as a selection criterion for improving data quality . depending on the myelination / demyelination event chosen , a choice of strain or genetic background may affect results . it is believed that specific demyelination models may work better in particular strains . such choice of model and strain would be considered routine as part of assay development . although cuprizone feeding is an excellent model in which to study demyelination and remyelination , there are strong genetic factors in this model apparently observed in strain differences . the mice from the fvb strain were chosen in part due to their white fur color . fvb mice offer a system suitable for most transgenic experiments and subsequent genetic analyses . for example , the inbred fvb strain is characterized by vigorous reproductive performance and consistently large litters . this reduces cost and effort in producing large populations . moreover , fertilized fvb eggs contain large and prominent pronuclei , which facilitate microinjection of dna . in addition , the fvb strain has albino fur color and makes it a first choice for bioimaging . these features make the fvb strain advantageous to use for research with transgenic bioimaging models . however , other strains can be used when they exhibit desired characteristics . fvb strain mice are very sensitive to 0 . 2 % cuprizone in term of weight loss . two to three times normal food / transgel supplement per week is required to avoid severe weight loss and toxicity . furthermore the inventors &# 39 ; experience showed that fvb strain mice show minimal histological demyelination from various cuprizone feeding regimens . accordingly , the mbp 10k - luci line 121 ( fvb strain ) was backcrossed to c57 bi / 6 to facilitate future validation and application . the b6c3 hybrid strain can be developed by intercrossing c57 bl / 6ntac female mice to c3h / hentac male mice from taconic us &# 39 ; s commercial colonies . it has black or agouti fur color . the b6c3 will be heterozygous at the loci where the c57bl / 6 and the c3h differ , and homozygous at the loci where they are the same . b6c3 / tac mice showed clear histological demyelination . specifically demyelination in the bioimaging model line 171 mbp 5k - luci homozygous mice was just mildly less extensive with mild variability as compared to wild type c57bl6 . demyelination in line 171 mbp 5k - luci heterozygous mice was considerably less severe , more localized and more variable as compared to c57bl6 & amp ; line 171 mbp 5k - luci homozygous mice . these results illustrate that the mbp - luci model can be useful in determining susceptibility of an individual , strain or species to a myelination affecting event . furthermore , the mbp - luci construct does not lose usefulness even in black furred mammals . effect of cuprizone on cortical demyelination in balb / cj mice was also investigated . in these mice , cortical demyelination was only partial . moreover , cortical microglia accumulation was markedly increased in balb / cj mice , whereas microglia were absent in the cortex of c57bl / 6 mice . thus strain differences may be useful to support different research goals . c57bl / 6 genetic background animals are suitable for many cuprizone model studies and have been used in several laboratories over the past 3 decades . when 8 week old c57bl / 6 mice are fed 0 . 2 % cuprizone in the diet , mature olidgodendroglia are specifically insulted ( cannot fulfill the metabolic demand of support of vast amounts of myelin ) and go through apoptosis . this event is closely followed by recruitment of microglia and phagocytosis of myelin . studies of myelin gene expression , coordinated with morphological studies , indicate that even in the face of continued metabolic challenge , oligodendroglial progenitor cells proliferate and invade demyelinated areas . if the cuprizone challenge is terminated , an almost complete remyelination takes place within a matter of weeks . intercellular communication between different cell types by soluble factors may be inferred . the method and model of the invention may there be useful for studying intercellular communication events , e . g ., determining whether a putative factor is involved in recruitment for myelination , screening for compounds that facilitate recruitment , and screening for compounds inhibiting recruitment . furthermore , the reproducibility of the mbp - luci model indicates that it may permit testing of manipulations ( e . g . available knockouts or transgenics on the common genetic background , or interfering rna or pharmacological treatments ) which may accelerate or repress the process of demyelination and or remyelination . although the line 171 ( b6c3h strain , heterozygote ) has been shown to work in myelination / demyelination studies , the model could be further improved by ( 1 ) breeding to homozygocity to increase bioimaging signal intensity and reduce model production and genotype cost ; ( 2 ) breeding to an albino strain such as the c57 strain to reduce imaging signal attenuation with white fur and to reduce skin reaction after multiple nair shavings ; ( 3 ) breeding the line 121 to the c57 bl / 6 strain to match the in - house developed cns cuprizone model strain . we have now demonstrated that line 171 homozygous showed an over 2 - fold bioimaging window than line 171 heterozygous line ( two copies of reporter gene cassette per cell ). other experiments also demonstrated albino c57 responded to cuprizone model . bioluminescence was measured noninvasively using the ivis imaging system ( xenogen corp ., alameda , calif .). the images were taken 10 min after i . p . injection of luciferin ( 250 mg / kg - 1 ; xenogene corp .) as a 60 - s acquisition , binning 10 , unless otherwise stated in the text . during image acquisition , mice were sedated continuously via inhalation of ˜ 2 % isoflurane ( abbott laboratories ltd ., kent , united kingdom ). the ivis ® imaging system 100 ( xenogene ) was used to collect the data proving this invention . xenogen &# 39 ; s sensitive ivis ® imaging system 100 series offers an adjustable rectangular field of view of , for example , 10 - 25 cm , allowing 5 mice or 2 large rats to be imaged , as well as one standard microtiter plate . the system features a 25 mm ( 1 . 0 inch ) square back - thinned , back - illuminated ccd ( charged couple device ) camera , which is cryogenically cooled to about − 90 to − 120 ° c ., for example , − 105 ° c . via a closed cycle refrigeration system ( without liquid nitrogen ) to minimize electronic background and maximize sensitivity . the ccd camera is designed for high - efficiency photon detection , particularly in the red region of the spectrum . it can detect very small numbers of photons , as well as operate as a traditional camera ; displaying images in that wide signal range is a function of xenogen &# 39 ; s living image ® software . there is a six - position filter wheel to isolate different bandwidths . this spectral information can reveal more about the depth and distribution of the source cells . the ccd is cooled and the electronic readout is optimized so that the data gathered to create the real - time in vivo images have extremely low noise . an extremely light - tight , low background imaging chamber allows the ivis ® imaging system 100 series to be used in standard lab lighting environments . the sample shelf in the imaging chamber moves up and down to adjust the field of view . researchers can view an entire animal , or focus on one portion for added detail . the shelf is heated to enhance the well - being of the anesthetized , e . g ., mice or rats . the system includes animal handling features such as a heated sample shelf , gas anesthesia connections , and a full gas anesthesia option from xenogen — the xgi - 8 gas anesthesia system , shown on the website page . a larger imaging chamber could allow use of larger test subjects or a larger number of test subjects d - luciferin firefly potassium salt 1 . 0 g / vial ( e . g ., xenogen xr - 1001 or biosynth l - 8220 ). dpbs without mg 2 + and ca 2 + . bottle top filter 0 . 2 um . a stock solution of luciferin at 25 mg / ml in dpbs was prepared and filter sterilized through a 0 . 2 um filter . 5 ml aliquots were store at − 20 ° c . injection dose was 10 ul / g of body weight . each mouse was targeted to receive 250 mg luciferin / kg body weight ( e . g . for 20 g mouse , inject 200 ul to deliver 2 . 0 mg of luciferin ). luciferin was injected sc , or ip , or iv several minutes before imaging . a luciferin kinetic study was optionally performed for each animal model to determine peak signal window . as described above , mice were injected with 250 mg / kg d - luciferin through sc , ip or iv . after 5 ( intravenous ) or 8 ( intraperitoneal or sc ) minutes , mice were imaged using the ivis 100 ( xenogen ) for 16 minutes ( 60 seconds imaging and 60 seconds interval for 8 pictures at bin size 8 ). to quantify bioluminescence , identical circular regions of interest were positioned to encircle each mouse head region , and the imaging signal was quantitated as average radiance ( photons / s / cm2 / steridian ) using livingimage software ( version 2 . 5 , xenogen ). the head region of interest was kept constant in area and positioning within all experiments . data were normalized to bioluminescence at the initiation of treatment for each animal . for statistical analysis , everstat v5 and sigma stat statistics software packages were used . the average of imaging in the group was taken as the mean , and se for all groups were calculated . when comparing two group means , a paired wilcoxon test or unpaired wilcoxon test was conducted . two - tailed values of p & lt ; 0 . 05 were considered statistically significant . “ long ” promoter is about 10 kb containing m1 , m2 , m3 , m4 and “ short ” promoter is about 5 kb containing m1 , m2 and m3 . these were cloned with a high fidelity pcr method from a mouse bacterial artificial chromosome ( bac ) containing a mbp gene . then each promoter fragment was cloned into a vector , for example into the into the poly link site of a pgl3 - hygro vector ( fig1 and fig2 ). the plasmids were restricted with not i and bamhi to release the mbp - luci transgenic expression cassettes ( fig3 ) that were used to generate transgenic mice in the fvb / tac and in b6c3 / tac strains using standard pronuclear microinjection techniques . general strategies for generating transgenic ( tg ) animals are well known in the art , for example as described in pinkert , c . a . ( ed .) 1994 . transgenic animal technology : a laboratory handbook . academic press , inc ., san diego , calif . ; monastersky g . m . and robl , j . m . ( ed .) ( 1995 ) strategies in transgenic animal science . asm press . washington d . c .). mbp10k - luci transgenic line 121 ( fvb strain ) with observed white matter region luciferase expression was used in the cuprizone model for validation experiments . as shown in the fig1 , the first cuprizone study , was conducted with repeated luci imaging at wk1 , 2 and 4 weeks ( on 0 . 2 % cuprizone diet ) followed by a return to normal cuprizone absent food with imaging at 5 , 6 and 7 weeks ( re wk1 through wk3 ). as shown in the figure , luciferase expression from this line 121 clearly correlated to cuprizone - induced demyelination and remyelination time courses . this is consistent with published endogenous mbp mrna studies ( jurevics et al ., journal of neurochemistry , 2002 , 82 , 126 - 136 ). fvb strain mice are but one strain and are known to be sensitive to 0 . 2 % cuprizone as seen by weight loss . routinely , two to three times normal food / transgel supplement per week is required to avoid severe weight loss and toxicity in this strain . one well known and widely used demyelination / remyelination model is the cuprizone model in the mouse . this model involves dietary consumption of cuprizone , a copper chelator ( typically about 0 . 2 % w / w ; biscyclohexanone oxaldihydrazone , cas # 370 - 81 - o , sigma c9012 ) administered in powdered rodent lab chow for a period of , for example , four to six consecutive weeks ( see , for example : matsushima and morell , 2001 ). cuprizone has been shown to be selectively toxic to matured oligodendrocytes . subsequent switch of the cuprizone food to normal food creates an environment conducive to recovery , such that four to six weeks after ceasing cuprizone feeding , the mice will exhibit extensive remyelination in the corpus callosum . thus , the cuprizone model provides a complete in vivo paradigm within which to study aspects of demyelination and remyelination ( fig1 and 12 ). as further proof , a mbp 5k - luci line 171 ( b6c3 strain ) was tested . this strain also showed a correlative imaging response to cuprizone - induced demyelination and remyelination events , as shown in the fig1 . 7 tg + mice were treated with 0 . 2 % cuprizone for 6 week and 3 tg + mice with normal food for 6 weeks . all 7 mice tolerated 0 . 2 % cuprizone diet and had an average weight loss between 15 to 25 %. there was significant imaging signal drop with cuprizone treatment ( demyelination ). for example , there is 43 % signal drop from wk 0 to wk 4 and 74 % signal drop from wk 0 to wk 6 . for histology validation , an objective was to confirm , in the bioimaging model , that the response of the reporter gene during cuprizone treatment correlated with structurally detectable demyelination in the corpus callosum of cuprizone - treated mice . these pathological conditions were visualized by luxol fast blue ( lfb ) staining ( see fig2 and 24 ). specifically , for the mbp 10k - luci line 121 ( fvb strain ), with 0 . 2 % cuprizone feeding , in initial trials , only minimal demyelination was detected through lfb staining . in order to generate clear histological demyelination for these fvb strain mice , various cuprizone feed regimens were followed to attempt to avoid severe weight loss . the 0 . 2 %, 0 . 175 % and 0 . 15 % cuprizone dose groups ( 6 week study ) required 3 - 4 times normal food / transgel supplement per week to avoid severe weight loss and toxicity . also , cuprizone concentration was further lowered with extended exposure time . studies with cuprizone concentrations ( 0 . 14 %, 0 . 12 % and 0 . 1 %) and treatment time ( 7 weeks and 9 weeks ) were tested with up to once a week normal food / transgel supplement . however , all data showed that fvb strain mice ( 8 weeks old , weight 28 . 5 g ± 3 g ) had lesser histological demyelination from varied cuprizone feeding regimens . the fvb line was not selected as an especially preferred embodiment for preliminary development of this research model . although fvb strain is good for imaging and sensitivity to cuprizone toxicity , weight loss might introduce confounding variables that could be easily avoided in these preliminary studies by using another strain . in another strain , mbp 5k - luci line 171 ( b6c3 ) mice ( 8 weeks old , weight 25 g ± 3 g ) showed clear histological demyelination . mouse brain tissues had been collected at the end of six weeks 0 . 2 % cuprizone treatment . all seven cuprizone treated mice had clear demyelination at the corpus callosum region and all three control mice showed normal myelination at the corpus callosum region . these data from the mbp 5k - luci line 171 provide further evidence that imaging signal tracks the cuprizone - induced demyelination phase . additional quantitative lfb analysis ( fig1 ) demonstrated that mbp - luci b6c3 line 171 homozygous mice ( 8 weeks old , weight 21 g ± 3 g ) showed more consistent and mildly more severe demyelination at 4 weeks compared to b6c3h line 171 heterozygous mice ( 8 weeks old , weight 25 . 5 g ± 3 g ). the denser regions in the ovals show stained myelin . furthermore , c57bi / 6 strain wild type male mice ( 8 weeks old , weight 20 g ± 3 g ) fed with 0 . 2 % cuprizone showed the most severe and consistent demyelination . c57 bl / 6 strain has been served as positive control line for cuprizone model and pparδ test compound effect described in preliminary studies . 1 . mbp - luci mice confirm a pparδ selective agonist tool compound &# 39 ; s positive effect on cns remyelination : mbp - luciferase mice have been used to assess whether this in vivo bioimaging model can be used to detect a peroxisome proliferator - activated receptor δ ( pparδ ) agonist tool compound (&# 39 ; 571 ) effect on cns remyelination . the peroxisome proliferator - activated receptors ( ppars ) belong to the nuclear receptor super - family that functions as transcription factors that regulate the expression of target genes . in contrast to other transcription factors , the activity of nuclear receptors can be modulated by binding to the corresponding ligands - small lipophilic molecules that easily penetrate biological membranes . despite the complex cell signal pathway for the nuclear receptor family , there has been a long successful history to use nuclear receptors as drug targets . ppars play essential roles in the regulation of cellular differentiation , development and metabolism . ppars have three closely related isoforms encoded by separate genes identified thus far : commonly known as pparα , pparγ and pparδ , also known as pparβ ; j . berger and d . e . miller , annu . rev . med ., 2002 , 53 , 409 - 435 ). each receptor subtype has a signature dna binding domain ( dbd ) and a ligand - binding domain ( lbd ), both being necessary for ligand activated gene expression . ppars bind as heterodimers with a retinoid x receptor ( rxr ). pparδ appears to be significantly expressed in the cns ; however much of its function there still remains undetermined . of singular interest however , is the discovery that pparδ was expressed in rodent oligodendrocytes , the major lipid producing cells of the cns ( j . granneman , et al ., j . neurosci . res ., 1998 , 51 , 563 - 573 ). moreover , it was also found that a pparδ selective agonist was found to significantly increase oligodendroglial myelin gene expression and myelin sheath diameter in mouse cultures ( i . saluja et al ., glia , 2001 , 33 , 194 - 204 ). pparδ knockout mice have smaller overall brain size and reduced levels of myelination in white matter ( mol cell biology 200 20 : 5119 ). additionally , pparδ agonists exert protective effects in an experimental autoimmune encephalomyelitis ( eae ) model of multiple sclerosis ( polak et al ., j neuroimmunology 2005 168 : 65 - 75 ). colleagues had previously demonstrated that selective pparδ agonists play a functional role in neural tissue and stimulates oligodendrocyte progenitor cell differentiation . sar117145 , an orally bioavailable brain penetrable pparδ selective agonist , stimulated rodent and human oligodendrocyte progenitor cells differentiation in vitro in a concentration dependent manner ; an effect that could be blocked with a pparδ selective antagonist . in rat oligodendrocytes , increased expression of myelin basic protein was preceded by increased mrna expression of the downstream ppar target , angptl4 , and this upregulation was blocked with lentiviral shrna knockdown of pparδ . in a mouse cuprizone model of acute demyelination where mice were fed a diet of 2 % cuprizone for 4 weeks , sar117145 , enhanced cns remyelination , increased angptl4 mrna expression , and improved axonal conduction across the corpus callosum . cns activation of angptl4 was accompanied by increased expression in gastrocnemius muscle , suggesting that this could serve as a potential surrogate marker . these data demonstrate that pparδ agonists can enhance cns remyelination and improve axonal function and suggest their potential use in stimulating endogenous repair processes for the treatment of demyelinating disorders ( us patent application 20070149580 , use of peroxisome proliferator activated receptor delta agonists for the treatment of ms and other demyelinating diseases ). a pparδ agonist tool compound (&# 39 ; 517 ; fig1 ) was tested in b6c3h line 171 heterozygous mice . eight week old mice were placed on a diet containing 0 . 2 % cuprizone for 4 weeks , then given normal diet for remyelination . mice were then orally dosed twice daily with either vehicle ( 0 . 6 % carboxymethylcellulose sodium salt and 0 . 5 % tween 80 ) or 30 mg / kg pparδ agonist tool compound &# 39 ; 517 for 8 days and imaged at the time points indicated in the graph . data were normalized to week 0 baseline signals . there was a 30 - 100 % relative luciferase signal increase in the tool compound &# 39 ; 517 group ( n = 15 ) over vehicle group ( n = 13 ), which we believe is due to enhancement of oligodendrocyte progenitor cell differentiation . the effect of &# 39 ; 517 was further histologically confirmed by luxol fast blue ( lfb ) staining in the same study ( fig1 ). parasagittal tissue sections from formalin fixed paraffin embedded brain were stained with lfb for qualitative assessment of myelin in the corpus callosum . the stained sections for each time point were scored and graded on a scale from 0 ( complete myelination ) to 5 ( complete demyelination ). scoring system was as follows : 0 = normal myelin , no demyelination , 1 = minimal , localized demyelination , 2 = mild to moderate , localized demyelination , 3 = moderate , locally extensive demyelination , 4 = severe , locally extensive demyelination , 5 = severe , diffuse demyelination . histological evaluation of lfb - stained brain sections from mice , after 4 weeks on cuprizone , confirmed moderate to severe demyelination of the corpus callosum in line 171 heterozygous mice ( n = 5 ). treatment with &# 39 ; 517 from week 4 to week 5 during remyelination phase resulted in a measurable increase in myelin as determined by lfb at the 7 week time point , tool compound &# 39 ; 517 group ( n = 5 ) compared to vehicle control group ( n = 3 ). despite small n - numbers , histological data support the in vivo luciferase bioimaging data , indicating increased remyelination in mice treated with the &# 39 ; 517 compound when compared to vehicle controls . a second ppar6517 study with line 171 heterozygous mice showed the similar results ( data not shown , and also extended &# 39 ; 517 treatment to three weeks ). consistent with the first study ( fig1 ), the second study also suggests that &# 39 ; 517 accelerated oligodendrocyte progenitor cell differentiation at the early recovery phase during remyelination process ( m lindner and s heine , et al , neuropathology and applied neurobiology , 34 , 105 - 114 , 2008 ). 2 . mbp - luci mice detect the protective effects of an erβagonist , &# 39 ; 5a or a positive control compound qtp on myelin expression . the estrogen receptors ( ers ) belong to the family of steroid nuclear receptors that act directly on the dna through specific responsive elements and modulate gene expression . there are two subtypes of ers , erα and erβ . erα is highly expressed in the uterus , prostate , ovary , bone , breast and brain , whereas erβ is present in the colon , prostate , ovary , bone marrow and brain . selective targeting of erβ is an attractive therapeutic approach to avoid erα side effects . er subtype - selective compounds have been identified . for example , erβ ( not erα ) agonists have been shown to protect oligodendrocytes and neuroblastoma cell apoptosis in vitro . in addition , erβ or er - agonist ameliorates eae and has neuroprotective effect ( preservation of myelin and axons ). based on previous pparδ agonist tool compound , &# 39 ; 517 , the mbp - luci line was used to profile an err agonist , &# 39 ; 5a in the cuprizone model . furthermore , we included astrazeneca &# 39 ; s schizophrenia drug , quetiapine ( 10 mg / kg , po , qd ) as a positive control based on its protective effect on cuprizone - induced demyelination ( schizophrenia research , 2008 december 106 , 182 - 91 ). two independent studies were performed with b6ch line 171 heterozygous mice . the first study ( fig1 ) showed that the erβ agonist , &# 39 ; 5a and a positive control , quetiapine ( qtp ), were protective during the period of demyelination in the cuprizone model . mbp - luc line 171 heterozygous b6c3h mice were fed a diet of cuprizone for 4 weeks and orally dosed with &# 39 ; 5a ( 10 mg / kg , n = 12 or 30 mg / kg n = 16 ) or qtp ( 10 mg / kg , n = 14 ). mice were imaged at week 0 ( baseline ), week 3 and week 4 data normalized to the week 0 baseline . similar to previous study ( fig1 ), the vehicle group resulted in a 49 % ( week 3 ) and 45 % ( week 4 ) bioimaging signal reduction . the qtp group showed significant increases in imaging signal vs . vehicle control for both week 3 and week 4 time points at 10 mg / kg . results for the qtp treatment group are consistent with data published by zhang et al ( schizophrenia research , 2008 , 106 : 182 - 91 ). compound &# 39 ; 5a at 30 mg / kg showed significant increases over vehicle at week 4 , but showed no significant difference over vehicle at 10 mg / kg at weeks 3 or 4 . these results suggest that the mbp - luci imaging model can be used to assess dose dependent protective effects in the cuprizone model . a further study ( fig1 ) was designed to confirm the first study result ( fig1 ) but with a larger cohort for the vehicle and the &# 39 ; 5a compound 30 mg / kg treatment groups . in agreement with the first study results , treating mice with qtp at 10 mg / kg ( n = 17 ) produced a statistically significant inhibition of cuprizone - induced signal decrease when compared to vehicle treated controls ( n = 25 ) at week 3 ( 25 % vs 47 % reduction , p = 0 . 028 ) and at week 4 ( 6 % increase vs 25 % reduction ). furthermore , &# 39 ; 5a at 30 mg / kg ( n = 27 ) results in significantly greater transgene activity compared to the vehicle control group at week 3 ( 31 % vs 47 % reduction , p = 0 . 0079 ) and week 4 ( 6 % reduction vs 25 % reduction , p = 0 . 0015 ). these two studies demonstrated that &# 39 ; 5a at 30 mg / kg significantly prevented the cuprizone diet induced reduction in the bioimaging signal in the cns although not to the same extent as the positive control qtp at 10 mg / kg ( under the conditions used in these experiments ). since previous studies have shown a direct relationship between the extent of cns myelination and the mbp - luci bioimaging signal , these current results suggest that both &# 39 ; 5a and qtp prevented demyelination in the cns during cuprizone diet administration . imaging model data support that both qtp and &# 39 ; 5a attenuate the cuprizone - induced brain demyelination and myelin breakdown . six transgenic lines on various strain backgrounds have been generated for distinct bioimaging applications . b6c3h line 171 homozygous mice and heterozygous imaging signal in the cuprizone model ( fig1 ) was compared . two copies of the reporter gene in the homozygotes showed greater than two - fold signal decrease during the demyelination phase and a two - fold signal increase during the remyelination phase . although it is demonstrated that the heterozygous line 171 ( b6c3h strain ) works in cuprizone model and can detect compound effects , it is anticipated that the model could be further improved by breeding to homozygosity to increase bioimaging signal intensity . this would also streamline model production and decrease genotyping costs , since mouse colonies can be maintained as homozygotes . moreover , the larger the imaging window , the more sensitive the model is towards detecting compound induced changes . fig2 shows comparison of histological lfb data from three different lines in the cuprizone model . quantitative lfb data confirmed the bioimaging results with line 171 b6c3h that homozygous mice exhibited the most severe cuprizone induced demyelination ; similar in severity to that seen in wild type c57 bl / 6 mouse strain typically used . line 171 heterozygous mice line showed less severe demyelination while these line 171 heterozygous mice showed the least amount of cuprizone induced demyelination . in fig2 , demonstrates that mbp - luci line with the largest bioimaging signal reduction also had the greatest demyelination , as assessed histologically . three different mbp - luci lines ( line 171 b6c3h het strain , line 121 c57bl / 6 heterozygous strain and line 171 b6c3h homozygous strain ) were compared by bioimaging and luxol fast blue ( lfb ; myelin stain ) histology . mice were placed on a diet containing 0 . 2 % cuprizone for 4 or 5 weeks . imaging data were normalized to week 0 baseline measurements . at the end of each study , mouse brains were harvested and serial paraffin sections were stained for myelin with lfb . average qualitative lfb score ( 0 to 5 ) was shown in the chart of fig2 . line 171 b6c3h homozygous mice showed the largest imaging signal decrease and also demonstrated the most severe demyelination as assessed by qualitative histological assessment . line 171 b6c3h heterozygous mice showed the smallest imaging window and also the least histological demyelination at week 4 . line 171 b6c3h homozygous mice had the largest bioimaging signal reduction during cuprizone food feeding in the reference to their base line imaging before cuprizone food feeding . for example , after three weeks on the cuprizone diet , 171 b6c3h homozygous mice had 72 % signal reduction ( week 3 reference to week 0 , p & lt ; 0 . 05 ), while line 171 b6c3h heterozygous mice had 45 % bioimaging signal reduction ( reference to week 0 , p & lt ; 0 . 05 ). line 121 c57 bl / 6 heterozygous mice had the smallest reduction in luciferase signal ( 33 % reduction at week 3 over week 0 , p & lt ; 0 . 05 ). the sensitivity and responsiveness of mbp - luci model was further confirmed by treatment of 171 b6c3h homozygous mice with qtp ( 10 mg / kg ) shown in fig2 . consistent with results using 171 b6c3h heterozygous mice ( fig1 and 18 ) that qtp ( 10 mg / kg ) significantly prevented bioimaging signal reduction . based on these results , line 171 b6c3h homozygous mice were identified as the optimal line for the cuprizone induced demyelination bioimaging model . mbp - luci mice have both brain and spinal cord luciferase expression . as shown in fig2 , luminescence signal was primarily from the white matter region of brain and spinal cord . besides luciferase imaging from brain that has been successfully demonstrated for cuprizone model applications , luciferase imaging signal from spinal cord could be used in the experimental allergic encephalitis ( eae ) model of ms or applied as a spinal cord model .
a myelin basic protein - luciferase bioimaging noninvasive model to visualize and quantify demyelination and remyelination events in the cns at transcriptional level in vivo is provided . luciferase - expressing transgenic animals were generated with myelin basic protein promoter coupled to firefly luciferase reporter . the mbp - luci bioimaging model provides a means to monitor myelination status and the efficacy of a remyelination modulating test compound . an advantage of bioimaging is that a subject in a longitudinal study can serve as its own control . the same subject can be tracked over a demyelination and remyelination process continuously over a period of at least 10 weeks . this model enables normalization of individual animal imaging response and provides quality data with considerably reduced variance . in addition , because cohorts of animals need not be sacrificed at different time points , reduction in the number necessary for a compound efficacy study is possible .