The goal of the proposed research is to use two powerful genetic techniques, chimeras and transgenic mice, to further explore the ways in which cell lineage relationships help to guide the morphogenesis and histogenesis of the developing central nervous system. First, quantitative analysis of the Purkinje cell population will further define the role of cell lineage relationships in the control of the numerical properties of a given population. Studies will focus on F1 hybrids between strains that have different intrinsic Purkinje cell clone sizes. In addition, chimeras in which beta-glucuronidase activity serves as an independent cell marker will be analyzed for lineage patterns among the cells of the lateral motor column of the spinal cord. Second, to enable these types of lineage studies to expand into new areas of the CNS, in particular cerebral cortex, work on the development of new independent cell markers through the technology of transgenic mouse production will continue. The gene constructs currently ready for injection include the structural gene for beta- galactosidase, a cytoplasmic marker, and for wild-type and mutant SV-40 T-antigen, both nuclear markers. These are driven by a neuron-localized regulatory element, the Thy-1 promoter. Successful transgenic lines will express high levels of an easily detectable marker in most neurons of the brain and spinal cord. Third, chimeras will be used to explore the relationship between cell lineage and the functional subdivisions of a neuronal populaton. Preliminary work has already revealed an important correlation in cerebellum between physiologically defined somatosensory map boundaries and lineage defined map boundaries; studies in spinal cord will extend this approach to the motor units of the lateral motor columns. Finally, in order to define a developmental basis for the sub-lineage relationships observed in cerebellum, the correlation between the lineage map boundaries and the glial cell "pre-pattern" illustrated by Cooper and Steindler (through the use of peanut lectin staining) will be examined. Together, these approaches render the inherent "genetic logic" of development clearer such that our understanding of human genetic disorders, ranging from neural tube defects to psychiatric disorders, becomes that much more complete.