Transcriptome response of pubertal male Clarias macrocephalus to dietary 17α-methyltestosterone

We studied the mechanism of the effects of 17α-methyltestosterone (MT) on previously reported enhanced growth and maturation of the Asian catfish Clarias macrocephalus. A total of 18 pubertal male (3 fish·tank-1) catfish (ABW=125.97 g) were stocked into six experimental circular tanks and fed with a basal diet (control) or a basal diet containing 60 mg MT kg-1 diet for 90 days. At the termination of the experiment, livers were excised, and total RNA was extracted, evaluated, and reverse transcribed to cDNA. Six libraries of cDNA (3 for the control and 3 for the MT-treated group) were subjected to bioinformatics. Differentially expressed genes (DEGs) were identified using similarity scores of the de novo assembled transcript with those in the seven public databases. There were 141 up- and 72 down-regulated DEGs, mostly belonging to uncharacterized/not yet identified proteins. Thus, DEGs in the top enriched KEGG pathways were used to characterize the effects of MT. Upregulated DEGs included tyrosine hydroxylase (TH), Cytoplasmic Polyadenylation Element Binding (CPEB), Fas-associated death domain (FADD), Major Histocompatibility Complex class 1 (MHC-1), other immune-related genes, among others. Down-regulated DEGs included Cytochrome P450 family one subfamily A member 1 (CYP1A1), Alternative oxidase (AOX), UDP-glycosyltransferase (UGT), Acyl-CoA Synthase Bubblegum Family Member 1 (ACSBG), Stearoyl-CoA Desaturase (SCD), among others. In conclusion, MT-treated male Clarias macrocephalus exhibited up-regulation of pathways protecting cellular conditions like cell proliferation, survival, development and homeostasis processes, for development and homeostasis processes. MT also affected changes in bile acid production and the inhibition of the production/conversion of testosterone. MT resulted in the down-regulation of a serotonergic system that possibly affected gonadal development, inhibition of the retinoid enzyme that would otherwise diminish the full effects of MT or its metabolite, and inhibition of the formation of estrogen, leading to down-regulation of several estrogen-related KEGG pathways. The results provide valuable information about the key genes for use as biomarkers of maturation and reproduction for the Asian catfish and contribute to our understanding of the molecular mechanisms and regulative pathways behind these two processes in fish.