title: Retinoic acid availability drives the asynchronous initiation of spermatogonial differentiation in the mouse.
abstract: Throughout the reproductive lifespan of most male mammals, sperm production is constant because of the regulated differentiation of spermatogonia. Retinoic acid (RA) and a downstream target, Stra8, are required for complete spermatogenesis. To examine the role of RA in initiating spermatogonial differentiation, a transgenic mouse model expressing beta-galactosidase under the control of an RA response element was used. Cells in the neonatal testis undergoing active RA signaling were visualized by beta-galactosidase activity, the relationship between RA and differentiation determined, and the role of RA-degrading enzymes in regulating RA demonstrated. Beta-galactosidase activity was found to be predominantly associated with differentiating, premeiotic germ cells and to be distributed nonuniformly throughout the seminiferous tubules. Additionally, beta-galactosidase activity in premeiotic germ cells colocalized with STRA8 protein and was induced in germ cells with exogenous RA treatment. The RA-degrading enzyme, CYP26B1, was found to have germ cell localization and nonuniform distribution between tubules via immunohistochemistry. Treatment with a CYP26 enzyme inhibitor resulted in an increased number of germ cells with both beta-galactosidase activity and STRA8 protein and an increase in the expression of genes associated with differentiation and reduced expression of a gene associated with undifferentiated germ cells. These results show the action of RA in a subset of spermatogonia leads to nonuniform initiation of differentiation throughout the neonatal testis, potentially mediated through the action of CYP26 enzymes. Thus, the presence of RA is a likely driving factor in the initiation of spermatogonial differentiation and may result in asynchronous spermatogenesis.
authors.affiliation: School of Molecular Biosciences, Washington State University, Pullman, Washington 99164, USA.
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Snyder
authors.forename: Christopher
authors.initials: C
authors.lastname: Small
authors.forename: Michael D
authors.initials: MD
authors.lastname: Griswold
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000375:Aging; D000818:Animals; D000831:Animals, Newborn; D000943:Antigens, Differentiation / Q000378:metabolism; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D015536:Down-Regulation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D017930:Genes, Reporter; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D009928:Organ Specificity; D011506:Proteins / Q000378:metabolism; D000072516:Retinoic Acid 4-Hydroxylase; D012671:Seminiferous Tubules / Q000166:cytology / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism; D015398:Signal Transduction; D013091:Spermatogenesis / Q000187:drug effects; D013093:Spermatogonia / Q000187:drug effects / Q000254:growth & development / Q000502:physiology*; D013737:Testis / Q000166:cytology* / Q000187:drug effects / Q000254:growth & development* / Q000378:metabolism; D014212:Tretinoin / Q000494:pharmacology* / Q000502:physiology*; D015854:Up-Regulation / Q000187:drug effects
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D000943:Antigens, Differentiation; D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors; D011506:Proteins; C102019:Stra8 protein, mouse; D014212:Tretinoin; D003577:Cytochrome P-450 Enzyme System; C000607081:Cyp26b1 protein, mouse; D000072516:Retinoic Acid 4-Hydroxylase