Retinoic acid receptors and retinoid X receptors in the rat testis during fetal and postnatal development: Immunolocalization and implication in the control of the number of gonocytes

Retinoids have pleiotropic effects on embryonic development and are essential for spermatogenesis in the adult, where they act via nuclear retinoid receptors: retinoic acid receptors (RARs) and retinoid X receptors (RXRs). We used immunohistochemistry to examine the cellular localization of RARs and RXRs in the rat testis from Day 13.5 postconception (13.5 dpc) until Day 8 postpartum (8 dpp), and these findings were compared with those for immature and adult testes. RAR alpha and RAR beta were detected in the interstitial tissue from 14.5 dpc, with intense staining in the gonocytes from 20.5 dpc to 8 dpp. The nuclei of all cell types stained faintly for RAR gamma from 8 dpp. Immunoreactivity for RXR alpha was intense in the gonocytes from 13.5 dpc and in the Leydig cells from 16.5 dpc, and persisted throughout the period studied. RXR beta was always detected in the Leydig cells and during a short neonatal period in the gonocytes. RXR gamma gave a faint reaction in the nuclei of all cell types from 20.5 dpc. Unexpectedly, immunostaining for all the receptors tested, except RAR gamma and RXR gamma, was detected in the cytoplasmic compartment of the cells of fetal and neonatal testes, while it was found in the nuclei in immature and adult testes. In cultures of dispersed testicular cells from 3 dpp pups, retinoic acid had a dose-dependent deleterious effect on the survival of the gonocytes and, to a lesser extent, of the somatic cells. These results suggest that retinoids act on the testicular development, especially on germ cells, via RARs and/or RXRs.