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

Abstract

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. RARα and RARβ 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 RARγ from 8 dpp. Immunoreactivity for RXRα was intense in the gonocytes from 13.5 dpc and in the Leydig cells from 16.5 dpc, and persisted throughout the period studied. RXRβ was always detected in the Leydig cells and during a short neonatal period in the gonocytes. RXRγ gave a faint reaction in the nuclei of all cell types from 20.5 dpc. Unexpectedly, immunostaining for all the receptors tested, except RARγ and RXRγ, 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.