RETINOIC ACID REGULATES KIT PROTEIN EXPRESSION IN PERITUBULAR MYOID CELLS IN THE MAMMALIAN TESTIS

Abstract

Spermatogenesis (production of sperm) takes place in the testis, which is composed of seminiferous tubules. Within mammalian seminiferous tubules, there are two cell types: germ cells and supporting somatic cells. The somatic cells found inside the tubules are Sertoli cells, and those surrounding the tubules are peritubular myoid cells (PTMs). Evidence supports roles for PTMs in multiple critical functions, however, almost nothing is known regarding how PTMs are instructed to regulate these distinct functions. Recent data from our lab are beginning to shed light on this – we made the exciting discovery that expression of the essential ‘KIT protooncogene receptor tyrosine kinase’ (KIT) is regulated in PTMs by retinoic acid (RA) signaling. As a morphogen, RA signals in discrete portions of the testis to drive germ cell differentiation, and we observed that RA dramatically modified the regional expression of KIT. In germ cells, RA upregulated KIT protein expression but did the opposite in PTMs; KIT protein was downregulated in PTMs in vivo by exogenous RA and upregulated by WIN 18,446/BDAD mediated inhibition of RA synthesis. We are currently investigating the extent to which RA regulates the regional and temporal expression of KIT in PTMs. We treated mice with WIN 18,446 for ten days and then injected exogenous RA. At different time points after RA injection, mice were euthanized and tissues were collected for immunostaining to detect KIT in PTMs, which express ‘actin, alpha 2, smooth muscle, aorta’ (ACTA2/a-SMA). We next determined the percentages of ACTA2+ PTMs that were KIT+. Our preliminary results suggest that numbers of KIT+ PTMs declines drastically, as early as two days in response to RA.