Regulation of c-ret expression by retinoic acid in rat metanephros: implication in nephron mass control

Vitamin A and its derivatives have been shown to promote kidney development in vitro in a dose-dependent fashion. To address the molecular mechanisms by which all-trans-retinoic acid (RA) may regulate the nephron mass, rat ki dneys were removed on embryonic day 14 (E14) and grown in organ culture und er standard or RA-stimulated conditions. By using RT-PCR, we studied the ex pression of the glial cell line-derived neurotrophic factor (GDNF), its cel l surface receptor-alpha (GDNFR-alpha), and the receptor tyrosine kinase c- ret, known to play a major role in renal organogenesis. Expression of GDNF and GDNFR-alpha transcripts was high at the time of explantation and remain ed unaffected in culture with or without RA. In contrast, c-ret mRNA level, which was low in E14 metanephros and dropped rapidly in vitro, was increas ed by RA in a dose-dependent manner. The same is true at the protein level. Exogenous GDNF barely promotes additional nephron formation in vitro. Thus the present data establish c-ret as a key target of retinoids during kidne y organogenesis.