Receptor protein tyrosine kinases in perinatal developing rat kidney

We have identified receptor protein tyrosine kinases (PTKs) that are expressed and/or activated during kidney development. mRNA from fetal rat kidneys in late gestation (embryonic day 21), was used to prepare cDNA template for polymerase chain reaction amplification with primers based on conserved regions of PTKs, and products were subcloned and sequenced. Among 346 clones, we identified epidermal growth factor receptor (EGFr), Tie 2, platelet derived growth factor receptor (PDGFr)-alpha, PDGFr-beta, Flk-1, Flt-4, fibroblast growth factor receptor (FGFr)-1, FGFr-3, FGFr-4, Met, and RYK//Nbtk-1. PTK expression was studied by immunoprecipitation and immunoblotting of kidney membrane proteins with specific antibodies. EGFr, PDGFr-alpha, FGFr-1, FGFr-3, Met, and in some cases Tie-2 protein expression was greater in fetal kidneys, as compared with kidneys from 12 week adult rats, (controls). Flk-1, PDGFr-beta, and FGFr-4 proteins were expressed comparably; Flt-4 was not detected. As a reflection of receptor PTK activity, we assessed endogenous tyrosine phosphorylation, and in vitro autophosphorylation. EGFr and PDGFr-alpha displayed activity in fetal, but not adult kidneys. FGFr-3 and Flk-1 were active in some fetal kidneys; the other PTKs were not active. Thus, in late gestational rat kidney, there are distinct patterns of receptor PTK expression and activity. EGFr, PDGFr-alpha, FGFr-3 and Flk-1 are among PTKs that are activated, and they may mediate perinatal development of renal epithelial, interstitial, or vascular structures