Protein tyrosine kinase expression in the porcine ovary

Various growth factor receptors contain intrinsic tyrosine kinase activity, indicating that protein tyrosine kinases (PTK) play an important role in signal transduction pathways for cell proliferation and differentiation. To identify oocyte-derived factors which control follicle cells as well as oocyte-controlling factors produced by follicle cells, we examined the expression of genes which contain the PTK domain in the porcine ovary, using a polymerase chain reaction-based amplification technique with degenerate oligonucleotide primers that are specific to the PTK domain. Clones for the porcine homologues of platelet-derived growth factor receptor alpha (PDGFRalpha) and of insulin-like growth factor-I receptor (IGF-IR) were found during follicle growth both in oocytes and follicle cells. Clones for the porcine homologues of focal adhesion kinase (FAK), of c-kit and of fms-like tyrosine kinase (FLT)-3 were found only in oocytes. Moreover, after 24 h of in-vitro maturation of the cumulus-oocyte complexes, clones for the porcine homologues of FLT-1, of FLT-4, of Tie2 and of RYK in oocytes were observed. Immunohistochemical studies revealed the existence of PDGFRalpha, platelet-derived growth factor A (PDGFA), FAK and FLT3 in oocytes at various stages of folliculogenesis. These results suggest that fluctuations in the expression of these PTK genes may be involved in follicle growth and maturation.