MESENCHYMAL-EPITHELIAL INTERACTIONS IN THE OVARIAN FOLLICLE INVOLVE KERATINOCYTE AND HEPATOCYTE GROWTH-FACTOR PRODUCTION BY THECAL CELLS AND THEIR ACTION ON GRANULOSA-CELLS

Mesenchymal-epithelial cell interactions between thecal and granulosa cells in bovine ovarian follicles were investigated. Experiments were designed to examine the local production and action of two mesenchymal (stromal)-derived growth factors, keratinocyte and hepatocyte growth factors (KGF and HGF). Using reverse transcription-polymerase chain reaction, gene expression for KGF and HGF was detected in the mesenchymal-derived thecal cells, but not in the epithelial granulosa cells. The bovine polymerase chain reaction products for KGF and HGF were sequenced and found to be similar to known mouse, rat, and human sequences. The bovine KGF sequence was found to have a high degree of identity (86-95%) with the other species, whereas bovine HGF has a lesser degree of identity (60-63%). Immunoprecipitation of radiolabeled thecal cell secreted proteins with a KGF antibody demonstrated production of the 28-kilodalton (kDa) KGF protein. An immunoblot of thecal cell secreted proteins with HGF antibodies detected the 87-kDa HGF as well as relevant 69- and 34-kDa subunits. Therefore, thecal cells were found to express the genes and secrete the proteins for KGF and HGF. Granulosa cells had no detectable KGF or HGF expression. Treatment with recombinant KGF or HGF stimulated the proliferation of granulosa cells, but not thecal cells. Therefore, the actions of KGF and HGF in the ovarian follicle appear to be restricted to granulosa cells. The combined results indicate that KGF and HGF are produced locally in the bovine ovarian follicle by thecal cells, and that both of these growth factors can act on granulosa cells to influence cell proliferation. These observations demonstrate that KGF and HGF can mediate mesenchymal-epithelial cell interactions between thecal and granulosa cells. The potential importance that the mesenchymal derived thecal cells may have in ovarian follicle development is discussed.