ROLE OF DIFFERENT FORMS OF FIBRONECTIN IN IN-VITRO BOVINE FOLLICULAR DEVELOPMENT

This study was aimed at testing the hypothesis that different forms of fibronectin (FN), produced as a consequence of the alternative splici ng of the precursor mRNA, play specific roles during follicular develo pment. In particular, we analyzed the presence of the ED-I region, whi ch is absent in the plasma form. Analysis of FN levels in follicular f luids corresponding to different stages of development of bovine folli cles revealed marked changes in the concentrations whereas total FN le vels remained constant. A negative correlation (P < 0.001) was detecte d between ED-I+FN and estradiol levels, This steroid was without effec t on the alternative splicing of FN in primary cultures of bovine gran ulosa cells. However, cAMP produced a marked decrease in the incorpora tion of the ED-I region. In contrast, transforming growth factor beta (TGF-beta) elicited both a stimulation on overall FN synthesis and an increase in the inclusion of ED-I. This effect was evident at the prot ein level (Western blots) and also in the mRNAs (Northern blots). A pe ptide corresponding to the ED-I region stimulated DNA synthesis in a b ovine granulosa cell line (BGC-I) whereas the peptide corresponding to the flanking sequences was without effect. Data presented herein sugg est a novel form of regulation by which changes in the primary structu re of FN may mediate some of the effects of gonadotropin and intraovar ian factors during follicular development.