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.