Submitted to: Biology of Reproduction
Publication Type: Abstract Only
Publication Acceptance Date: April 8, 2000
Publication Date: N/A
Semiquantitative in situ molecular hybridization and immunocytochemistry for low-density lipoprotein receptor (LDLR), steroidogenic acute regulatory protein (StAR), cytochrome P450side-chain cleavage (P450scc) enzyme and cytochrome P450 17alpha-hydroxylase/C17-20 lyase (P450C17) were applied to individual nonatretic follicles (N=54) harvested from cycling gilts slaughtered on days 1, 3, 5, and 7 (N=3 per day) following withdrawal of altrenogest. Low levels of LDL receptor mRNA and protein expression were detectable in only theca cells on day 7. StAR mRNA and protein levels rose progressively in theca cells with follicular maturation, reaching maximal expression on day 5, then declining slightly on day 7 after the LH surge. In granulosa cells, small amounts of StAR mRNA and protein were detected on days 5 and 7. P450scc mRNA content and protein expression were highest in theca cells, increasing at each time point studied. Granulosa cells expressed minimal P450scc message on days 3, 5, and 7, while protein level became detectable at moderate levels on day 7 only. Expression of P450c17 was localized exclusively in theca cells with protein and mRNA content increasing at each time point to a maxima on days 5 (mRNA) and 7 (protein). Analysis of follicular fluid concentrations of androstenedione, estradiol, and progesterone in contralateral ovaries showed strong correlations between levels of these sex-steroids and expression of StAR, P450scc, and P450c17 proteins. These analyses demonstrate that preovulatory follicular development proceeds with the coordinate induction of selected pivotal genes and proteins mediating the uptake, delivery and utilization of cholesterol substrate in steroidogenesis.