ISWI proteins constitute the catalytic subunits of many chromatin remodeling complexes that alter nucleosome positioning to regulate gene expression. In rodents there exists two ISWI paralogs, Snf2H and Snf2L, the latter of which is expressed mainly in the brain and gonads. Following our observation that Snf2L expression temporally correlates with luteinization of the follicle, we hypothesized that it may positively regulate the expression of genes involved in steroidogenesis. Consistent with this hypothesis we find that treatment of granulosa (SVOG-40) and Leydig (MA-10) cell lines with 1mM of dibutyryl-cAMP (db-cAMP) induces expression of Snf2L concomitantly with StAR, a classic marker of differentiation, and a rate limiting enzyme of the steroid biosynthesis pathway. Furthermore siRNAs targeted against Snf2L are sufficient to significantly reduce StAR activation in SVOG-40 cells stimulated with db-cAMP. In order to identify other genes which may be regulated by Snf2L in differentiating granulosa cells, Snf2L knockout mice were derived and used in a superovulation experiment. PMSG was administered in both Snf2L knockout (KO) and wildtype (WT) 22 days old mice and two days later ovaries were collected either prior to human chorionic gonadotropin (hCG) adminstration, or 4h after, and gene expression was compared by microarray in mechanically isolated granulosa cells. Several genes involved in the steroid biosynthesis pathway were found to be downregulated in presence of hCG in the KO mice including StAR, HSD-11b2, HSD-3B1, P450 cyp24, p450 cyp17, P450 cyp19 (aromatase), p450scc, and DHCR-24. A preliminary screening of the mice for gross anatomical defects or fertility have failed to uncover any differences between the groups. In conclusion, we report here a subtle reproductive phenotype in which the Snf2L KO mice is fertile despite being deficient in many steroidogenic enzymes normally upregulated by LH.