NCBI Summary:
Squalene epoxidase catalyzes the first oxygenation step in sterol biosynthesis and is thought to be one of the rate-limiting enzymes in this pathway.
General function
Enzyme
Comment
Cellular localization
Cytoplasmic
Comment
Ovarian function
Steroid metabolism
Comment
CYP51A1 Induced by Growth Differentiation Factor 9 and Follicle-Stimulating Hormone in Granulosa Cells Is a Possible Predictor for Unfertilization. Nakamura T 2014 et al.
Growth differentiation factor 9 (GDF9), an oocyte-secreted factor, whose receptors exist in granulosa cells, is involved in follicle progression. Therefore, GDF9 is considered to potentially mediate signals necessary for follicular growth. However, the effect of GDF9 on human granulosa cells is not fully understood. Human immortalized nonluteinized granulosa cell line (HGrC1) which we have previously reported was stimulated with GDF9 and/or follicle-stimulating hormone (FSH). Granulosa cells obtained from in vitro fertilization (IVF) patients were also evaluated with quantitative reverse transcription polymerase chain reaction (RT-PCR). Real-time RT-PCR showed that GDF9 increased messenger RNA (mRNA) levels of enzymes required for cholesterol biosynthesis, such as 3-hydroxy-3-methylglutanyl-CoA synthase 1 (HMGCS1), farnesyl-diphosphate farnesyltransferase 1, squalene epoxidase, lanosterol synthase, and cytochrome P450, family 51, subfamily A, polypeptide 1 (CYP51A1). A greater increase in mRNA levels of HMGCS1 and CYP51A1 was observed by combined treatment with GDF9 and FSH. Clinical samples showed a significant increase in CYP51A1 mRNA in the group of granulosa cells connected with unfertilized oocytes. Our results suggest that GDF9, possibly with FSH, may play significant roles in the regulation of cholesterol biosynthesis and the expression of CYP51A1 which might be a predictor for unfertilization.
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Genes in sterol/steroid and lipid biosynthetic pathways are targets of FSH and FOXO1 regulation in granulosa cells: evidence from cells expressing mutant forms of FOXO1. Liu Z et al. The forkhead box transcription factor FOXO1 is highly expressed in granulosa cells of growing follicles but is down-regulated by FSH in culture or by LH-induced luteinization in vivo. To analyze the function of FOXO1, we infected rat and mouse granulosa cells with adenoviral vectors expressing two FOXO1 mutants: a gain-of-function mutant FOXOA3 that has three serine residues mutated to alanines rendering this protein constitutively active and nuclear and FOXOA3-mDBD in which the DNA binding domain is mutated. The infected cells were then treated with vehicle or FSH for specific time intervals. Infection of the granulosa cells was highly efficient, caused only minimal apoptosis and maintained FOXO1 protein at levels of the endogenous protein observed in cells prior to exposure to FSH. RNA was prepared from control and adenoviral infected cells exposed to vehicle or FSH for 12 and 24h. Affymetrix microarray and data-base analyses identified, and real time RT-PCR verified, that genes within the lipid, sterol and steroidogenic biosynthetic pathways (Hmgcs1, Hmgcr, Mvk, Sqle, Lss, Cyp51, Tm7sf2, Dhcr24 and Star, Cyp11a1 and Cyp19), including two key transcriptional regulators Srebf1 and Srebf2 of cholesterol biosynthesis and steroidogenesis (Nr5a1, Nr5a2) were major targets induced by FSH and suppressed by FOXOA3 and FOXOA3-mDBD in the cultured granulosa cells. By contrast, FOXOA3 and FOXOA3-mDBD induced expression of Cyp27a1 mRNA that encodes an enzyme involved in cholesterol catabolism to oxysterols. The genes up-regulated by FSH in cultured granulosa cells were also induced in granulosa cells of preovulatory follicles and corpora lutea collected from immature mice primed with FSH (eCG) and LH (hCG), respectively. Conversely, Foxo1 and Cyp27a1 mRNAs were reduced by these same treatments. Collectively, these data provide novel evidence that FOXO1 may play a key role in granulosa cells to modulate lipid and sterol biosynthesis, thereby preventing elevated steroidogenesis during early stages of follicle development.
Expression regulated by
Growth Factors/ cytokines, GDF9
Comment
Ovarian localization
Cumulus, Granulosa, Luteal cells
Comment
Oocyte regulation of metabolic cooperativity between mouse cumulus cells and oocytes: BMP15 and GDF9 control cholesterol biosynthesis in cumulus cells. Su YQ et al. Oocyte-derived bone morphogenetic protein 15 (BMP15) and growth differentiation factor 9 (GDF9) are key regulators of follicular development. Here we show that these factors control cumulus cell metabolism, particularly glycolysis and cholesterol biosynthesis before the preovulatory surge of luteinizing hormone. Transcripts encoding enzymes for cholesterol biosynthesis were downregulated in both Bmp15(-/-) and Bmp15(-/-) Gdf9(+/-) double mutant cumulus cells, and in wild-type cumulus cells after removal of oocytes from cumulus-cell-oocyte complexes. Similarly, cholesterol synthesized de novo was reduced in these cumulus cells. This indicates that oocytes regulate cumulus cell cholesterol biosynthesis by promoting the expression of relevant transcripts. Furthermore, in wild-type mice, Mvk, Pmvk, Fdps, Sqle, Cyp51, Sc4mol and Ebp, which encode enzymes required for cholesterol synthesis, were highly expressed in cumulus cells compared with oocytes; and oocytes, in the absence of the surrounding cumulus cells, synthesized barely detectable levels of cholesterol. Furthermore, coincident with reduced cholesterol synthesis in double mutant cumulus cells, lower levels were also detected in cumulus-cell-enclosed double mutant oocytes compared with wild-type oocytes. Levels of cholesterol synthesis in double mutant cumulus cells and oocytes were partially restored by co-culturing with wild-type oocytes. Together, these results indicate that mouse oocytes are deficient in synthesizing cholesterol and require cumulus cells to provide products of the cholesterol biosynthetic pathway. Therefore, oocyte-derived paracrine factors, particularly, BMP15 and GDF9, promote cholesterol biosynthesis in cumulus cells, probably as compensation for oocyte deficiencies in cholesterol production.
Analysis of gene expression in the bovine corpus luteum through generation and characterisation of 960 ESTs.
Casey OM, et al .
To gain new insights into gene identity and gene expression in the bovine corpus luteum (CL) a directionally cloned CL cDNA library was constructed, screened with a total CL cDNA probe and clones representing abundant and rare mRNA transcripts isolated. The 5'-terminal DNA sequence of 960 cDNA clones, composed of 192 abundant and 768 rare mRNA transcripts was determined and clustered into 351 non-redundant expressed sequence tag (EST) groups. Bioinformatic analysis revealed that 309 (88%) of the ESTs showed significant homology to existing sequences in the protein and nucleotide public databases. Several previously unidentified bovine genes encoding proteins associated with key aspects of CL function including extracellular matrix remodelling, lipid metabolism/steroid biosynthesis and apoptosis, were identified. Forty-two (12%) of the ESTs showed homology with human or with other uncharacterised ESTs, some of these were abundantly expressed and may therefore play an important role in primary CL function. Tissue-specificity and temporal CL gene expression of selected clones previously unidentified in bovine CL tissue was also examined. The most interesting finds indicated that mRNA encoding squalene epoxidase was constitutively expressed in CL tissue throughout the oestrous cycle and 7-fold down-regulated (P<0.05) in late luteal tissue, concomitant with the disappearance of systemic progesterone, suggesting that de novo cholesterol biosynthesis plays an important role in steroidogenesis.