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The pre-ovulatory LH surge elicits different effects on the granulosa- and theca-specific expression profiles in bovine follicles

ABSTRACT: The molecular mechanisms that regulate the pivotal transformation processes observed in the follicular wall following the pre-ovulatory LH-surge, are still not established, particularly for cells of the thecal layer. To elucidate thecal and granulosa cell type-specific biological functions and signaling pathways, large dominant bovine follicles were collected before and 21 hrs after an exogenous GnRH induced LH surge. Because LH receptor density varies within the granulosa cell populations, antral granulosa (aGC; those aspirated by follicular puncture) and membrane associated granulosa (mGC; those scraped from the follicular wall) were compared to thecal cell expression profiles determined by mRNA microarrays. Thecal cell gene expression was less affected in the peri-ovulatory follicle when compared to granulosa cells, as evidenced by only 2% versus 25% of the ~11,000 genes expressed changing in response to the LH surge, respectively. The majority of the 203 LH-regulated thecal genes were also LH regulated in granulosa cells, leaving a total of 58 genes as LH-regulated theca cell specific genes. Most of the 58 genes (i.e., 74%) thecal specific genes including several known thecal markers (CYP17A1, NR5A1) were downregulated, while most genes identified are new to theca. Many of the newly identified upregulated thecal genes (e.g., PTX3, RND3, PPP4R4) were also upregulated in granulosa. Minimal expression differences were observed between aGC and mGC, however, transcripts encoding extracellular proteins (NID2) and matrix modulators (ADAMTS1, SASH1) predominated these differences. We also identified large numbers of unknown LH-regulated granulosa cell genes and discuss their putative roles in ovarian function.

ORGANISM(S): Bos taurus

PROVIDER: GSE46996 | GEO | 2013/05/17

SECONDARY ACCESSION(S): PRJNA203249

REPOSITORIES: GEO

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Project description:The molecular mechanisms that regulate the pivotal transformation processes observed in the follicular wall following the pre-ovulatory LH-surge, are still not established, particularly for cells of the thecal layer. To elucidate thecal and granulosa cell type-specific biological functions and signaling pathways, large dominant bovine follicles were collected before and 21 hrs after an exogenous GnRH induced LH surge. Because LH receptor density varies within the granulosa cell populations, antral granulosa (aGC; those aspirated by follicular puncture) and membrane associated granulosa (mGC; those scraped from the follicular wall) were compared to thecal cell expression profiles determined by mRNA microarrays. Thecal cell gene expression was less affected in the peri-ovulatory follicle when compared to granulosa cells, as evidenced by only 2% versus 25% of the ~11,000 genes expressed changing in response to the LH surge, respectively. The majority of the 203 LH-regulated thecal genes were also LH regulated in granulosa cells, leaving a total of 58 genes as LH-regulated theca cell specific genes. Most of the 58 genes (i.e., 74%) thecal specific genes including several known thecal markers (CYP17A1, NR5A1) were downregulated, while most genes identified are new to theca. Many of the newly identified upregulated thecal genes (e.g., PTX3, RND3, PPP4R4) were also upregulated in granulosa. Minimal expression differences were observed between aGC and mGC, however, transcripts encoding extracellular proteins (NID2) and matrix modulators (ADAMTS1, SASH1) predominated these differences. We also identified large numbers of unknown LH-regulated granulosa cell genes and discuss their putative roles in ovarian function. The single dominant ovarian follicle was collected from each cow before the LH surge or 22 hours after GnRH (used to induce LH surge). RNA was extracted from three independent cells within each follicle and there were hybridized on Affymetrix microarrays.

Project description:Gonadotropin surge acts on the preovulatory follicle of the ovary to induce luteinization of follicular cells, oocyte meiotic maturation, cumulus expansion and follicular rupture leading to ovulation. These processes are brought about by spatial and temporal changes in transcriptional regulation of genes in the follicular cells in response to the gonadotropin surge. Analysis of gene expression changes in the periovulatory follicular cells will help in delineating the signal transduction pathways involved in the above mentioned processes. In monoovulatory species like bovines, the time interval of 24-28 hours between gonadotropin surge and ovulation provides distinct advantage for studying the temporal changes in the gene expression pattern. Thus, in the present study, we attempt to identify the temporal changes in the global gene expression profile in the periovulatory follicle of buffalo cows in response to gonadotropin surge and the results suggest the involvement of Insulin-like Growth Factor 1 and cytokine signaling pathways in the periovulatory events. Experiment Overall Design: To study the periovulatory gene expression changes in buffalo cows, an induced-ovulation model system involving sequential treatment with PGF2alpha and GnRH was standardized. The follicular wave containing at least one large follicle of ~7mm size was determined by ultrasonography on day 7 of the estrous cycle before administering exogenous PGF2alpha to induce luteolysis and follicular growth. Exogenous GnRH (100Âµg i.m) was administered 36h post PGF2alpha to induce LH surge. The time course of increase in LH levels post GnRH injection was monitored. Since peak LH levels are attained 2 h post GnRH administration, the time intervals of 3 h post GnRH (corresponding to1 h post LH surge) and 24 h post GnRH (corresponding to 22 h post LH surge) were chosen to identify the gene expression profile associated with immediate early and delayed changes in periovulatory follicle respectively. Thus ovaries were collected before, 1 h and 22 h post LH surge and follicle wall and granulosa cells were isolated from the ovaries and snap frozen for the purpose of RNA isolation.

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The pre-ovulatory LH surge elicits different effects on the granulosa- and theca-specific expression profiles in bovine follicles

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