Transcriptome profiling of granulosa cells of bovine ovarian follicles during growth from small to large antral sizes

Abstract

BackgroundAt later stages of folliculogenesis, the mammalian ovarian follicle contains layers of epithelial granulosa cells surrounding an antral cavity. During follicle development granulosa cells replicate, secrete hormones and support the growth of the oocyte. In cattle, the follicle needs to grow > 10 mm in diameter to allow an oocyte to ovulate, following which the granulosa cells cease dividing and differentiate into the specialised cells of the corpus luteum. To better understand the molecular basis of follicular growth and granulosa cell maturation, we undertook transcriptome profiling of granulosa cells from small (< 5 mm; n = 10) and large (> 10 mm, n = 4) healthy bovine follicles using Affymetrix microarrays (24,128 probe sets).ResultsPrincipal component analysis for the first two components and hierarchical clustering showed clustering into two groups, small and large, with the former being more heterogeneous. Size-frequency distributions of the coefficient of variation of the signal intensities of each probe set also revealed that small follicles were more heterogeneous than the large. IPA and GO enrichment analyses revealed that processes of axonal guidance, immune signalling and cell rearrangement were most affected in large follicles. The most important networks were associated with: (A) Notch, SLIT/ROBO and PI3K signalling, and (B) ITGB5 and extracellular matrix signalling through extracellular signal related kinases (ERKs). Upstream regulator genes which were predicted to be active in large follicles included STAT and XBP1. By comparison, developmental processes such as those stimulated by KIT, IHH and MEST were most active in small follicles. MGEA5 was identified as an upstream regulator in small follicles. It encodes an enzyme that modifies the activity of many target proteins, including those involved in energy sensing, by removal of N-acetylglucosamine from serine and threonine residues.ConclusionsOur data suggest that as follicles enlarge more genes and/or pathways are activated than are inactivated, and gene expression becomes more uniform. These findings could be interpreted that either the cells in large follicles are more uniform in their gene expression, or that follicles are more uniform or a combination of both and that additional factors, such as LH, are additionally controlling the granulosa cells.

Molecular characterization and hormonal regulation of tissue inhibitor of metalloproteinase 1 in goat ovarian granulosa cells

“…Real-time PCR data revealed that the expression of Timp1 mRNA had a significant increase in its expression levels with increasing follicular size and higher level in corpus luteum. Similar finding has been reported that the expression of Timp1 mRNA in the GCs of bovine antral follicles were significantly higher in large follicles than that in small follicles [37]. Therefore, we guess that the increasing expression of Timp1 during the process of follicle growth may be crucial for ovarian follicle development and ovulation.…”

Evidence of a molecular clock in the ovine ovary and the influence of photoperiod

“…It is likely that the extracted ovine stromal tissue in this study contained microscopic follicles. Our finding that temporal gene expression in stroma is not synchronized by LH as previously reported in rodent whole ovaries [22] can be explained by the fact that microscopic follicles likely do not possess receptors for LH [32,33]. This is supported by the finding that LH receptor mRNA only appears after antral formation in bovine follicles [34].…”

PI3K/PTEN/Akt and TSC/mTOR signaling pathways, ovarian dysfunction, and infertility: an update

“…To understand the molecular basis of follicular growth and GC maturation, Hatzirodos et al (2014) undertook transcriptome profiling of GCs from small and large healthy bovine follicles. Substantial changes in gene expression were observed in GCs as follicles enlarged from small to large antral sizes.…”