Oocyte Secreted Factors in Follicular Development

Oocyte secreted factors are crucial paracrine mediators that orchestrate the growth and maturation of ovarian follicles. Among these, growth differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15), both members of the transforming growth factor-β superfamily, act directly on adjacent granulosa and cumulus cells to regulate their proliferation, differentiation and steroidogenic activity. These factors drive cumulus expansion, support nutrient and signal exchange, and fine-tune receptor expression for follicle-stimulating hormone. Heterodimeric assemblies of GDF9 and BMP15, known as cumulin, exhibit synergistic potency in activating SMAD pathways. Through species-specific modulation of glycosylation and pro-mature domain processing, oocyte factors define ovulation rate, follicular survival or atresia and ultimately fertility. Understanding their mechanisms informs reproductive medicine and livestock breeding, offering routes to enhance assisted-reproduction outcomes and to mitigate ovarian dysfunction worldwide.

Research from Nature Portfolio

Recent studies have compared the molecular forms of GDF9 and BMP15 across species with divergent litter sizes. Analysis of pro-mature and mature ligand ratios revealed that strict monovulatory mammals exhibit elevated BMP15 levels and distinct glycosylation patterns that correlate with single-ovulation programmes, whereas GDF9 remains uniformly important. In a separate experimental model, conditional ablation of an endoplasmic reticulum chaperone in oocytes uncovered its essential role in correct folding and secretion of GDF9 and BMP15. Deficient processing led to impaired granulosa cell proliferation, disrupted folliculogenesis and reduced ovulatory rates, emphasising the interdependence of oocyte biosynthetic machinery and paracrine signalling in ovarian function.

Oocyte Secreted Factors in Follicular Development publication trend

The graph below shows the total number of articles in oocyte secreted factors in follicular development across all publications each year (not limited to Nature Index journals).

Technical terms

Oocyte secreted factors: Signalling proteins produced by the oocyte that act locally on neighbouring somatic follicle cells to control their behaviour and support follicle maturation.

Granulosa cells: Follicular somatic cells surrounding the oocyte that proliferate and produce hormones under endocrine and paracrine influence.

Cumulus cells: A specialised subgroup of granulosa cells in direct contact with the oocyte, essential for metabolic coupling and expansion of the cumulus-oocyte complex.

Paracrine signalling: Communication in which cells secrete factors that act on adjacent cells within the same tissue.

Folliculogenesis: The sequential process of ovarian follicle growth from the primordial pool to the pre-ovulatory stage.

SMAD pathway: Intracellular signalling route activated by transforming growth factor-β ligands, culminating in transcriptional regulation of target genes.

References

1. GDF9His209GlnfsTer6/S428T and GDF9Q321X/S428T bi-allelic variants caused female subfertility with defective follicle enlargement. Cell Communication and Signaling (2024).
2. Molecular forms of BMP15 and GDF9 in mammalian species that differ in litter size. Scientific Reports (2023).
3. Cumulin, an Oocyte-secreted Heterodimer of the Transforming Growth Factor-β Family, Is a Potent Activator of Granulosa Cells and Improves Oocyte Quality*. Journal of Biological Chemistry (2015).
4. Calreticulin is required for development of the cumulus oocyte complex and female fertility. Scientific Reports (2015).
5. A variant of human growth differentiation factor-9 that improves oocyte developmental competence. Journal of Biological Chemistry (2020).