GO:0001545 primary ovarian follicle growth: Folliculogenesis Pathway, Genes, Functions and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0001545 primary ovarian follicle growth is the biological process by which primary follicles enlarge through oocyte growth and granulosa and/or theca cell proliferation until more than one granulosa cell layer is present, forming a preantral follicle.
• The transition from a single-layer primary follicle to a multi-layer preantral follicle is a rate-limiting step in folliculogenesis and is controlled by intraovarian growth factors such as AMH, TGF-beta family ligands, and hyaluronan synthesis [1,4,5,7].
• Mouse primary follicles grow slowly immediately after activation and then progressively accelerate, which determines the duration of the primary follicle phase.
• Disruption of primary follicle growth contributes to premature ovarian insufficiency, and experimental interventions such as bone marrow stem cell infusion, mesenchymal stem cell exosomes, and finerenone can restore follicle growth in animal models [2,3,6].
• Key genes and pathways implicated in this process include AMH, GDF9, BMP15, TGFBR1, SMAD2/3, HAS2, YAP/TAZ, and PI3K/AKT/mTOR signaling [1,4,5,6,7].
• CRISPR knockout, point-mutation, knock-in, and overexpression cell models combined with CRISPR library screening and bioinformatics are powerful tools to dissect the causal roles of genes in primary ovarian follicle growth [1,8].
Description
Primary ovarian follicle growth (GO:0001545) is a defined stage of ovarian folliculogenesis in which a primary follicle, characterized by a single layer of cuboidal granulosa cells surrounding the oocyte, enlarges through oocyte growth and proliferation of granulosa and/or theca cells until more than one granulosa cell layer is present, forming a preantral follicle. This process is a critical checkpoint in female fertility because the number and quality of follicles that progress beyond the primary stage determine the ovarian reserve and the subsequent capacity for ovulation [1,8]. Understanding the molecular control of primary follicle growth is therefore central to reproductive biology and to the pathophysiology of ovarian insufficiency [1,2]. The process is regulated by a complex interplay of intraovarian paracrine factors, extracellular matrix remodeling, and intracellular signaling cascades [1,7]. For example, anti-Mullerian hormone (AMH) regulates ovary size by counteracting the positive influence of clustered ovarian follicle growth, while transforming growth factor-beta (TGF-beta) family members modulate granulosa cell proliferation and differentiation during follicle development. Hyaluronan synthesis has also been shown to be involved in ovarian follicle growth in rats. Recent studies have revealed that mouse primary follicles experience slow growth rates after activation followed by progressive increases that influence the duration of the primary follicle phase. Moreover, experimental interventions such as bone marrow stem cell infusion and human umbilical cord mesenchymal stem cell-derived exosomes can promote ovarian follicle growth and improve ovarian function in models of premature ovarian insufficiency [3,6]. These findings highlight the importance of primary follicle growth as a target for fertility preservation and therapeutic intervention [2,3,6]. This article provides a research-grade overview of GO:0001545, covering its definition, mechanisms, key genes, disease relevance, and the CRISPR-based models and methods used to study it.
primary ovarian follicle growth At A Glance
| GO ID | GO:0001545 |
|---|---|
| GO term | primary ovarian follicle growth |
| Ontology | biological_process |
| Synonym | none |
| Major function | Increase in size of primary follicles including oocyte growth and granulosa and/or theca cell proliferation until more than one layer of granulosa cells is present (preantral follicle) |
| Related process | Ovarian folliculogenesis, granulosa cell proliferation, oocyte growth |
| Key regulators | AMH, TGF-beta family ligands, hyaluronan, PI3K/AKT/mTOR, Hippo signaling |
| Disease relevance | Premature ovarian insufficiency, infertility, ovarian dysfunction |
What Is GO:0001545?
According to the Gene Ontology, GO:0001545 primary ovarian follicle growth is defined as the increase in size of primary follicles, including oocyte growth and granulosa and/or theca cell proliferation, until more than one layer of granulosa cells is present, forming a preantral follicle. In simpler terms, it is the developmental step in which a small, single-layer follicle grows into a larger, multi-layer follicle that is ready for further maturation.
Why Is primary ovarian follicle growth Important in Cell Biology?
Primary ovarian follicle growth is a decisive step in female reproduction because it determines the size of the pool of follicles that can subsequently mature and ovulate. Dysregulation of this process leads to premature ovarian insufficiency and infertility, and it is a major focus of research into fertility preservation and assisted reproduction [1,2,3,6]. Understanding the molecular mechanisms of primary follicle growth also provides insights into ovarian aging and the effects of environmental or therapeutic interventions on ovarian function [4,8].
• It is a rate-limiting step in folliculogenesis that controls the number of follicles available for ovulation.
• It is regulated by intraovarian growth factors such as AMH and TGF-beta family members, which are critical for normal ovarian function [4,7].
• Disruption of primary follicle growth is a hallmark of premature ovarian insufficiency and infertility [2,3,6].
• Mouse primary follicle growth kinetics influence the duration of the primary follicle phase and overall reproductive lifespan.
• Hyaluronan synthesis and extracellular matrix remodeling are required for follicle growth in animal models.
• Stem cell-based therapies and antifibrotic drugs can restore follicle growth in preclinical models of ovarian insufficiency [2,3,6].
• The process is a target for CRISPR-based functional genomics to identify causal genes in fertility disorders [1,8].
• It provides a model system to study the interplay between cell proliferation, differentiation, and oocyte-granulosa communication [1,7].
• Understanding it aids in the development of in vitro follicle culture systems for fertility preservation [3,6].
• It is relevant to reproductive toxicology and the assessment of environmental impacts on ovarian reserve [4,5].
What Happens During primary ovarian follicle growth?
Activation of primordial follicles to primary follicles
In simple terms: Dormant primordial follicles wake up and become primary follicles.
The first step in primary follicle growth is the activation of primordial follicles, which are quiescent structures consisting of an oocyte surrounded by a single layer of flattened granulosa cells. Upon activation, granulosa cells become cuboidal and the follicle is classified as a primary follicle. This transition is regulated by intraovarian factors such as PI3K/AKT/mTOR signaling and is influenced by the local environment. The rate of activation and subsequent growth is critical for maintaining the ovarian reserve over the reproductive lifespan [1,8].
Oocyte growth and granulosa cell proliferation
In simple terms: The egg cell grows larger and the surrounding support cells multiply.
During primary follicle growth, the oocyte enlarges and granulosa cells proliferate to form multiple layers. This phase is characterized by a slow initial growth rate followed by progressive acceleration, as demonstrated in mouse primary follicles. The proliferation of granulosa cells is driven by paracrine signals, including TGF-beta family members such as GDF9 and BMP15, which are secreted by the oocyte and act on granulosa cells. Hyaluronan synthesis also contributes to follicle growth, likely by remodeling the extracellular matrix to accommodate the expanding follicle.
Formation of the preantral follicle
In simple terms: The follicle becomes a multi-layered structure called a preantral follicle.
As granulosa cells continue to proliferate, the follicle acquires more than one layer of granulosa cells and is termed a preantral follicle. This stage marks the completion of primary follicle growth and prepares the follicle for antrum formation. The transition is accompanied by the recruitment of theca cells and the establishment of a vascular network. AMH, produced by granulosa cells, regulates this transition by counteracting the positive influence of clustered follicle growth, thereby controlling ovary size. Disruption of this step can lead to follicle arrest and ovarian insufficiency [2,6].
Regulation by intraovarian signaling pathways
In simple terms: Signals inside the ovary tell the follicle when to grow and when to stop.
Primary follicle growth is tightly regulated by a network of intraovarian signaling pathways. The TGF-beta superfamily, including activins, inhibins, and bone morphogenetic proteins (BMPs), plays a central role in modulating granulosa cell proliferation and differentiation. The Hippo signaling pathway has been implicated in the regulation of ovarian function and granulosa cell proliferation, as shown in models of premature ovarian insufficiency treated with mesenchymal stem cell-derived exosomes. Additionally, the PI3K/AKT/mTOR pathway is a key intracellular regulator of follicle activation and growth. These pathways integrate endocrine and paracrine signals to coordinate follicle development.
Extracellular matrix remodeling and hyaluronan synthesis
In simple terms: The follicle's surrounding scaffold is remodeled to allow it to expand.
As the follicle grows, the extracellular matrix (ECM) must be remodeled to accommodate the increasing size. Hyaluronan, a major component of the ECM, is synthesized by hyaluronan synthases (HAS1, HAS2, HAS3) and has been shown to be involved in ovarian follicle growth in rats. The accumulation of hyaluronan and other ECM components provides structural support and may also serve as a reservoir for growth factors. Dysregulation of ECM remodeling can impair follicle growth and contribute to ovarian pathology.
Key Genes Involved in GO:0001545 primary ovarian follicle growth
The following genes and proteins have been implicated in the regulation of primary ovarian follicle growth based on published literature.
| Gene | Major Role | Research Relevance |
|---|---|---|
| AMH | Regulates ovary size by counteracting clustered follicle growth | Knockout models show altered follicle recruitment and ovary size |
| GDF9 | Oocyte-secreted TGF-beta family ligand that promotes granulosa cell proliferation | Mutations linked to premature ovarian insufficiency; key target for functional studies |
| BMP15 | Oocyte-derived growth factor regulating granulosa cell function | Associated with ovarian dysgenesis and POI; studied in KO and knock-in models |
| TGFBR1 | Receptor for TGF-beta family ligands | Mediates signaling in granulosa cells; potential target for point mutations |
| SMAD2/3 | Intracellular transducers of TGF-beta signaling | Phosphorylation status reflects pathway activity; used in pathway analysis |
| HAS2 | Hyaluronan synthase 2, synthesizes hyaluronan in ECM | Involved in follicle growth; KO models show impaired expansion |
| YAP/TAZ | Hippo pathway effectors regulating cell proliferation | Modulated by MSC exosomes in POI models; targets for overexpression |
| PIK3CA | Catalytic subunit of PI3K, activates AKT | Central to follicle activation; overexpression models used |
| AKT1 | Serine/threonine kinase promoting cell survival and growth | Phosphorylation is a readout of PI3K pathway activity |
| MTOR | Kinase integrating nutrient and growth signals | Regulates granulosa cell proliferation; target of rapamycin inhibition |
| FOXO3 | Transcription factor repressed by AKT, maintains dormancy | Knockout leads to premature follicle activation |
| INHA | Inhibin alpha subunit, regulates FSH secretion | Marker of granulosa cell function; KO models available |
| INHBA | Activin beta A subunit, promotes granulosa cell proliferation | Overexpression and KO models used to study follicle growth |
| BMPR2 | BMP receptor type II | Mediates BMP signaling in granulosa cells; point mutations studied |
| CTNNB1 | Beta-catenin, WNT signaling effector | Regulates granulosa cell fate; conditional KO models exist |
| CCND2 | Cyclin D2, cell cycle regulator | Promotes granulosa cell proliferation; overexpression models |
| CDKN1B | p27Kip1, cell cycle inhibitor | Knockout leads to increased follicle growth |
| FSHR | FSH receptor on granulosa cells | Mediates endocrine control of follicle growth; mutations cause POI |
How Is primary ovarian follicle growth Regulated?
Primary ovarian follicle growth is regulated by a combination of endocrine and intraovarian paracrine signals. The PI3K/AKT/mTOR pathway is a central intracellular regulator that controls the activation of primordial follicles and subsequent growth. The Hippo signaling pathway has been shown to modulate granulosa cell proliferation and ovarian function, as evidenced by the effects of mesenchymal stem cell-derived exosomes in premature ovarian insufficiency models. TGF-beta family ligands, including GDF9, BMP15, and activins, regulate granulosa cell proliferation and differentiation through SMAD-dependent signaling. AMH, produced by granulosa cells, acts as a negative regulator of follicle recruitment and growth, thereby controlling the size of the growing follicle pool. Additionally, hyaluronan synthesis and ECM remodeling are required for follicle expansion. The rate of primary follicle growth is also intrinsically programmed, with mouse primary follicles exhibiting slow initial growth followed by progressive acceleration.
primary ovarian follicle growth and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| AMH | Premature ovarian insufficiency, polycystic ovary syndrome | Knockout mouse, overexpression in granulosa cell lines |
| GDF9 | POI, infertility | Point mutation knock-in, KO mouse |
| BMP15 | POI, ovarian dysgenesis | Knock-in of patient mutations, KO |
| HAS2 | Impaired follicle growth | Conditional KO, overexpression |
| YAP/TAZ | POI, ovarian fibrosis | Overexpression, KO in MSC exosome models |
Premature ovarian insufficiency (POI)
Premature ovarian insufficiency is characterized by loss of ovarian function before the age of 40 and is often associated with impaired follicle growth. Disruption of primary follicle growth can lead to follicle arrest and depletion of the ovarian reserve [2,3,6]. Experimental therapies such as bone marrow stem cell infusion and human umbilical cord mesenchymal stem cell-derived exosomes have been shown to promote follicle growth and restore fertility in POI models [3,6]. Finerenone, an antifibrotic drug, has also been reported to restore fertility in POI by targeting fibrosis-related pathways.
Infertility and ovarian dysfunction
Infertility can result from defects in primary follicle growth that prevent the formation of mature preantral follicles. Studies in animal models have shown that hyaluronan synthesis is required for normal follicle growth, and its inhibition impairs follicular development. Similarly, dysregulation of TGF-beta signaling leads to abnormal granulosa cell proliferation and follicle arrest. Understanding these mechanisms is essential for developing diagnostic and therapeutic strategies for infertility.
Ovarian aging and reduced ovarian reserve
The rate of primary follicle growth influences the duration of the primary follicle phase and the overall reproductive lifespan. Mouse studies have shown that slow initial growth rates followed by progressive increases determine how long follicles remain in the primary stage. Accelerated follicle growth can lead to premature depletion of the ovarian reserve, while slowed growth may extend the reproductive lifespan but reduce fertility [4,8]. AMH levels are used clinically as a marker of ovarian reserve, reflecting the number of growing follicles.
From primary ovarian follicle growth-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does gene X regulate primary follicle growth? | CRISPR knockout in mouse granulosa cell lines or primary follicle culture [1,8] |
| Does a specific point mutation in gene X cause POI? | Point-mutation knock-in in mice or human granulosa cell lines |
| Does overexpression of gene X promote follicle growth? | Overexpression cell models and in vivo electroporation |
| What is the role of gene X in TGF-beta signaling? | Knock-in of tagged SMAD proteins for live imaging |
| How does gene X affect hyaluronan synthesis? | KO of HAS2 and measurement of hyaluronan in follicle cultures |
| Can gene X rescue follicle growth in POI models? | Knock-in or overexpression in POI mouse models [2,3,6] |
How to Study the primary ovarian follicle growth Process
| Method | What It Measures | Typical Application |
|---|---|---|
| RNA-seq | Transcriptome changes | Identify differentially expressed genes during follicle growth [1,6] |
| Proteomics | Protein abundance and modifications | Study signaling pathway activation [1,7] |
| Phosphoproteomics | Phosphorylation events | Map kinase cascades (PI3K/AKT, SMAD) [1,7] |
| Immunofluorescence | Protein localization and proliferation markers | Assess granulosa cell proliferation and follicle staging [4,8] |
| CRISPR knockout screening | Gene essentiality | Discover novel regulators of follicle growth [1,8] |
| Bioinformatics pathway analysis | Enriched pathways and networks | Interpret omics data in the context of GO:0001545 [1,6] |
| In situ hybridization | Spatial gene expression | Localize mRNA of key genes in follicle compartments |
| Follicle culture and live imaging | Dynamic growth and morphology | Measure growth rates and responses to treatments |
RNA sequencing (RNA-seq)
RNA-seq can be used to profile gene expression changes during primary follicle growth. By comparing primary follicles at different stages, researchers can identify differentially expressed genes and pathways, such as TGF-beta and Hippo signaling, that regulate this process [1,6,7].
Proteomics and phosphoproteomics
Proteomic analysis of granulosa cells or follicular fluid can reveal changes in protein abundance and post-translational modifications during follicle growth. Phosphoproteomics is particularly useful for studying signaling pathways such as PI3K/AKT/mTOR and SMAD activation [1,7].
Imaging and histological analysis
Histological sections of ovaries can be used to classify follicle stages and measure follicle size. Immunofluorescence for markers such as Ki67 (proliferation) and AMH can provide spatial information about granulosa cell proliferation and differentiation [4,8].
CRISPR screening and functional genomics
Pooled CRISPR knockout screens in granulosa cell lines or primary follicle cultures can identify genes essential for primary follicle growth. Bioinformatics analysis of screening data can prioritize candidate genes for further validation [1,8].
How CRISPR Can Be Used to Study GO:0001545 primary ovarian follicle growth
Knockout
CRISPR knockout of candidate genes in granulosa cell lines or primary follicle cultures can determine whether a gene is required for primary follicle growth. For example, knockout of AMH or HAS2 would test their roles in follicle expansion and granulosa cell proliferation [4,5]. Knockout models can also be generated in mice to study the in vivo consequences on ovarian reserve and fertility [1,8].
Point Mutation
Point mutations identified in patients with premature ovarian insufficiency can be introduced into cell lines or mice using CRISPR base editing or homology-directed repair. This allows researchers to test whether a specific variant is causal for defective primary follicle growth. For instance, mutations in GDF9 or BMP15 can be modeled to study their impact on granulosa cell signaling.
Knock-in
Knock-in of reporter genes or epitope tags (e.g., GFP, HA) into endogenous loci enables live imaging and biochemical analysis of proteins involved in follicle growth. Tagged SMAD proteins can be used to monitor TGF-beta signaling dynamics in real time. Knock-in of human disease variants into mouse models can also create more accurate models of POI [2,3].
Overexpression
CRISPR activation (CRISPRa) or lentiviral overexpression can be used to increase the expression of genes that promote follicle growth, such as YAP/TAZ or GDF9. Overexpression models can test whether a gene is sufficient to enhance follicle growth or rescue POI phenotypes [6,7]. These models are particularly useful for studying gain-of-function mechanisms.
How EDITGENE Supports primary ovarian follicle growth Research
Researchers studying primary ovarian follicle growth-related genes often need to determine whether a candidate gene is causally involved in follicle development or is merely a bystander. EDITGENE provides a comprehensive suite of CRISPR-based services to enable precise functional interrogation of genes in ovarian biology.
Contact EDITGENE today to design your custom CRISPR model for primary ovarian follicle growth research.
Frequently Asked Questions About primary ovarian follicle growth
What is GO:0001545 primary ovarian follicle growth?
GO:0001545 is a Gene Ontology biological process term defined as the increase in size of primary follicles, including oocyte growth and granulosa and/or theca cell proliferation, until more than one layer of granulosa cells is present, forming a preantral follicle.
What genes are involved in primary ovarian follicle growth?
Key genes include AMH, GDF9, BMP15, TGFBR1, SMAD2/3, HAS2, YAP/TAZ, PIK3CA, AKT1, MTOR, FOXO3, INHA, INHBA, BMPR2, CTNNB1, CCND2, CDKN1B, and FSHR [1,4,5,6,7,8].
How is primary ovarian follicle growth regulated?
It is regulated by intraovarian signaling pathways such as PI3K/AKT/mTOR, Hippo, and TGF-beta, as well as by endocrine factors like FSH and AMH [1,4,6,7].
What diseases are associated with defects in primary ovarian follicle growth?
Defects are associated with premature ovarian insufficiency, infertility, and reduced ovarian reserve [2,3,6].
How can CRISPR be used to study primary ovarian follicle growth?
CRISPR knockout, point mutation, knock-in, and overexpression models can be used to test the causal role of specific genes in follicle growth and to model patient mutations [1,7,8].
What is the role of AMH in primary ovarian follicle growth?
AMH regulates ovary size by counteracting the positive influence of clustered ovarian follicle growth, thereby controlling the number of growing follicles.
What is the role of hyaluronan in follicle growth?
Hyaluronan synthesis is involved in ovarian follicle growth in rats, likely by remodeling the extracellular matrix to support follicle expansion.
How fast do primary follicles grow?
Mouse primary follicles experience slow growth rates after activation followed by progressive increases that influence the duration of the primary follicle phase.
Can stem cell therapy restore primary follicle growth?
Bone marrow stem cell infusion and human umbilical cord mesenchymal stem cell-derived exosomes have been shown to promote ovarian follicle growth and improve ovarian function in premature ovarian insufficiency models [3,6].
What methods are used to study primary ovarian follicle growth?
Common methods include RNA-seq, proteomics, immunofluorescence, CRISPR screening, and follicle culture with live imaging [1,6,7,8].
Conclusion
Primary ovarian follicle growth (GO:0001545) is a fundamental process in female reproduction that determines the size and quality of the ovarian reserve. It is regulated by a complex network of intraovarian signaling pathways and is disrupted in premature ovarian insufficiency and infertility. Advances in CRISPR-based functional genomics and stem cell therapies are providing new insights into the mechanisms of follicle growth and potential therapeutic strategies. Continued research into this process will be essential for improving fertility preservation and treating ovarian disorders.
References
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- 2. Lin Z et al.. 2026. Antifibrotic drug finerenone restores fertility in premature ovarian insufficiency.. Science 391(6785):eadz4075 PMID: 41643022
- 3. Herraiz S et al.. 2018. Fertility rescue and ovarian follicle growth promotion by bone marrow stem cell infusion.. Fertil Steril 109(5):908-918.e2 PMID: 29576341
- 4. Lim C et al.. 2026. AMH regulates ovary size by counteracting the positive influence of clustered ovarian follicle growth.. Hum Reprod 41(5):795-808 PMID: 41742785
- 5. Takahashi N et al.. 2014. Involvement of hyaluronan synthesis in ovarian follicle growth in rats.. Reproduction 147(2):189-97 PMID: 24218629
- 6. Li Z et al.. 2021. Human Umbilical Cord Mesenchymal Stem Cell-Derived Exosomes Improve Ovarian Function and Proliferation of Premature Ovarian Insufficiency by Regulating the Hippo Signaling Pathway.. Front Endocrinol (Lausanne) 12:711902 PMID: 34456868
- 7. Rosairo D et al.. 2008. Transforming growth factor-beta: its role in ovarian follicle development.. Reproduction 136(6):799-809 PMID: 18780765
- 8. Richard S et al.. 2023. Mouse primary follicles experience slow growth rates after activation and progressive increases that influence the duration of the primary follicle phase†.. Biol Reprod 109(5):684-692 PMID: 37552056
