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Control of early ovarian follicular development
K P McNatty1, D A Heath, T Lundy
1Wallaceville Animal Research Centre, Upper Hutt, New Zealand.
Journal of Reproduction and Fertility. Supplement
|February 29, 2000
Summary
Early follicular growth in sheep and cows involves distinct stages, with initial variations in primordial follicles influencing later development. Most growth phases are independent of gonadotropins and occur hierarchically.
Area of Science:
- Reproductive Biology
- Developmental Biology
- Cell Biology
Background:
- Early follicular growth encompasses development from primordial to early antral stages.
- Follicular development in sheep and cows is classified into types 1-5 based on granulosa cell configuration.
- Type 1 primordial follicles exhibit significant variability in granulosa cell number and oocyte diameter, potentially impacting later growth stages.
Purpose of the Study:
- To investigate the characteristics and variability of early follicular growth phases in sheep and cows.
- To explore the species-specific differences in granulosa cell number and function during early follicular development.
- To examine the role of gonadotropins and various growth factors in follicular development.
Main Methods:
- Classification of follicular growth phases (types 1-5) based on granulosa cell morphology in sheep and cows.
- Analysis of oocyte diameter and granulosa cell composition in primordial follicles.
- Review of existing evidence on gonadotropin independence and hierarchical follicular development.
- Examination of the expression patterns of growth factors, receptors, and gonadotropin receptors (e.g., c-kit, GDF-9, FSH-R, LH-R) in different follicular types and species.
Main Results:
- Significant variability exists in type 1 primordial follicles regarding granulosa cell number and oocyte diameter, potentially established during follicle formation.
- Species-specific differences (sheep vs. cattle) are noted in granulosa cell characteristics relative to oocyte size during early follicular growth.
- Evidence suggests that follicular growth phases (types 1-5) are largely gonadotropin-independent and follow a hierarchical pattern.
- Numerous growth factors, receptors, and gonadotropin receptors are expressed in a phase- and cell-specific manner across follicular types 1-5 in sheep, cows, and pigs.
Conclusions:
- Variability in early follicular development, particularly in primordial follicles, may influence subsequent follicular growth dynamics.
- Follicular growth is primarily a hierarchical, gonadotropin-independent process, regulated by specific growth factors and their receptors.
- While many regulatory factors are identified, their precise roles in early follicular development require further investigation.