Mouse oocytes regulate granulosa cell steroidogenesis throughout follicular development

Area of Science:

• Reproductive Biology
• Endocrinology
• Cell Biology

Background:

• Mouse oocytes influence the steroidogenesis of surrounding granulosa cells.
• Oocyte-secreted factors play a role in regulating progesterone and estradiol production.

Purpose of the Study:

• To investigate the secretion of a steroid-regulating factor by mouse oocytes during follicular development.
• To determine the responsiveness of granulosa cells to this oocyte-secreted factor throughout follicular growth.

Main Methods:

• Oocyte-granulosa cell complexes from preantral and antral follicles were oocytectomized (OOX).
• OOX complexes were cultured with FSH and testosterone.
• Steroid production (progesterone and estradiol) was measured in intact and OOX complexes, with and without oocytes.

Main Results:

• Oocytectomized complexes produced significantly more progesterone than intact complexes at all developmental stages.
• Estradiol production was primarily observed in intact complexes from late antral follicles.
• Oocytectomy increased progesterone production 1.45-fold in early follicles and up to 23-fold in antral follicles.
• Oocytes inhibited progesterone accumulation in OOX complexes, with maximal inhibition by fully grown oocytes.
• Cumulus cells showed desensitization to the oocyte factor during terminal differentiation, leading to high progesterone production in ovulated complexes.
• Oocyte factors appear to regulate 3beta-hydroxysteroid dehydrogenase activity or progesterone metabolism.

Conclusions:

• Oocytes secrete increasing amounts/potency of a steroid-regulating factor during follicular development.
• Granulosa cell/cumulus cell responsiveness to the oocyte factor decreases during luteinization.
• Oocyte-granulosa cell interactions are crucial for precise control of steroidogenesis during folliculogenesis.