Oocyte numbers are reduced in developing mouse ovaries cultured in testis-conditioned medium

Area of Science:

• Reproductive biology
• Developmental biology
• Endocrinology

Background:

• Early ovarian development involves complex signaling between fetal ovaries and testes.
• Antimüllerian hormone (AMH) is known to influence both ovarian oocyte numbers and Müllerian duct regression.

Purpose of the Study:

• To investigate the effect of testis-conditioned medium on fetal mouse ovarian development, specifically oocyte numbers.
• To identify potential factors secreted by fetal testes that influence ovarian cell populations.

Main Methods:

• Fetal mouse ovaries (13 days post coitum) were cultured in medium conditioned by fetal testes (testis-CM) or standard medium.
• Ovaries were analyzed after 4 days of culture for oocyte numbers, differentiation, and Müllerian duct development.
• Testis-CM was heat-inactivated and compared to unconditioned medium; electrophoretic analysis was performed.

Main Results:

• Testis-CM significantly reduced oocyte numbers in cultured fetal ovaries compared to controls.
• This oocyte reduction was abolished by heat-inactivating the testis-CM, indicating a heat-labile factor.
• Ovarian differentiation, gonadal volume, ovigerous cord organization, and Müllerian duct development were not significantly affected.

Conclusions:

• Fetal testes secrete a heat-labile factor that reduces oocyte numbers in developing ovaries.
• This factor appears distinct from antimüllerian hormone, as it reduces oocytes without inhibiting Müllerian duct development.
• These findings suggest an additional testicular factor plays a role in regulating early oocyte attrition.