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An early and massive wave of germinal cell apoptosis is required for the development of functional spermatogenesis
1Department of Pathology, Centre Médical Universitaire, Geneva, Switzerland.
Abstract:
Transgenic mice expressing high levels of the BclxL or Bcl2 proteins in the male germinal cells show a highly abnormal adult spermatogenesis accompanied by sterility. This appears to result from the prevention of an early and massive wave of apoptosis in the testis, which occurs among germinal cells during the first round of spermatogenesis. In contrast, sporadic apoptosis among spermatogonia, which occurs in normal adult testis, is not prevented in adult transgenic mice. The physiological early apoptotic wave in the testis is coincident, in timing and localization, with a temporary high expression of the apoptosis-promoting protein Bax, which disappears at sexual maturity. The critical role played by the intracellular balance, probably hormonally controlled, of the BclxL and Bax proteins (Bcl2 is apparently not expressed in normal mouse testis) in this early apoptotic wave is shown by the occurrence of a comparable testicular syndrome in mice defective in the bax gene. The apoptotic wave appears necessary for normal mature spermatogenesis to develop, probably because it maintains a critical cell number ratio between some germinal cell stages and Sertoli cells, whose normal functions and differentiation involve an elaborate network of communication.
Insights
High levels of BclxL or Bcl2 proteins disrupt male germ cell development by preventing essential early apoptosis, leading to sterility. This highlights the critical role of apoptosis regulation in spermatogenesis.
Area of Science:
- Reproductive Biology
- Cell Biology
- Developmental Biology
Background:
- Spermatogenesis involves precise regulation of germ cell development and survival.
- Apoptosis, or programmed cell death, plays a crucial role in eliminating excess or abnormal cells during development.
- The balance of apoptosis-regulating proteins, such as Bcl-2 family members, is critical for tissue homeostasis.
Purpose of the Study:
- To investigate the role of anti-apoptotic proteins BclxL and Bcl2 in male germ cell development.
- To determine the impact of preventing early testicular apoptosis on spermatogenesis.
- To elucidate the relationship between apoptosis, Bcl-xL, Bax, and Sertoli cell communication in male fertility.
Main Methods:
- Generation of transgenic mice overexpressing BclxL or Bcl2 in male germinal cells.
- Analysis of spermatogenesis, germ cell apoptosis, and protein expression in transgenic and bax-deficient mice.
- Histological examination and cell counting to assess testicular morphology and cell ratios.
Main Results:
- Transgenic mice with high BclxL or Bcl2 levels exhibited abnormal spermatogenesis and sterility.
- Overexpression of anti-apoptotic proteins prevented a critical early wave of germ cell apoptosis during the first spermatogenic wave.
- Bax deficiency phenocopied the testicular abnormalities observed in transgenic mice, indicating a critical role for Bax in this apoptotic wave.
- The early apoptotic wave appears essential for establishing the correct germ cell-to-Sertoli cell ratio required for mature spermatogenesis.
Conclusions:
- The study demonstrates that preventing early germ cell apoptosis via BclxL or Bcl2 overexpression severely impairs male fertility.
- A physiological wave of apoptosis, regulated by the balance of proteins like Bax, is indispensable for the proper development of mature spermatogenesis.
- Maintaining appropriate germ cell numbers relative to Sertoli cells, facilitated by this apoptotic wave, is crucial for male reproductive function.