Testicles of most mammals are cooled in the scrotum, and elevated testicular temperatures lead to spermatogenesis failure and male infertility. A team of researchers led by Shosei Yoshida at the National Institute for Basic Biology in Japan detailed this process using organ cultures and revealed that spermatogenesis is impaired at multiple steps in a delicate temperature-dependent manner.
Spermatogenesis is the process by which haploid spermatozoa develop from germ cells in the seminiferous tubules of the testis.
In particular, although spermatogenesis is completed at 34°C/93°F (the scrotal temperature), warming to 37–38°C/98.6–100°F (temperatures in the abdomen) severely affects meiosis—the process of segregating homologous chromosomes into haploid sperms—and the damaged cells undergo cell death. Demonstrating the utility of organ culture, this study will boost the study of heat vulnerability in spermatogenesis.
Many studies have been conducted on the heat impairment of spermatogenesis by raising the testis temperature using animal models, for example, surgical relocation of the testis to the abdomen. However, actual testicular temperature could not be controlled in these experiments. Furthermore, the effects of extra-testicular factors such as the endocrine and nervous systems cannot be excluded.
To overcome these limitations, the research group took advantage of the testis organ culture setting that supports complete spermatogenesis in incubators, which was developed by Takehiko Ogawa and colleagues at Yokohama City University. By culturing mouse testes at different temperatures, spermatogenesis was found to fail at multiple steps (e.g., progression of meiosis, and generation and transformation of haploid cells), showing sharp temperature dependencies between 30°C/86°F and 40°C/104°F.
Yoshida says, “We did not expect such a delicate ensemble of multiple temperature-dependent events to underpin this well-known phenomenon. This discovery could only have been achieved using an organ culture system.”
This study has been published in Communications Biology.
Reference: “Temperature sensitivity of DNA double-strand break repair underpins heat-induced meiotic failure in mouse spermatogenesis” by Kodai Hirano, Yuta Nonami, Yoshiaki Nakamura, Toshiyuki Sato, Takuya Sato, Kei-ichiro Ishiguro, Takehiko Ogawa and Shosei Yoshida, 26 May 2022, Communications Biology.