Scientists have figured out exactly how heat stress damages sperm

In humans, the optimal temperature for sperm production is slightly below body temperature, in the range of around 32-35°C.

Human studies have shown that the effectsTemperatures just 1 degree Celsius above this normal range negatively impact male fertility, explains Diana Libuda, a professor in the Department of Biology at the University of Oregon's Institute of Molecular Biology.

The phenomenon of male infertility caused by hightemperature is well known. The effects of modern heat exposure and the causes of overheating - such as hot baths, tight clothing and long periods of travel - have been extensively studied. However, the underlying mechanisms that damage sperm and impair fertilization have not been fully identified.

“In both humans and C. elegans, a relatively small increase in temperature is enough to reduce male fertility,” explains Libuda's use of nematodes in the study.

An increase of 2 ° C above normal in C. elegans, a type of roundworm, resulted in a 25-fold increase in DNA damage in developing sperm compared to untreated sperm. The eggs fertilized with this damaged sperm did not produce offspring.

According to R. Scott Hawley, an expert in meiosis research, the new discovery provides scientists with a blueprint for research in mammals and humans to confirm whether the same mechanisms contribute to male infertility.

3D modeling of developingsperm cells allows you to identify areas of DNA damage caused by heat. Chromosomes are shown in gray. Areas of DNA damage are visible in yellow-red foci. Each nucleus of heat-shock spermatocytes contains multiple sites of DNA damage. Image captured using an ultra-high resolution DeltaVision wide-angle microscope. 3D simulations were performed using Imaris Microscopy Image Analysis software from Bitplane. Credit: Nicole Kurkhanevich

By the way, the research team usedmicroscopy to observe the development of sperm and eggs both under normal conditions and under heat stress. In the latter case, the researchers found more DNA damage in the sperm, but not in the eggs.

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