A missing gene. It could be the absence of a strategic protein that explains male infertility. An absence that has consequences on the spermatozoa, which find themselves without a connection between the tail and the head. This is the thesis put forward by researchers at the University of Gothenburg in Sweden. Scientists have identified a new protein, which they nickname 'MC2', which appears to play a crucial role in the formation of sperm capable of 'swimming'. Mice lacking the offending gene – the one that controls the MC2 protein – are unable to produce offspring. The hypothesis paves the way for the study of new diagnostic methods and treatments, but also for research into a possible future male contraceptive.
The protein that has attracted the attention of experts is necessary to ensure that the head and tail of the spermatozoa 'talk to each other'. “The connection is located in the 'neck' of the sperm head and facilitates coordinated movement and function as the sperm swims towards the egg. Of course, the tail and head will be created perfectly even without such a connection, but to no avail, as they will not be able to achieve their goal,” says Kexin Zhang, a doctoral candidate in the Department of Chemistry and Molecular Biology at the University of Gothenburg.
Experiments in mice indicated to Kexin Zhang and colleagues that the production of the MC2 protein was controlled by a specific gene in the genome. Ironically, this appears unimportant for females. In fact, the gene is not found on the sex chromosome and had no impact on the ability of females to produce offspring. When it was removed in male mice using 'genetic scissors', the researchers saw that they stopped producing the protein and became completely sterile. It is already known that genetic factors are responsible for 15-30% of male infertility. The one identified by the researchers could be a cause that falls into the category.
“My research has contributed to improving understanding of the causes of infertility due to the absence of the sperm head, known as acephalous sperm syndrome. Until now, the cause of this diagnosis was unknown,” highlights Kexin Zhang.
The discovery of the MC2 protein provides new information on the molecular structure of sperm cells that then develop into spermatozoa. Researchers will be able to study this information further, the Swedish work explains. “It is estimated that about 15% of all heterosexual couples have problems having children. In about half of cases the man is responsible for the problems. I hope that our research will eventually lead to new diagnostic methods and new treatments for “male infertility. It may also be possible – concludes Kexin Zhang – to create a male contraceptive by deactivating this gene”.
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