Infertility of mice and men

A team of Chinese researchers has used mice to identify a gene that causes male infertility, which may pave a way towards treatment.

Male infertility affects 20 million people globally, and – unsurprisingly – contributes to about 50% of infertility in couples. There are a variety of reasons for it, but one of the causes is malformations in the tails of sperm, preventing them from swimming towards eggs.

Researchers at the Guangzhou Women and Children’s Medical Center collected sperm and genetic samples from infertile men. In one individual, they found a genetic mutation that caused defects in a protein in the sperm tail, FSIP2 (Fibrous Sheath-Interacting Protein 2).

“The fibrous sheath covers the tails of sperm found in humans, mice and other species in which fertilisation occurs within the animal’s body,” says Na Li, co-lead investigator on the project.

“It offers the sperm tails flexibility and strength, which is necessary for sperm to swim in the dense and sticky medium of the human body before they meet the egg. Interestingly, animals whose sperm swim through water because fertilization occurs outside of the body, such as fish, either do not have the FSIP2 protein or, at most, a defective version.”

The researchers bred two populations of mice: one with the same FSIP2 mutation as the human patient, and one that overproduced the normal FSIP2 protein.

Mice with the mutation were infertile. Mice that overproduced the protein, however, had sperm tails that were seven times longer than normal mice, and they remained fertile.

The researchers hope their findings in mice will be useful for developing treatments for male infertility, as it highlights the importance of the fibrous sheath in the tails of sperm.

A paper describing the research is published in Development.

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