Medical research says it's a protein called CIB1 linked to fertility

Nov 1, 2006 11:39 GMT  ·  By

Recently, a team at the University of North Carolina at Chapel Hill School of Medicine found that a protein associated with blood clotting is essential for sperm formation.

Scientists noticed that male mice lacking both copies of the gene encoding the protein, called CIB1, have reduced testes, less spermatogonia cells (cells that produce spermatozoa) and produce no mature spermatozoa at all. Instead, female mice lacking the gene were fertile, as were males lacking just one copy of the gene.

Animals - including mammals (so, also, mice and humans) - have two genes encoding every protein (and roughly, every trait), which can be identical, or one functional - one mutant, or two mutants. Usually, there is a standard gene for a function, meaning that it encodes the fittest protein for that function. The mutants can encode a protein with exactly similar function, slightly different (to a positive or negative degree) or can render the gene inactive. "All male mice bred without both copies of the gene were infertile," said Dr. Weiping Yuan, UNC research assistant professor of pharmacology.

Genes linked to fertility have been also found in mice on studies researching conditions such as cancer, diabetes and heart disease. "In 2000, UNC researchers found several genes essential for male mouse fertility while studying how cells transport chloride, sodium and potassium," Yuan continued.

Previous teams works proved the protein is implied in blood clotting in humans by keeping blood platelets from sticking together, being a body's anti-coagulant that impedes uncontrolled blood clotting, involved in heart attacks and strokes. "From initial observations, the CIB1 defect in mice appears to disrupt sperm formation in its final stage," said Dr. Deborah O'Brien, associate professor of cell and developmental biology.

"To make a sperm, you have to go from a fairly typical cell to one that has a very distinctive shape and half the number of chromosomes. The male mice missing CIB1 appear to have a problem very late in this process, when the cell differentiates into a sperm cell. Further study would be needed to determine if the finding has implications for human infertility," she said.

"Some infertility (in human males) could be due to a mutation in CIB1."

"This protein is known to regulate cell migration in other cells. Whether that ability is linked to this problem with spermatogenesis, we don't know," said Dr. Leslie Parise, professor of biochemistry and biophysics and pharmacology, the discoverer of CIB1 in 1997.