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Gene defects that may be behind male infertility identified

Scientists at the University of North Carolina at Chapel Hill say that they have identified a gene which is crucial to the final steps of the formation of a functional sperm cell called spermiogenesis.

London, October 18 : Scientists at the University of North Carolina at Chapel Hill say that they have identified a gene which is crucial to the final steps of the formation of a functional sperm cell called spermiogenesis.

In a study, the researchers engineered mice to lack the Jhdm2a gene, and found that the rodents had stopped producing many mature sperm. The fewer sperm that the mice produced were also found to have abnormally shaped heads and immotile tails.

"Defects in this gene could be the cause for some cases of male infertility," Nature magazine quoted senior author Dr. Yi Zhang, Howard Hughes Medical Institute investigator and professor of biochemistry and biophysics in the UNC School of Medicine, as saying.

"Because this gene has a very specific effect on the development of functional sperm, it holds great potential as a target for new infertility treatments that are unlikely to disrupt other functions within the body," he added.

The study, funded by the Howard Hughes Medical Institute and the National Institutes of Health, provides evidence that Jhdm2a directly controls expression of several genes required for DNA packaging in sperm cells.

In a study published in Cell last year, Zhang's laboratory had shown that the enzyme Jhdm2a removes a methyl tag carried by one of the histones-spools of protein that package the DNA so it fits into the nucleus-to allow the gene to become switched on, or expressed.

"Although a number of histone demethylases have been identified, very little is known regarding their biological functions, particularly in the context of whole animals," said Dr. Yuki Okada, a postdoctoral fellow in Zhang's laboratory and lead author on the study.

In their latest study, the researchers found that mice genetically engineered to lack Jhdm2a had smaller testes, a significantly lower sperm count, and were infertile.

Furthermore, the fewer sperm produced by the mutant mice displayed significant morphological defects, including abnormally shaped heads and immotile tails.

With a view to assessing the packaging state of the sperm DNA, the scientists used electron microscopy and a fluorescent dye called acridine orange, which fluoresces differently depending on the packaging state of a sperm.

The two techniques showed that there was a defect in sperm DNA packaging in the mutant mice.

According to the researchers, this finding indicates that incomplete DNA packaging was the cause of infertility.

"There are several mouse models that exhibit the male infertility seen in human syndromes such as azoospermia (absence of sperm) or globozoospermia (sperm with round heads)," said Zhang,

"However, most of the genes required for normal spermatogenesis in mice are intact in human patients, raising the possibility that we might consider the jhdm2a gene as a culprit in these human male infertility syndromes," he added.

The researchers are now looking for mutations in this gene in infertility patients. They are also trying to identify the cofactors in the cell that may be behind this effect.

ANI