Male infertility can be transmitted through the maternal line
Scientists at the University of Pennsylvania, working under the guidance of Dr. Jeremy Wang, identified the TEX11 gene located on the mouse X chromosome, mutations of which cause male infertility and reduce the fertility of females.
The human X chromosome also contains the TEX11 gene. Considering that mutations of this gene lead to azoospermia (absence of motile spermatozoa in the seminal fluid) in mice, mutations of its human counterpart may well be the cause of male infertility. The male genome contains only one X chromosome inherited from the mother and, accordingly, only one copy of the TEX11 gene, any mutation of which can theoretically lead to sterility. The authors suggested that TEX11 gene screening can be used for prenatal diagnosis of male infertility.
The TEX11 gene is the first meiosis-specific factor found on the X chromosome. Meiosis is a process of cell division without chromosome doubling, as a result of which gametes of both sexes are formed. During meiosis, homologous chromosomes conjugate, recombine and diverge. At the same time, fragments of genetic material obtained by the body from the parents are exchanged, which ensures the formation of genetically diverse gametes (sperm and eggs). Therefore, meiosis defects are the main cause of both infertility and birth defects.
According to statistics, about 15% of couples in the world are infertile, but the genetic causes of infertility for the most part are still unclear. For decades, it was believed that the X chromosome has no relation to male infertility, because during male meiosis it is in an inactive state. These ideas led to the fact that when studying infertility problems, scientists focused on the Y chromosome and autosomes (non-sex chromosomes).
However, in an earlier study of mouse spermatogenic cells, the authors found that about 30% of the genes specific to these cells are localized on the X chromosome, which indicates its participation in meiosis. Despite the fact that these genes are inactivated in the late stages of meiosis, they play an important role in the early stages of this process.
In particular, experiments on genetically modified mice have shown that the absence of TEX11 protein is the cause of chromosomal asynapsis (lack of conjugation) during the formation of gametes. This means that homologous chromosomes do not form pairs and form fewer crossings – chromosome recombination zones – in the early stages of meiosis. This leads to the death of spermatocytes at later stages of the process of genetic recombination and male infertility.
According to the authors, since the TEX11 protein interacts with the SYCP2 molecule – an important component of the protein complex that provides conjugation of chromosomes during meiosis – it is not only necessary for conjugation and genetic recombination, but also provides a physical relationship between these two meiotic processes.
Portal "Eternal youth" www.vechnayamolodost.ru based on the materials of ScienceDaily
18.03.2008