In genetic engineering and fertility, sperm sorting is a technique allowing the selection of the type of sperm cell to fertilize the egg cell with. It can be used to distinguish which sperm are the most healthy, as well as for determination of more specific traits, such as sex selection in which sperm are separated into X- (female) and Y- (male) chromosome bearing populations based on their difference in DNA content. The resultant ‘sex-sorted’ spermatozoa are then used in artificial insemination when farming animals or in-vitro fertilization (IVF) in human medical practice. Newly applied methods such as flow cytometry expand the possibilities of sperm sorting, however, these techniques are cumbersome, expensive, and risk damaging the DNA of the sperm. Now, a study from researchers at Hiroshima University develops a simple, reversible chemical treatment capable of separating X-bearing sperm from Y-bearing sperm. The team states even though their study was performed in mice, the technique is likely to be widely applicable to other mammals also. The opensource study is published in the journal PLOS.
Previous studies show during sperm development in male mammals, the X and Y chromosomes are segregated into different cells meaning an individual sperm will carry either one or the other. Therefore, X chromosome carrying sperm give rise to female offspring and sperm bearing a Y chromosome produce male offspring. The Y chromosome, is known to carry very few genes, however, the X chromosome carries many, some of which remain active in the maturing sperm. This difference in gene expression between X- and Y-bearing sperm provides a theoretical basis for distinguishing the two. The current study identifies chemicals with the ability to bind to two proteins on the female sperm cell’s surface, coded specifically by the X-bearing sperm’s genes, which slow down the movement of X-carrying sperm without affecting the Y-carrying ones.
The current study identifies almost 500 active genes only present in X-bearing sperm, of which 18 genes encode receptors on the sperm cell’s surface. Results show a chemical which binds to a pair of receptors on the X-bearing sperm cells’ surface, called Toll-like receptor 7 and 8 (TLR7/8), slowed sperm motility without impairing either sperm fertilization ability or viability. Data findings show the effect was due to impaired energy production within the X-bearing sperm and could be reversed by the removal of the chemical from the medium.
Results show treatment of mouse sperm with this retarding chemical, followed by IVF with the fastest swimmers, led to litters 90% male. Data findings show when the slower swimmers were used instead, the litters were 81% female. The lab states they have also succeeded in the selective production of male or female offspring in cattle and pigs using this method.
The team surmises they have developed a cheap and simple technique allowing them to separate mouse sperm carrying an X chromosome from those carrying a Y chromosome. For the future, the researchers state their technique has the potential to greatly simplify sex selection for either IVF or artificial insemination in animals.
Source: Hiroshima University
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