How chromosomes meet in the dark -- Switch that turns on X chromosome m...( A research group lead by scientists ...)

A research group lead by scientists at the University of Warwick has discovered the trigger that pulls together X chromosomes in female cells at a crucial stage of embryo development. Their discovery could also provide new insights into how other similar chromosomes spontaneously recognize each other and are bound together at key parts of analogous cell processes. This is an important mechanism as the binding togetgher of too many of too few of a particular chromosome can cause a number of medical conditions such as Down's Syndrome or Turner's Syndrome.

In our cells most genes are expressed from both types of each chromosome linked gene, but the most notable exception to this rule are X-linked genes in female mammals. During embryo development, in a step necessary to survival, one of the X chromosomes is silenced in each female cell to ensure that the levels of X-derived products are equalized in XX females and XY males, via a process known as X-Chromosome Inactivation (XCI). Recent discoveries have revealed that for that stage in the process to happen the X chromosomes have to quickly pair off (or colocalize) in a way that allows each part of those pairs of X chromosomes to be very close together and be aligned in a particular way. Failure to achieve this close physical colocalization of the two X chromosomes will lead to XCI failure and cell death.

Chromosome colocalization events are common in cells. A prominent example being mesiosis: for sexual reproduction to succeed in producing viable cells all of the homologous chromosomes in the process have to, almost simultaneously, bind together in pairs.

Yet until now the mechanisms of chromosome self-recognition and colocalization remain deeply mysterious. Researchers have had no clear understanding of how the X chromosomes actually suddenly pair off so quickly and consistently allowing this to happen.

Dr Mario Nicodemi, from the Department of Physics at the University of Warw
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