X chromosome exposed( Researchers from the European Molecu...)

Researchers from the European Molecular Biology Laboratory (EMBL) in Heidelberg, Germany, and the EMBL-European Bioinformatics Institute (EMBL-EBI) in Hinxton, UK, have revealed new insights into how sex chromosomes are regulated. A chromatin modifying enzyme helps compensate for the fact that males have only one copy of the sex chromosome X, while females have two. The enzyme distinguishes between male and female sex chromosomes in fruit flies and binds to different locations on the male and female X chromosome, the scientists report in the current issue of the journal Cell. The evolutionarily conserved enzyme is also found in humans.

In species ranging from insects to humans, sex chromosomes, the famous X and Y, are responsible for determining gender. Females have two copies of the X chromosome while males have one X and one Y. This could mean that females produce twice as many proteins from the genes carried on the X chromosome as males. However, fruit flies compensate for the sex chromosome difference by doubling the activity of genes on the X chromosome in males a vital process called dosage compensation. Biologists already know that a molecular machine called the MSL complex achieves dosage compensation in flies, but it remains unclear how exactly it accomplishes its function.

Now researchers from the lab of Asifa Akhtar at EMBL and the groups of Nick Luscombe and Paul Bertone at EMBL-EBI have uncovered how one component of the MSL complex, an enzyme called MOF, ensures that the activity of only male X chromosome genes get ratcheted up. MOF relaxes the structure of chromatin tightly packaged DNA, to allow the transcription machinery to access genes on the DNA.

We were very surprised to find MOF bound not only to the X chromosome in males, but also to all the other chromosomes in the nucleus. This suggests the enzyme as a universal regulator of transcription that has evolved to play a specific role in dosage compensation, says
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