Williams N (1995) Science "How males and females achieve X equality."

Williams N

[Science, 1995]

Sex has lots of advantages, as the number of species that indulge in it shows. But it also poses a potentially lethal problem. Most species use distinct X and Y sex chromosomes to determine who develops as female and who as male-and the female generally has more copies of the X chromosome than the male. But the X chromosome contains many genes needed equally by males and females, threatening females with what could be a lethal excess of X-chromosome gene products-or males with an equally serious deficiency. Researchers have known for decades that humans and other sexually reproducing species survive because of a correcting mechanism known as "dosage compensation" that equalizes the expression of X-linked genes between the sexes. But only now are they beginning to figure out how

Reinke V (2007) Nat Genet "Think globally, act locally."

Reinke V

[Nat Genet, 2007]

In the nematode Caenorhabditis elegans, dosage compensation is mediated by a subtle twofold downregulation of both X chromosomes. A new study provides a significant advance in our understanding of how the X is targeted for dosage compensation and how this global regulation is integrated with regulation of the expression of each gene.

Swain A et al. (1998) Nature "Developmental genetics. Too much sex is bad for males."

Lovell-Badge R, Swain A

[Nature, 1998]

Many species rely on chromosome-based systems-such as one X versus two X chromosomes-to trigger the differences between males and females. To do this they must find ways to count the sex chromosomes and to activate the process of dosage compensation, which corrects the imbalance of sex-linked genes. A paper by Carmi, Kopczynski and Meyer on page 168 of this issue brings us closer to understand chromosome counting in the nematode worm Caenorhabditis elegans. The authors have identified an X-linked gene that encodes a protein related to nuclear-hormone receptors. This protein, SEX-1, represses the transcription of xol-1, the pivotal gene involved in both dosage compensation and sex determination.