DIFFERENTIAL EXPRESSION PATTERN OF XQPAR-LINKED GENES SYBL1 AND IL9R CORRELATES WITH THE STRUCTURE AND EVOLUTION OF THE REGION

The recently discovered second pseudoautosomal region (XqPAR) contains at least two genes, IL9R and SYBL1. Recent findings show that, like X pPAR genes, IL9R escapes X inactivation and its Y allele is also expre ssed, but SYBL1 seems to act like an X-linked gene, expressed from the active X chromosome but not from the inactive X or Y. Here we show th at differences are also seen in the evolution of the sex chromosome lo cations of IL9R and SYBL1, IL9R is known to be autosomal in mice, and is X-linked only in primates. SYBL1, however, has been found to be on the X chromosome in all mammals tested, from marsupials to humans, Bot h genes were duplicated on the Y homologue of the terminal portion of the X chromosome during the evolution of Homo sapiens from other highe r primates. The inactivation pattern of SYBL1 may be correlated with i ts longer history of X linkage, and at a more centromeric chromosomal position during evolution; the more recent X linkage and more telomeri c position of the IL9R gene may explain its autosomal, 'uninactivated' transcriptional status.