Vol. 12, Issue 9, 1316-1322, September 2002

LETTER
Four-Hundred Million Years of Conserved Synteny of Human Xp and Xq Genes on Three Tetraodon Chromosomes

¹ Comparative Genomics Group, Research School of Biological Sciences, Australian National University, Canberra, ACT 2601, Australia; ² Genoscope, CNRS UMR8030, 91057 Evry Cedex, France; ³ Max Planck Institute of Molecular Genetics, 14195 Berlin, Germany; ⁴ Institute of Human Genetics, Mainz University School of Medicine, 55101 Mainz, Germany

The freshwater pufferfish Tetraodon nigroviridis (TNI) has become highly attractive as a compact reference vertebrate genome for gene finding and validation. We have mapped genes, which are more or less evenly spaced on the human chromosomes 9 and X, on Tetraodon chromosomes using fluorescence in situ hybridization (FISH), to establish syntenic relationships between Tetraodon and other key vertebrate genomes. PufferFISH revealed that the human X is an orthologous mosaic of three Tetraodon chromosomes. More than 350 million years ago, an ancestral vertebrate autosome shared orthologous Xp and Xq genes with Tetraodon chromosomes 1 and 7. The shuffled order of Xp and Xq orthologs on their syntenic Tetraodon chromosomes can be explained by the prevalence of evolutionary inversions. The Tetraodon 2 orthologous genes are clustered in human Xp11 and represent a recent addition to the eutherian X sex chromosome. The human chromosome 9 and the avian Z sex chromosome show a much lower degree of synteny conservation in the pufferfish than the human X chromosome. We propose that a special selection process during vertebrate evolution has shaped a highly conserved array(s) of X-linked genes long before the X was used as a mammalian sex chromosome and many X chromosomal genes were recruited for reproduction and/or the development of cognitive abilities.

[Sequence data reported in this paper have been deposited in GenBank and assigned the following accession no: AJ308098.]