Four-hundred million years of conserved synteny of human Xp and Xq genes on three Tetraodon chromosomes.
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.]
Grützner
Frank
F
Comparative Genomics Group, Research School of Biological Sciences, Australian National University, Canberra, ACT 2601, Australia.
Roest Crollius
Hugues
H
Lütjens
Götz
G
Jaillon
Olivier
O
Weissenbach
Jean
J
Ropers
Hans-Hilger
HH
Haaf
Thomas
T
D000818:Animals; D002645:Chickens / Q000235:genetics; D002899:Chromosomes, Human, Pair 9 / Q000235:genetics; D017124:Conserved Sequence / Q000235:genetics*; D004247:DNA / Q000235:genetics; D019143:Evolution, Molecular; D005796:Genes / Q000235:genetics*; D005819:Genetic Markers / Q000235:genetics; D006801:Humans; D008969:Molecular Sequence Data; D026801:Synteny / Q000235:genetics*; D023721:Tetraodontiformes / Q000235:genetics*; D014960:X Chromosome / Q000235:genetics*
D005819:Genetic Markers; D004247:DNA