Enrichment of brain-related genes on the mammalian X chromosome is ancient and predates the divergence of synapsid and sauropsid lineages.
Previous studies have revealed an enrichment of reproduction- and brain-related genes on the human X chromosome. In the present study, we investigated the evolutionary history that underlies this functional specialization. To do so, we analyzed the orthologous building blocks of the mammalian X chromosome in the chicken genome. We used Affymetrix chicken genome microarrays to determine tissue-selective gene expression in several tissues of the chicken, including testis and brain. Subsequently, chromosomal distribution of genes with tissue-selective expression was determined. These analyzes provided several new findings. Firstly, they showed that chicken chromosomes orthologous to the mammalian X chromosome exhibited an increased concentration of genes expressed selectively in brain. More specifically, the highest concentration of brain-selectively expressed genes was found on chicken chromosome GGA12, which shows orthology to the X chromosomal regions with the highest enrichment of non-syndromic X-linked mental retardation (MRX) genes. Secondly, and in contrast to the first finding, no enrichment of testis-selective genes could be detected on these chicken chromosomes. These findings indicate that the accumulation of brain-related genes on the prospective mammalian X chromosome antedates the divergence of sauropsid and synapsid lineages 315 million years ago, whereas the accumulation of testis-related genes on the mammalian X chromosome is more recent and due to adaptational changes.
Kemkemer
Claus
C
Institute of Human Genetics, University of Ulm, Ulm, Germany.
Kohn
Matthias
M
Kehrer-Sawatzki
Hildegard
H
Fundele
Reinald H
RH
Hameister
Horst
H
D000818:Animals; D001921:Brain / Q000378:metabolism*; D002645:Chickens / Q000235:genetics*; D002874:Chromosome Mapping; D019143:Evolution, Molecular; D020869:Gene Expression Profiling; D005796:Genes / Q000502:physiology*; D008297:Male; D020411:Oligonucleotide Array Sequence Analysis; D009928:Organ Specificity; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013737:Testis / Q000378:metabolism*; D014960:X Chromosome / Q000235:genetics*
D012333:RNA, Messenger