Global analysis of X-chromosome dosage compensation.
BACKGROUND
Drosophila melanogaster females have two X chromosomes and two autosome sets (XX;AA), while males have a single X chromosome and two autosome sets (X;AA). Drosophila male somatic cells compensate for a single copy of the X chromosome by deploying male-specific-lethal (MSL) complexes that increase transcription from the X chromosome. Male germ cells lack MSL complexes, indicating that either germline X-chromosome dosage compensation is MSL-independent, or that germ cells do not carry out dosage compensation.


RESULTS
To investigate whether dosage compensation occurs in germ cells, we directly assayed X-chromosome transcripts using DNA microarrays and show equivalent expression in XX;AA and X;AA germline tissues. In X;AA germ cells, expression from the single X chromosome is about twice that of a single autosome. This mechanism ensures balanced X-chromosome expression between the sexes and, more importantly, it ensures balanced expression between the single X chromosome and the autosome set. Oddly, the inactivation of an X chromosome in mammalian females reduces the effective X-chromosome dose and means that females face the same X-chromosome transcript deficiency as males. Contrary to most current dosage-compensation models, we also show increased X-chromosome expression in X;AA and XX;AA somatic cells of Caenorhabditis elegans and mice.


CONCLUSIONS
Drosophila germ cells compensate for X-chromosome dose. This occurs by equilibrating X-chromosome and autosome expression in X;AA cells. Increased expression of the X chromosome in X;AA individuals appears to be phylogenetically conserved.
Gupta
Vaijayanti
V
Laboratory of Cellular and Developmental Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA. vaijayanti@strandls.com
Parisi
Michael
M
Sturgill
David
D
Nuttall
Rachel
R
Doctolero
Michael
M
Dudko
Olga K
OK
Malley
James D
JD
Eastman
P Scott
PS
Oliver
Brian
B
D000818:Animals; D017173:Caenorhabditis elegans / Q000235:genetics / Q000378:metabolism; D004303:Dosage Compensation, Genetic; D004331:Drosophila melanogaster / Q000235:genetics* / Q000378:metabolism; D005260:Female; D018628:Gene Dosage; D020869:Gene Expression Profiling; D008297:Male; D051379:Mice; D020411:Oligonucleotide Array Sequence Analysis; D010053:Ovary / Q000378:metabolism; D013737:Testis / Q000378:metabolism; D014158:Transcription, Genetic; D014960:X Chromosome