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.