Abstract
Microarray data analysis revealed a cluster of well compensated genes in the MHM (male-hypermethylated) region on chicken chromosome Zp, whereas Zq is enriched in non-compensated genes. The non-coding MHM RNA may therefore play a role in dosage compensation in the female.
Highlights
Most Z chromosome genes in birds are expressed at a higher level in ZZ males than in ZW females, and are relatively ineffectively dosage compensated
By mapping the male to female ratios of mRNA expression of Z genes according to their positions on the Z chromosome, we report here that dosage compensated genes are located all along the chromosome, but that the male hypermethylated (MHM) region contains a higher percentage of compensated genes than other regions
We propose that detrimental effects of a lack of overall dosage compensation on the Z chromosome may be mitigated by selective compensation of genes that are most dosage-critical, both in the MHM region and elsewhere on the Z chromosome
Summary
Most Z chromosome genes in birds are expressed at a higher level in ZZ males than in ZW females, and are relatively ineffectively dosage compensated. Like the mammalian X and Y chromosomes, the euchromatic Z is large (over 500 genes) and the heterochromatic W small (probably containing tens of genes) [1,2,3,4] In both groups, the difference in copy number of the Z or X chromosomes results in one sex having a higher genomic dose of Z or X genes. Mammalian dosage compensation is accomplished through inactivation of one of the X chromosomes in every female cell, and upregulation of the single active X chromosome in both males and females [9,10] These combined mechanisms effectively equate the expressed gene dose between the X chromosome and autosomes [9,11]. In Caenorhabditis elegans, XO males and XX hermaphrodites both upregulate X gene expression and the hermaphrodite downregulates each X chromosome, again resulting in compensation of X genes between the sexes and with autosomes [8,12]
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