DPY-27: A chromosome condensation protein homolog that regulates C. elegans dosage compensation through association with the X chromosome

dpy-27 is an essential dosage compensation gene that acts to reduce expression of both hermaphrodite X chromosomes. The DPY-27 protein becomes specifically localized to the X chromosomes of wild-type XX embryos, but remains diffusely distributed throughout the nuclei of male (XO) embryos. In xol-1 mutant XO embryos that activate the XX mode of dosage compensation and die from inappropriately low X chromosome transcript levels, DPY-27 becomes localized to X. Therefore, sex specificity of the dosage compensation process is regulated at the step of DPY-27 X chromosome localization. DPY-27 exhibits striking similarity to proteins required for assembly and structural maintenance of Xenopus chromosomes in vitro and for segregation of yeast chromosomes in vivo. These findings suggest a link between global regulation of gene expression and higher order chromosome structure. We propose that DPY-27 implements dosage compensation by condensing the chromatin structure of X in a manner that causes general reduction of X chromosome expression.