The Caenorhabditis elegans Dosage Compensation Machinery Is Recruited to X Chromosome DNA Attached to an Autosome

Abstract

The dosage compensation machinery of Caenorhabditis elegans is targeted specifically to the X chromosomes of hermaphrodites (XX) to reduce gene expression by half. Many of the trans-acting factors that direct the dosage compensation machinery to X have been identified, but none of the proposed cis-acting X chromosome-recognition elements needed to recruit dosage compensation components have been found. To study X chromosome recognition, we explored whether portions of an X chromosome attached to an autosome are competent to bind the C. elegans dosage compensation complex (DCC). To do so, we devised a three-dimensional in situ approach that allowed us to compare the volume, position, and number of chromosomal and subchromosomal bodies bound by the dosage compensation machinery in wild-type XX nuclei and XX nuclei carrying an X duplication. The dosage compensation complex was found to associate with a duplication of the right 30% of X, but the complex did not spread onto adjacent autosomal sequences. This result indicates that all the information required to specify X chromosome identity resides on the duplication and that the dosage compensation machinery can localize to a site distinct from the full-length hermaphrodite X chromosome. In contrast, smaller duplications of other regions of X appeared to not support localization of the DCC. In a separate effort to identify cis-acting X recognition elements, we used a computational approach to analyze genomic DNA sequences for the presence of short motifs that were abundant and overrepresented on X relative to autosomes. Fourteen families of X-enriched motifs were discovered and mapped onto the X chromosome.

Sex-specific developmental gene expression atlas unveils dimorphic gene networks in C. elegans

“…1a) 32 . Consequently, defective DCC will result in a lethal overdose of gene expression from the X chromosomes only in hermaphrodites [33][34][35] . We used a temperature-sensitive allele (y1) in the DCC gene dpy-28 36 combined with a him-8 mutation that spontaneously leads to a high incidence of males (Fig.…”

Sex-Specific Developmental Gene Expression Atlas Unveils Dimorphic Gene Networks inC. elegans

“…The dosage compensation complex (DCC), a specialized regulatory mechanism that downregulates gene expression from the two X chromosomes, is only formed in C. elegans hermaphrodites (males carry just one X chromosome) (Figure 1A) 33 . Consequently, defective DCC will result in a lethal overdose of gene expression from the X chromosomes only in hermaphrodites [34][35][36] . We used a temperature-sensitive allele (y1) in the DCC gene dpy-28 37 with a him-8 mutation that spontaneously leads to a high incidence of males (Figure 1B).…”