Aspects of Dosage Compensation and Sex Determination in Caenorhabditis elegans

Molecular analysis of X chromosome dosage compensation in Caenorhabditis elegans.

“…The recessive mutation in dpy-22 would be expected to cause decreased levels of X-linked-gene expression, based on the genetic analyses discussed in the Introduction (5,6). This expectation was tested in experiments similar to those described in the preceding section, using RNA preparations from wild-type and dpy-22 synchronized populations of first-larval-stage and adult animals.…”

“…As shown in Table 3, the dpy-22 mutation appears to have little effect on either myo-2 or act-4 transcript levels at the stages examined, except for a marginal but statistically significant decrease of act-4 transcript levels in both first-stage larvae and adults. DISCUSSION These studies were initiated to address two questions: (i) does C. elegans compensate for the difference in X chromosome dosage between males and hermaphrodites by regulating transcript levels of X-linked genes, and (it) do mutations in the genes dpy-21 and dpy-22, postulated to be involved in the dosage-compensation process (5)(6)(7)9), affect transcript levels of X-linked genes in the manner predicted by genetic analysis? With regard to the first question, our results confirm, by a somewhat different assay, the recent report of Meyer and Casson (9) that adult XX hermaphrodites and XO males have the same levels of myo-2 X transcripts relative to autosomal reference transcripts.…”

“…These are mutations causing partial loss of function such that the resulting phenotype varies with the level of the mutant gene product. Hypomorphic mutations of X-linked genes in C. elegans are observed to cause similar phenotypes in XX and X0 animals, indicating similar levels of the corresponding gene products, and thereby providing evidence for some mechanism of compensation for the difference in X chromosome dosage (5,6).…”

“…These are mutations causing partial loss of function such that the resulting phenotype varies with the level of the mutant gene product. Hypomorphic mutations of X-linked genes in C. elegans are observed to cause similar phenotypes in XX and X0 animals, indicating similar levels of the corresponding gene products, and thereby providing evidence for some mechanism of compensation for the difference in X chromosome dosage (5,6).To achieve dosage compensation, the level of X chromosome expression must presumably be dictated by the X/A ratio, but the genetic basis for this regulation is still unclear. At least four autosomal and two X-linked loci have been identified as possible-regulators of X chromosome expression.…”

“…Recessive mutations in dpy-21 and dpy-26 cause an increase in X expression based on the observation that they suppress the phenotypes resulting from hypomorphic alleles of several X-linked genes (5,6). A second class may be represented by the X-linked gene dpy-22 (7), in which a recessive mutation appears to cause a decrease in X expression, enhancing the phenotypes resulting from hypomorphic alleles of several X-linked genes (5,6).…”