title: Sex in the wormcounting and compensating X-chromosome dose.
abstract: The nematode Caenorhabditis elegans counts its X chromosomes to determine sex and to activate the process of dosage compensation, which ensures that males (XO) and hermaphrodites (XX) express equal levels of most X-chromosome products. The number of X chromosomes is communicated by a set of X-linked genes called X-signal elements, which repress the master sex-determination switch gene xol-1 via two distinct, dose-dependent molecular mechanisms in XX embryos. X-chromosome gene dosage is compensated by a specialized protein complex that includes evolutionarily conserved components of mitotic and meiotic machinery. This complex assembles on both X chromosomes of hermaphrodites to repress transcription by half. The recruitment of chromosome segregation proteins to the new task of regulating X-chromosome-wide gene expression points to the evolutionary origin of nematode dosage compensation.
authors.affiliation: Howard Hughes Medical Institute, Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720-3204, USA. bjmeyer@uclink4.berkeley.edu
authors.forename: B J
authors.initials: BJ
authors.lastname: Meyer
mesh_terms: D000818:Animals; D017173:Caenorhabditis elegans / Q000502:physiology*; D004303:Dosage Compensation, Genetic; D005260:Female; D005786:Gene Expression Regulation; D008297:Male; D012723:Sex; D019849:Sex Determination Processes; D014960:X Chromosome