X-chromosome-counting mechanisms that determine nematode sex

Nature. 1997 Jul 10;388(6638):200-4. doi: 10.1038/40669.


Sex is determined in Caenorhabditis elegans by an X-chromosome-counting mechanism that reliably distinguishes the twofold difference in X-chromosome dose between males (1X) and hermaphrodites (2X). This small quantitative difference is translated into the 'on/off' response of the target gene, xol-1, a switch that specifies the male fate when active and the hermaphrodite fate when inactive. Specific regions of X contain counted signal elements whose combined dose sets the activity of xol-1. Here we ascribe the dose effects of one region to a discrete, protein-encoding gene, fox-1. We demonstrate that the dose-sensitive signal elements on chromosome X control xol-1 through two different molecular mechanisms. One involves the transcriptional repression of xol-1 in XX animals. The other uses the putative RNA-binding protein encoded by fox-1 to reduce the level of xol-1 protein. These two mechanisms of repression act together to ensure the fidelity of the X-chromosome counting process.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Caenorhabditis elegans / genetics*
  • Caenorhabditis elegans / physiology
  • Caenorhabditis elegans Proteins*
  • Chromosome Mapping
  • Disorders of Sex Development / genetics
  • Gene Dosage
  • Gene Expression Regulation
  • Genes, Helminth*
  • Genes, Reporter
  • Helminth Proteins / genetics
  • Helminth Proteins / physiology
  • Karyotyping
  • Male
  • Mutation
  • RNA-Binding Proteins / genetics
  • RNA-Binding Proteins / physiology
  • Sex Differentiation / genetics*
  • Transcription, Genetic
  • X Chromosome*


  • Caenorhabditis elegans Proteins
  • Helminth Proteins
  • RNA-Binding Proteins
  • XOL-1 protein, C elegans