Genetic and molecular analysis of fox-1, a numerator element involved in Caenorhabditis elegans primary sex determination

Abstract

fox-1 was previously identified as a candidate numerator element based on its overexpression phenotype. FOX-1 is an RRM-typc RNA-binding protein, which can bind RNAs in vitro. Western analysis detects FOX-1 throughout development, fox-1::lacZ comes on ubiquitously early during embryogenesis. Postembryonically, fox-1::lacZ is expressed sex specifically in a subset of cells in the head and tail. We describe a Tc1-derived deletion allele [fox- 1(Δ)] that removes the RRM domain, fox-1(Δ) confers no phenotype in XXs, but can rescue XO-specific lethality and feminization caused by duplications of the left end of tile X. fox-1(Δ) synergizes with putative numerators, resulting in abnormal XX development. Genetic analysis indicated that fox- 1(Δ) leads to a slight increase in xol-1 activity, while fox-1(gf) leads to partial loss of xol-1 activity, and xol-1 is epistatic to fox-1. RNase protection experiments revealed increased levels of the 2.2:kb xol-1 message in fox-1(Δ) animals, and reduced levels in fox-1(gf) animals. Additionally, fox-1(Δ) impairs male mating efficiency, which, we propose, represents another function of fox-1, independent of xol-1 and its role in sex determination.