Male and hermaphrodite C.elegans differ significantly at the anatomical and behavioural level. The difference begins in their X chromosome complement. Males have a single X while hermaphrodites have two. It is the assessment of the ratio of X chromosomes to autosome set (1X:2A vs 2X:2A) that sets a C.elegans embryo on a male or hermaphrodite developmental pathway. FOX-1 is an RNP-type RNA-binding protein involved in assessing this ratio. It, along with a few other X-linked genes (often referred to as numerator elements), acts to set the level of activity of
xol-1, the regulatory gene at the head of the sex determination pathway. High levels of
xol-1 results in male development while low levels results in hermaphrodite development.
fox-1 and the other numerators act to down regulate
xol-1 activity. FOX-1 appears to act post-transcriptionally as might be expected from an RNA-binding protein. I have identified two alternative transcripts of
fox-1, both of which contain the RNA-binding motif. I have shown, using antibodies against FOX-1, that four different forms of FOX-1 can be observed throughout development with one form being predominant in the embryo. Further characterisation of these forms will be discussed with reference to their influence on the state of the sex determination pathway. I have also identified a second putative RNA-binding protein ETR-1 which interacted specifically with FOX-1 in a yeast two-hybrid screen. This protein has similarity to the elav-like family of RNA-binding proteins. It has two RNP motifs in succession at the amino terminus separated from a third by a 280 amino acid tether region. RNAi experiments with this gene result in non-sex specific lethality suggesting
etr-1 plays an essential role. Overexpression of the cDNA using a heat shock promoter shows no obvious phenotype. Analysis of the expression pattern using GFP-Lac-Zis underway.