Posttranscriptional regulation offem-3, a sex-determining gene of Caenorhabditis elegans

The fem-3 gene is required for male development; in hermaphrodites fem-3 directs spermatogenesis in the germ line whereas in males it is needed for somatic development and for spermatogenesis in the germ line. Loss-of-function mutations in fem-3 transform hermaphrodites and males into females; fem-3 gain-of-function mutations (fem-3(gf)) affect only hermaphrodites and cause continuous spermatogenesis due to unregulated fem-3 activity.

fem-3(gf) mutations were shown to lie in the fem-3 3$\sp\prime$untranslated region (3$\sp\prime$UTR). fem-3(gf) mutations do not cause an increase in the steady state levels of fem-3 RNA over wild-type amounts. However, fem-3(gf) RNA does have an increased polyadenylation that is coincident with unregulated fem-3 activity. Expression of exogenous wild-type fem-3 3$\sp\prime$UTR in vivo results in continuous spermatogenesis whereas fem-3(gf) 3$\sp\prime$UTR had not effect on the germ line, suggesting the wild-type 3$\sp\prime$UTR may be titrating a negative regulator from endogenous fem-3 RNA. In vitro binding experiments identified a factor that specifically binds the fem-3 3$\sp\prime$UTR. The factor is present in hermaphrodites and males, and may be a general regulator of RNAs. A model for the germline regulation of fem-3 was presented: fem-3 RNA with a long poly(A) tail is active to direct spermatogenesis; binding of a negative regulator and shortening of the poly(A) tail inactivates fem-3 RNA leading to the switch to oogenesis. The regulation is proposed to be translational.

Polyadenylation of fem-3 RNA decreases during development, and this decrease correlates with when fem-3 must be inactivated to allow oogenesis. In addition, maternal fem-3 RNA is degraded during the first few cell divisions of the embryo, suggesting it is translated early in development. These results indicate post-transcriptional regulation of fem-3 are important for the control of fem-3 activity.