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Comments on SW Jin et al. (1999) International C. elegans Meeting "FOG-1 is a Cytoplasmic Polyadenylation Element Binding protein" (0)
Overview
SW Jin, J Kimble, & RE Ellis (1999). FOG-1 is a Cytoplasmic Polyadenylation Element Binding protein presented in International C. elegans Meeting. Unpublished information; cite only with author permission.
The fog-1 and fog-3 genes are required to specify that germ cells differentiate as sperm. Although mutations in either gene cause germ cells to develop as oocytes instead, they have no effect on somatic fates. Thus, one simple model is that fog-1 and fog-3 act in response to the sex-determination genes to regulate germ cell fates. We cloned fog-1 to test this model. First, we used RFLP mapping and deletion mapping to define a region of the YAC Y54E10 that contains fog-1 . Second, we used sequence data from this region to identify candidate genes, and tested these by Southern analysis for lesions associated with fog-1 alleles. We found that q241 is a deletion of most of fog-1 and q492 is a small deletion located within the gene. Third, we used transformation rescue experiments to confirm our identification of fog-1 . Northern analyses, RACE and RT-PCR experiments show that fog-1 produces four transcripts. These transcripts fall into two groups — two long transcripts of 2138 and 2237 nucleotides differ in their polyadenylation sites, and two short transcripts of 1612 and 1711 nucleotides lack the first four exons. All four messages are transpliced to SL1. Using RNA-mediated inactivation, we found that the large transcripts are necessary for germ cells to become sperm. Furthermore, Northern analyses show that the quantity of large transcripts is regulated by the sex-determination genes. Finally, the promotor for the large transcripts contains three potential TRA-1A binding sites. Thus, we propose that the sex-determination genes act through TRA-1A to control expression of fog-1 . The large transcripts encode a protein of 619 amino acids, which resembles Cytoplasmic Polyadenylation Element Binding proteins. These proteins regulate translation of target messages by controlling the lengths of their poly-A tails. Genetic and molecular tests show that nonsense mutations behave like null alleles of fog-1 , but that missense mutations in the conserved RNA-binding domains have a strong dominant negative effect. Thus, we propose that FOG-1 acts as part of a complex that controls translation of key messenger RNAs in the developing germ line.
