The Hox gene
ceh-13 is first expressed in the Ep cell and in certain cells in the AB lineage during early embryogenesis. We screened for mutations causing alternations in the early
ceh-13::gfp expression. We have isolated several mutations and cloned two genes.
yt2 is a fully penetrant maternal effect early embryonic lethal mutation that we mapped on the center of LG II. We found an opal mutation in the second last exon of the predicted gene EEED8.1. Transformation rescue and RNAi experiments confirmed that this mutation is the cause for the
yt2 phenotype. EEED8.1 has two distinctive domains namely an RNA recognition motif that is located at N terminus and a Tudor domain that lies in the center. We therefore named this gene
tudr-1 (TUdor Domain RNA recognition motif). The localization of P-granules, PIE-1::GFP, PAR-2::GFP, and POP-1::GFP indicate that the initial cell polarities re correct in
tudr-1 (
yt2 or RNAi) embryos. After the 4 cell stage the cell divisions and cell movements become abnormal and the mutants arrest as grossly disorganized embryos with
ceh-13::gfp expressing cells distributed all over the embryo.
yt5 is a temperature sensitive maternal effect lethal mutation which causes loss of the
ceh-13::gfp expression. All embryos arrest without any signs of morphogenesis at the restrictive temperature of 25<
sym05>C. At 15<
sym05>C about 5% of the worms survive and many express
ceh-13::gfp normally. The mutation does not cause a general failure of the transcriptional or translational machineries since
sur-5::gfp is expressed. We mapped it on the right tip of LG IV and found an ochre mutation at the C terminus of the predicted gene T06A10.1. We were able to phenocopy
yt5 by RNAi against T06A10.1. We named the gene
mel-46 (Maternal Effect Lethal). T06A10.1 contains a highly conserved DEAD box helicase at the N terminus and is a putative ortholog of mammalian DDX20/Dp103/Gemin3. However, not all of the several transcripts we detected contain the DEAD box.