We have long been searching for localized maternal mRNA in early embryos of the worm by a range of approaches of differential screening. In the course of the systematic analysis of in situ hybridization with a set of classified cDNA clones which have been generated by our cDNA project (see '95 IWM abstract #2), we found that the clone,
yk61h1, of the cDNA group CELK01662 (= YK1662 in ACEDB) showed an asymmetric distribution of its mRNA at 2-cell stage embryos. Closer examinations on behavior of the mRNA in gonads and embryos by in situ hybridization showed that (1) the mRNA started to appear at the turn of gonad, (2) it was distributed evenly in oocytes, (3) it was segregated posteriorly as the first cleavage proceeded, (4) the mRNA remained in P4 but disappeared in other somatic blastmeres (perhaps by a mechanism of degradation). In situ analysis using
nop-1 embryos which lacked pseudo-cleavage suggested that the segregation of the mRNA occurred during the first cleavage. Northern hybridization showed that the mRNA (1.3 Kb) was detected in embryos and adults but not in L1 larva. We named this gene
pos-1 (posterior segregation), and have analyzed it further. Full sequencing of the cDNA clone showed that the
pos-1 mRNA has the trans-spliced leader SL1 and strong homology to the zinc-finger region of the mammalian Tsi11 growth factor inducible genes. This zinc- finger motif is also found in the maternally expressed C.elegans gene
pie-1. Interestingly, the position of
pos-1 turned out to be very close to a second maternal gene,
skn-2. The
skn-2 gene like
pie-1 is required for proper development of the P lineage and
skn-2 and
pie-1 mutants exhibit dominant genetic interactions (see '95 IWM abstract #215 and 441). These genetic interactions and the physical and genetic proximity of
pos-1 and
skn-2 led us to invetigate the possibility that
pos-1 =
skn-2. Preliminary evidence supports this hypothesis: (1) injection experiments using
pos-1 anitsense RNA caused phenocopies of
skn-2, and (2) a missense mutation was found in the zinc finger region of
pos-1 in a
skn-2 mutant (
zu148). Injection-rescue experiments and genomic sequencing of
pos-1 region in more
skn-2 mutant alleles are in progress. We are also raising antibodies against
pos-1 protein and continuing our analysis of the
skn-2 mutant phenotype.