mRNA localization has been observed in diverse cells and organisms. In C. elegans, there are also several maternal mRNAs, which is known to be localized during early development. Distribution patterns of these mRNAs suggest involvement of mRNA degradation in the localization. However, there is little information about cis- and trans-elements for the mRNA localization. To understand how cells regulate the localization, identification of these elements are desired. In this study, we are focusing on the maternal
pos-1 mRNA. The
pos-1 mRNA is localized to the posterior half of embryos during the 1st cleavage and is localized to germ lineage in early development. To investigate cis-elements of the localization, we first developed a vector, which maternally expresses fusion mRNA of VENUS CDS and arbitrary sequences from the
pos-1 promoter. By using the vector, we generated transgenic worms that express the VENUS::
pos-1 3''UTR fusion mRNA and tested localization of the mRNA. In situ hybridization revealed that the mRNA is localized as intrinsic
pos-1 mRNA. Thus, we analyzed the
pos-1 sequences by using the vector. Deletion analysis of the
pos-1 3''UTR revealed that 59 nt of the
pos-1 3''UTR (bases 178-236 downstream of the
pos-1 stop codon.) is required for the localization. Interestingly, there are evolutionary conserved CYCACA tandem repeats (191-196 and 199-204) and 30nt (207-236). Hence, we next tested whether these sequences are involved in the localization by making series of constructs, which contain substitutions in these sequences. This analysis revealed that these conserved sequences are actually required for the localization. We also found that, the VENUS protein is also localized in the transgenic embryos of VENUS::
pos-1 3''UTR mRNA. In the embryos, the VENUS protein was first detected just after fertilization and was uniformly expressed at the time. After that, the protein was preferentially accumulated in posterior half by the four-cell stage. Such localization is not observed in the VENUS::
mel-11 3''UTR worms; in these worms, the VENUS protein was expressed in adult gonad and was uniformly distributed in early embryos. Thus, the VENUS protein localization is
pos-1 3''UTR dependent and should be accomplished by local translation rather than post-translational protein localization. Strikingly, the
pos-1 3''UTR dependent protein localization is abolished in
mex-5 mutant, in which the
pos-1 mRNA localization is also abolished. It suggests a close correlation between
pos-1 3''UTR dependent local translation and mRNA localization. We are now trying to identify trans-elements of the
pos-1 mRNA localization by using yeast three-hybrid assay. At the meeting, we will also presents the result.