In C. elegans embryos, several maternal mRNAs are localized to a subset of blastomeres, yet little is known about the mechanisms. We have been studying on localization mechanisms of maternal
mex-3 mRNA, which is localized to anterior blastomeres in embryos. After fertilization the
mex-3 mRNA is gradually localized to the anterior half at the one-cell stage, and is predominantly localized in the anterior AB cell at the two-cell stage. To identify the cis-element for
mex-3 mRNA localization, we firstly produced a reporter plasmid construct consisting of the
mex-3 coding sequence fused in-frame to the VENUS sequence and the
mex-3 3'' untranslated region (3''UTR) , which is driven by the
pos-1 promoter. The plasmid construct was introduced into C. elegans by bombardment to generate transgenic lines. mRNAs transcribed from the construct was detected by in situ hybridization using the venus antisense sequence as a probe. The localization of the mRNA was the same as that of the endogenous
mex-3 mRNA, suggesting that the mRNA transcribed from the construct is under control of
mex-3 mRNA localization machinery. Secondary, we generated transgenic lines of reporter plasmid constructs that contained various parts of the
mex-3 gene by bombardment. As a result, the mRNA containing the 3''UTR of the
mex-3 gene was localized to the anterior blastomere, suggests
mex-3 3''UTR has major activity for mRNA localization. On the other hand, the 3''UTR dependent mRNA localization was disrupted by deletion of a 35-nucleotide sequence in the 3''UTR, indicating that the 35-nucleotide sequence is important for the
mex-3 mRNA localization. We are currently testing whether the 35-nucleotide is sufficient for mRNA localization.