Identification and analysis of localizedmaternal determinants in ascidian egg cytoplasm

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Maternal information within eggcytoplasm plays crucial roles in animal embryogenesis. In ascidians, the posterior-vegetal egg cytoplasm is involved in important events such as the antero-posterior axis specification, muscle and mesenchyme cell fate determination, germ cell formation, unequal cleavage, localization of specific maternal mRNAs, and cell cycle control. So far, we isolated nine localized maternal mRNAs and sequenced them. Then we carried out functional analysis of seven RNAs (HrPEM, HrPOPK-1, HrWnt-S, HrGLUT, HrPEM-3, HrPEN-1, HrPEM-2) by inhibition of translation with morpholino antisense oligonucleotides. The results demonstrated that these localized maternal mRNAs play various roles in embryogenesis. Especially, HrPEM (with no similarity) is involved in successive unequal cleavage in the posterior pole of embryos. Another localized mRNA, HrPOPK-1 (kinase), is required for concentration and relocalization of certain mRNAs to the centrosome-attracting body. These findings are interesting and worth for further extensive analysis.