T-cell internal antigen 1 counteracts somatic RNA degradation during early Xenopus embryogenesis.

In Xenopus laevis, maternal transcripts that localize to the vegetal cortex of the oocyte are specifically inherited by prospective germ cells during cleavage stages. While a large fraction of maternal transcripts is degraded during the maternal to zygotic transition (MZT), transcripts associated with the germ-line are stable. A sequence in the dead end 1 3'UTR mediates vegetal localization in the oocyte as well as miR mediated clearance in somatic cells and germ cell specific stabilization during the MZT in embryos. We could identify Tia1 to co-precipitate with known components of vegetal localization RNPs in X. laevis oocytes. Tia1 interacts and co-localizes with various localization elements from vegetally localizing RNAs. In X. laevis embryos, ectopic expression of Tia1 counteracts somatic degradation of dnd1 localization element reporter RNAs and it can synergize with Dnd1 protein in reporter RNA stabilization. Ectopic Tia1 also protects several endogenous localizing and germ cell specific mRNAs from somatic degradation. Thus, proteins that protect germ-line transcripts from miR mediated decay during the MZT in embryos might bind these RNAs already in the oocyte.