Xtr, a plural tudor domain-containing protein, coexists with FRGY2 both in cytoplasmic mRNP particle and germ plasm in Xenopus embryo: its possible role in translational regulation of maternal mRNAs.

Xtr is present exclusively in early embryonic and germline cells. We have previously shown that loss-of-function of the Xtr in embryos causes arrest of karyokinesis progression. Since Xtr contains plural tudor domains, which are known to associate with target proteins directly, we examined Xtr-interacting proteins by immunoprecipitation with an anti-Xtr monoclonal antibody and detected a few RNA-binding proteins such as FRGY2, a component of messenger ribonucleoprotein (mRNP) particle. The coexistence of Xtr with FRGY2 by constituting an mRNP particle was further confirmed by gel filtration assay. Search of mRNAs in the immunoprecipitate with Xtr suggested that the Xtr-associated molecules included several mRNAs, of which translational products were known to play crucial roles in karyokinesis progression (RCC1, XRHAMM, and so on) and in germ cell development (XDead end). Immunohistochemical observation clearly showed the co-localization of Xtr with FRGY2 also in germ plasm, in which XDead end mRNA has been shown to be localized specifically. Taken together, we proposed the possible role of Xtr in translational activation of the maternal mRNAs repressed in mRNP particle.