Abstract
The establishment of the dorso-ventral axis is a fundamental process that occurs after fertilization. Dorsal axis specification in frogs starts immediately after fertilization, and depends upon activation of Wnt/β-catenin signaling. The protein kinase CK2α can modulate Wnt/β-catenin signaling and is necessary for dorsal axis specification in Xenopus laevis. Our previous experiments show that CK2α transcripts and protein are animally localized in embryos, overlapping the region where Wnt/β-catenin signaling is activated. Here we determined whether the animal localization of CK2α in the embryo is preceded by its localization in the oocyte. We found that CK2α transcripts were detected from stage I, their levels increased during oogenesis, and were animally localized as early as stage III. CK2α transcripts were translated during oogenesis and CK2α protein was localized to the animal hemisphere of stage VI oocytes. We cloned the CK2α 3’UTR and showed that the 2.8 kb CK2α transcript containing the 3’UTR was enriched during oogenesis. By injecting ectopic mRNAs, we demonstrated that both the coding and 3’UTR regions were necessary for proper CK2α transcript localization. This is the first report showing the involvement of coding and 3’UTR regions in animal transcript localization. Our findings demonstrate the pre-localization of CK2α transcript and thus, CK2α protein, in the oocyte. This may help restrict CK2α expression in preparation for dorsal axis specification.
Highlights
The establishment of the dorso-ventral axis is a fundamental process that occurs after fertilization
Transcript and protein for the catalytic (α) and regulatory (β) subunits of CK2 are enriched in animal blastomeres of the Xenopus morula [19] and are present in animal and equatorial blastomeres in the Xenopus blastula [15,19]. is precise CK2 localization may be required for proper regulation of β-catenin, as the distribution of endogenous CK2 [15] overlaps the equatorial region where β-catenin upregulation occurs in the embryo [11,20]
CK2α transcripts are enriched in the animal hemisphere of stage 3 embryos by whole mount in situ hybridization (WISH) [15] and realtime PCR (RT-qPCR, not shown)
Summary
The establishment of the dorso-ventral axis is a fundamental process that occurs after fertilization. Is interaction results in the activation of Wnt/βcatenin signaling [10,11], a pathway required for dorsal axis formation in Xenopus laevis [12,13,14]. A number of components of Wnt/β-catenin signaling have been identi ed to play a role in dorsal axis formation in Xenopus laevis [12]. Enriched transcripts code for proteins that are essential for dorsal axis formation, e.g. dorsal determinants such as XWnt11 [26], germ layer speci cation, e.g. VegT [27,28,29], germ cell lineage speci cation, e.g. Xdazl [30] and cell movements, e.g. Vg1 [31,32]. Two mechanisms have been proposed for vegetal localization of transcripts during oogenesis, an early and a late pathway (reviewed in [33,34,35])
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