Localized molecules and the establishment of polarity in zebrafish

Abstract

The generation of polarity and patterning during both vertebrate and invertebrate embryogenesis depends in part on the asymmetric localization of molecules. In the zebrafish, Danio rerio maternally deposited molecules of Wnt and TGF-b signaling pathways contribute to DV axis formation. Specifically, the Nodal related molecules Cyclops, Squint and Southpaw (which belong to TGF-b super family) are essential for dorsal and mesendoderm specification as well as specification of left-right asymmetry. In this study, I have found that transcripts of the nodal related gene squint are expressed maternally and distributed uniformly through all stages of oocytes. Upon fertilization, squint transcripts are initially localized to the blastoderm and subsequently to two blastomeres at the 4-cell stage, which depends on its 3a?? untranslated region. Disruption of the microtubule cytoskeleton by nocodazole treatment affects squint RNA transport to the blastoderm. Removal of cells containing squint transcripts from 4-8 cell embryos or injection into oocytes of antisense morpholino oligonucleotides targeting squint can cause loss of dorsal structures. Thus, the DV axis is apparent by the 4-8 cell stage during embryogenesis, and requires the maternally encoded morphogen Squint and its associated factors.