beta-catenin signaling activity dissected in the early Xenopus embryo: A novel antisense approach

Xenopus embryos develop dorsal/ventral and anterior/posterior axes as a res ult of the activity of a maternal Xwnt pathway, in which beta-catenin is an essential component, acting as a transactivator of transcription of zygoti c genes. However, the questions of where and when beta-catenin is required in early embryogenesis have not been addressed directly, because no loss-of -function method has been available. Here we report the use of a novel anti sense approach that allows us to target depletion of protein to individual blastomeres. When a "morpholino" oligo complementary to beta-catenin mRNA i s injected into early embryos, it depletes beta-catenin protein effectively through the neurula stage. By targeting the oligo to different cleavage bl astomeres, we block beta-catenin activity in different areas and at differe nt times. Dorsal vegetal injection at the 2- and 4-cell stages blocks dorsa l axis formation and at the 8-cell stage blocks head formation, while A-tie r injection at the 32-cell stage causes abnormal cement gland formation. Th is approach shows the complex involvement of Xwnt pathways in embryonic pat terning and offers a rapid method for the functional analysis of both mater nal and early zygotic gene products in Xenopus. (C) 2000 Academic Press.