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

Abstract

Xenopus embryos develop dorsal/ventral and anterior/posterior axes as a result of the activity of a maternal Xwnt pathway, in which β-catenin is an essential component, acting as a transactivator of transcription of zygotic genes. However, the questions of where and when β-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 antisense approach that allows us to target depletion of protein to individual blastomeres. When a 'morpholino' oligo complementary to β-catenin mRNA is injected into early embryos, it depletes β-catenin protein effectively through the neurula stage. By targeting the oligo to different cleavage blastomeres, we block β-catenin activity in different areas and at different times. Dorsal vegetal injection at the 2- and 4-cell stages blocks dorsal axis formation and at the 8-cell stage blocks head formation, while A- tier injection at the 32-cell stage causes abnormal cement gland formation. This approach shows the complex involvement of Xwnt pathways in embryonic patterning and offers a rapid method for the functional analysis of both maternal and early zygotic gene products in Xenopus. (C) 2000 Academic Press.