Cleavage in Xenopus Development

Oregon Health & Science University, Portland OR

Investigators

Abstract

A. PROJECT SUMMARY One of the most critical phases in the life of a new organism is embryonic cleavage, a series of rapid, synchronous cell divisions that populates the fertilized egg's volume with zygotic nuclei, clonally segregates its developmental potential, and reduces cell volume to that of somatic cells. Cleavage differs in several ways from somatic-cell mitosis, particularly by its synchrony, rapidity, and reliance on maternally synthesized components. The long-term objective of the proposed research is to understand the morphogenetic role of embryonic cleavage in the development of the frog Xenopus laevis. During cleavage, a large amount of new basolateral membrane is laid down along the early cleavage planes by localized exocytosis. As it expands, this new membrane carries out a number of integrated activities that are important for embryonic development, including establishment of tight junctions along the apical-basolateral boundaries, maintenance of cell-cell adhesion, and formation of the blastocoel. Recent work reveals a burst of protrusive activity along the expanding cleavage furrow, including the extension of filopodia that form attachment sites across the furrow gap. The aims of the proposed research are to test the idea that the protrusive activity is important for cadherin-dependent blastomere adhesion, and that the newly established apical and basolateral membrane domains are maintained by flow of membrane and underlying cortex from the furrow base outward to the apical-basolateral boundary. The proposed experiments will advance our understanding of the respective developmental roles of specific cell-biological functions, including cell-cell adhesion, protrusive activity, and cortical flow in a key early morphogenetic process. In a broader context, the research activities will provide a useful training ground for graduate students, undergraduates and high school students interested in the basic cell biology of early amphibian development.