Cleavage in Xenopus Development

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Fertilized eggs become multicellular through a series of rapid, synchronous cell divisions, or cleavages, that serve to populate the egg's volume with zygotic nuclei, clonally segregate the egg' s developmental potential, and reduce daughter cells' volume to that of somatic cells. In animal cells, cleavage furrowing is generally recognized to be a microfilament-dependent process. Recently, however, Dr. Danilchik discovered a novel microtubule-containing array in the early cleavage furrows in eggs of the frog Xenopus laevis. This structure consists of numerous thick, short bundles of radially arranged, acetylated microtubules that emanate from the vicinity of the contractile ring of all cleavage furrows until the midblastula stage. Dr. Danilchik hypothesizes that the microtubule array functions to recruit membrane vesicles to the site of new membrane formation at the furrow's leading edge. Since all receptor-mediated, cell-cell interactions depend on the composition of the membranes deposited between cells, it is clear that the directed membrane deposition and ingression have potentially significant roles in events of early development, such as specification of the primary tissue layers. The specific aims of this proposal are: 1) to examine in further detail the composition of the FMA via confocal immunocytochemistry, to determine whether the FMA arises as a de novo MT structure; 2) to learn the polarity of MTs in the FMA and the midzone; 3) to test whether vesicle movements in the vicinity of the new' cleavage membrane depend on an intact FMA; and 4) to test the role of known MT motor proteins in new membrane delivery.