Pregastrular morphogenesis in Xenopus

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). The main objective of this project is to investigate the developmental role of a newly discovered class of membranous protrusions interconnecting blastomeres of early, cleavage-stage Xenopus laevis embryos. Time lapse confocal microscopy of live, surgically opened embryos expressing a membrane-tethered fluorescent protein unexpectedly reveals hundreds of extremely long, stable filopodia traversing the entire volume of the blastocoel, interconnecting blastomeres separated by as much as 300 microns. Most blastomeres appear to be simultaneously interconnected and in long-term contact with as many as half a dozen adjacent and nonadjacent cells via these long filopodia. These processes are filled with f-actin, and small membranous blebs translocate bidirectionally within them. Near the 512-cell stage, most of the long filopodia settle onto nearby blastomere surfaces and vesiculate, producing clusters of small membrane-bound, cytoplasm-bearing particles. The time of appearance and distribution of these remarkable structures suggest a direct role in early embryonic patterning, perhaps via the vectorial transport of maternal components or via blastomere-blastomere communication. The aims of this project are to explore this hypothesis by asking 1) whether the spatial pattern of traversing filopodia is biased with respect to the primary embryonic axes; 2) whether early perturbation of dorsal-ventral patterning alters their deployment or function. Intellectual merit: These activities explore the potential of a novel physical pathway for transporting maternal morphogens or signaling between early blastomeres, and thus represents a new facet on a problem of long standing in developmental biology. Broader impact: The PI is committed to the mentoring of projects by students, teachers, and visiting scientists. The experiments described here will provide a useful training ground for graduate students, undergraduates, and others interested in early development.