As a consequence, certain gastrulation movements, such as convergent extension of the mesoderm 2 and vegetal rotation of the endoderm 12, have been analysed in vitro. However, these two-dimensional (2D) imaging methods are limited in their capacity to reveal deep tissue dynamics. It has been studied in living and fixed gastrulae using time-lapse light microscopy 4, 8– 11, and in fixed, cleaved or dissected embryos 3 by electron microscopy. Gastrulation is a morphogenetic milestone in which complex cell and tissue rearrangements position the embryonic germ layers. When combined with perturbation experiments to investigate molecular and biomechanical underpinnings of morphogenesis, our technique should help to advance our understanding of the fundamentals of development. A transient ectodermal ridge, formed in association with the confrontation of ventral and head mesendoderm on the blastocoel roof, is identified. Moreover, digitally determined volume balances confirm that early archenteron inflation occurs through the uptake of external water. Differential flow analysis separates collective from relative cell motion to assign propulsion mechanisms. laevis embryos, including vegetal endoderm rotation, archenteron formation, changes in the volumes of cavities within the porous interstitial tissue between archenteron and blastocoel, migration/confrontation of mesendoderm and closure of the blastopore. We demonstrate that this powerful four-dimensional imaging technique provides high-resolution views of gastrulation processes in wild-type X. Here we use non-invasive in vivo, time-lapse X-ray microtomography, based on single-distance phase contrast and combined with motion analysis, to examine the course of embryonic development. None of these methods allows cell behaviours to be observed with micrometre-scale resolution throughout the optically opaque, living embryo over developmental time. In Xenopus laevis, the South African clawed frog and also in zebrafish, cell and tissue movements have been studied in explants 2, 3, in fixed embryos 4, in vivo using fluorescence microscopy 5, 6 or microscopic magnetic resonance imaging 7.
#Blastopore closure high salt series
Important morphogenetic movements occur throughout embryogenesis, but in particular during gastrulation when a series of dramatic, coordinated cell movements drives the reorganization of a simple ball or sheet of cells into a complex multi-layered organism 1. An ambitious goal in biology is to understand the behaviour of cells during development by imaging- in vivo and with subcellular resolution-changes of the embryonic structure.
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