Cell mixing during early epiboly in the zebrafish embryo

Abstract

Descendants of early blastomeres in the zebrafish come to populate distinctive regions of the fate map. We present a model suggesting that the distribution of cells in the early gastrula (the fate map stage) results from the passive response of cells to reproducible forces that change the overall shape of the blastoderm just prior to gastrulation. We suggest that one of the morphogenetic changes that accompanies epiboly, the upward doming of the yolk cell into the overlying blastoderm, could be responsible for cell mixing. In support of the model, we show that the timing, extent, and directions of cell mixing in the embryo accurately reflect the expectations of the model. Finally, we show that one portion of the gastrula, a marginal region that later gives rise to many of the mesendodermal derivatives, experiences little cell mixing during the doming process.As a result, this region in the gastrula is populated by the descendants of the subset of the early blastomeres that were originally at the margin. The finding that cytoplasm initially at the edge of the 1 -celled blastodisc is transmitted specifically to mesendodermal precursors at the fate map stage raises the possibility that maternal determinants may contribute to initiation of embryonic patterning in the zebrafish embryo. o 1995 WiIey-Liss, Inc.

Mutations inhalf baked/E-cadherin block cell behaviors that are necessary for teleost epiboly

“…It is notable that in all the above examples, frog and fish, it is not clear if radial intercalation by itself is a force generating movement or if the movement is a passive response of a tissue to outside forces, e.g. being stretched or being compressed between two opposing tissues, as has been suggested by Wilson et al (Wilson et al, 1995).…”

“…Using scanning electron micrographs of freeze-fractured blastulae, radial intercalation was classically described in the amphibian blastocoel roof (Keller, 1980), and this process is thought to be a driving force for the expansion of the amphibian animal cap. Radial intercalation is also known to occur in the zebrafish blastula as the blastoderm thins during the doming stage, and is renowned for its annoying property of mixing blastula cell lineages, thus causing the indeterminate early fate map of zebrafish (Helde et al, 1994;Kimmel and Warga, 1987;Warga and Kimmel, 1990;Wilson et al, 1995). It is notable that in all the above examples, frog and fish, it is not clear if radial intercalation by itself is a force generating movement or if the movement is a passive response of a tissue to outside forces, e.g.…”

Zebrafish protocadherin 10 is involved in paraxial mesoderm development and somitogenesis

“…2c). Cells with GFP fluorescence remained coherent during gastrulation, despite generalized cell mixing (Ho, 1992;Wilson et al, 1995;Woo et al, 1995), to form patches of fluorescent cells (Fig. 2a).…”

Dynamic regulation of the microtubule and actin cytoskeleton in zebrafish epiboly

“…At the midblastula transition, deep cells become motile with active blebs extending in random directions until cells begin to move radially outward [2]. It is generally believed that deep cells are pushed outward by the doming yolk cell due to the fact that most cells disperse into the center of the embryo [9]. However, whether deep cells move actively or passively during epiboly initiation needs further investigation.…”