Zebrafish Dynamin is required for maintenance of enveloping layer integrity and the progression of epiboly

Abstract

Epiboly, the first morphogenetic cell movement that occurs in the zebrafish embryo, is the process by which the blastoderm thins and spreads to engulf the yolk cell. This process requires the concerted actions of the deep cells, the enveloping layer (EVL) and the extra-embryonic yolk syncytial layer (YSL). The EVL is mechanically coupled to the YSL which acts as an epiboly motor, generating the force necessary to draw the blastoderm towards the vegetal pole though actomyosin flow and contraction of the actomyosin ring. However, it has been proposed that the endocytic removal of yolk cell membrane just ahead of the advancing blastoderm may also play a role. To assess the contribution of yolk cell endocytosis in driving epiboly movements, we used a combination of drug- and dominant-negative-based approaches to inhibit Dynamin, a large GTPase with a well-characterized role in vesicle scission. We show that Dynamin-dependent endocytosis in the yolk cell is dispensable for epiboly of the blastoderm. However, global inhibition of Dynamin function revealed that Dynamin plays a fundamental role within the blastoderm during epiboly, where it maintains epithelial integrity and the transmission of tension across the EVL. The epithelial defects were associated with disrupted tight junctions and a striking reduction of cortically localized phosphorylated ezrin/radixin/moesin (P-ERM), key regulators of epithelial integrity in other systems. Furthermore, we show that Dynamin maintains EVL and promotes epiboly progression by antagonizing Rho A activity.

Zebrafish epiboly: Spreading thin over the yolk

“…As few perturbations that impair epiboly affect marginal endocytosis, there is a lack of experimental data to support the model. To test this long‐standing view, the large GTPase Dynamin was inhibited in an attempt to block marginal endocytosis and assess the impact on epiboly progression (Lepage et al, ). Both pharmacological (dynasore) and dominant‐negative (DN‐dynamin) inhibition of Dynamin function reduced marginal endocytosis and produced a significant epiboly delay that was more severe for the blastoderm than for the YSL.…”

The Physical Basis of Coordinated Tissue Spreading in Zebrafish Gastrulation

“…Doming has predominantly been associated with deep cells undergoing radial intercalations (Lepage and Bruce, 2010, Warga and Kimmel, 1990). In addition, upward pushing by the yolk cell (Wilson et al., 1995) and epithelial integrity of surface cells (Lepage et al., 2014) have been involved. Still, how these different processes are spatiotemporally coordinated during doming, and how they contribute to the force-generating processes underlying tissue shape changes during doming is only poorly understood.…”

The involvement of PCP proteins in radial cell intercalations during Xenopus embryonic development

“…Similarly, the two-layered embryonic skin develops from multi-layered epidermal ectoderm (Deblandre et al, 1999; Drysdale, 1992; Stubbs et al, 2006). These processes involve diverse molecular events including changes in cell adhesion and microtubule-dependent vesicular trafficking (Itoh et al, 2014; Kim et al, 2012; Lepage et al, 2014; Marsden and DeSimone, 2001; Solnica-Krezel and Sepich, 2012; Song et al, 2013; Werner et al, 2014). …”