Abstract
ABSTRACTThe zebrafish endoderm begins to develop at gastrulation stages as a monolayer of cells. The behaviour of the endoderm during gastrulation stages is well understood. However, knowledge of the morphogenic movements of the endoderm during somitogenesis stages, as it forms a mesenchymal rod, is lacking. Here we characterise endodermal development during somitogenesis stages, and describe the morphogenic movements as the endoderm transitions from a monolayer of cells into a mesenchymal endodermal rod. We demonstrate that, unlike the overlying mesoderm, endodermal cells are not polarised during their migration to the midline at early somitogenesis stages. Specifically, we describe the stage at which endodermal cells begin to leave the monolayer, a process we have termed ‘midline aggregation’. The planar cell polarity (PCP) signalling pathway is known to regulate mesodermal and ectodermal cell convergence towards the dorsal midline. However, a role for PCP signalling in endoderm migration to the midline during somitogenesis stages has not been established. In this report, we investigate the role for PCP signalling in multiple phases of endoderm development during somitogenesis stages. Our data exclude involvement of PCP signalling in endodermal cells as they leave the monolayer.
Highlights
During early development, the zebrafish endoderm undergoes a number of distinct morphogenetic stages to generate the gut and associated organs
This indicates that the loss of both vangl2 and gpc4 causes a greater defect than the loss of vangl2 or gpc4 alone, and demonstrates that these genes do not play redundant roles during endodermal morphogenesis
We extended this study into endodermal cells, to determine whether they generate a polarised microtubule organising centres (MTOC) during convergence to the midline, which would indicate that their movement to the midline constitutes an active migration
Summary
The zebrafish endoderm undergoes a number of distinct morphogenetic stages to generate the gut and associated organs. The stages that have been characterised are: specification of the endoderm, migration of the endoderm during early gastrulation, formation of the endodermal rod, and organogenesis stages. The exact movements of the endoderm between mesoderm-dependent midline migration and during the formation of the endodermal rod have not been examined in detail. This study aims to fill that knowledge gap. Received 19 September 2016; Accepted 6 March 2017
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