The requirements for PCP signalling in early zebrafish endoderm morphogenesis

Abstract

The vertebrate endodermal cell layer gives rise to the intestine and related organs such as the liver and pancreas. The endodermal organs control many critical metabolic processes including the absorption of nutrients, homoeostasis of blood sugar levels, and detoxification of the blood. The cell fate specification and organogenesis of the zebrafish endoderm is well characterised, however the morphogenic processes during migration to the midline at somitogenesis stages and the formation of the primitive endodermal rod were unknown. This study used the Tg(sox17:EGFP) endodermal reporter line to determine the process of endoderm development at somitogenesis stages during two important phases of morphogenesis, the migration to the dorsal midline, and the formation of the endodermal rod (termed “midline aggregation”). Analysis of the polarisation of the microtubule organising centre (MTOC) in respect to the direction of cell migration reveals a contrasting difference between the endoderm and the surrounding mesoderm, indicating the directed migration of these two cell types are not regulated by the same mechanisms. The Planar cell Polarity (PCP) signalling pathway is known to regulate convergence and extension (CE Jessen et al., 2002). This study analysed endodermal development in the PCP mutants trilobite and knypek, and reports on the requirements of individual components of the PCP signalling pathway for endoderm development and morphogenesis during somitogenesis stages. The role of PCP signalling components during brain morphogenesis was also investigated, identifying a requirement of specific PCP signalling components for brain vesicle expansion. This study also describes the generation of a transgenic line that enables the inducible disruption of the PCP signalling to analyse the time-specific roles of this signalling pathway during development. This novel transgenic line enabled the identification of a time-specific role of PCP signalling in the regulation of hindbrain axis morphogenesis.