Stretching Morphogenesis of the Roof Plate and Formation of the Central Canal

Cathleen Teh,Moises Mallo,Vladimir Korzh,Melvin Sin,Igor Kondrychyn

doi:10.1371/journal.pone.0056219

Abstract

BackgroundNeurulation is driven by apical constriction of actomyosin cytoskeleton resulting in conversion of the primitive lumen into the central canal in a mechanism driven by F-actin constriction, cell overcrowding and buildup of axonal tracts. The roof plate of the neural tube acts as the dorsal morphogenetic center and boundary preventing midline crossing by neural cells and axons.Methodology/Principal FindingsThe roof plate zebrafish transgenics expressing cytosolic GFP were used to study and describe development of this structure in vivo for a first time ever. The conversion of the primitive lumen into the central canal causes significant morphogenetic changes of neuroepithelial cells in the dorsal neural tube. We demonstrated that the roof plate cells stretch along the D–V axis in parallel with conversion of the primitive lumen into central canal and its ventral displacement. Importantly, the stretching of the roof plate is well-coordinated along the whole spinal cord and the roof plate cells extend 3× in length to cover 2/3 of the neural tube diameter. This process involves the visco-elastic extension of the roof place cytoskeleton and depends on activity of Zic6 and the Rho-associated kinase (Rock). In contrast, stretching of the floor plate is much less extensive.Conclusions/SignificanceThe extension of the roof plate requires its attachment to the apical complex of proteins at the surface of the central canal, which depends on activity of Zic6 and Rock. The D–V extension of the roof plate may change a range and distribution of morphogens it produces. The resistance of the roof plate cytoskeleton attenuates ventral displacement of the central canal in illustration of the novel mechanical role of the roof plate during development of the body axis.

Highlights

It is thought that neurulation ends after the neural tube is formed [1,2]
SqET33 Transgenic Line Expresses GFP in roof plate (RP) Cells The SqET33 transgenic line used in this study has been established during Tol2 transposon-mediated enhancer trap screen [38]
In the 3 days-old larva GFP fluorescence is detected in the neural tube along the A–P axis (Fig. 1A) largely in the dorsal aspect of the forebrain (Fig. 1B), midbrain, hindbrain (Fig. 1C) and spinal cord (Fig. 1D)

Summary

Introduction

It is thought that neurulation ends after the neural tube is formed [1,2]. Once formed the neural tube could be divided from dorsal to ventral into the roof plate (RP), alar plate, basal plate and floor plate. Sevc et al [13] recognized interdependence of RP elongation and conversion of the primitive lumen into the central canal in rat, but suggested that the rearrangement and migration of radial glial cells is behind the transformation of the primitive lumen into the central canal These authors along with others recognized a role of two other factors behind conversion of the primitive lumen into central canal: cell proliferation in the neural tube and build-up of axonal pathways. Neurulation is driven by apical constriction of actomyosin cytoskeleton resulting in conversion of the primitive lumen into the central canal in a mechanism driven by F-actin constriction, cell overcrowding and buildup of axonal tracts. The roof plate of the neural tube acts as the dorsal morphogenetic center and boundary preventing midline crossing by neural cells and axons

Methods

Results

Conclusion