Igor Kondrychyn, Cathleen Teh, Melvin Sin and Vladimir Korzh.
Published in PLoS ONE on 7 February 2013.
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Neurulation is driven by apical constriction of actomyosin cytoskeleton resulting in conversion of the primitive lumen is converted 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.
The 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 3x 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.
The 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.
Figure Legend: It was shown in vivo for the first time that during late neurulation cells at the dorsal midline of the neural tube - the roof plate extend in coordination with rearrangement of the primitive lumen into the central canal of the spinal cord (A, B). This process depends on activity of the transcriptional factor Zic6, which regulates adhesion of the roof plate cells to other cells at the primitive lumen (C, D), and cytoskeleton (E and not shown). This is important due to the well-known roles of the roof plate as one of the two main signaling centers that determine differentiation of neurons, and as the midline barrier and last, but not least, its mechanical role in formation of the body axis in vertebrates demonstrated in this study.
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