Ernst, S., Liu, K., Agarwala, S., Moratscheck, N., Avci, M.E., Nogare, D.D., Chitnis, A.B., Ronneberger, O., and Lecaudey, V. (2012) Shroom3 is required downstream of FGF signalling to mediate proneuromast assembly in zebrafish. Development (Cambridge, England). 139(24):4571-4581.
During development, morphogenetic processes require a precise coordination of cell differentiation, cell shape changes and,
often, cell migration. Yet, how pattern information is used to orchestrate these different processes is still unclear. During
lateral line (LL) morphogenesis, a group of cells simultaneously migrate and assemble radially organized cell clusters, termed
rosettes, that prefigure LL sensory organs. This process is controlled by Fibroblast growth factor (FGF) signalling, which
induces cell fate changes, cell migration and cell shape changes. However, the exact molecular mechanisms induced by FGF activation
that mediate these changes on a cellular level are not known. Here, we focus on the mechanisms by which FGFs control apical
constriction and rosette assembly. We show that apical constriction in the LL primordium requires the activity of non-muscle
myosin. We demonstrate further that shroom3, a well-known regulator of non-muscle myosin activity, is expressed in the LL primordium and that its expression requires
FGF signalling. Using gain- and loss-of-function experiments, we demonstrate that Shroom3 is the main organizer of cell shape
changes during rosette assembly, probably by coordinating Rho kinase recruitment and non-muscle myosin activation. In order
to quantify morphogenesis in the LL primordium in an unbiased manner, we developed a unique trainable ‘rosette detector’.
We thus propose a model in which Shroom3 drives rosette assembly in the LL downstream of FGF in a Rho kinase- and non-muscle
myosin-dependent manner. In conclusion, we uncovered the first mechanistic link between patterning and morphogenesis during
LL sensory organ formation.