Regulation of cell contacts and cell shape during mouth formation in Caenorhabditis elegans

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Mouth formation in C. elegans represents a concerted series of changes in cell behaviour, shape and cell contacts that are not well understood mechanistically. We found that mouth formation is initiated by cell shape changes and invagination of approximately 50 cells from the neuroectoderm. These processes lead to the formation of a transient pore which gradually connects to the foregut lumen. We observe that the initial cell contacts characterised by interdigitated protrusions and absence of apical junctions are transformed into apical junctions, while neuroectodermal cells invaginate. Thus, invaginating cells seem to apically constrict while apical junctions form simultaneously. This suggests that the dynamic regulation of cell contacts plays a central role in mouth formation. We will perform cell segmentation as well as tracking and quantitative analysis of cortical, junctional, and cell adhesion dynamics to dissect the functional relationship of apical constriction and junction formation. Moreover, apical constriction is initiated in eight small clusters of four to six cells that converge into a continuous pore. But the mechanism of convergence is unknown. We found that neuroectoderm requires the conserved Ets transcription factor AST-1/Etv1/ER81 for maintenance of apical constriction. We will address the role of AST-1 in regulating cluster formation and convergence during mouth formation.