Figure 6.

Model for how the force-producing mechanisms that drive apical constriction are spatially regulated. (A) Active CDC-42, restricted to apical membranes by basolateral inhibition (black inhibitory arrow), recruits MRCK-1 apically via MRCK-1’s Cdc42/Rac-interactive binding domain. MRCK-1 activates myosin and increases tension in the apical cortex. MRCK-1 apical enrichment occurs specifically in the two endodermal precursor cells, dependent on the END-1/END-3 transcription factors (dotted arrow) by unknown mechanisms. (B and C) MRCK-1-dependent myosin activity contributes through as-yet-unexplored mechanisms to junctional cadherin enrichment. Modified from Marston et al. (2016).