Differential Expression of a Classic Cadherin Directs Tissue-Level Contractile Asymmetry during Neural Tube Closure

Embryos control force generation at tissue bound-aries, but how they do so remains poorly understood.Here we show how tissue-specific expression of thetype II cadherin, Cadherin2, patterns actomyosincontractility along tissue boundaries to control zip-pering and neural tube closure in the basal chordate,Ciona robusta. Cadherin2 is differentially expressedand homotypically enriched in neural cells along theneural/epidermal (Ne/Epi) boundary, where RhoAand myosin are activated during zipper progression.Homotypically enriched Cadherin2 sequesters theRho GTPase-activating protein, Gap21/23, to homo-typic junctions. Gap21/23 in turn redirects RhoA/myosin activity to heterotypic Ne/Epi junctions. Byactivating myosin II along Ne/Epi junctions aheadof the zipper and inhibiting myosin II alongnewly formed Ne/Ne junctions behind the zipper,Cadherin2 promotes tissue-level contractile asym-metry to drive zipper progression. We propose thatdynamic coupling of junction exchange to localchanges in contractility may control fusion and sep-aration of epithelia in many other contexts.