Durney, C. H. | bioRxiv Science

bioRxiv2022

Zasp52 strengthens whole embryo tissue integrity through supracellular actomyosin networks

During morphogenesis, large scale changes of tissue primordia occur that are all coordinated across an embryo. In Drosophila, several tissue primordia and embryonic regions are bordered or encircled by supracellular actomyosin cables, junctional actomyosin enrichments networked between many neighbouring cells. We show that the single Drosophila Alp/Enigma family protein Zasp52, which is most prominently found in Z-discs of muscles, is a component of many supracellular actomyosin structures during embryogenesis, including the ventral midline and the boundary of the salivary gland placode. Zasp52, we uncover, contains within its central coiled-coil region a type of actin-binding motif usually found in CapZbeta proteins, and this domain displays actin binding activity. Using endogenously-tagged lines we identify that Zasp52 interacts with a subset of junctional components, including APC2, Polychaetoid/ZO-1, and Sidekick, as well as actomyosin regulators. Analysis of zasp52 mutant embryos revealed that the severity of the embryonic defects observed scales inversely with the amount of functional protein left. Large tissue deformations occur at sites where actomyosin cables are found during embryogenesis, suggesting a model whereby supracellular cables containing Zasp52 aid to insulate morphogenetic changes from one another. This is further supported by the analysis of in vivo processes as well as by an in silico vertex model of morphogenetic domains separated by a stiffness boundary.

developmental biology↗

bioRxiv2018

Dynamics of PAR proteins explain the oscillation and ratcheting mechanisms in dorsal closure

We present a vertex-based model for Drosophila dorsal closure that predicts the mechanics of cell oscillation and contraction from the dynamics of the PAR proteins. Based on experimental observations of how aPKC, Par-6 and Bazooka migrate from the circumference of the apical surface to the medial domain, and how they interact with each other and ultimately regulate the apicomedial actomyosin, we formulate a system of differential equations that capture the key features of the process. The oscillation in cell area in the early phase of dorsal closure results from an intracellular negative feedback loop that involves myosin, an actomyosin regulator, aPKC and Bazooka. In the slow phase, gradual sequestration of apicomedial aPKC into Bazooka clusters causes incomplete disassembly of the myosin network over each cycle of oscillation, thus producing the so-called ratchet. The fast phase of rapid cell and tissue contraction arises when medial myosin, no longer hindered by aPKC, builds up in time and produces sustained contraction. Thus, a minimal set of rules governing the dynamics of the PAR proteins, extracted from experimental observations, can account for all major mechanical outcomes of dorsal closure, including the transitions between its three distinct phases.\n\nInsert Received for publication Date and in final form Date

developmental biology↗