Non-canonical apical constriction shapes emergent matrices in C. elegans.

Abstract

Specialized epithelia produce apical matrices with distinctive topographies by enigmatic mechanisms. Here, we describe a holistic mechanism that integrates cortical actomyosin dynamics with apical matrix remodeling to pattern C. elegans cuticles. Therein, axial AFBs appear near the surface of lateral epidermal syncytia during an interval of transverse apical constriction (AC). AC gives rise to three temporary semi-circular cellular protrusions beneath a provisional matrix (sheath). In turn, sheath components pattern durable ridges along the midline of adult cuticles (alae). We propose that forces generated by AC are relayed via the sheath to sculpt the the acellular adult cuticle manifest several hours later. Furthermore, we provide evidence that circumferential actin filament bundles (CFBs) near the surface of the adjacent syncytia (hyp7) are largely dispensable for the propagation of annular cuticle structures from one larval stage to the next. Rather, the temporary CFBs extend from actin bundles overlying body wall muscles, which are situated between Ce. hemidesmosomes. Similar mechanisms may contribute to the morphogenesis of integumentary organs in higher metazoans.