The small GTPase Arf6 regulates sea urchin morphogenesis

Abstract

The small GTPase Arf6 is a conserved protein that is expressed in all metazoans. Arf6 remodels cytoskeletal actin and mediates membrane protein trafficking between the plasma membrane in its active form and endosomal compartments in its inactive form. While a rich knowledge exists for the cellular functions of Arf6, relatively little is known about its physiological role in development. This study examines the function of Arf6 in mediating cellular morphogenesis in early development. We dissect the function of Arf6 with a loss-of-function morpholino and constitutively active Arf6-Q67L construct. We focus on the two cell types that undergo active directed migration: the primary mesenchyme cells (PMCs) that give rise to the sea urchin skeleton and endodermal cells that form the gut. Our results indicate that Arf6 plays an important role in skeleton formation and PMC migration, in part due to its ability to remodel actin. We also found that embryos injected with Arf6 morpholino have gastrulation defects and embryos injected with constitutively active Arf6 have endodermal cells detached from the gut epithelium with decreased junctional cadherin staining, indicating that Arf6 may mediate the recycling of cadherin. Thus, Arf6 impacts cells that undergo coordinated movement to form embryonic structures in the developing embryo.

SAC-1 ensures epithelial endocytic recycling by restricting ARF-6 activity

“…A recent study in sea urchin primary mesenchyme cells showed that constitutively active Arf6 induced mislocalization of junctional cadherin ( Stepicheva et al, 2017 ). In C. elegans , apical junctions contain cadherin, HMP-1 (α-catenin), and HMP-2 (β-catenin; Cox and Hardin, 2004 ).…”

Inhibition of microRNA suppression of Dishevelled results in Wnt pathway-associated developmental defects in sea urchin

“…To examine the actin dynamics in control TP and Dvl miRNATP, we microinjected newly fertilized eggs with 500 ng mCherry-LifeAct reporter mRNA, 0.5 µl 100% glycerol and 0.5 µl of Texas Red in a 2.5 µl injection solution (Riedl et al, 2008;Stepicheva et al, 2017).…”

ROCK and the actomyosin network control biomineral growth and morphology during sea urchin skeletogenesis

“…Calcium bearing vesicles perform an active diffusion motion in the skeletogenic cells with a diffusion length that inversely correlates with the strength and activity of the actomyosin network [46]. Actin filaments are formed around the spicule [46, 47] and F-actin signal is enriched at the tips of the growing skeletal rods in skeletogenic cell culture [48]. Genetic and pharmacological perturbations of the GTPase, CDC42, prevent the formation of filopodia in the skeletogenic cells and inhibit spicule formation and elongation [49].…”