14-3-3εa directs the pulsatile transport of basal factors toward the apical domain for lumen growth in tubulogenesis

Abstract

SignificanceAscidians have become a powerful model system in which to uncover basic mechanisms that govern body plan specification and elaboration. In particular, the ascidian notochord is a highly tractable model for tubulogenesis. Here, we use chemical genetics to identify roles for 14-3-3εa, and its binding partner ezrin/radixin/moesin (ERM), in tubulogenesis. Combining genetic and chemical perturbations with live cell imaging, we present evidence that 14-3-3εa–ERM interactions are required for tubulogenesis and that they act by promoting a directed cytoplasmic flow, previously uncharacterized, which carries lumen-associated components from the basal domain to the apical domain to feed lumen growth. Because many core components of this system are highly conserved, these results have broad implications for tubulogenesis in many other contexts.

Ascidian caveolin induces membrane curvature and protects tissue integrity and morphology during embryogenesis

“…47 However, little is known about how the extracellular lumen formation initiates. 51 FRAP has been used to determine the dynamics of the membrane proteins in diverse model organisms. 48 During lumen expansion, the junctional actomyosin network regulates the shape of the lumen by exerting contractile force, 49 and, as a consequence, the luminal membrane experiences a constant force, but how lumen morphology is maintained intact is not known.…”

Admp regulates tail bending by controlling ventral epidermal cell polarity via phosphorylated myosin localization

“…Because during st. 21 to 24, the notochord changes the cell shape using circumferential contraction force (Lu et al, 2019; Mizotani et al, 2018; Sehring et al, 2014). The transverse loading generated by the circumferential constrictive force on a compression-resisting system is converted into a pushing force that is especially higher along the longitudinal axis (Lu et al, 2019; Miyamoto & Crowther, 1985).…”

Morphogenesis: a focus on marine invertebrates

“…Anion transporter Ci-Slc26aα is indispensable for lumen expansion, but is not involved in apical/luminal domain specification and biogenesis (Deng et al 2013). At the onset of lumen pocket formation, cytoplasmic flow in the notochord cells is observed (Mizotani et al 2018), which might be interpreted as transportation of material for apical membrane growth and lumen inflation. Such cytoplasmic flow requires the interaction of the scaffold protein 14-3-3εa with ERM (ezrin/radixin/moesin) at the basal cortex of the cell.…”

“…Chemical inhibition of 14-3-3εa leads to the disappearance of cytoplasmic flow, thereby hampering lumen formation. This phenotype can be copied by morpholino knock-down of ERM (Mizotani et al 2018). However, the physical nature underlying the cytoplasmic flow is unknown.…”