# Spontaneous Calcium Bursts Organize the Apical Actin Cytoskeleton of Multiciliated Cells

## TL;DR

Calcium bursts help organize the actin structures in multiciliated cells, which are important for cilia function during development and in adult tissues.

## Contribution

The study reveals that spontaneous calcium bursts drive the self-organization of the apical actin cytoskeleton in multiciliated cells.

## Key findings

- Calcium bursts trigger fusion and extension of actin structures via non-muscle myosin activation.
- Repeated calcium cycles promote assembly of the apical actin network in multiciliated cells.
- Blocking calcium signaling disrupts actin structures, but can be rescued by active RhoA.

## Abstract

Motile cilia perform crucial functions during embryonic development and in adult tissues. They are anchored by an apical actin network that forms microridge-like structures on the surface of multiciliated cells. Using Xenopus as a model system to investigate the mechanisms underlying the formation of these specialized actin structures, we observed stochastic bursts of intracellular calcium concentration in developing multiciliated cells. Through optogenetic manipulation of calcium signaling, we found that individual calcium bursts triggered the fusion and extension of actin structures by activating non-muscle myosin. Repeated cycles of calcium activation promoted assembly and coherence of the maturing apical actin network. Inhibition of the endogenous inositol triphosphate-calcium pathway disrupted the formation of apical actin/microridge-like structures by reducing local centriolar RhoA signaling. This disruption was rescued by transient expression of constitutively active RhoA in multiciliated cells. Our findings identify repetitive calcium bursts as a driving force that promotes the self-organization of the highly specialized actin cytoskeleton of multiciliated cells.