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

Abstract

Biomineralization, the ability of organisms to use minerals to harden their tissues, has attracted scientists from various disciplines to decipher the molecular mechanisms that control it. Many of these studies focus on the gene regulatory networks (GRNs) that control biomineralization and are apparently, phylum specific. Yet, downstream to the GRNs lays the cellular machinery that drives morphogenetic processes that are commonly used in biomineralization, such as, vesicular motion and secretion. The actomyosin network is a key regulator of these processes and participates in biomineralization across Eukaryotes, from unicellular organisms to vertebrates, yet, little is known about its regulation of biomineral growth. Here we reveal that the actomyosin remodeling protein, Rho-associated coiled-coil kinase (ROCK), controls the formation, growth and morphology of the calcite spicules in the sea urchin larva. We show that ROCK expression is elevated in the sea urchin skeletogenic cells and its inhibition impairs the organization of F-actin around the spicules and leads to skeletal loss. We discovered that ROCK inhibition after spicule formation, slows down mineral deposition, induces ectopic spicule branching and disrupts skeletogenic gene expression. We propose that ROCK and the actomyosin network are an essential part of the common biomineralization tool-kit in Eukaryotes.

Larval development of Holothuria tubulosa, a new tractable system for evo-devo

“…The only report available on the ossicle formation of another sea cucumber species, A. parvimensis, shows that the gene Alx1 plays an important role for ossicle specification (McCauley et al, 2012) as it happens in sea urchins. Moreover, the enriched F-actin staining around the ossicle (Figure 3C) resembles what observed around the spicules of sea urchin larvae (Winter et al, 2021;Hijaze et al, 2024). This advocates for a similar role of cytoskeleton in biomineral formation, suggesting that these two structures might be evolutionary related.…”