Arrested in Glass: Actin within Sophisticated Architectures of Biosilica in Sponges
Hermann Ehrlich✉ ,Magdalena Luczak, Rustam Ziganshin, Ivan Mikšík, Marcin Wysokowski, Paul Simon, Irena Baranowska-Bosiacka, Patrycja Kupnicka, Alexander Ereskovsky, Roberta Galli, Sergey Dyshlovoy, Jonas Fischer, Konstantin R. Tabachnick, Iaroslav Petrenko, Teofil Jesionowski, Anna Lubkowska, Marek Figlerowicz, Viatcheslav N. Ivanenko, Adam P. Summers✉
Advanced Science 2022, 2105059
Abstract
Actin is a fundamental member of an ancient superfamily of structural intracellular proteins and plays a crucial role in cytoskeleton dynamics, ciliogenesis, phagocytosis, and force generation in both prokaryotes and eukaryotes. It is shown that actin has another function in metazoans: patterning biosilica deposition, a role that has spanned over 500 million years. Species of glass sponges (Hexactinellida) and demosponges (Demospongiae), representatives of the first metazoans, with a broad diversity of skeletal structures with hierarchical architecture unchanged since the late Precambrian, are studied. By etching their skeletons, organic templates dominated by individual F-actin filaments, including branched fibers and the longest, thickest actin fiber bundles ever reported, are isolated. It is proposed that these actin-rich filaments are not the primary site of biosilicification, but this highly sophisticated and multi-scale form of biomineralization in metazoans is ptterned.