Desmosomal connectomics of all somatic muscles in an annelid larva

Abstract

AbstractCells form networks in animal tissues through synaptic, chemical and adhesive links. In muscle tissue, cells often connect through desmosomes, adhesive structures anchored by intermediate filaments. To study desmosomal networks, we reconstructed 852 muscle cells and their desmosomal partners by serial electron microscopy in an entire larva of the annelid Platynereis. Muscle cells adhere to each other, to epithelial, glial, ciliated, and bristle-producing cells and to the basal lamina, forming a desmosomal connectome of over 2,000 cells. The aciculae – chitin rods that form an endoskeleton in the segmental parapodia – are highly connected hubs in this network. This agrees with the many degrees of freedom of their movement, as revealed by video microscopy. Mapping motoneuron synapses to the desmosomal connectome highlighted the extent of tissue influenced by individual motoneuron classes. Our work shows how cellular-level maps of synaptic and adherent force networks can elucidate body mechanics.