An ancient and essential miRNA family controls cellular interaction pathways in <i>C. elegans</i>

The transition from unicellular to multicellular life required the acquisition of coordinated and regulated cellular behaviors, including adhesion and migration. In metazoans, this involves adhesion proteins, signaling systems, and an elaborate extracellular matrix (ECM) that contributes to adhesion and signaling interactions. Innovations that enabled complex multicellularity occurred through new genes in these pathways, novel functions for existing genes, and regulatory changes. Gene regulation by microRNAs (miRNAs) expanded with multicellularity. A single miRNA, miR-100, arose in the last common eumetazoan ancestor and is widely conserved across animals. We reveal the molecular function of its <i>C. elegans</i> homolog, the miR-51 family. This family acts in a dose-dependent manner to control morphogenesis by regulating several genes involved in cell signaling, adhesion, and migration, including ECM modifiers-specifically heparan sulfate sulfotransferases (HSTs). Some of these targets are also predicted to be conserved targets across vertebrates. Our work suggests that this miRNA provided an innovation in the regulation of cellular interactions early in metazoan evolution.