Muscle cell type diversification driven by extensive gene duplications

The evolutionary mechanisms underlying the emergence of new cell types are still unclear. Here, we address the origin and diversification of muscle cells in the diploblastic sea anemone Nematostella vectensis. We discern two fast and two slow-contracting muscle cell populations in Nematostella differing by extensive sets of paralogous genes. The regulatory gene set of the slow cnidarian muscles and the bilaterian cardiac muscle are remarkably similar. By contrast, the two fast muscles differ substantially from each other, while driving the same set of paralogous structural protein genes. Our data suggest that extensive gene duplications and co-option of individual effector modules may have played an important role in cell type diversification during metazoan evolution. One Sentence SummaryThe study of the simple sea anemone suggests a molecular mechanism for cell type evolution and morphological complexity.