Loss of Twist impairs tentacle development and induces epithelial neoplasia in the sea anemone Nematostella vectensis
The basic helix-loop helix transcription factor Twist plays diverse roles in mesodermal development across bilaterians, but its function in cnidarians remains unclear. Here, we investigate the role of Twist in tentacle morphogenesis and tissue homeostasis in the sea anemone Nematostella vectensis. Using a CRISPR/Cas9 generated knockout, we show that twist mutants exhibit impaired secondary tentacle formation, reduced proliferation in budding tentacles, and absence of micronemes, structures that demarcate tentacle boundaries-suggesting defects in spatial patterning. We demonstrate that twist expression is regulated by Wnt, BMP, and Notch signalling but is independent of MAPK and Hedgehog pathways. Loss of Twist disrupts expression of mesodermal transcription factors paraxis and tbx15 and perturbs the TOR-FGF signalling feedback loop necessary for normal tentacle growth. Moreover, starting at juveniles, mutants develop neoplasm-like epithelial overgrowth with tentacle-like molecular and morphological profiles, indicating a role for Twist in maintaining tissue homeostasis at the oral pole.  Together, our findings reveal that Twist integrates major signalling pathways to regulate secondary tentacle patterning and maintain spatial tissue organisation in the diploblastic Nematostella vectensis. Overall design: CRISPR/Cas9-generated twist knockout mutants of Nematostella vectensis were raised to adulthood. Tissue samples from tentacles and neoplasm-like outgrowths were excised at defined developmental days and processed for RNA sequencing.