An NKX2-3/5/6 homolog is required downstream of BMP signaling to pattern the sensory-adhesive organ of a tunicate larva.

NK4, an NKX2-3/5/6 homolog, acts downstream of BMP signaling to pattern the three papillae in Ciona larvae, with loss or overexpression altering papilla formation.

• Why it matters: Understanding how BMP signaling influences sensory-adhesive organ development in tunicates can shed light on evolutionary links to vertebrate placodes and sensory structures, filling gaps in developmental mechanisms.
• What they did: The study used gene expression analysis and functional experiments in Ciona embryos to show that BMP-activated NK4 represses Foxg, and its dorsal expression is restricted by Chordin while Msx modulates its activity, affecting papilla patterning.
• The result: Disruption of NK4 function leads to a single large papilla, while overexpression eliminates papillae, indicating NK4's critical role in establishing the three-organ pattern essential for larval sensory and adhesive functions.