CTENO64 Is Required for Coordinated Paddling of Ciliary Comb Plate in Ctenophores

Ctenophores, or comb jellies, are one of the earliestbranching basal metazoan groups, whose phyloge-netic position continues to be controversial. Theyhave eight rows of iridescent structures, calledcomb plates, which are huge multiciliated paddle-like structures used for locomotion and uniquelyfound in this group of animals [1]. Despite a numberof morphological and physiological studies over thepast 50 years, the molecular nature of comb platesremains completely unknown. Here, we identified aprotein CTENO64 that is specifically localized in thecomb plates. This protein is only found in cteno-phores and not in other animals or eukaryotic spe-cies that possess multiciliary cells or tissues. It islocalized to regions, called compartmenting lamella(CL), which are uniquely seen in ctenophore multici-lia, connecting adjacent cilia in the comb plates.Knockdown of theCTENO64gene did not affect theformation of comb plates but caused the loss or mis-formation of CLs and the disruption of ciliary orienta-tion, resulting in aberrant and non-planar waveformsin the mid-distal region of the comb plates. We pro-pose that CLs have been convergently acquired inctenophores to overcome the hydrodynamic con-straints of possessing extremely long multicilia. Ourfindings provide the initial step in unveiling the mo-lecular structure and evolutionary significance ofciliary comb plates and shed light not only on the hid-den biology of ctenophores but also on the uniqueevolutionary pathway of these animals.