A pseudoenzyme controls the architecture of the extreme distal tip of motile cilia

Abstract

Motile cilia are evolutionarily conserved organelles performing essential roles in development and tissue homeostasis. Unlike the core scaffold of motile cilia, the distal regions remain relatively less explored and display great diversity across species. Here, we describe a previously uncharacterized ciliary protein Jhc1, localizing at the extreme distal tip of multiciliated cell (MCC) cilia and encoded only in the genomes of non-mammalian vertebrates. Jhc1 is essential for cilia structure and length in Xenopus, an activity that is conserved in Jhc1 from reptiles and fish. Phylogenetic analysis and structure modeling suggests that Jhc1 arose by duplication and neofunctionalization of thiamine triphosphatase, and we show that residues crucial for that enzymes function have been lost and replaced by new residues essential for ciliary localization. These data provide new insights into the molecular mechanisms underlying the broad diversification of the structures at the tip of motile cilia during evolution.