Cilia and flagella are evolutionarily conserved organelles that protrude from cell surfaces. Most cilia and flagella are single rod-shaped but some cilia show a variety of shapes. For example, human airway epithelial cells are multiciliated, flagella of crayfish spermatozoon are star-like shaped, and fruit fly spermatozoon extends long flagella. In Caenorhabditis elegans, cilia display morphological diversity of shapes (single, dual rod-type and wing-like and highly-branched shapes). Here we show that DCAP-1 and DCAP-2, which are the homologues of mammalian DCP1 and DCP2 mRNA decapping enzymes, respectively, are involved in formation of dual rod-type and wing-like shaped cilia in C. elegans. mRNA decapping enzyme catalyzes hydrolysis of 5' cap structure of mRNA, which leads to degradation of mRNA. Rescue experiments showed that DCAP-2 acts not in glial cells surrounding cilia but in neurons. This is the first evidence to demonstrate that mRNA decapping is involved in ciliary shape formation. (C) 2017 Elsevier Inc. All rights reserved.