How centriole assembly and outgrowth of motile cilia are driven during multiciliate cell (MCC) differentiation is unclear, although Notch signalling is known to inhibit MCC formation in epithelia. Stubbs et al. observed that a gene encoding a small coiled-coiled protein, which they termed multicilin (MCI), is repressed by Notch in Xenopus laevis skin, so they assessed its ability to promote MCC differentiation. Depletion of MCI prevented MCC formation, whereas its overexpression induced ectopic MCC formation. But, how might MCI promote MCC differentiation? Experiments showed that MCI promotes centriole assembly by inducing cell cycle exit (centriole assembly in MCCs occurs postmitotically) and extension of motile cilia through the transcription factor Forkhead box J1 (FOXJ1). Furthermore, microarray analysis revealed that MCI upregulates genes that are expressed in MCCs, including genes encoding centriole components. Thus, MCI, which the authors validate as a transcriptional activator, is a novel regulator of MCC formation.