Regulatory factor X (RFX)-family proteins are transcription factors involved in ciliogenesis in worms, flies and mice. In mice, it has been shown that RFX3 regulates the growth of primary cilia. However, further investigation of the biological role of RFX3 has been a challenge because Rfx3–/– mouse embryos die at birth, and ciliogenesis is completed only postnatally. Bénédicte Durand and colleagues (p. 3180) now provide new evidence that RFX3 also has a crucial role in the biogenesis of motile cilia. Here, they describe a novel primary-cell culture system that allows multiciliated ependymal cells to be differentiated from E18.5 neural stem cells in vitro. Using this system, they show that Rfx3–/– cultures exhibit a marked decrease in the number of multiciliated cells compared with wild-type cultures, and that cilia in Rfx3–/– cultures are significantly shorter. Furthermore, ciliary beating efficiency is defective in Rfx3–/– cultures, indicating that...

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