Centrin4p, a novel mammalian centrin specifically expressed in ciliated cells

Centriole assembly plays an important role in centrosome duplication during the cell cycle and is a prerequisite for cilia formation during the differentiation of ciliated cells. In spite of numerous investigations, the molecular machinery that governs centriole/basal body formation remains enigmatic. Recent reports suggest that the ubiquitously expressed mammalian centrins, centrin2p and centrin3p, could be involved in the centriole duplication process. To better understand the specific functions of these proteins, we performed a systematic search for novel mammalian centrins. We isolated a cDNA and the corresponding gene coding for a novel murine centrin, centrin4p, which is more closely related to centrin2p. Like centrin2p, centrin4p accumulates to centrioles and procentrioles when ectopically expressed in HeLa cells. However, centrin4p possesses two splice variants that do not localize to centrioles, suggesting a posttranscriptional regulation mechanism. We also observed that centrin4p does not share the same centriolar targeting properties with centrin2p and 3p, indicating that these proteins could recognize different centriolar partners. Centrin4 mRNA possesses a restricted expression profile and is only detected in brain, kidney, lung, and ovary. In brain, centrin4p is exclusively expressed in ependymal and choroidal ciliated cells where it is localized to basal bodies. Together, our present data suggest that centrin4p could be more specifically involved in basal bodies assembly or in a subsequent step of ciliogenesis.