Cilia are extended from mother centrioles in quiescent G0/G1 cells and retracted in dividing cells. Diverse post-translational modifications play roles in the assembly and disassembly of the cilium. Here, we examined class I histone deacetylases (HDACs) as positive regulators of cilia assembly in serum-deprived RPE1 and HK2 cells. We observed that the number of cells with cilia was significantly reduced in HDAC3- and HDAC8-depleted cells. The ciliary length also decreased in HDAC3- and HDAC8-depleted cells compared to that in control cells. A knockdown-rescue experiment showed that wild-type HDAC3 and HDAC8 rescued the cilia assembly and ciliary length in HDAC3- and HDAC8-depleted cells, respectively; however, deacetylase-dead HDAC3 and HDAC8 mutants did not. This suggests that deacetylase activity is critical for both HDAC3 and HDAC8 function in cilia assembly and ciliary length control. This is the first study to report that HDACs are required for the assembly and elongation of the primary cilia.
Cep215 (also known as Cdk5rap2) is a centrosome protein which is involved in microtubule organization. Cep215 is also placed at specific subcellular locations and organizes microtubules outside the centrosome. Here, we report that Cep215 is involved in morphological differentiation of astrocytes. Cep215 was specifically localized at the glial processes as well as centrosomes in developing astrocytes. Morphological differentiation of astrocytes was suppressed in the Cep215-deleted P19 cells and in the Cep215-depleted embryonic hippocampal culture. We confirm that the microtubule organizing function of Cep215 is critical for the glial process formation. However, Cep215 is not involved in the regulation of cell proliferation nor cell specification. Based on the results, we propose that Cep215 organizes microtubules for glial process formation during astrocyte differentiation.
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