Differential expression and cellular distribution of centrin isoforms during human ciliated cell differentiation in vitro

Centrin protein is an ubiquitously expressed cytoskeletal component and is a member of the EF-hand superfamily of calcium-binding proteins. It was fir st discovered in the flagellar apparatus of unicellular green algae where i t is involved in contraction of Ca2+-sensitive structures. Centrin protein is associated with centrosome-related structures such as spindle pole body in yeast, and centriole/basal bodies in flagellar and ciliated cells. Three centrin genes have been cloned in human cells. In this work, we have perfo rmed a comparative biochemical and functional analysis of centrin isoforms using a primary culture of human nasal epithelial cells which provides an e fficient way to obtain a complete cililated cell differentiation process. R T-PCR experiments show that the expression of the three human centrin genes increases during cell differentiation, and that only centrin 2 and 3 are e xpressed during cell proliferation. Using polyclonal antibodies raised agai nst recombinant human centrin 2 and 3, we show a specific pattern of protei n expression. Ultrastructural immunolocalization suggests that centrin prot eins are involved in the early process of centriole assembly, as they are c oncentrated within the precursor structures of centriole/basal bodies. It a lso shows a differential localisation of centrin proteins in mature centrio le/basal bodies, suggesting different functions for centrins 1/2 and centri n 3, This is also supported by functional analyses showing that centrin 1 a nd/or centrin 2 are involved in ciliary beating.