Ninein is essential for apico-basal microtubule formation and CLIP-170 facilitates its redeployment to non-centrosomal microtubule organizing centres

Differentiation of columnar epithelial cells involves a dramatic reorganisation of the microtubules and centrosomal components into an apico-basal array no longer anchored at the centrosome. Instead, the minus-ends of the microtubules become anchored at apical non-centrosomal Microtubule Organising Centres (n-MTOCs). Formation of n-MTOCs is critical as they determine the spatial organisation of microtubules, which in turn influences cell shape and function. However, how they are formed is poorly understood. We have previously shown that the centrosomal anchoring protein ninein is released from the centrosome, moves in a microtubule dependent manner and accumulates at n-MTOCs during epithelial differentiation. Here we report using depletion and knockout approaches that ninein expression is essential for apico-basal array formation and epithelial elongation, and that CLIP-170 is required for its redeployment to n-MTOCs. Functional inhibition also revealed that IQGAP1 and active Rac1 co-ordinate with CLIP-170 to facilitate microtubule plus-end cortical targeting and ninein redeployment. Intestinal tissue and in vitro organoids from the Clip1/Clip2 double knockout mouse with deletions in the genes encoding CLIP-170 and CLIP-115, respectively, confirmed requirement of CLIP-170 for ninein recruitment to n-MTOCs, with possible compensation by other anchoring factors such as p150Glued and CAMSAP2 ensuring apico-basal microtubule formation despite loss of ninein at n-MTOCs.