Tubb4b is required for multi-ciliogenesis in the mouse

Abstract

Cilia are microtubule (MT)-based organelles present on the surface of nearly all vertebrate cells. MTs are polymers of alpha and beta tubulins that are each encoded by multiple, individual isotype genes. Tubulin isotype composition is thought to influence MT behaviors. Ciliary MTs differ from other MTs in the cell in terms of organization, stability and post-translational modifications. However, little is known about the tubulin isotypes that build ciliary MTs and the functional requirements for tubulin isotypes in cilia have not been examined in vertebrates. Here we tested the role of the beta tubulin isotype genes in the mouse that harbor a conserved amino acid motif associated with ciliated organisms. We found that Tubb4b localizes to cilia in multi-ciliated cells (MCC) specifically. In respiratory and oviduct MCC, Tubb4b is asymmetrically localized within multi-cilia, indicating that the tubulin isotype composition changes along the length of the ciliary axonemal MTs. Deletion of Tubb4b resulted in striking structural defects within the axonemes of multi-cilia without affecting primary cilia. These studies show that Tubb4b is essential for the formation of a specific MT-based subcellular organelle and sheds light on the requirements of tubulin isotypes in cilia.

Ciliopathy patient variants reveal organelle-specific functions for TUBB4B in axonemal microtubules

“…2, L to T). These phenotypes (25) have been confirmed by a recent publication on an additional Tubb4b allele (27). On examining serial sections, we observed axonemal defects including the loss or duplication of central pairs, loss of microtubule doublets, and microtubule disorganization arising at or just proximal to the transition zone (fig.…”