The secretory epithelial cells of the choroid plexus employ a novel kinesin-related protein.

The proteins of the kinesin superfamily (KIFs) are microtubule-based molecular motors whose functions include the transport of membrane-bound organelles. We have isolated the cDNA encoding a novel kinesin by reverse transcription and polymerase chain reaction using degenerate primers that flank the highly conserved motor domain. The deduced amino acid sequence of this protein shows considerable similarity to both KIF1A and KIF1B thus defining it as a new member of the monomeric KIF1/unc104 family. The C-terminal domain of KIF1D is the most divergent by comparison with the other members of the family, which supports the view that the tail region is responsible for conferring specificity on the interactions of these kinesins with their cargoes. In the adult rat brain KIF1D mRNA is expressed in neurons in the hippocampus and in the Purkinje cells of the cerebellum. However, the levels of KIF1D are particularly high in the choroid plexus which is a polarised epithelium that lines the lateral, third and fourth ventricles. The major function of the epithelial cells in the choroid plexus is to produce cerebrospinal fluid, which suggests that KIF1D plays an important role in their secretory function.