The role of Rabconnectin3a in cilia length regulation

Background

Using the zebrafish mutant for the deltaD gene (dld^-/- ), it was shown the involvement of Notch signaling in the control of cilia length in the cells of the fish laterality organ (Kupffer's Vesicle, KV) [1]. Further research based on KV specific microarray screening allowed the discovery of several genes with differential expression. Of these, 23% were associated with ciliogenesis and upon analysis, many proved to be involved in cellular trafficking.

Rabconnectin3a or rbcn3a was strongly downregulated in dld^-/- KV cells. Homologs of this gene have been associated with Notch signaling in Drosophila and mammalian cells through the regulation of the V-ATPase activity [2, 3]. Rbcn3a had also been associated with vesicular acidification in zebrafish hair cells [4] and with vesicular endocytosis and maturation in zebrafish neural crest migration [5].

Objective

We investigated the role of Rbcn3a in cilia length regulation.

Methods

We used a Morpholino against rbcn3a and fluorescent confocal imaging to explore cilia length. Furthermore we observed the consequences of reduced Rbcn3a in organ situs by ISH. We also performed rescue experiments by injecting rbcn3a full length mRNA at 1-cell stage dld^-/- KO mutants.

Results

We showed that the downregulation of rbcn3a negatively regulates cilia length and that this can be rescued by rbcn3a overexpression in dld^-/- embryos.

Conclusion

The ciliary phenotype in dld^-/- mutants is partially due to the downregulation of rbcn3a. Our hypothesis is that a generalized decrease in endocytic acidification, by deregulating the V-ATPase activity, results in shorter cilia.