A Centrosomal Protein Molecularly Links Usher Syndrome to Leber Congenital Amaurosis and Bardet-Biedl Syndrome in the Retina

Abstract

Purpose: : Usher syndrome (USH) is the most common cause for hereditary deaf-blindness in man. Ten loci are known for Usher syndrome, and recently we and others provided evidence for the existence of a common supramolecular protein network of the USH1 and USH2 proteins at different subcellular sites in the retina and inner ear. Disruption of one of the members of the USH protein network can lead to malfunction and degeneration of both photoreceptor cells and hair cells. The molecular mechanisms underlying these disruptions however still remain largely elusive.

Methods: : Yeast two-hybrid screening of a retinal cDNA library and in vivo knockdown studies by injection of morpholino-modified antisense oligonucleotides (MOs).

Results: : To elucidate the pathogenic mechanism underlying Usher syndrome, we searched for novel interacting partners for the intracellular region of USH2A isoform B. This revealed the interaction with a centrosomal protein. Interestingly, simultaneous screens for interactors of the recently identified protein lebercilin (encoded by LCA5, and associated with Leber congenital amaurosis, LCA), identified the same centrosomal protein. In order to clarify the role of this protein in vivo, knockdown studies in zebrafish were performed. This gave rise to a classical planar cell polarity phenotype, similar to the defects observed after knockdown of the genes involved in Bardet-Biedl syndrome (BBS). Yeast two-hybrid interaction analysis subsequently revealed a specific physical interaction between the centrosomal protein and BBS6.

Conclusions: : Our data indicate that the same centrosomal protein interacts physically with USH2A, lebercilin and BBS6, thereby linking the retinal ciliopathies Usher syndrome, Leber congenital amaurosis and Bardet-Biedl syndrome at the molecular level. The physical and genetic interaction between proteins/genes involved in Usher syndrome and Bardet-Biedl syndrome suggests a putative role for the Usher interactome in the establishment of planar cell polarity, with a central role of the cilia.

Keywords: retinal degenerations: hereditary • ciliary processes • photoreceptors