Interaction between CEP290 and BBSome genes is required for mediating cilia function in retina

Abstract

Purpose: Bardet-Biedl syndrome (BBS) is a heterogeneous autosomal recessive inherited disorder with clinical features that include retinal degeneration, obesity and developmental anomalies. At least 17 BBS genes have been reported. Seven BBS proteins form a molecular complex known as the BBSome, and three additional BBS proteins form a second complex known as the BBS chaperone complex, which is required for BBSome assembly. Studies suggest that mutation of a novel centrosomal protein, CEP290, results in BBS and other ciliopathies. The purpose of the current study is to characterize physical and genetic interactions between CEP290 and other BBS genes, and determine whether these interactions likely contribute to BBS-like symptoms using mouse models.

Methods: We evaluated the physical interaction between CEP290 and other BBS proteins by immunoprecipitation and tested whether this interaction is required for the correct cocalization of CEP290 using immunofluorescence microscopy. To determine whether genetic interaction occurs between Cep290 and Bbs4, we crossed Bbs4 null mice with rd16 mice, in which there is an in frame-deletion in Cep290 from exon 35 to exon 39. We examined the effects of the combination of Cep290^rd16 and Bbs4^ko alleles on photoreceptor degeneration in the offspring resulting from this cross by electroretinography (ERG) and H&E staining.

Results: We found that CEP290 interacts with the BBSome through its N-terminal domain. In addition, the BBSome is required for correct localization of CEP290 in RPE Cells. Furthermore, Cep290 is mis-localized in the retinas of Bbs1^M390R/M390R mice, which are homozygous for a methionine to arginine substitution at codon 390 of Bbs1, one component of the BBSome. Similar phenotype is also observed in the Bbs4 null mice. Moreover, worse photoreceptor morphology and rhodopsin mis-localization were found in Bbs4^+/-/Cep290^rd/rd and Bbs4^-/-/Cep290^rd/rd mice compared to mice that are homozygous at a single locus (Bbs4^-/- mice or Cep290^rd/rd mice). Furthermore, diminished electroretinography (ERG) responses were observed in 1-month old Bbs4^+/-/Cep290^rd/rd mice compared to Cep290^rd/rd single homozygous mice.

Conclusions: These data show that there are both physical and genetic interactions between CEP290 and the BBSome. Moreover, it reveals that the N-terminus of Cep290 is required for normal retinal function, possibly through its interaction with the BBSome.

Keywords: 695 retinal degenerations: cell biology • 457 ciliary processes • 648 photoreceptors