Human Molecular Genetics Advance Access published online on August 23, 2008
Human Molecular Genetics, doi:10.1093/hmg/ddn260
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Genetic and physical interaction between the NPHP5 and NPHP6 gene products
1 Renal Division, University Hospital Freiburg, Hugstetter Strasse 55, D-79106 Freiburg, Germany 2 Department of Pediatrics, University of Michigan, 1150 West Medical Center Drive, Ann Arbor, MI 48109-0640, USA 3 Equal contribution
Correspondence: Gerd Walz Renal Division University Hospital Freiburg Hugstetter Str. 55 D-79106 Freiburg Germany Tel: +49 761 2703250 Fax: +49 761 2703245 Email: gerd.walz{at}uniklinik-freiburg.de
Received June 20, 2008; Revised August 20, 2008; Accepted August 21, 2008
Nephronophthisis is an autosomal recessive cystic kidney disease, caused by mutations of at least nine different genes. Several extrarenal manifestations characterize this disorder, including cerebellar defects, situs inversus, and retinitis pigmentosa. While the clinical manifestations vary significantly in nephronophthisis, mutations of NPHP5 and NPHP6 are always associated with progressive blindness. This clinical finding suggests that the gene products, nephrocystin-5 and nephrocystin-6, participate in overlapping signaling pathways to maintain photoreceptor homeostasis. To analyze the genetic interaction between these two proteins in more detail, we studied zebrafish embryos after depletion of NPHP5 and NPHP6. Knockdown of zebrafish zNPHP5 and zNPHP6 produced similar phenotypes, and synergistic effects were observed after the combined knockdown of zNPHP5 and zNPHP6. The N-terminal domain of nephrocystin-6 bound nephrocystin-5, and mapping studies delineated the interacting site to amino acid 696 to 896 of NPHP6. In Xenopus laevis, knockdown of NPHP5 caused substantial neural tube closure defects. This phenotype was copied by expression of the nephrocystin-5-binding fragment of nephrocystin-6, and rescued by co-expression of nephrocystin-5, supporting a physical interaction between both gene products in vivo. Since the N- and C-terminal fragments of nephrocystin-6 engage in the formation of homo- and heteromeric protein complexes, conformational changes seem to regulate the interaction of nephrocystin-6 with its binding partners.