NPHP4 is necessary for normal photoreceptor ribbon synapse maintenance and outer segment formation, and for sperm development

Abstract

Nephronophthisis (NPHP) is an autosomal recessive kidney disease that is often associated with vision and/or brain defects. To date, 11 genes are known to cause NPHP. The gene products, while structurally unrelated, all localize to cilia or centrosomes. Although mouse models of NPHP are available for 9 of the 11 genes, none has been described for nephronophthisis 4 (Nphp4). Here we report a novel, chemically induced mutant, nmf192, that bears a nonsense mutation in exon 4 of Nphp4. Homozygous mutant Nphp4(nmf192/nmf192) mice do not exhibit renal defects, phenotypes observed in human patients bearing mutations in NPHP4, but they do develop severe photoreceptor degeneration and extinguished rod and cone ERG responses by 9 weeks of age. Photoreceptor outer segments (OS) fail to develop properly, and some OS markers mislocalize to the inner segments and outer nuclear layer in the Nphp4(nmf192/nmf192) mutant retina. Despite NPHP4 localization to the transition zone in the connecting cilia (CC), the CC appear to be normal in structure and ciliary transport function is partially retained. Likewise, synaptic ribbons develop normally but then rapidly degenerate by P14. Finally, Nphp4(nmf192/nmf192) male mutants are sterile and show reduced sperm motility and epididymal sperm counts. Although Nphp4(nmf192/nmf192) mice fail to recapitulate the kidney phenotype of NPHP, they will provide a valuable tool to further elucidate how NPHP4 functions in the retina and male reproductive organs.

The centriolar satellite protein CCDC66 interacts with CEP290 and functions in cilium formation and trafficking

“…There have been discrepancies between human ciliopathies and their respective mouse models, which are likely due to differences in species and/or functional nature of the mutation (Hall et al, 2013;Jiang et al, 2008;Mykytyn et al, 2004;Won et al, 2011). For most ciliopathies, mouse models fail to completely recapitulate the human phenotype.…”

Germline deletion of Cetn1 causes infertility in male mice

“…BBS knockouts manifest a broad syndromic phenotype which includes retinal degeneration, obesity, development of renal cysts, and olfactory abnormalities, among others. Deletion of the nephrocystin-4 gene (Nphp4) leads to infertility caused by sperm immobility paired with retina degeneration (Won et al, 2011), while deletion of nephrocystin-1 is associated with defects in spermiogenesis at much earlier steps (Jiang et al, 2008). Here we show that Cetn1 2/2 spermatid development is affected after the cap phase, namely at the transition from late acrosome phase to the early maturation phase of spermiogenesis, producing an altered rearrangement of the two centrioles and the centriolar adjunct, the effects of which manifest later as dysmorphic spermatid heads and tails.…”

Nephrocystin-4 controls ciliary trafficking of membrane and large soluble proteins at the transition zone

“…A study of Nphp4-mutant mice has shown that Nphp4 is necessary for normal photoreceptor formation and maintenance as well as sperm development (Won et al, 2011). In zebrafish, nphp4 morphants exhibit classic ciliary phenotypes, including abnormal body curvature and pronephric cysts (Burcklé et al, 2011;Slanchev et al, 2011).…”

“…LAP-tagged NPHP4 in IMCD3 cells is present at sites of cell-cell contact and at the base of the primary cilium, specifically in the transition zone (Sang et al, 2011). Others have reported the presence of NPHP4 in the transition zone of cultured mouse renal epithelial cells (Shiba et al, 2010) and in the connecting ciliuma greatly elongated transition zone -of mouse photoreceptor cells (Roepman et al, 2005;Patil et al, 2012;Won et al, 2011). In Chlamydomonas reinhardtii, NPHP4 was identified in a proteomic study of basal bodies, which included the transition zone (Keller et al, 2005).…”