Differential tissue distribution of the Invs gene product inversin

Loss of inversin decreases transepithelial sodium transport in murine renal cells

Type II nephronophthisis (NPHP2) is an autosomal recessive renal cystic disorder characterized by mutations in the inversin gene. Humans and mice with mutations in inversin have enlarged cystic kidneys that may be due to fluid accumulation resulting from altered ion transport. To address this, transepithelial ion transport was measured in shRNA-mediated inversin-depleted mouse cortical collecting duct (mCCD) cells. Loss of inversin decreased the basal ion flux in mCCD cells compared with controls. Depletion of inversin decreased vasopressin-induced Na⁺ absorption but did not alter Cl^- secretion by mCCD cells. Addition of amiloride, a specific blocker of the epithelial sodium channel (ENaC), abolished basal ion transport in both inversin knockdown and control cells, indicating ENaC involvement. Transcript levels of ENaC β-subunit were reduced in inversin-knockdown cells consistent with decreased ENaC activity. Furthermore, Nedd4l (neural precursor cell expressed, developmentally downregulated 4 like), an upstream negative regulator of ENaC, was evaluated. The relative amount of the phosphorylated, inactive Nedd4l was decreased in inversin-depleted cells consistent with decreased ENaC activity. The protein levels of Sgk1 (serum and glucocorticoid-inducible kinase), which phosphorylates Nedd4l, remained unchanged although the transcript levels were increased in inversin-depleted cells. Interestingly, mRNA and protein levels of Crtc2 (Creb-regulated transcription coactivator) kinase, a positive regulator of Sgk1, were decreased in inversin-depleted cells. Together these results suggest that loss of inversin decreases Na⁺ transport via ENaC, mediated in part by transcriptional and posttranslational regulation of Crtc2/Sgk1/Nedd4l axis as a contributory mechanism for enlarged kidneys in NPHP2.

Genome-wide analysis of positively selected genes in seasonal and non-seasonal breeding species

Some mammals breed throughout the year, while others breed only at certain times of year. These differences in reproductive behavior can be explained by evolution. We identified positively-selected genes in two sets of species with different degrees of relatedness including seasonal and non-seasonal breeding species, using branch-site models. After stringent filtering by sum of pairs scoring, we revealed that more genes underwent positive selection in seasonal compared with non-seasonal breeding species. Positively-selected genes were verified by cDNA mapping of the positive sites with the corresponding cDNA sequences. The design of the evolutionary analysis can effectively lower the false-positive rate and thus identify valid positive genes. Validated, positively-selected genes, including CGA, DNAH1, INVS, and CD151, were related to reproductive behaviors such as spermatogenesis and cell proliferation in non-seasonal breeding species. Genes in seasonal breeding species, including THRAP3, TH1L, and CMTM6, may be related to the evolution of sperm and the circadian rhythm system. Identification of these positively-selected genes might help to identify the molecular mechanisms underlying seasonal and non-seasonal reproductive behaviors.

Garbage in, garbage out: a critical evaluation of strategies used for validation of immunohistochemical biomarkers

The use of immunohistochemistry (IHC) in clinical cohorts is of paramount importance in determining the utility of a biomarker in clinical practice. A major bottleneck in translating a biomarker from bench-to-bedside is the lack of well characterized, specific antibodies suitable for IHC. Despite the widespread use of IHC as a biomarker validation tool, no universally accepted standardization guidelines have been developed to determine the applicability of particular antibodies for IHC prior to its use. In this review, we discuss the technical challenges faced by the use of immunohistochemical biomarkers and rigorously explore classical and emerging antibody validation technologies. Based on our review of these technologies, we provide strict criteria for the pragmatic validation of antibodies for use in immunohistochemical assays.

N-cadherin is depleted from proximal tubules in experimental and human acute kidney injury

Ischemia remains the most common cause of acute kidney injury (AKI). Decreased intercellular adhesion and alterations in adhesion molecules may contribute to the loss of renal function observed in AKI. In the present study, we evaluated the distribution of adhesion molecules in the human kidney and analyzed their expression in human and experimental AKI. Specimens of human kidneys obtained from patients with and without AKI were stained for the cell adhesion molecules E-cadherin, N-cadherin and beta-catenin. Experimental AKI in rats was induced by renal artery clamping. Immunostaining and immunoblotting were carried out for E-cadherin, N-cadherin and beta-catenin. Proximal tubule cells from opossum kidneys (OKs) were used to analyze the effect of chemical hypoxia (ATP depletion) in vitro. In the adult human kidney, N-cadherin was expressed in proximal tubules, while E-cadherin was expressed in other nephron segments. beta-Catenin was expressed in both proximal and distal tubules. In human AKI and in ischemic rat kidneys, N-cadherin immunostaining was depleted from proximal tubules. There was no change in E-cadherin or beta-catenin. In vitro, OK cells expressed N-cadherin only in the presence of collagen, and ATP depletion led to a depletion of N-cadherin. Collagen IV staining was reduced in ischemic rat kidneys compared to controls. The results of the study suggest that N-cadherin may play a significant role in human and experimental AKI.

Is left-right asymmetry a form of planar cell polarity?

Consistent left-right (LR) patterning is a clinically important embryonic process. However, key questions remain about the origin of asymmetry and its amplification across cell fields. Planar cell polarity (PCP) solves a similar morphogenetic problem, and although core PCP proteins have yet to be implicated in embryonic LR asymmetry, studies of mutations affecting planar polarity, together with exciting new data in cell and developmental biology, provide a new perspective on LR patterning. Here we propose testable models for the hypothesis that LR asymmetry propagates as a type of PCP that imposes coherent orientation onto cell fields, and that the cue that orients this polarization is a chiral intracellular structure.

Nephronophthisis

Nephronophthisis (NPH) is an autosomal recessive disease characterized by a chronic tubulointerstitial nephritis that progress to terminal renal failure during the second decade (juvenile form) or before the age of 5 years (infantile form). In the juvenile form, a urine concentration defect starts during the first decade, and a progressive deterioration of renal function is observed in the following years. Kidney size may be normal, but loss of corticomedullary differentiation is often observed, and cysts occur usually after patients have progressed to end-stage renal failure. Histologic lesions are characterized by tubular basement membrane anomalies, tubular atrophy, and interstitial fibrosis. The infantile form is characterized by cortical microcysts and progression to end-stage renal failure before 5 years of age. Some children present with extrarenal symptoms: retinitis pigmentosa (Senior-Løken syndrome), mental retardation, cerebellar ataxia, bone anomalies, or liver fibrosis. Positional cloning and candidate gene approaches led to the identification of eight causative genes (NPHP1, 3, 4, 5, 6, 7, 8, and 9) responsible for the juvenile NPH and one gene NPHP2 for the infantile form. NPH and associated disorders are considered as ciliopathies, as all NPHP gene products are expressed in the primary cilia, similarly to the polycystic kidney disease (PKD) proteins.

Multiple immunofluorescence labelling of formalin-fixed paraffin-embedded (FFPE) tissue

BACKGROUND

Investigating the expression of candidate genes in tissue samples usually involves either immunohistochemical labelling of formalin-fixed paraffin-embedded (FFPE) sections or immunofluorescence labelling of cryosections. Although both of these methods provide essential data, both have important limitations as research tools. Consequently, there is a demand in the research community to be able to perform routine, high quality immunofluorescence labelling of FFPE tissues.

RESULTS

We present here a robust optimised method for high resolution immunofluorescence labelling of FFPE tissues, which involves the combination of antigen retrieval, indirect immunofluorescence and confocal laser scanning microscopy. We demonstrate the utility of this method with examples of immunofluorescence labelling of human kidney, human breast and a tissue microarray of invasive human breast cancers. Finally, we demonstrate that stained slides can be stored in the short term at 4 degrees C or in the longer term at -20 degrees C prior to images being collected. This approach has the potential to unlock a large in vivo database for immunofluorescence investigations and has the major advantages over immunohistochemistry in that it provides higher resolution imaging of antigen localization and the ability to label multiple antigens simultaneously.

CONCLUSION

This method provides a link between the cell biology and pathology communities. For the cell biologist, it will enable them to utilise the vast archive of pathology specimens to advance their in vitro data into in vivo samples, in particular archival material and tissue microarrays. For the pathologist, it will enable them to utilise multiple antibodies on a single section to characterise particular cell populations or to test multiple biomarkers in limited samples and define with greater accuracy cellular heterogeneity in tissue samples.

Defects in ciliary localization of Nek8 is associated with cystogenesis

Mutations in the human NIMA (Never in Mitosis gene A)-related kinase 8 (Nek8) are associated with a rare form of the juvenile renal cystic disease, nephronophthisis type 9, and mutations in murine Nek8 cause renal cysts in jck mice. Cystogenesis involves dysfunctional ciliary signaling, and we have previously reported that Nek8 localizes to the primary cilium in mouse kidney epithelial cells. We now report that in developing mouse kidney, Nek8 is detected in the cilia of a subset of ureteric-bud-derived tubules at embryonic day (E)15.5. An increasing proportion of ureteric-bud-derived tubules express ciliary Nek8 until E18.5. Postnatal day 1 and 7 Nek8 is observed with equal frequency in both ureteric-bud and non-ureteric-bud-derived tubules. To investigate the cell biological consequences of kinase-deficient and jck mutant forms of Nek8, we transiently expressed green fluorescent protein (GFP)-tagged constructs in vitro. Mutations in the kinase and C-terminal domains of Nek8 adversely affected ciliary targeting but did not affect ciliogenesis or ciliary length. Consistent with these in vitro observations, kidneys from homozygous jck mice revealed reduced ciliary expression of Nek8 compared with kidneys from heterozygous (unaffected) mice. These data indicate that the ciliary localization of Nek8 in a subset of ureteric-bud-derived kidney tubules is essential for maintaining the integrity of those tubules in the mammalian kidney.

The retinal ciliopathies

While the functions of many of the proteins located in or associated with the photoreceptor cilia are poorly understood, disruption of the function of these proteins may result in a wide variety of phenotypes ranging from isolated retinal degeneration to more pleiotropic phenotypes. Systemic findings include neurosensory hearing loss, developmental delay, situs-inversus, infertility, disorders of limb and digit development, obesity, kidney disease, liver disease, and respiratory disease. The concept of "retinal ciliopathies" brings to attention the importance of further molecular analysis of this organelle as well as provides a potential common target for therapies for these disorders. The retinal ciliopathies include retinitis pigmentosa, macular degeneration, cone-dystrophy, cone-rod dystrophy, Leber congenital amaurosis, as well as retinal degenerations associated with Usher syndrome, primary ciliary dyskinesia, Senior-Loken syndrome, Joubert syndrome, Bardet-Biedl syndrome, Laurence-Moon syndrome, McKusick-Kaufman syndrome, and Biemond syndrome. Mutations for these disorders have been found in retinitis pigmentosa-1 (RP1), retinitis pigmentosa GTPase regulator (RPGR), retinitis pigmentosa GTPase regulator interacting protein (RPGR-IP), as well as the Usher, Bardet-Biedl, and nephronophthisis genes. Other systemic disorders associated with retinal degenerations that may also involve ciliary abnormalities include: Alstrom, Edwards-Sethi, Ellis-van Creveld, Jeune, Meckel-Gruber, Orofaciodigital Type 9, and Gurrieri syndromes. Understanding these conditions as ciliopathies may help the ophthalmologist to recognize associations between seemingly unrelated diseases and have a high degree of suspicion that a systemic finding may be present.