Inverse regulation of SOS1 and HKT1 protein localization and stability by SOS3/CBL4 in Arabidopsis thaliana.

To control net sodium (Na+) uptake, Arabidopsis plants utilize the plasma membrane (PM) Na+/H+ antiporter SOS1 to achieve Na+ efflux at the root and Na+ loading into the xylem, and the channel-like HKT1;1 protein that mediates the reverse flux of Na+ unloading off the xylem. Together, these opposing transport systems govern the partition of Na+ within the plant yet they must be finely co-regulated to prevent a futile cycle of xylem loading and unloading. Here, we show that the Arabidopsis SOS3 protein acts as the molecular switch governing these Na+ fluxes by favoring the recruitment of SOS1 to the PM and its subsequent activation by the SOS2/SOS3 kinase complex under salt stress, while commanding HKT1;1 protein degradation upon acute sodic stress. SOS3 achieves this role by direct and SOS2-independent binding to previously unrecognized functional domains of SOS1 and HKT1;1. These results indicate that roots first retain moderate amounts of salts to facilitate osmoregulation, yet when sodicity exceeds a set point, SOS3-dependent HKT1;1 degradation switches the balance toward Na+ export out of the root. Thus, SOS3 functionally links and co-regulates the two major Na+ transport systems operating in vascular plants controlling plant tolerance to salinity.

S-acylated and nucleus-localized SALT OVERLY SENSITIVE3/CALCINEURIN B-LIKE4 stabilizes GIGANTEA to regulate Arabidopsis flowering time under salt stress.

The precise timing of flowering in adverse environments is critical for plants to secure reproductive success. We report a mechanism in Arabidopsis (Arabidopsis thaliana) controlling the time of flowering by which the S-acylation-dependent nuclear import of the protein SALT OVERLY SENSITIVE3/CALCINEURIN B-LIKE4 (SOS3/CBL4), a Ca2+-signaling intermediary in the plant response to salinity, results in the selective stabilization of the flowering time regulator GIGANTEA inside the nucleus under salt stress, while degradation of GIGANTEA in the cytosol releases the protein kinase SOS2 to achieve salt tolerance. S-acylation of SOS3 was critical for its nuclear localization and the promotion of flowering, but partly dispensable for salt tolerance. SOS3 interacted with the photoperiodic flowering components GIGANTEA and FLAVIN-BINDING, KELCH REPEAT, F-BOX1 and participated in the transcriptional complex that regulates CONSTANS to sustain the transcription of CO and FLOWERING LOCUS T under salinity. Thus, the SOS3 protein acts as a Ca2+- and S-acylation-dependent versatile regulator that fine-tunes flowering time in a saline environment through the shared spatial separation and selective stabilization of GIGANTEA, thereby connecting two signaling networks to co-regulate the stress response and the time of flowering.

Pathogen-induced pH changes regulate the growth-defense balance in plants.

Environmental adaptation of organisms relies on fast perception and response to external signals, which lead to developmental changes. Plant cell growth is strongly dependent on cell wall remodeling. However, little is known about cell wall-related sensing of biotic stimuli and the downstream mechanisms that coordinate growth and defense responses. We generated genetically encoded pH sensors to determine absolute pH changes across the plasma membrane in response to biotic stress. A rapid apoplastic acidification by phosphorylation-based proton pump activation in response to the fungus Fusarium oxysporum immediately reduced cellulose synthesis and cell growth and, furthermore, had a direct influence on the pathogenicity of the fungus. In addition, pH seems to influence cellulose structure. All these effects were dependent on the COMPANION OF CELLULOSE SYNTHASE proteins that are thus at the nexus of plant growth and defense. Hence, our discoveries show a remarkable connection between plant biomass production, immunity, and pH control, and advance our ability to investigate the plant growth-defense balance.

Next-generation sequencing of uveal melanoma with clinical and histological correlations: Prognostic value of new mutations in the PI3K/AKT/mTOR pathway.

BACKGROUND: Uveal melanoma (UM) is the eye's most common primary malignancy and there are no effective therapies for disseminated disease. It is important to try to know the patient's prognosis. The aim of this study was to reflect genetic variants, studied using NGS, of a series of 69 cases of UM and its correlation with histopathology and clinical progression. METHODS: We performed targeted NGS using a 519-gene panel. RESULTS: There were selected 28 different mutated genes, showing a total of 231 genetic variants that affected the function of the protein. The most common secondary mutations occurred in SF3B1 (in 26%), followed by BAP1 (in 23%), LRP1B (22%) and FGFR4 (20%). BAP1 mutation was associated with a greater likelihood of metastases and with greater presence of epithelioid cells. LRP1B was also associated with presence of epithelioid cells SF3B1 mutation was significantly associated with a spindle morphology. We found variants in the RAD51B, TOP2A, PTPRD, TSC2, DHX9, PDK1 and MTOR that have not been previously reported in consulted databases. The presence of a mutation in: CHEK2, DHX9 and PDK1 was associated with metastases. CONCLUSIONS: BAP1 is the most solid biomarker of a poor prognosis in UM and mutations can be detected using NGS. SF3B1 is associated with the spindle cell subtype of UM, which gives it probably a favourable prognostic value. Our study suggests that mutations in DHX9 and PDK1 can have prognostic value. These potential biomarkers are related to the PI3K/AKT/mTOR pathway and makes them candidates for developing new directed therapies.

mTOR-Activating Mutations in RRAGD Are Causative for Kidney Tubulopathy and Cardiomyopathy.

BACKGROUND: Over the last decade, advances in genetic techniques have resulted in the identification of rare hereditary disorders of renal magnesium and salt handling. Nevertheless, approximately 20% of all patients with tubulopathy lack a genetic diagnosis. METHODS: We performed whole-exome and -genome sequencing of a patient cohort with a novel, inherited, salt-losing tubulopathy; hypomagnesemia; and dilated cardiomyopathy. We also conducted subsequent in vitro functional analyses of identified variants of RRAGD, a gene that encodes a small Rag guanosine triphosphatase (GTPase). RESULTS: In eight children from unrelated families with a tubulopathy characterized by hypomagnesemia, hypokalemia, salt wasting, and nephrocalcinosis, we identified heterozygous missense variants in RRAGD that mostly occurred de novo. Six of these patients also had dilated cardiomyopathy and three underwent heart transplantation. We identified a heterozygous variant in RRAGD that segregated with the phenotype in eight members of a large family with similar kidney manifestations. The GTPase RagD, encoded by RRAGD, plays a role in mediating amino acid signaling to the mechanistic target of rapamycin complex 1 (mTORC1). RagD expression along the mammalian nephron included the thick ascending limb and the distal convoluted tubule. The identified RRAGD variants were shown to induce a constitutive activation of mTOR signaling in vitro. CONCLUSIONS: Our findings establish a novel disease, which we call autosomal dominant kidney hypomagnesemia (ADKH-RRAGD), that combines an electrolyte-losing tubulopathy and dilated cardiomyopathy. The condition is caused by variants in the RRAGD gene, which encodes Rag GTPase D; these variants lead to an activation of mTOR signaling, suggesting a critical role of Rag GTPase D for renal electrolyte handling and cardiac function.

Neurotrophic Keratitis in a Pediatric Patient With Goldenhar Syndrome and Trigeminal Aplasia Successfully Treated by Corneal Neurotization.

Herein, the authors report an unusual case of a 6-year-old boy with right-sided Goldenhar syndrome and trigeminal nerve aplasia who developed neurotrophic keratopathy (NK). Despite the use of therapeutic contact lenses and multiple temporary tarsorrhaphy, NK worsened showing a central corneal scar, neovascularization, and significant stromal thinning, with risk of corneal perforation. Cochet-Bonnet esthesiometry revealed complete corneal anesthesia. To minimize additional corneal complications, the patient underwent indirect corneal neurotization by a sural nerve autograft anastomosed to the contralateral supratrochlear nerve. At 24-month follow up, no epithelial defects, complications, or recurrence were observed. Significant improvements in corneal sensitivity with esthesiometry score of 20 mm and reflex blinking were achieved. This case highlights corneal anesthesia should be suspected among Goldenhar syndrome ophthalmologic abnormalities and monitored before corneal changes become irreversible. Since corneal neurotization can successfully improve corneal sensation, it could be considered as an early therapeutic option to avoid refractory NK.

Pannexin-1 mediates fluid shear stress-sensitive purinergic signaling and cyst growth in polycystic kidney disease.

Tubular ATP release is regulated by mechanosensation of fluid shear stress (FSS). Polycystin-1/polycystin-2 (PC1/PC2) functions as a mechanosensory complex in the kidney. Extracellular ATP is implicated in polycystic kidney disease (PKD), where PC1/PC2 is dysfunctional. This study aims to provide new insights into the ATP signaling under physiological conditions and PKD. Microfluidics, pharmacologic inhibition, and loss-of-function approaches were combined to assess the ATP release in mouse distal convoluted tubule 15 (mDCT15) cells. Kidney-specific Pkd1 knockout mice (iKsp-Pkd1-/- ) and zebrafish pkd2 morphants (pkd2-MO) were as models for PKD. FSS-exposed mDCT15 cells displayed increased ATP release. Pannexin-1 inhibition and knockout decreased FSS-modulated ATP release. In iKsp-Pkd1-/- mice, elevated renal pannexin-1 mRNA expression and urinary ATP were observed. In Pkd1-/- mDCT15 cells, elevated ATP release was observed upon the FSS mechanosensation. In these cells, increased pannexin-1 mRNA expression was observed. Importantly, pannexin-1 inhibition in pkd2-MO decreased the renal cyst growth. Our results demonstrate that pannexin-1 channels mediate ATP release into the tubular lumen due to pro-urinary flow. We present pannexin-1 as novel therapeutic target to prevent the renal cyst growth in PKD.

A Critical Role of Sodium Flux via the Plasma Membrane Na+/H+ Exchanger SOS1 in the Salt Tolerance of Rice.

Rice (Oryza sativa) stands among the world's most important crop species. Rice is salt sensitive, and the undue accumulation of sodium ions (Na+) in shoots has the strongest negative correlation with rice productivity under long-term salinity. The plasma membrane Na+/H+ exchanger protein Salt Overly Sensitive 1 (SOS1) is the sole Na+ efflux transporter that has been genetically characterized to date. Here, the importance of SOS1-facilitated Na+ flux in the salt tolerance of rice was analyzed in a reverse-genetics approach. A sos1 loss-of-function mutant displayed exceptional salt sensitivity that was correlated with excessive Na+ intake and impaired Na+ loading into the xylem, thus indicating that SOS1 controls net root Na+ uptake and long-distance Na+ transport to shoots. The acute Na+ sensitivity of sos1 plants at low NaCl concentrations allowed analysis of the transcriptional response to sodicity stress without effects of the osmotic stress intrinsic to high-salinity treatments. In contrast with that in the wild type, sos1 mutant roots displayed preferential down-regulation of stress-related genes in response to salt treatment, despite the greater intensity of stress experienced by the mutant. These results suggest there is impaired stress detection or an inability to mount a comprehensive response to salinity in sos1 In summary, the plasma membrane Na+/H+ exchanger SOS1 plays a major role in the salt tolerance of rice by controlling Na+ homeostasis and possibly contributing to the sensing of sodicity stress.

Tubular flow activates magnesium transport in the distal convoluted tubule.

Magnesium (Mg2+) is an important cofactor of many enzymes crucial for life; therefore, maintaining a Mg2+ balance in the body is essential. In the kidney, the distal convoluted tubule (DCT) determines the final urinary Mg2+ excretion. The nephron is subjected to variable urinary flow, but little is known about the influence of flow on Mg2+ transport. Primary cilia, which are mechanosensory organelles that sense changes in flow, are expressed on tubular epithelial cells. This study aimed to elucidate whether urinary flow facilitates DCT Mg2+ transport. To this end, mouse DCT15 cells, with and without primary cilia, were exposed to physiologic fluid flow generating 0.3, 0.6, and 1.2 dyn/cm2 fluid shear stress (FSS). FSS stimulated Mg2+ uptake significantly. Net Mg2+ uptake ( i.e., the difference between static and FSS) followed a single component saturable first-order transport function and was independent of FSS magnitude and primary cilia. FSS did not affect the expression of magnesiotropic genes, including Cnnm2, Kcna1, Proegf, Trpm6, and Trpm7. Transient receptor potential cation channel subfamily melastatin (TRPM) member 7 (Trmp7) inhibition by 2-aminoethyl diphenyl borinate or knockout of TRPM6 did not alter net Mg2+ uptake, suggesting that TRPM6/TRPM7 homo/heterodimeric channels are not involved in FSS-activated Mg2+ transport. In summary, FSS generated by physiologic fluid flow is a new factor activating Mg2+ transport in DCT independent of primary cilia.-Verschuren, E. H. J., Hoenderop, J. G. J., Peters, D. J. M., Arjona, F. J., Bindels, R. J. M. Tubular flow activates magnesium transport in the distal convoluted tubule.

Water temperature affects osmoregulatory responses in gilthead sea bream (Sparus aurata L.).

Sea bream (Sparus aurata Linneaus) was acclimated to three salinity concentrations, viz. 5 (LSW), 38 (SW) and 55psµ (HSW) and three water temperatures regimes (12, 19 and 26 °C) for five weeks. Osmoregulatory capacity parameters (plasma osmolality, sodium, chloride, cortisol, and branchial and renal Na+,K+-ATPase activities) were also assessed. Salinity and temperature affected all of the parameters tested. Our results indicate that environmental temperature modulates capacity in sea bream, independent of environmental salinity, and set points of plasma osmolality and ion concentrations depend on both ambient salinity and temperature. Acclimation to extreme salinity resulted in stress, indicated by elevated basal plasma cortisol levels. Response to salinity was affected by ambient temperature. A comparison between branchial and renal Na+,K+-ATPase activities appears instrumental in explaining salinity and temperature responses. Sea bream regulate branchial enzyme copy numbers (Vmax) in hyperosmotic media (SW and HSW) to deal with ambient temperature effects on activity; combinations of high temperatures and salinity may exceed the adaptive capacity of sea bream. Salinity compromises the branchial enzyme capacity (compared to basal activity at a set salinity) when temperature is elevated and the scope for temperature adaptation becomes smaller at increasing salinity. Renal Na+,K+-ATPase capacity appears fixed and activity appears to be determined by temperature.

Upstream kinases of plant SnRKs are involved in salt stress tolerance.

Sucrose non-fermenting 1-related protein kinases (SnRKs) are important for plant growth and stress responses. This family has three clades: SnRK1, SnRK2 and SnRK3. Although plant SnRKs are thought to be activated by upstream kinases, the overall mechanism remains obscure. Geminivirus Rep-Interacting Kinase (GRIK)1 and GRIK2 phosphorylate SnRK1s, which are involved in sugar/energy sensing, and the grik1-1 grik2-1 double mutant shows growth retardation under regular growth conditions. In this study, we established another Arabidopsis mutant line harbouring a different allele of gene GRIK1 (grik1-2 grik2-1) that grows similarly to the wild-type, enabling us to evaluate the function of GRIKs under stress conditions. In the grik1-2 grik2-1 double mutant, phosphorylation of SnRK1.1 was reduced, but not eliminated, suggesting that the grik1-2 mutation is a weak allele. In addition to high sensitivity to glucose, the grik1-2 grik2-1 mutant was sensitive to high salt, indicating that GRIKs are also involved in salinity signalling pathways. Salt Overly Sensitive (SOS)2, a member of the SnRK3 subfamily, is a critical mediator of the response to salinity. GRIK1 phosphorylated SOS2 in vitro, resulting in elevated kinase activity of SOS2. The salt tolerance of sos2 was restored to normal levels by wild-type SOS2, but not by a mutated form of SOS2 lacking the T168 residue phosphorylated by GRIK1. Activation of SOS2 by GRIK1 was also demonstrated in a reconstituted system in yeast. Our results indicate that GRIKs phosphorylate and activate SnRK1 and other members of the SnRK3 family, and that they play important roles in multiple signalling pathways in vivo.

SLC41A1 is essential for magnesium homeostasis in vivo.

Solute carrier family 41 member A1 (SLC41A1) has been suggested to mediate magnesium (Mg2+) transport by several in vitro studies. However, the physiological function of SLC41A1 remains to be elucidated. In this study, cellular Mg2+ transport assays combined with zebrafish slc41a1 knockdown experiments were performed to disclose SLC41A1 function and its physiological relevance. The gene slc41a1 is ubiquitously expressed in zebrafish tissues and is regulated by water and dietary Mg2+ availability. Knockdown of slc41a1 in zebrafish larvae grown in a Mg2+-free medium resulted in a unique phenotype characterized by a decrease in zebrafish Mg content. This decrease shows that SLC41A1 is required to maintain Mg2+ balance and its dysfunction results in renal Mg2+ wasting in zebrafish larvae. Importantly, the Mg content of the larvae is rescued when mouse SLC41A1 is expressed in slc41a1-knockdown zebrafish. Conversely, expression of mammalian SLC41A1-p.Asp262Ala, harboring a mutation in the ion-conducting SLC41A1 pore, did not reverse the renal Mg2+ wasting. 25Mg2+ transport assays in human embryonic kidney 293 (HEK293) cells overexpressing SLC41A1 demonstrated that SLC41A1 mediates cellular Mg2+ extrusion independently of sodium (Na+). In contrast, SLC41A1-p.Asp262Ala expressing HEK293 cells displayed similar Mg2+ extrusion activities than control (mock) cells. In polarized Madin-Darby canine kidney cells, SLC41A1 localized to the basolateral cell membrane. Our results demonstrate that SLC41A1 facilitates renal Mg2+ reabsorption in the zebrafish model. Furthermore, our data suggest that SLC41A1 mediates both Mg2+ uptake and extrusion.

Primary cilia-regulated transcriptome in the renal collecting duct.

Renal tubular cells respond to mechanical stimuli generated by urinary flow to regulate the activity and transcript abundance of important genes for ion handling, cellular homeostasis, and proper renal development. The primary cilium, a mechanosensory organelle, is postulated to regulate this mRNA response. The aim of this study is to reveal the transcriptome changes of tubular epithelia in response to fluid flow and determine the role of primary cilia in this process. Inner-medullary collecting duct (CD) cells were subjected to either static or physiologically relevant fluid flow (∼0.6 dyn/cm2). RNA-sequencing analysis of ciliated cells subjected to fluid flow showed up-regulation of 1379 genes and down-regulation of 1294 genes compared with static control cells. Strikingly, only 54 of these genes were identified as gene candidates sensitive to primary cilia sensing of fluid flow, of which 16 were linked to ion or water transport pathways in the CD. Validation by quantitative real-time PCR revealed that only the expression of transferrin receptor, which is involved in iron transport; and tribbles pseudokinase 3, which is involved in insulin signaling, were unequivocally regulated by primary cilia sensing of fluid flow. This study shows that the involvement of primary cilia in ion transport in the collecting duct is exceptionally specific.-Mohammed, S. G., Arjona, F. J., Verschuren, E. H. J., Bakey, Z., Alkema, W., van Hijum, S., Schmidts, M., Bindels, R. J. M., Hoenderop, J. G. J. Primary cilia-regulated transcriptome in the renal collecting duct.

Genome-Wide Meta-Analysis Unravels Interactions between Magnesium Homeostasis and Metabolic Phenotypes.

Magnesium (Mg2+) homeostasis is critical for metabolism. However, the genetic determinants of the renal handling of Mg2+, which is crucial for Mg2+ homeostasis, and the potential influence on metabolic traits in the general population are unknown. We obtained plasma and urine parameters from 9099 individuals from seven cohorts, and conducted a genome-wide meta-analysis of Mg2+ homeostasis. We identified two loci associated with urinary magnesium (uMg), rs3824347 (P=4.4×10-13) near TRPM6, which encodes an epithelial Mg2+ channel, and rs35929 (P=2.1×10-11), a variant of ARL15, which encodes a GTP-binding protein. Together, these loci account for 2.3% of the variation in 24-hour uMg excretion. In human kidney cells, ARL15 regulated TRPM6-mediated currents. In zebrafish, dietary Mg2+ regulated the expression of the highly conserved ARL15 ortholog arl15b, and arl15b knockdown resulted in renal Mg2+ wasting and metabolic disturbances. Finally, ARL15 rs35929 modified the association of uMg with fasting insulin and fat mass in a general population. In conclusion, this combined observational and experimental approach uncovered a gene-environment interaction linking Mg2+ deficiency to insulin resistance and obesity.

Polycystin-1 dysfunction impairs electrolyte and water handling in a renal precystic mouse model for ADPKD.

The PKD1 gene encodes polycystin-1 (PC1), a mechanosensor triggering intracellular responses upon urinary flow sensing in kidney tubular cells. Mutations in PKD1 lead to autosomal dominant polycystic kidney disease (ADPKD). The involvement of PC1 in renal electrolyte handling remains unknown since renal electrolyte physiology in ADPKD patients has only been characterized in cystic ADPKD. We thus studied the renal electrolyte handling in inducible kidney-specific Pkd1 knockout (iKsp- Pkd1-/-) mice manifesting a precystic phenotype. Serum and urinary electrolyte determinations indicated that iKsp- Pkd1-/- mice display reduced serum levels of magnesium (Mg2+), calcium (Ca2+), sodium (Na+), and phosphate (Pi) compared with control ( Pkd1+/+) mice and renal Mg2+, Ca2+, and Pi wasting. In agreement with these electrolyte disturbances, downregulation of key genes for electrolyte reabsorption in the thick ascending limb of Henle's loop (TA;, Cldn16, Kcnj1, and Slc12a1), distal convoluted tubule (DCT; Trpm6 and Slc12a3) and connecting tubule (CNT; Calb1, Slc8a1, and Atp2b4) was observed in kidneys of iKsp- Pkd1-/- mice compared with controls. Similarly, decreased renal gene expression of markers for TAL ( Umod) and DCT ( Pvalb) was observed in iKsp- Pkd1-/- mice. Conversely, mRNA expression levels in kidney of genes encoding solute and water transporters in the proximal tubule ( Abcg2 and Slc34a1) and collecting duct ( Aqp2, Scnn1a, and Scnn1b) remained comparable between control and iKsp- Pkd1-/- mice, although a water reabsorption defect was observed in iKsp- Pkd1-/- mice. In conclusion, our data indicate that PC1 is involved in renal Mg2+, Ca2+, and water handling and its dysfunction, resulting in a systemic electrolyte imbalance characterized by low serum electrolyte concentrations.

Fluid shear stress increases transepithelial transport of Ca2+ in ciliated distal convoluted and connecting tubule cells.

In kidney, transcellular transport of Ca2+ is mediated by transient receptor potential vanilloid 5 and Na+-Ca2+ exchanger 1 proteins in distal convoluted and connecting tubules (DCTs and CNTs, respectively). It is not yet understood how DCT/CNT cells can adapt to differences in tubular flow rate and, consequently, Ca2+ load. This study aims to elucidate the molecular mechanisms by which DCT/CNT cells sense fluid dynamics to control transepithelial Ca2+ reabsorption and whether their primary cilia play an active role in this process. Mouse primary DCT/CNT cultures were subjected to a physiologic fluid shear stress (FSS) of 0.12 dyn/cm2 Transient receptor potential vanilloid 5 and Na+-Ca2+ exchanger 1 mRNA levels were significantly increased upon FSS exposure compared with static controls. Functional studies with 45Ca2+ demonstrated a significant stimulation of transepithelial Ca2+ transport under FSS compared with static conditions. Primary cilia removal decreased Ca2+ transport in both static and FSS conditions, a finding that correlated with decreased expression of genes involved in transepithelial Ca2+ transport; however, FSS-induced stimulation of Ca2+ transport was still observed. These results indicate that nephron DCT and CNT segments translate FSS into a physiologic response that implicates an increased Ca2+ reabsorption. Moreover, primary cilia influence transepithelial Ca2+ transport in DCTs/CNTs, yet this process is not distinctly coupled to FSS sensing by these organelles.-Mohammed, S. G., Arjona, F. J., Latta, F., Bindels, R. J. M., Roepman, R., Hoenderop, J. G. J. Fluid shear stress increases transepithelial transport of Ca2+ in ciliated distal convoluted and connecting tubule cells.

Ion transport in the zebrafish kidney from a human disease angle: possibilities, considerations, and future perspectives.

Unique experimental advantages, such as its embryonic/larval transparency, high-throughput nature, and ease of genetic modification, underpin the rapid emergence of the zebrafish (Danio rerio) as a preeminent model in biomedical research. Particularly in the field of nephrology, the zebrafish provides a promising model for studying the physiological implications of human solute transport processes along consecutive nephron segments. However, although the zebrafish might be considered a valuable model for numerous renal ion transport diseases and functional studies of many channels and transporters, not all human renal electrolyte transport mechanisms and human diseases can be modeled in the zebrafish. With this review, we explore the ontogeny of zebrafish renal ion transport, its nephron structure and function, and thereby demonstrate the clinical translational value of this model. By critical assessment of genomic and amino acid conservation of human proteins involved in renal ion handling (channels, transporters, and claudins), kidney and nephron segment conservation, and renal electrolyte transport physiology in the zebrafish, we provide researchers and nephrologists with an indication of the possibilities and considerations of the zebrafish as a model for human renal ion transport. Combined with advanced techniques envisioned for the future, implementation of the zebrafish might expand beyond unraveling pathophysiological mechanisms that underlie distinct genetic or environmentally, i.e., pharmacological and lifestyle, induced renal transport deficits. Specifically, the ease of drug administration and the exploitation of improved genetic approaches might argue for the adoption of the zebrafish as a model for preclinical personalized medicine for distinct renal diseases and renal electrolyte transport proteins.

CNNM2 mutations cause impaired brain development and seizures in patients with hypomagnesemia.

Intellectual disability and seizures are frequently associated with hypomagnesemia and have an important genetic component. However, to find the genetic origin of intellectual disability and seizures often remains challenging because of considerable genetic heterogeneity and clinical variability. In this study, we have identified new mutations in CNNM2 in five families suffering from mental retardation, seizures, and hypomagnesemia. For the first time, a recessive mode of inheritance of CNNM2 mutations was observed. Importantly, patients with recessive CNNM2 mutations suffer from brain malformations and severe intellectual disability. Additionally, three patients with moderate mental disability were shown to carry de novo heterozygous missense mutations in the CNNM2 gene. To elucidate the physiological role of CNNM2 and explain the pathomechanisms of disease, we studied CNNM2 function combining in vitro activity assays and the zebrafish knockdown model system. Using stable Mg(2+) isotopes, we demonstrated that CNNM2 increases cellular Mg2+ uptake in HEK293 cells and that this process occurs through regulation of the Mg(2+)-permeable cation channel TRPM7. In contrast, cells expressing mutated CNNM2 proteins did not show increased Mg(2+) uptake. Knockdown of cnnm2 isoforms in zebrafish resulted in disturbed brain development including neurodevelopmental impairments such as increased embryonic spontaneous contractions and weak touch-evoked escape behaviour, and reduced body Mg content, indicative of impaired renal Mg(2+) absorption. These phenotypes were rescued by injection of mammalian wild-type Cnnm2 cRNA, whereas mammalian mutant Cnnm2 cRNA did not improve the zebrafish knockdown phenotypes. We therefore concluded that CNNM2 is fundamental for brain development, neurological functioning and Mg(2+) homeostasis. By establishing the loss-of-function zebrafish model for CNNM2 genetic disease, we provide a unique system for testing therapeutic drugs targeting CNNM2 and for monitoring their effects on the brain and kidney phenotype.

Surgical Approaches for Vitreomacular Tractions.

PURPOSE: The aim is to describe the main characteristics of different approaches in vitreomacular traction surgery. Setting/Venue: The video (see www.karger.com/doi/10.1159/ 000442579) about vitreomacular traction surgery was created at the Department of Ophthalmology, Virgin Macarena University Hospital, Seville, Spain. METHODS: We present the surgical release of vitreomacular tractions in three different pathologies: (1) idiopathic epimacular membrane; (2) proliferative diabetic retinopathy with long-term hemovitreous, and (3) Coats' disease. RESULTS: Although functional success is less common than anatomical success, we will never be able to improve vision without restoring retinal anatomy. CONCLUSIONS: Vitreomacular tractions are perfectly well known by ophthalmologists. However, the method used to release them must be the least aggressive possible in order to avoid retinal tears or macular holes with subsequent visual loss.

Delayed Boston Keratoprosthesis Exchange due to a Preceding Vitreoretinal Surgery with Intraoperative Choroidal Detachment.

PURPOSE: The aim is to describe the main characteristics of an anterior/posterior segment surgery and how to resolve intraoperative complications. Setting/Venue: The anterior and posterior segment surgical video was created at the Department of Ophthalmology, Virgin Macarena University Hospital, Seville, Spain. METHODS: We present the case of a male with Stevens-Johnson syndrome and severe limbal deficiency who needed a Boston type 1 keratoprosthesis, reaching a visual acuity of 0.4 (0.05 before surgery). In the course of follow-up, he developed corneal melting with perforation, immune vitritis, and a large epimacular membrane. We decided to perform a 23-gauge vitrectomy associated with keratoprosthesis exchange. As a consequence of inappropriate anesthesia, the patient woke up during the surgery, provoking a retinal tear besides a choroidal detachment. These damages needed endolaser photocoagulation as well as silicone oil tamponade, forcing us to postpone the exchange. An intravitreal dexamethasone implant was also injected. Two months later, the silicone oil was removed, and the Boston keratoprosthesis was replaced by a new type 1 model with a titanium back plate, which likely improves biocompatibility and retention and may reduce complications such as retroprosthetic membranes and stromal corneal melts. RESULTS: Good anatomical results were achieved, and visual acuity slightly improved to 0.2. CONCLUSIONS: Combined anterior and posterior segment surgery represents a great challenge that can improve not only visual acuity but also quality of life in patients with severe diseases such as Stevens-Johnson syndrome.