Aldosterone and tight junctions: modulation of claudin-4 phosphorylation in renal collecting duct cells

Aldosterone classically modulates Na transport in tight epithelia such as the renal collecting duct (CD) through the transcellular route, but it is not known whether the hormone could also affect paracellular permeability. Such permeability is controlled by tight junctions (TJ) that form a size- and charge-selective barrier. Among TJ proteins, claudin-4 has been highlighted as a key element to control paracellular charge selectivity. In RCCD2 CD cells grown on filters, we have identified novel early aldosterone effects on TJ. Endogenous claudin-4 abundance and cellular localization were unaltered by aldosterone. However, the hormone promoted rapid (within 15-20 min) and transient phosphorylation of endogenous claudin-4 on threonine residues, without affecting tyrosine or serine; this event was fully developed at 10 nM aldosterone and appeared specific for aldosterone (because it is not observed after dexamethasone treatment and it depends on mineralocorticoid receptor occupancy). Within the same delay, aldosterone also promoted an increased apical-to-basal passage of 125I (a substitute for 36Cl), whereas 22Na passage was unaffected; paracellular permeability to [3H]mannitol was also reduced. Later on (45 min), a fall in transepithelial resistance was observed. These data indicate that aldosterone modulates TJ properties in renal epithelial cells.     

Kallmann syndrome: mutations in the genes encoding prokineticin-2 and prokineticin receptor-2

Kallmann syndrome combines anosmia, related to defective olfactory bulb morphogenesis, and hypogonadism due to gonadotropin-releasing hormone deficiency. Loss-of-function mutations in KAL1 and FGFR1 underlie the X chromosome-linked form and an autosomal dominant form of the disease, respectively. Mutations in these genes, however, only account for approximately 20% of all Kallmann syndrome cases. In a cohort of 192 patients we took a candidate gene strategy and identified ten and four different point mutations in the genes encoding the G protein-coupled prokineticin receptor-2 (PROKR2) and one of its ligands, prokineticin-2 (PROK2), respectively. The mutations in PROK2 were detected in the heterozygous state, whereas PROKR2 mutations were found in the heterozygous, homozygous, or compound heterozygous state. In addition, one of the patients heterozygous for a PROKR2 mutation was also carrying a missense mutation in KAL1, thus indicating a possible digenic inheritance of the disease in this individual. These findings reveal that insufficient prokineticin-signaling through PROKR2 leads to abnormal development of the olfactory system and reproductive axis in man. They also shed new light on the complex genetic transmission of Kallmann syndrome.     

Diversity and Epidemiology of Mokola Virus

Mokola virus (MOKV) appears to be exclusive to Africa. Although the first isolates were from Nigeria and other Congo basin countries, all reports over the past 20 years have been from southern Africa. Previous phylogenetic studies analyzed few isolates or used partial gene sequence for analysis since limited sequence information is available for MOKV and the isolates were distributed among various laboratories. The complete nucleoprotein, phosphoprotein, matrix and glycoprotein genes of 18 MOKV isolates in various laboratories were sequenced either using partial or full genome sequencing using pyrosequencing and a phylogenetic analysis was undertaken. The results indicated that MOKV isolates from the Republic of South Africa, Zimbabwe, Central African Republic and Nigeria clustered according to geographic origin irrespective of the genes used for phylogenetic analysis, similar to that observed with Lagos bat virus. A Bayesian Markov-Chain-Monte-Carlo- (MCMC) analysis revealed the age of the most recent common ancestor (MRCA) of MOKV to be between 279 and 2034 years depending on the genes used. Generally, all MOKV isolates showed a similar pattern at the amino acid sites considered influential for viral properties.     

The γ-crystallin gene families: Sequence and evolutionary patterns

Summary The -crystallin proteins consist of two topologically equivalent domains, each built up out of two similar motifs. They are encoded by a gene family, which already contained five members before the divergence of rodents and primates. A further gene duplication took place in each lineage. To analyze the pattern of evolution within this gene family, the coding sequences of six human genes, six rat genes, and four mouse genes were compared. Between species, a uniform rate of evolution of all regions of the protein is seen. The ratio of synonymous to nonsynonymous substitution in the human/rat or human/mouse comparison is much lower than the ratio when rat and mouse are compared indicating that the -crystallin proteins are better conserved in the rodent lineage. Within species, the regions encoding the two external motifs I and III of the protein show a greater extent of nonsynonymous substitution than the regions encoding the two internal protein motifs II and IV. The low extent of synonymous substitution between the second exons (encoding motifs I and II) of the rat -crystallin genes suggests the frequent occurrence of gene conversion. In contrast, a high extent of synonymous substitution is found in exon 3 (encoding motifs III and IV) of the rat genes. The same phenomenon is seen within the human gene family. The frequencies of occurrence of the various dinucleotides deviate less from those predicted from the frequencies of occurrence of each individual nucleotide in the second exons than in the third exons. The sequences of the third exons are significantly depleted in CpG, ApA, and GpT and enriched in CpT and GpA.     

Oligomerization and phase transitions in aqueous solutions of native and truncated human beta B1-crystallin

Human betaB1-crystallin is a major eye-lens protein that undergoes in vivo truncation at the N-terminus with aging. By studying native betaB1 and truncated betaB1DeltaN41, which mimics an age-related in vivo truncation, we have determined quantitatively the effect of truncation on the oligomerization and phase transition properties of betaB1 aqueous solutions. The oligomerization studies show that the energy of attraction between the betaB1DeltaN41 proteins is about 10% greater than that of the betaB1 proteins. We have found that betaB1DeltaN41 aqueous solutions undergo two distinct types of phase transitions. The first phase transition involves an initial formation of thin rodlike assemblies, which then evolve to form crystals. The induction time for the formation of rodlike assemblies is sensitive to oligomerization. The second phase transition can be described as liquid-liquid phase separation (LLPS) accompanied by gelation within the protein-rich phase. We refer to this process as heterogeneous gelation. These two phase transitions are not observed in the case of betaB1 aqueous solutions. However, upon the addition of poly(ethylene glycol) (PEG), we observe heterogeneous gelation also for betaB1. Our PEG experiments allow us to estimate the difference in phase separation temperatures between betaB1 and betaB1DeltaN41. This difference is consistent with the increase in energy of attraction found in our oligomerization studies. Our work suggests that truncation is a cataractogenic modification since it favors protein condensation and the consequent formation of light scattering elements, and highlights the importance of the N-terminus of betaB1 in maintaining lens transparency.     

Development of captive bongos (Tragelaphus eurycerus): Activity budgets and developmental milestones

The development of changes in visual orientation, posture, activity budgets, and behavioral milestones was examined in five bongo calves which were observed from birth to 4 or 6 months of age. The only significant change in the calves' visual orientation was an increase in orientation to food. Reclining declined significantly over weeks, while standing increased and moving did not change. Overall, stationary behaviors dominated the activity budget, but decreased significantly over the study. The category that included locomotion, object exploration, and auto-play did not change, while forage and rumination increased significantly. Contrary to expectation, the decline in suckling was not significant. Affiliative interactions with the dam decreased significantly during the study, but increases in affiliation with other bongos were not significant. Levels of agonistic behavior between the calves and their dams and other herd members were low throughout the study, and did not change significantly. One female calf achieved several developmental milestones later than the others. It is suggested that these differences may have been influenced by the dominance status of her dam. The results conform to the general developmental pattern of “hider” bovids. Bongos, however, show somewhat different patterns of social development than eland, which are reported to be more precocial in expression of aggressive and sexual behaviors. © 1992 Wiley-Liss, Inc.     

Exploring the role of galectin 3 in kidney function: a genetic approach

Galectin 3 belongs to a family of glycoconjugate-binding proteinsthat participate in cellular homeostasis by modulating cellgrowth, adhesion, and signaling. We studied adult galectin 3null mutant (Gal 3–/–) and wild-type (WT) mice togain insights into the role of galectin 3 in the kidney. Byimmunofluorescence, galectin 3 was found in collecting duct(CD) principal and intercalated cells in some regions of thekidney, as well as in the thick ascending limbs at lower levels.Compared to WT mice, Gal 3–/– mice had ~11% fewerglomeruli (p < 0.04), associated with kidney hypertrophy(p < 0.006). In clearance experiments, urinary chloride excretionwas found to be higher in Gal 3–/– than in WT mice(p < 0.04), but there was no difference in urinary bicarbonateexcretion, in glomerular filtration, or urinary flow rates.Under chronic low sodium diet, Gal 3–/– mice hadlower extracellular fluid (ECF) volume than WT mice (p <0.05). Plasma aldosterone concentration was higher in Gal 3–/–than in WT mice (p < 0.04), which probably caused the observedincrease in -epithelial sodium channel (-ENaC) protein abundancein the mutant mice (p < 0.001). Chronic high sodium dietresulted paradoxically in lower blood pressure (p < 0.01)in Gal 3–/– than in WT. We conclude that Gal 3–/–mice have mild renal chloride loss, which causes chronic ECFvolume contraction and reduced blood pressure levels.