The molecular basis of cystinuria: the role of the rBAT gene

Summary The cDNAs of mammalian amino acid transporters already identified could be grouped into four families. One of these protein families is composed of the protein rBAT and the heavy chain of the cell surface antigen 4F2 (4F2hc). The cRNAs of rBAT and 4F2hc induce amino acid transport activity via systems b^0,+ -like and y⁺L -like inXenopus oocytes respectively. Surprisingly, neither rBAT nor 4F2hc is very hydrophobic, and they seem to be unable to form a pore in the plasma membrane. This prompted the hypothesis that rBAT and 4F2hc are subunits or modulators of the corresponding amino acid transporters. The association of rBAT with a light subunit of ~40kDa has been suggested, and such an association has been demonstrated for 4F2hc.The b^0,+-like system expressed in oocytes by rBAT cRNA transports L-cystine, L-dibasic and L-neutral amino acids with high-affinity. This transport system shows exchange of amino acids through the plasma membrane ofXenopus oocytes, suggesting a tertiary active transport mechanism. The rBAT gene is mainly expressed in the outer stripe of the outer medulla of the kidney and in the mucosa of the small intestine. The protein localizes to the microvilli of the proximal straight tubules (S3 segment) of the nephron and the mucosa of the small intestine. All this suggested the participation of rBAT in a high-affinity reabsorption system of cystine and dibasic amino acids in kidney and intestine, and indicated rBAT (named SLC3A1 in Gene Data Bank) as a good candidate gene for cystinuria. This is an inherited aminoaciduria due to defective renal and intestinal reabsorption of cystine and dibasic amino acids. The poor solubility of cystine causes the formation of renal cystine calculi. Mutational analysis of the rBAT gene of patients with cystinuria is revealing a growing number (~20) of cystinuria-specific mutations, including missense, nonsense, deletions and insertions. Mutations M467T (substitution of methionine 467 residue for threonine) and R270X (stop codon at arginine residue 270) represent approximately half of the cystinuric chromosomes where mutations have been found. Mutation M467T reduces transport activity of rBAT in oocytes. All this demonstrates that mutations in the rBAT gene cause cystinuria.Three types of cystinuria (types, I, II and III) have been described on the basis of the genetic, biochemical and clinical manifestations of the disease. Type I cystinuria has a complete recessive inheritance; type I heterozygotes are totally silent. In contrast, type II and III heterozygotes show, respectively, high or moderate hyperaminoaciduria of cystine and dibasic amino acids. Type III homozygotes show moderate, if any, alteration of intestinal absorption of cystine and dibasic amino acids; type II homozygotes clearly show defective intestinal absorption of these amino acids. To date, all the rBAT cystinuria-specific mutations we have found are associated with type I cystinuria (~70% of the chromosomes studied) but not to types II or III. This strongly suggests genetic heterogeneity for cystinuria. Genetic linkage analysis with markers of the genomic region of rBAT in chromosome 2 (G band 2p16.3) and intragenic markers of rBAT have demonstrated genetic heterogeneity for cystinuria; the rBAT gene is linked to type I cystinuria, but not to type III. Biochemical, genetic and clinical studies are needed to identify the additional cystinuria genes; a low-affinity cystine reabsortion system and the putative light subunit of rBAT are additional candidate genes for cystinuria.     

Nucleotide variation at the hypervariable esterase 6 isozyme locus of Drosophila simulans

Esterase 6 (Est-6/EST6) is polymorphic in both Drosophila melanogaster and D. simulans for two common allozyme forms, as well as for several other less common variants. Parallel latitudinal clines in the frequencies of the common EST6-F and EST6-S allozymes in these species have previously been interpreted in terms of a shared amino acid polymorphism that distinguishes the two variants and is subject to selection. Here we compare the sequences of four D. simulans Est-6 isolates and show that overall estimates of nucleotide heterozygosity in both coding and 5' flanking regions are more than threefold higher than those obtained previously for this gene in D. melanogaster. Nevertheless, the ratio of replacement to exon silent-site polymorphism in D. simulans is less than the ratio of replacement to silent divergence between D. simulans and D. melanogaster, which could be the result of increased efficiency of selection against replacement polymorphisms in D. simulans or to divergent selection between the two species. We also find that the amino acid polymorphisms separating EST6- F and EST6-S in D. simulans are not the same as those that separate these allozymes in D. melanogaster, implying that the shared clines do not reflect shared molecular targets for selection. All comparisons within and between the two species reveal a remarkable paucity of variation in a stretch of nearly 400 bp immediately 5' of the gene, indicative of strong selective constraint to retain essential aspects of Est-6 promoter function.      

Production of endothelial progenitor cells obtained from human Wharton's jelly using different culture conditions

Endothelial progenitor cells (EPC) participate in revascularization and angiogenesis. EPC can be cultured in vitro from mononuclear cells of peripheral blood, umbilical cord blood or bone marrow; they also can be transdifferentiated from mesenchymal stem cells (MSC). We isolated EPCs from Wharton's jelly (WJ) using two methods. The first method was by obtaining MSC from WJ and characterizing them by flow cytometry and their adipogenic and osteogenic differentiation, then applying endothelial growth differentiating media. The second method was by direct culture of cells derived from WJ into endothelial differentiating media. EPCs were characterized by morphology, Dil-LDL uptake/UEA-1 immunostaining and testing the expression of endothelial markers by flow cytometry and RT-PCR. We found that MSC derived from WJ differentiated into endothelial-like cells using simple culture conditions with endothelium induction agents in the medium.     

Calvatia sporocristata sp. nov. (Gasteromycetes) from Costa Rica

Calvatia sporocristata, Gasteromycetes, is described and illustrated as a new species. Its taxonomic characters are discussed and compared with other closely related species of the genus. Few studies have been carried out on tropical Gasteromycetes. The new species here proposed has, as the main features: exoperidium corky, smooth, one-layered, pseudoparenchymatous; endoperidium thin, papyraceous, dextrinoid; subgleba cellular; capillitium septate, dissociated at the septal site, lycoperdon type, without pores, elastic and spores amigdaloid, 4-6 (-7) x 2.5-4.5 microns with spines aligned, forming crests, 0.8 micron high.     

Rga5p is a specific Rho1p GTPase-activating protein that regulates cell integrity in Schizosaccharomyces pombe

Schizosaccharomyces pombe Rho1p regulates (1,3)beta-d-glucan synthesis and is required for cell integrity maintenance and actin cytoskeleton organization, but nothing is known about the regulation of this protein. At least nine different S. pombe genes code for proteins predicted to act as Rho GTPase-activating proteins (GAPs). The results shown in this paper demonstrate that the protein encoded by the gene named rga5+ is a GAP specific for Rho1p. rga5+ overexpression is lethal and causes morphological alterations similar to those reported for Rho1p inactivation. rga5+ deletion is not lethal and causes a mild general increase in cell wall biosynthesis and morphological alterations when cells are grown at 37 degrees C. Upon mild overexpression, Rga5p localizes to growth areas and possesses both in vivo and in vitro GAP activity specific for Rho1p. Overexpression of rho1+ in rga5Delta cells is lethal, with a morphological phenotype resembling that of the overexpression of the constitutively active allele rho1G15V. In addition (1,3)beta-d-glucan synthase activity, regulated by Rho1p, is increased in rga5Delta cells and decreased in rga5-overexpressing cells. Moreover, the increase in (1,3)beta-d-glucan synthase activity caused by rho1+ overexpression is considerably higher in rga5Delta than in wild-type cells. Genetic interactions suggest that Rga5p is also important for the regulation of the other known Rho1p effectors, Pck1p and Pck2p.     

Evolution of spore release mechanisms in the saprolegniaceae (Oomycetes): evidence from a phylogenetic analysis of internal transcribed spacer sequences

Classical studies on spore release within the Saprolegniaceae (Oomycetes) led to the proposition that different mechanisms of sporangial emptying represent steps in an evolutionary transition series. We have reevaluated this idea in a phylogenetic framework using internal transcribed spacer sequences of four genera. These data were compared with the response to osmotic stress exhibited by each taxon. Saprolegnia emerges as the most basal genus, sister to Achlya, Thraustotheca, and Dictyuchus. Achlya and Thraustotheca are most closely related, while Dictyuchus appears to have evolved along a separate evolutionary lineage. The resulting phylogenetic framework is consistent with the idea that the mechanism of sporangial emptying exhibited by Saprolegnia represents the plesiomorphic condition from which the other mechanisms were derived independently. These alternative mechanisms of spore release may have resulted from a small number of mutations that inhibited axonemal development and altered the temporal and spatial expression of lytic enzymes that degrade the sporangial wall. Copyright 1998 Academic Press.     

Effect of coculturing canine notochordal,nucleus pulposus and mesenchymal stromal cells for intervertebral disc regeneration

IntroductionEarly degenerative changes in the nucleus pulposus (NP) are observed after the disappearance of notochordal cells (NCs). Thus, it has been suggested that NCs play an important role in maintaining the NP and may have a regenerative potential on other cells of the NP. As the number of resident NP cells (NPCs) decreases in a degenerating disc, mesenchymal stromal (stem) cells (MSCs) may be used for cell supplementation. In this study, using cells of one species, the regenerative potential of canine NCs was assessed in long-term three-dimensional coculture with canine NPCs or MSCs.MethodsCanine NCs and canine NPCs or MSCs were cocultured in alginate beads for 28 days under hypoxic and high-osmolarity conditions. Cell viability, cell morphology and DNA content, extracellular matrix production and expression of genes related to NC markers (Brachyury, KRT18) and NP matrix production (ACAN, COL2A1, COL1A1) were assessed after 1, 15 and 28 days of culture.ResultsNCs did not completely maintain their phenotype (morphology, matrix production, gene expression) during 28 days of culture. In cocultures of NPCs and NCs, both extracellular matrix content and anabolic gene expression remained unchanged compared with monoculture groups, whereas cocultures of MSCs and NCs showed increased glycosaminoglycan/DNA. However, the deposition of these proteoglycans was observed near the NCs and not the MSCs. Brachyury expression in the MSC and NC coculture group increased in time. The latter two findings indicate a trophic effect of MSCs on NCs rather than vice versa.ConclusionsNo regenerative potential of canine NCs on canine NPCs or MSCs was observed in this study. However, significant changes in NC phenotype in long-term culture may have resulted in a suboptimal regenerative potential of these NCs. In this respect, NC-conditioned medium may be better than coculture for future studies of the regenerative potential of NCs.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-015-0569-6) contains supplementary material, which is available to authorized users.