Loss of ninein interferes with osteoclast formation and causes premature ossification.

Ninein is a centrosome protein that has been implicated in microtubule anchorage and centrosome cohesion. Mutations in the human NINEIN gene have been linked to Seckel syndrome and to a rare form of skeletal dysplasia. However, the role of ninein in skeletal development remains unknown. Here, we describe a ninein knockout mouse with advanced endochondral ossification during embryonic development. Although the long bones maintain a regular size, the absence of ninein delays the formation of the bone marrow cavity in the prenatal tibia. Likewise, intramembranous ossification in the skull is more developed, leading to a premature closure of the interfrontal suture. We demonstrate that ninein is strongly expressed in osteoclasts of control mice, and that its absence reduces the fusion of precursor cells into syncytial osteoclasts, whereas the number of osteoblasts remains unaffected. As a consequence, ninein-deficient osteoclasts have a reduced capacity to resorb bone. At the cellular level, the absence of ninein interferes with centrosomal microtubule organization, reduces centrosome cohesion, and provokes the loss of centrosome clustering in multinucleated mature osteoclasts. We propose that centrosomal ninein is important for osteoclast fusion, to enable a functional balance between bone-forming osteoblasts and bone-resorbing osteoclasts during skeletal development.

Impaired Mineral Ion Metabolism in a Mouse Model of Targeted Calcium-Sensing Receptor (CaSR) Deletion from Vascular Smooth Muscle Cells.

BACKGROUND: Impaired mineral ion metabolism is a hallmark of CKD-metabolic bone disorder. It can lead to pathologic vascular calcification and is associated with an increased risk of cardiovascular mortality. Loss of calcium-sensing receptor (CaSR) expression in vascular smooth muscle cells exacerbates vascular calcification in vitro. Conversely, vascular calcification can be reduced by calcimimetics, which function as allosteric activators of CaSR. METHODS: To determine the role of the CaSR in vascular calcification, we characterized mice with targeted Casr gene knockout in vascular smooth muscle cells ( SM22α CaSR Δflox/Δflox ). RESULTS: Vascular smooth muscle cells cultured from the knockout (KO) mice calcified more readily than those from control (wild-type) mice in vitro. However, mice did not show ectopic calcifications in vivo but they did display a profound mineral ion imbalance. Specifically, KO mice exhibited hypercalcemia, hypercalciuria, hyperphosphaturia, and osteopenia, with elevated circulating fibroblast growth factor 23 (FGF23), calcitriol (1,25-D3), and parathyroid hormone levels. Renal tubular α-Klotho protein expression was increased in KO mice but vascular α-Klotho protein expression was not. Altered CaSR expression in the kidney or the parathyroid glands could not account for the observed phenotype of the KO mice. CONCLUSIONS: These results suggest that, in addition to CaSR's established role in the parathyroid-kidney-bone axis, expression of CaSR in vascular smooth muscle cells directly contributes to total body mineral ion homeostasis.

Neonatal vascularization and oxygen tension regulate appropriate perinatal renal medulla/papilla maturation.

Congenital medullary dysplasia with obstructive nephropathy is a common congenital disorder observed in paediatric patients and represents the foremost cause of renal failure. However, the molecular processes regulating normal papillary outgrowth during the postnatal period are unclear. In this study, transcriptional profiling of the renal medulla across postnatal development revealed enrichment of non-canonical Wnt signalling, vascular development, and planar cell polarity genes, all of which may contribute to perinatal medulla/papilla maturation. These pathways were investigated in a model of papillary hypoplasia with functional obstruction, the Crim1(KST264/KST264) transgenic mouse. Postnatal elongation of the renal papilla via convergent extension was unaffected in the Crim1(KST264/KST264) hypoplastic renal papilla. In contrast, these mice displayed a disorganized papillary vascular network, tissue hypoxia, and elevated Vegfa expression. In addition, we demonstrate the involvement of accompanying systemic hypoxia arising from placental insufficiency, in appropriate papillary maturation. In conclusion, this study highlights the requirement for normal vascular development in collecting duct patterning, development of appropriate nephron architecture, and perinatal papillary maturation, such that disturbances contribute to obstructive nephropathy.

Hspa9 is required for pronephros specification and formation in Xenopus laevis.

BACKGROUND: Development of the pronephros in Xenopus laevis is largely dependent on retinoic acid signaling at the time of kidney field specification with the simultaneous occurrence of a necessary calcium signaling. At the crossroads of these two signaling pathways, we studied the role of Hspa9 (heat shock 70 kDa protein 9) encoding a mitochondrial chaperone in pronephros development. RESULTS: We first showed that Hspa9 is highly expressed in the pronephros territory and elongating nephric duct. We then observed that upon reduced retinoic acid signaling hspa9 expression was reduced as pax8 and pax2. Overexpression of hspa9 enlarged the pax8 positive pronephros territory, leading to a larger pronephric tubule. Loss of function of hspa9 in the kidney field using morpholino approach severely reduced pax8 expression and pronephros formation. Phenotypic rescue was achieved by co-injection of the full-length murine Hspa9 mRNA. However, no rescue was observed when Hspa9 mRNA lacking the mitochondrial-targeting sequence was injected, as this truncated form is able to interfere with pronephros formation when injected solely. CONCLUSIONS: Hspa9 is an important mediator for pronephros development through modulation of pax8. Mitochondrial functions of hspa9 are likely to be involved in specification of pronephric cell fate.

Nephron formation adopts a novel spatial topology at cessation of nephrogenesis.

Nephron number in the mammalian kidney is known to vary dramatically, with postnatal renal function directly influenced by nephron complement. What determines final nephron number is poorly understood but nephron formation in the mouse kidney ceases within the first few days after birth, presumably due to the loss of all remaining nephron progenitors via epithelial differentiation. What initiates this event is not known. Indeed, whether nephron formation occurs in the same way at this time as during embryonic development has also not been examined. In this study, we investigate the key cellular compartments involved in nephron formation; the ureteric tip, cap mesenchyme and early nephrons; from postnatal day (P) 0 to 6 in the mouse. High resolution analyses of gene and protein expression indicate that loss of nephron progenitors precedes loss of ureteric tip identity, but show spatial shifts in the expression of cap mesenchyme genes during this time. In addition, cap mesenchymal volume and rate of proliferation decline prior to birth. Section-based 3D modeling and Optical Projection Tomography revealed a burst of ectopic nephron induction, with the formation of multiple (up to 5) nephrons per ureteric tip evident from P2. While the distal-proximal patterning of these nephrons occurred normally, their spatial relationship with the ureteric compartment was altered. We propose that this phase of nephron formation represents an acceleration of differentiation within the cap mesenchyme due to a displacement of signals within the nephrogenic niche.

Control of kidney development by calcium ions.

From the formation of a simple kidney in amphibian larvae, the pronephros, to the formation of the more complex mammalian kidney, the metanephros, calcium is present through numerous steps of tubulogenesis and nephron induction. Several calcium-binding proteins such as regucalcin/SMP-30 and calbindin-D28k are commonly used to label pronephric tubules and metanephric ureteral epithelium, respectively. However, the involvement of calcium and calcium signalling at various stages of renal organogenesis was not clearly delineated. In recent years, several studies have pinpointed an unsuspected role of calcium in determination of the pronephric territory and for conversion of metanephric mesenchyme into nephrons. Influx of calcium and calcium transients have been recorded in the pool of renal progenitors to allow tubule formation, highlighting the occurrence of calcium-dependent signalling events during early kidney development. Characterization of nuclear calcium signalling is emerging. Implication of the non-canonical calcium/NFAT Wnt signalling pathway as an essential mechanism to promote nephrogenesis has recently been demonstrated. This review examines the current knowledge of the impact of calcium ions during embryonic development of the kidney. It focuses on Ca(2+) binding proteins and Ca(2+) sensors that are involved in renal organogenesis and briefly examines the link between calcium-dependent signals and polycystins.

Non-cell-autonomous retinoid signaling is crucial for renal development.

In humans and mice, mutations in the Ret gene result in Hirschsprung's disease and renal defects. In the embryonic kidney, binding of Ret to its ligand, Gdnf, induces a program of epithelial cell remodeling that controls primary branch formation and branching morphogenesis within the kidney. Our previous studies showed that transcription factors belonging to the retinoic acid (RA) receptor family are crucial for controlling Ret expression in the ureteric bud; however, the mechanism by which retinoid-signaling acts has remained unclear. In the current study, we show that expression of a dominant-negative RA receptor in mouse ureteric bud cells abolishes Ret expression and Ret-dependent functions including ureteric bud formation and branching morphogenesis, indicating that RA-receptor signaling in ureteric bud cells is crucial for renal development. Conversely, we find that RA-receptor signaling in ureteric bud cells depends mainly on RA generated in nearby stromal cells by retinaldehyde dehydrogenase 2, an enzyme required for most fetal RA synthesis. Together, these studies suggest that renal development depends on paracrine RA signaling between stromal mesenchyme and ureteric bud cells that regulates Ret expression both during ureteric bud formation and within the developing collecting duct system.

Loss of renal microvascular integrity in postnatal Crim1 hypomorphic transgenic mice.

Crim1 is a cell-surface, transmembrane protein that binds to a variety of cystine knot-containing growth factors, including vascular endothelial growth factor A. In the developing renal glomerulus, Crim1 acts to tether vascular endothelial growth factor A to the podocyte cell surface, thus regulating its release to glomerular endothelial cells. The hypomorphic transgenic mouse (Crim1(KST264/KST264)) has glomerular cysts and severe glomerular vascular defects because of the lack of functional Crim1 in the glomerulus. Adult transgenic mice have a reduced glomerular filtration rate and glomerular capillary defects. We now show that, in these adult transgenic mice, renal vascular defects are not confined to the glomerulus but also extend to the peritubular microvasculature, as live imaging revealed leakiness of both glomerular and peritubular capillaries. An ultrastructural analysis of the microvasculature showed an abnormal endothelium and collagen deposition between the endothelium and the tubular basement membrane, present even in juvenile mice. Overt renal disease, including fibrosis and renin recruitment, was not evident until adulthood. Our study suggests that Crim1 is involved in endothelial maintenance and integrity and its loss contributes to a primary defect in the extraglomerular vasculature.

The gene responsible for Dyggve-Melchior-Clausen syndrome encodes a novel peripheral membrane protein dynamically associated with the Golgi apparatus.

Dyggve-Melchior-Clausen dysplasia (DMC) is a rare inherited dwarfism with severe mental retardation due to mutations in the DYM gene which encodes Dymeclin, a 669-amino acid protein of yet unknown function. Despite a high conservation across species and several predicted transmembrane domains, Dymeclin could not be ascribed to any family of proteins. Here we show, using in situ hybridization, that DYM is widely expressed in human embryos, especially in the cortex, the hippocampus and the cerebellum. Both the endogenous and the recombinant protein fused to green fluorescent protein co-localized with Golgi apparatus markers. Electron microscopy revealed that Dymeclin associates with the Golgi apparatus and with transitional vesicles of the reticulum-Golgi interface. Moreover, permeabilization assays revealed that Dymeclin is not a transmembrane but a peripheral protein of the Golgi apparatus as it can be completely released from the Golgi after permeabilization of the plasma membrane. Time lapse confocal microscopy experiments on living cells further showed that the protein shuttles between the cytosol and the Golgi apparatus in a highly dynamic manner and recognizes specifically a subset of mature Golgi membranes. Finally, we found that DYM mutations associated with DMC result in mis-localization and subsequent degradation of Dymeclin. These data indicate that DMC results from a loss-of-function of Dymeclin, a novel peripheral membrane protein which shuttles rapidly between the cytosol and mature Golgi membranes and point out a role of Dymeclin in cellular trafficking.

Use of dual section mRNA in situ hybridisation/immunohistochemistry to clarify gene expression patterns during the early stages of nephron development in the embryo and in the mature nephron of the adult mouse kidney.

The kidney is the most complex organ within the urogenital system. The adult mouse kidney contains in excess of 8,000 mature nephrons, each of which can be subdivided into a renal corpuscle and 14 distinct tubular segments. The histological complexity of this organ can make the clarification of the site of gene expression by in situ hybridisation difficult. We have defined a panel of seven antibodies capable of identifying the six stages of early nephron development, the tubular nephron segments and the components of the renal corpuscle within the embryonic and adult mouse kidney. We have analysed in detail the protein expression of Wt1, Calb1 Aqp1, Aqp2 and Umod using these antibodies. We have then coupled immunohistochemistry with RNA in situ hybridisation in order to precisely identify the expression pattern of different genes, including Wnt4, Umod and Spp1. This technique will be invaluable for examining at high resolution, the structure of both the developing and mature nephron where standard in situ hybridisation and histological techniques are insufficient. The use of this technique will enhance the expression analyses of genes which may be involved in nephron formation and the function of the mature nephron in the mouse.

A high-resolution anatomical ontology of the developing murine genitourinary tract.

Cataloguing gene expression during development of the genitourinary tract will increase our understanding not only of this process but also of congenital defects and disease affecting this organ system. We have developed a high-resolution ontology with which to describe the subcompartments of the developing murine genitourinary tract. This ontology incorporates what can be defined histologically and begins to encompass other structures and cell types already identified at the molecular level. The ontology is being used to annotate in situ hybridisation data generated as part of the Genitourinary Development Molecular Anatomy Project (GUDMAP), a publicly available data resource on gene and protein expression during genitourinary development. The GUDMAP ontology encompasses Theiler stage (TS) 17-27 of development as well as the sexually mature adult. It has been written as a partonomic, text-based, hierarchical ontology that, for the embryological stages, has been developed as a high-resolution expansion of the existing Edinburgh Mouse Atlas Project (EMAP) ontology. It also includes group terms for well-characterised structural and/or functional units comprising several sub-structures, such as the nephron and juxtaglomerular complex. Each term has been assigned a unique identification number. Synonyms have been used to improve the success of query searching and maintain wherever possible existing EMAP terms relating to this organ system. We describe here the principles and structure of the ontology and provide representative diagrammatic, histological, and whole mount and section RNA in situ hybridisation images to clarify the terms used within the ontology. Visual examples of how terms appear in different specimen types are also provided.

Crim1KST264/KST264 mice implicate Crim1 in the regulation of vascular endothelial growth factor-A activity during glomerular vascular development.

Crim1, a transmembrane cysteine-rich repeat-containing protein that is related to chordin, plays a role in the tethering of growth factors at the cell surface. Crim1 is expressed in the developing kidney; in parietal cells, podocytes, and mesangial cells of the glomerulus; and in pericytes that surround the arterial vasculature. A gene-trap mouse line with an insertion in the Crim1 gene (Crim1(KST264/KST264)) displayed perinatal lethality with defects in multiple organ systems. This study further analyzed the defects that are present within the kidneys of these mice. Crim1(KST264/KST264) mice displayed abnormal glomerular development, illustrated by enlarged capillary loops, podocyte effacement, and mesangiolysis. When outbred, homozygotes that reached birth displayed podocyte and glomerular endothelial cell defects and marked albuminuria. The podocytic co-expression of Crim1 with vascular endothelial growth factor-A (VEGF-A) suggested a role for Crim1 in the regulation of VEGF-A action. Crim1 and VEGF-A were shown to interact directly, providing evidence that cysteine-rich repeat-containing proteins can bind to non-TGF-beta superfamily ligands. Crim1(KST264/KST264) mice display a mislocalization of VEGF-A within the developing glomerulus, as assessed by immunogold electron microscopy and increased activation of VEGF receptor 2 (Flk1) in the glomerular endothelial cells, suggesting that Crim1 regulates the delivery of VEGF-A by the podocytes to the endothelial cells. This is the first in vivo demonstration of regulation of VEGF-A delivery and supports the hypothesis that Crim1 functions to regulate the release of growth factors from the cell of synthesis.

Expression of retinoic acid-synthesizing and -metabolizing enzymes during nephrogenesis in the rat.

Vitamin A signaling through its active form retinoic acid (RA) plays a critical role during kidney development and vitamin A deficiency in the rat induces renal hypoplasia. Here, we describe the distribution of four enzymes of the RA synthetic pathway (aldehyde dehydrogenases ALDH1A1-3 and ALDH8A1) and two enzymes of the degradative pathway (CYP26A1 and CYP26B1) in the developing rat metanephros. We provide evidence that each enzyme displays a cell-type specific expression pattern that changes considerably in the course of renal organogenesis and nephron differentiation. ALDH1A2 expression was restricted to the cortical stroma cell population, whereas ALDH8A1 transcripts were present in emerging renal vesicles. CYP26A1 and CYP26B1 mRNAs were absent during this time. Following nephron induction, ALDH1A1 remained weakly expressed in the UB ends, but was highly expressed in the UB-connected tubule and in all differentiating tubular segments of the developing nephron. ALDH1A2 was strongly expressed in the visceral layer of the developing glomeruli, as well as in cortical collecting tubules. ALDH1A3 mRNAs were found in the developing papilla and ureter. During postnatal nephrogenesis, ALDH1A3 and ALDH8A1 were co-expressed in the ureteric bud ends. CYP26A1 and CYP26B1 were both expressed from E18.5 onwards in S-shaped bodies, in tubular and glomerular anlagen, respectively. On the last day of nephrogenesis in the rat, CYP26B1 expression extended to UB ends. Our results indicate that tubular and glomerular differentiation of the nephron relies upon precise control of the RA metabolic pathway.

Recent advances in Dyggve-Melchior-Clausen syndrome.

Dyggve-Melchior-Clausen (DMC) is a rare autosomal-recessive disorder characterized by the association of a progressive spondylo-epi-metaphyseal dysplasia and mental retardation ranging from mild to severe. Electron microscopy studies of both DMC chondrocytes and fibroblasts reveal an enlarged endoplasmic reticulum network and a large number of intracytoplasmic membranous vesicles, suggesting that DMC syndrome may be a storage disorder. Indeed, DMC phenotype is often compared to that of type IV mucopolysaccharidosis (Morquio disease), a lysosomal disorder due to either N-acetylgalactosamine-6-sulphatase or beta-galactosidase deficiency. To date, however, the lysosomal pathway appears normal in DMC patients and biochemical analyses failed to reveal any enzymatic deficiency or accumulated substrate. Linkage studies using homozygosity mapping have led to the localization of the disease-causing gene on chromosome 18q21.1. The gene was recently identified as a novel transcript (Dym) encoding a 669-amino acid product (Dymeclin) with no known domains or function. Sixteen different Dym mutations have now been described in 21 unrelated families with at least five founder effects in Morocco, Lebanon, and Guam Island. Smith-MacCort syndrome (SMC), a rare variant of DMC syndrome without mental retardation, was shown to be allelic of DMC syndrome and to result from mutations in Dym that would be less deleterious to the brain. The present review focuses on clinical, radiological, and cellular features and evolution of DMC/SMC syndromes and discusses them with regard to identified Dym mutations and possible roles of the Dym gene product.

Long-term effects of in utero exposure to cyclosporin A on renal function in the rabbit.

The number of pregnant women who receive cyclosporin A (CsA) after transplantation or for autoimmune disease has increased. CsA and its metabolites can cross the placental barrier and thus interfere with fetal development. It was shown previously that rabbits that were exposed in utero to 10 mg/kg per d CsA from the 14th to the 18th day of gestation presented a 25% nephron reduction. Thus, this study was conducted to assess the long-term systemic and renal effects of a CsA-induced nephron reduction. Twenty-two pregnant New Zealand white rabbits were randomly divided into two groups: Twelve received 10 mg/kg per d CsA from day 14 to day 18 of gestation, and 10 were used as controls. Rabbits that were born to these animals were evaluated at 4, 11, 18, and 35 wk of life. Pups that were exposed antenatally to CsA presented first a permanent nephron deficit; second, glomerular, tubular, and intrarenal hemodynamics dysfunction; third, enlarged kidneys with numerous tubular and glomerular lesions; and, fourth, an endothelin-dependent systemic hypertension that worsened with age. In utero exposure to CsA induced a nephron reduction that led to systemic hypertension and progressive chronic renal insufficiency in adulthood. A long-term clinical survey is mandatory in infants who are born to mothers who were treated with cyclosporin during pregnancy.

In vivo expression of podocyte slit diaphragm-associated proteins in nephrotic patients with NPHS2 mutation.

BACKGROUND: Mutations in NPHS2, encoding podocin, are a prevalent cause of autosomal-recessive steroid-resistant nephrotic syndrome (SRNS). Podocin is a protein associated with the slit diaphragm that interacts with nephrin and CD2-associated protein (CD2AP) within lipid rafts. METHODS: Using renal biopsies of six patients, we analyzed the in vivo consequences of different types of NPHS2 mutations on (1) the podocyte expression and distribution of podocin using in situ hybridization and immunohistology and (2) the distribution of related podocyte proteins and glomerular extracellular matrix components. RESULTS: In two patients with homozygous 855_856delAA or 419delG mutation, absence of podocyte labeling with the antibodies against the C-terminal domain contrasted with the normal expression of the N-terminal domain of the protein along the glomerular basement membrane (GBM). In patients carrying compound heterozygous mutations or variants (R168S/467_468insT, R138Q/V180M, and R291W/R229Q), or single heterozygous 976_977insA, podocin transcription appeared unchanged but the distribution of the protein was modified. Podocin was restricted to the podocyte body in the patient carrying the R168S/467_468insT mutation whereas strong immunolabeling of the podocyte body was associated with discrete labeling along the GBM in the three others. In all cases, podocin defect was associated with changes in the distribution of nephrin, CD2AP, and alpha-actinin: the proteins were mainly detected in the podocyte body, with mild expression along the GBM. There were no detectable changes in the distribution of other podocyte proteins or glomerular extracellular matrix components. CONCLUSION: NPHS2 mutations result in profound alteration of podocin expression and/or distribution. Secondary changes in the distribution of nephrin, CD2AP, and alpha-actinin are additional evidences for the scaffolding role of podocin in the organization of the slit diaphragm.

Reverse transcription-PCR analysis of bottled and natural mineral waters for the presence of noroviruses.

A seminested reverse transcription-PCR method coupled to membrane filtration was optimized to investigate the presence of norovirus (NV) RNA sequences in bottled and natural mineral waters. The recovery of viral particles by filtration varied between 28 and 45%, while the limit of detection of the overall method ranged from 6 to 95 viral particles. The assay was broadly reactive, as shown by the successful detection of 27 different viral strains representing 12 common genotypes of NVs. A total of 718 bottled and natural mineral water samples were investigated, including 640 samples of finished, spring, and line products (mostly 1 to 1.5 liters), collected from 36 different water brands of various types and from diverse geographic origins over a 2-year period. In addition, 78 samples of larger volume (10 and 400 to 500 liters) and environmental swabs were investigated. From the 1,436 analyses that were performed for the detection of NVs belonging to genogroups I and II, 34 samples (2.44%) were presumptively positive by seminested RT-PCR. However, confirmation by DNA sequence analysis revealed that all presumptive positive results were either due to nonspecific amplification or to cross-contamination. In conclusion, these results do not provide any evidence for the presence of NV genome sequences in bottled waters.

Cyclosporin A administration during pregnancy induces a permanent nephron deficit in young rabbits.

Cyclosporin A (CsA) is an immunosuppressive agent used to prevent graft rejection and to treat autoimmune disorders. Successful pregnancies can be achieved among CsA-treated women, although it is known that CsA is nephrotoxic and crosses the human placenta. The aim of this study was to evaluate the harmlessness of CsA toward the embryonic kidney. Twenty-one pregnant rabbits were divided into four groups. Groups of six and four female animals were subjected to daily injections of 10 mg/kg per d CsA (administered subcutaneously) for 5 d, from day 14 to day 18 of gestation or from day 20 to day 24 of gestation, respectively. In the third group, five female animals received the CsA diluent (Cremophor) from day 14 to day 18 of gestation. The fourth group consisted of six untreated female animals. Pregnancy outcomes among CsA-treated does demonstrated a reduced number of living pups, which were also growth-retarded, with exposure to CsA from day 20 to day 24 of gestation. However, pups exposed to CsA from day 14 to day 18 of gestation exhibited normal fetal growth, and blood concentrations of CsA matched human data. Examinations of kidneys at birth demonstrated vacuolation of proximal and collecting tubules and ureteric bud ends. Increased glomerular volumes and decreased nephron densities suggested nephron mass reduction, which was quantitatively evaluated in 1-mo-old animals. The nephron numbers were reduced by 25 and 33% in day 14 to 18 CsA-treated and day 20 to 24 CsA-treated animals, respectively, which displayed compensatory adaptation of the existing nephrons. However, foci of segmental glomerular sclerosis were already present, which would possibly jeopardize renal function later in life.

Vitamin A and kidney development.

Recent advances in developmental nephrology have provided new evidence that retinoids, vitamin A and its active metabolites such as all-trans retinoic acid, profoundly influence renal organogenesis. Retinoids are acknowledged as potent nephron mass regulators. They regulate embryonic kidney patterning through control of Ret expression in a dose-dependent manner, which modulates ureteric bud branching morphogenesis. Analysis of retinoid availability and utilization provides additional evidence of retinoid involvement at sites of epithelial-mesenchymal interactions, suggesting a tight control of vitamin A homeostasis for proper renal morphogenesis and differentiation. This provides a rationale for the search for and identification of retinoid target genes.

Genetic and biochemical characterization of exopolysaccharide biosynthesis by Lactobacillus delbrueckii subsp. bulgaricus.

Lactobacillus delbrueckiisubsp. bulgaricus produces exopolysaccharides (EPSs), which play a role in the rheological properties of fermented food products. Lb. bulgaricus Lfi5 produces a high-molecular-weight EPS composed of galactose, glucose, and rhamnose in the molar ratio 5:1:1. An 18-kb DNA region containing 14 genes, designated epsA to epsN, was isolated by genomic DNA library screening and inverted PCR. The predicted gene products are homologous to proteins involved in the biosynthesis of other bacterial polysaccharides and the genetic organization was found to be similar to that of other eps clusters from lactic acid bacteria. Transcriptional analysis revealed that the 14 eps genes are co-ordinately expressed and transcribed as a single mRNA of 15-16 kb. The transcription start site of the promoter was mapped upstream of the first gene, epsA. Genes encoding glycosyltranferases were further studied by heterologous expression and functional assays. We showed that the epsE gene product is a phospho-glucosyltransferase initiating the biosynthesis of EPS. Heterologous expression of epsE in a Lactococcus lactis epsDmutant restored EPS production, demonstrating its role and importance in EPS biosynthesis. Functional assays of other glycosyltransferases allowed their sugar specificity to be elucidated and an overall biosynthetic pathway for EPS synthesis by Lb. bulgaricus to be proposed.