Phenotypic plasticity and terminal differentiation of the intercalated cell: the hensin pathway

The physiology of fish at low pH: the zebrafish as a model system

Ionic regulation and acid–base balance are fundamental to the physiology of vertebrates including fish. Acidification of freshwater ecosystems is recognized as a global environmental problem, and the physiological responses to acid exposure in a few fish species are well characterized. However, the underlying mechanisms promoting ionic and acid–base balance for most fish species that have been investigated remain unclear. Zebrafish (Danio rerio) has emerged as a powerful model system to elucidate the molecular basis of ionic and acid–base regulation. The utility of zebrafish is related to the ease with which it can be genetically manipulated, its suitability for state-of-the-art molecular and cellular approaches, and its tolerance to diverse environmental conditions. Recent studies have identified several key regulatory mechanisms enabling acclimation of zebrafish to acidic environments, including activation of the sodium/hydrogen exchanger (NHE) and H+-ATPase for acid secretion and Na+ uptake, cortisol-mediated regulation of transcellular and paracellular Na+ movements, and ionocyte proliferation controlled by specific cell-fate transcription factors. These integrated physiological responses ultimately contribute to ionic and acid–base homeostasis in zebrafish exposed to acidic water. In the present review, we provide an overview of the general effects of acid exposure on freshwater fish, the adaptive mechanisms promoting extreme acid tolerance in fishes native to acidic environments, and the mechanisms regulating ionic and acid–base balance during acid exposure in zebrafish.

The conserved scavenger receptor cysteine-rich superfamily in therapy and diagnosis

The scavenger receptor cysteine-rich (SRCR) superfamily of soluble or membrane-bound protein receptors is characterized by the presence of one or several repeats of an ancient and highly conserved protein module, the SRCR domain. This superfamily (SRCR-SF) has been in constant and progressive expansion, now up to more than 30 members. The study of these members is attracting growing interest, which parallels that in innate immunity. No unifying function has been described to date for the SRCR domains, this being the result of the limited knowledge still available on the physiology of most members of the SRCR-SF, but also of the sequence versatility of the SRCR domains. Indeed, involvement of SRCR-SF members in quite different functions, such as pathogen recognition, modulation of the immune response, epithelial homeostasis, stem cell biology, and tumor development, have all been described. This has brought to us new information, unveiling the possibility that targeting or supplementing SRCR-SF proteins could result in diagnostic and/or therapeutic benefit for a number of physiologic and pathologic states. Recent research has provided structural and functional insight into these proteins, facilitating the development of means to modulate the activity of SRCR-SF members. Indeed, some of these approaches are already in use, paving the way for a more comprehensive use of SRCR-SF members in the clinic. The present review will illustrate some available evidence on the potential of well known and new members of the SRCR-SF in this regard.

A novel terminal web-like structure in cortical lens fibers: architecture and functional assessment

This study describes a novel cytoskeletal array in fiber cells of the ocular lens of the rat and shows its relationship to the classical terminal web of other epithelial tissues. Naive adult Sprague-Dawley rats (n = 28) were utilized. F-actin, fodrin, myosin IIA, and CP49 distribution was assessed in anterior and posterior polar sections. For functional analysis, lenses were cultured with or without cytochalasin-D for 3 hr, then processed for confocal microscopy or assessed by laser scan analysis along sutures. Phalloidin labeling demonstrated a dense mesh of F-actin adjacent to posterior sutural domains to a subcapsular depth of 400 μm. Anterior polar sections revealed a comparable actin structure adjacent to anterior suture branches however, it was not developed in superficial fibers. Fodrin and myosin were localized within the web-like actin apparatus. The data was used to construct a model showing that the cytoskeletal array is located within the blunt, variable-width fiber ends that abut at sutures such that the "terminal web" flanks the suture on either side. Treatment with cytochalasin-D resulted in partial disassembly of the "terminal web" and perturbed cellular organization. Laser scan analysis revealed that cytochalasin-D treated lenses had significantly greater focal variability than control lenses (P = 0.020). We conclude that cortical fibers of rat lenses contain a bipolar structure that is structurally and compositionally analogous to classical terminal webs. The results indicate that the lens "terminal web" functions to stabilize lens fiber ends at sutures thus minimizing structural disorder, which in turn, promotes the establishment and maintenance of lens transparency.

Interaction between DMBT1 and galectin 3 is modulated by the structure of the oligosaccharides carried by DMBT1

DMBT1 (deleted in malignant brain tumor 1), a human mucin-like glycoprotein, belonging to the scavenger receptor cysteine-rich (SRCR) superfamily, is mainly secreted from mucosal epithelia. It has been shown previously that interaction of hensin, the rabbit ortholog of DMBT1, with galectin 3, a β-galactoside-binding lectin, induces a terminal differentiation of epithelial cells. In this paper, we have used surface plasmon resonance (SPR), to analyse the binding of galectin 3 to two purified samples of human DMBT1:recombinant DMBT1 produced in CHO cells and DMBT1 isolated from intestinal tissues. Characterization of their glycosylation profile by nano-ESI-Q-TOF tandem mass spectrometry showed significant differences in O-glycans between the two DMBT1 samples. Results obtained by SPR demonstrated that the oligosaccharide side chains of DMBT1 are recognized by the carbohydrate-recognition domain (CRD) of galectin 3 and modification in the pattern of oligosaccharides modulates the binding parameters of DMBT1 with galectin 3. Moreover, using immunohistochemistry on paraffin-embedded colonic tissue sections, we could show a co-localisation of DMBT1 and galectin 3 in human intestine, suggesting a potential physiological interaction.

Regulation of DMBT1 via NOD2 and TLR4 in intestinal epithelial cells modulates bacterial recognition and invasion

Mucosal epithelial cell layers are constantly exposed to a complex resident microflora. Deleted in malignant brain tumors 1 (DMBT1) belongs to the group of secreted scavenger receptor cysteine-rich proteins and is considered to be involved in host defense by pathogen binding. This report describes the regulation and function of DMBT1 in intestinal epithelial cells, which form the primary immunological barrier for invading pathogens. We report that intestinal epithelial cells up-regulate DMBT1 upon proinflammatory stimuli (e.g., TNF-alpha, LPS). We demonstrate that DMBT1 is a target gene for the intracellular pathogen receptor NOD2 via NF-kappaB activation. DMBT1 is strongly up-regulated in the inflamed intestinal mucosa of Crohn's disease patients with wild-type, but not with mutant NOD2. We show that DMBT1 inhibits cytoinvasion of Salmonella enterica and LPS- and muramyl dipeptide-induced NF-kappaB activation and cytokine secretion in vitro. Thus, DMBT1 may play an important role in the first line of mucosal defense conferring immune exclusion of bacterial cell wall components. Dysregulated intestinal DMBT1 expression due to mutations in the NOD2/CARD15 gene may be part of the complex pathophysiology of barrier dysfunction in Crohn's disease.

Maternal diet influences gene expression in intestine of offspring in chicken (Gallus gallus)

The diet of the mother during pregnancy influences the onset of different diseases and health-related traits in the offspring. We investigated the influence of the mother hen diet on the intestinal gene expression pattern in the offspring. Hens received for 11 weeks either a commercial feed or a commercial feed supplemented with vitamins and minerals. The offspring of the two groups showed no changes in growth rate or feed conversion. Of this offspring, gene expression patterns in the intestine were measured at 3 and 14 days of age with an intestinal cDNA-microarray. Between the two groups, 11 genes were found to be differentially expressed both at 3 and 14 days of age. Thus, these genes were differently regulated when the intestine is developing as well as when the intestine is more mature. Genes that are differentially expressed at day 3 and/or day 14 affect intestinal turnover, proliferation and development, metabolism and feed absorption. To confirm that differences in gene expression are related to intestinal development, we investigated intestinal proliferation. This indeed also showed differences in proliferation between the two groups at day 3 and day 14 of age. The gene expression and proliferation results indicate that feed of the hens influences the functionality of intestine of the offspring at day 3 and 14 of age.

Gene expression changes related to growth and differentiation in the fetal and juvenile reproductive system of the female rat: evaluation of microarray results

Microarrays make it possible to evaluate the responses of a major fraction of the genome in response to physiological perturbation or exogenous insult. This represents a huge advance in our ability to detect changes in gene expression that may be responsible for physiological or toxicological responses. Our laboratory is interested in the effects of estrogens on female reproductive system development and function. We have evaluated the changes in gene expression in response to estrogens in the female reproductive tract of rats during embryo/fetal development and in the juvenile rat (which is capable of mounting a uterotrophic response). The results of these experiments indicate that a number of genes (dozens to hundreds) are changed in a reproducible, dose-related manner in response to estrogens. These results have been published elsewhere; the purpose of this review is to evaluate, based on information from the literature, the potential role of selected genes on processes of cell proliferation and differentiation, and to suggest plausible relationships among these genes in eliciting responses at the tissue or organ level. We also discuss the utility of gene-expression experiments in elucidating the shape of the dose-response curve at low doses. In particular, we show that the dose-response for gene expression in the juvenile rat uterus is monotonic down to levels a few orders of magnitude below the NOEL for a uterotrophic response, suggesting that gene expression (and by inference higher order responses) do not follow patterns that are unpredictable based on response at higher dosages.

Induction of DMBT1 expression by reduced ERK activity during a gastric mucosa differentiation-like process and its association with human gastric cancer

Abnormalities in the expression of DMBT1 (deleted in malignant brain tumors 1) have been implicated in the development of esophageal, gastric and colorectal cancers of the alimentary tract, but the underlying mechanism remains unclear. In the present study, using the gastric cell line AGS, we identified two intracellular signaling molecules protein kinase C (PKC) and extracellular signal-related kinase (ERK). They mediated both the phorbol myristate acetate (PMA) downregulation of DMBT1 expression and the initiation of cell differentiation, which was measured by cell cycle withdrawal and the induction of the tissue-specific marker trefoil factor 1 (TFF1). A time-course study showed that following the PMA activation of ERK kinase, the induction of TFF1 and the reduction of DMBT1 were detected at the same time point. We then demonstrated a minimal level of DMBT1 in proliferating AGS cells seeded at low density, where ERK activity was high. Reduction of ERK activity, either by an ERK inhibitor PD98059 or by high-density seeding, significantly reduced AGS cell growth judged by CFSE labeling. This cellular effect was elicited by cyclin D/p21 (Cip/Waf1) and G(0)/G(1) arrest, and was accompanied by a marked increase in DMBT1-expressing cells. Finally, we showed that siRNA directed against DMBT1 had no effect on the induction of a cell growth arrest marker, gut-enriched Kruppel-like factor (GKLF), but reduced the PMA induction of TFF1. Along with its upregulation coinciding with G(0)/G(1) arrest, and its attenuation in differentiated cells, these results suggest that the transient induction of DMBT1 is apparently specific at an early stage of gastric epithelial differentiation-like process, when it may play a role in cell fate decision. Consistent with such a potential function, we detected frequent abnormalities of the DMBT1 expression in the specimens of human gastric adenocarcinoma.

Role of extracellular matrix in kidney development and repair

Extracellular matrix (ECM) molecules and their receptors exert a dynamic role in cell-matrix interactions during kidney development and repair processes. They provide a physical substratum for the spatial organization of the cells, but also regulate cell growth and proliferation by interacting with growth factors. In addition, they can regulate signal transduction pathways by binding to integrins or by modulating the activity of signaling molecules such as Wnts. ECM and ECM-related molecules control multiple (if not all) steps of kidney development, including ureteric bud branching morphogenesis, mesenchymal condensation, nephron formation, terminal differentiation of renal tubules, and glomerular basement membrane assembly. Their role still needs to be better documented in renal repair. The emergence of conditionally mutated mice for basement membrane components will provide a useful tool to demonstrate further the involvement of ECM and ECM-related proteins in development and repair.

DMBT1, a regulator of mucosal homeostasis through the linking of mucosal defense and regeneration?

DMBT1 (deleted in malignant brain tumor 1), which encodes a large scavenger receptor cysteine rich (SRCR) B protein, has been proposed to be a tumor suppressor gene, due to the high frequency of its homozygous deletion and the lack of expression in a variety of cancers. However, studies on its physiological functions and its relationship with tumorigenesis are still at an initial stage. Two mucosal defense-related molecules, gp-340 and salivary agglutinin, have been identified to be alternatively spliced products of DMBT1, which suggests that DMBT1 is a pattern recognition receptor in innate immunity. Meanwhile, results from immunohistochemical staining and studies at the cellular level, began to associate DMBT1 with a proliferation to differentiation switching process in gastrointestinal epithelial cells. Together with its up-regulation in inflammation, these findings suggest that DMBT1 might be a local regulator of homeostasis, possibly through linking mucosal inflammation to the modulation of epithelial regeneration, and whose abnormality is a frequent cause of malignancy.

The scavenger receptor, cysteine-rich domain-containing molecule gp-340 is differentially regulated in epithelial cell lines by phorbol ester

Gp-340 is a glycoprotein belonging to the scavenger receptor cysteine rich (SRCR) group B family. It binds to host immune components such as lung surfactant protein D (SP-D). Recent studies found that gp-340 interacts directly with pathogenic microorganisms and induces their aggregation, suggesting its involvement in innate immunity. In order to investigate further its potential immune functions in the appropriate cell lines, the expression of gp-340 in four conventional immune cell lines (U937, HL60, Jurkat, Raji), and two innate immune-related epithelial cell lines (A549 derived from lung and AGS from stomach), was examined by RT-PCR and immunohistochemistry. The resting immune cell lines showed weak or no gp-340 mRNA expression; while the two epithelial cell lines expressed gp-340 at much higher level, which was differentially regulated by phorbol myristate acetate (PMA) treatment. In the A549 cells, gp-340 was up-regulated along with the PMA-induced proinflammatory expression of both IL-6 and IL-8. In AGS cells, PMA down-regulation of gp-340 was seen in parallel with an up-regulation of the two mature gastric epithelial specific proteins TFF1 (trefoil factor 1) and TFF2, which are implicated as markers of terminal differentiation. Analysis of the distribution of gp-340, together with the TFFs and SP-D in normal lung and gastric mucosa, supported further our in vitro data. We conclude that the differential regulation of gp-340 in the two epithelial cell lines by PMA indicates that gp-340 s involvement in mucosal defence and growth of epithelial cells may vary at different body locations and during different stages of epithelial differentiation.

Analysis of losses of heterozygosity of the candidate tumour suppressor gene DMBT1 in melanoma resection specimens

Deleted in malignant brain tumours 1 (DMBT1), a candidate tumour suppressor gene located on chromosome 10q25.3-q26.1, has recently been identified and found to be deleted in several different types of human tumours. In melanomas, the chromosomal region 10q22-qter is commonly affected by losses, hence we screened primary melanoma samples for losses of heterozygosity (LOH), and acquired melanocytic naevi and melanomas for transcription of DMBT1 and protein expression. Of 38 informative melanomas, 1 nodular melanoma and 2 subcutaneous metastases showed LOH of both microsatellites flanking the gene, suggesting loss of 1 DMBT1 allele. Three further melanomas showed LOH at 1 informative locus but were heterozygous for the second marker. Applying reverse-transcription polymerase chain reaction (RT-PCR), DMBT1 transcription was not found in melanomas. However, DMBT1 transcription was also absent from the majority of naevi from which melanomas frequently arise, making down-regulation of gene transcription during transformation from naevus to melanoma unlikely. Immunohistochemistry showed nerves, sweat glands and the stratum spinosum of the epidermis to be DMBT1 protein positive, whereas the naevi and melanoma cells themselves were negative. All considered, the candidate tumour suppressor gene DMBT1 does not appear to be a major inactivation target in the development of melanomas.

Isolation and characterization of mitochondria-rich cell types from the gill of freshwater rainbow trout

A magnetic cell separation technique (MACS) was developed for isolating and characterizing peanut lectin agglutinin positive (PNA(+)) cells from rainbow trout gills. Percoll density separated mitochondria-rich (MR) cells were serially labeled with PNA-FITC and an anti-FITC antibody covalently coupled to a 50-nm iron particle and then applied to a magnetic column. PNA(+) MR cells were enriched to >95% purity. Transmission electron microscopy analysis of both the PNA(+) and PNA negative (PNA(-)) fraction showed that PNA binds to MR chloride cells while the PNA(-) cell fraction is comprised of MR cells with features characteristic of pavement cells. Western blotting demonstrated that both PNA(+) and PNA(-) fractions had high levels of Na(+)-K(+)-ATPase and Sco1 expression; however, relative expression of H(+)-ATPase in PNA(+) and PNA(-) cells demonstrated that untreated fish had twofold higher H(+)-ATPase levels in PNA(-) cells relative to the PNA(+) cells. Furthermore, hypercapnic acidosis significantly increased the relative H(+)-ATPase expression on PNA(-) cells only, whereas metabolic alkalosis had no significant effect.