Normal development of mice carrying a null mutation in the gene encoding the L14 S-type lectin

Participation of pigment epithelium in ocular immune privilege. 3. Epithelia cultured from iris, ciliary body, and retina suppress T-cell activation by partially non-overlapping mechanisms

PURPOSE

The ocular microenvironment is immunosuppressive and anti-inflammatory. Since various ocular pigmented epithelia contribute to this microenvironment, we studied the relative capacities of pigment epithelial (PE) cells cultured from the iris, ciliary body, and retina of mouse eyes to suppress T-cell activation in vitro.

METHODS

Pigment epithelium was cultured from iris, ciliary body, and retina for 14 days, then assayed for the capacity, directly or across transwell membranes, to suppress mixed lymphocyte reactions and anti-CD3 stimulation of T cells. Potential molecules responsible for suppression were examined by attempting to block suppression with appropriate reagents, and by using mice with pertinent mutant or disrupted genes.

RESULTS

We found that PE cells from all three ocular tissue sources profoundly suppressed T-cell activation in vitro. While iris PE suppressed poorly when separated from T cells by a transwell membrane (implying that cell contact is necessary), retina PE suppressed fully even in the presence of such a membrane (implying that soluble factors were responsible). Ciliary body PE used both soluble factors as well as cell contact to achieve suppression. Suppression could not be ascribed to TGFbeta, IFNgamma, TNFalpha, CD48, or ICAM-1, or to interactions between CD40 and CD154, or CD95 and CD95 ligand. Galectin-1, a galactoside-binding protein, was found to be expressed on all cultured PE cells, but only retinal pigment epithelium (RPE) from galectin-1 KO mice showed reduced capacity to inhibit T-cell activation.

CONCLUSIONS

Cultured pigment epithelia from iris, ciliary body, and retina comparably suppress T-cell activation in vitro, but by partially different mechanisms. Although RPE cells suppress in part through expression of galectin-1, the molecular mediators of suppression by iris and ciliary body PE remain to be identified.

Ah, sweet mystery of death! Galectins and control of cell fate

Control of cell death is critical in eukaryotic development, immune system homeostasis, and control of tumorigenesis. The galectin family of lectins is implicated in all of these processes. Other families of molecules function as death receptors or death effectors, but galectins are uniquely capable of acting both extracellularly and intracellularly to control cell death. Extracellularly, galectins cross-link glycan ligands to transduce signals that lead directly to death or that influence other signals regulating cell fate. Intracellular expression of galectins can modulate other signals controlling cell viability. Individual galectins can act on multiple cell types, and multiple galectins can act on the same cell. Understanding how galectins regulate cell viability and function will broaden our knowledge of the roles of galectins in basic biological processes and facilitate development of therapeutic applications for galectins in autoimmunity, transplant-related disease, and cancer.

Regulated expression and ultrastructural localization of galectin-1, a proapoptotic beta-galactoside-binding lectin, during spermatogenesis in rat testis

Galectin-1, a highly conserved beta-galactoside-binding protein, induces apoptosis of activated T cells and suppresses the development of autoimmunity and chronic inflammation. To gain insight regarding the potential role of galectin-1 as a novel mechanism of immune privilege, we investigated expression and ultrastructural localization of galectin-1 in rat testis. Galectin-1 expression was assessed by Western blot analysis and immunocytochemical localization in testes obtained from rats aged from 9 to 60 days. Expression of this carbohydrate-binding protein was developmentally regulated, and its immunolabeling exhibited a stage-specific pattern throughout the spermatogenic process. Immunogold staining using the anti-galectin-1 antibody revealed the typical Sertoli cell profile in the seminiferous epithelium, mainly at stages X-II. During spermiation (stages VI-VIII), a strong labeling was observed at the luminal pole of seminiferous epithelium, localized on apical stalks of Sertoli cells, on heads of mature spermatids, and on bodies of residual cytoplasm. Moreover, spermatozoa released into the lumen showed a strong immunostaining. Following spermiation (stage VIII), galectin-1 expression was restored at the basal portion of Sertoli cells and progressively spread out through the whole cells as differentiation of germinal cells proceeded. Immunoelectron microscopy confirmed distribution of galectin-1 in nuclei and cytoplasmic projections of Sertoli cells and on heads and tails of late spermatids and residual bodies. Surface localization of galectin-1 was evidenced in spermatozoa from caput epididymis. Thus, the regulated expression of galectin-1 during the spermatogenic cycle suggests a novel role for this immunosuppressive lectin in reproductive biology.

Stage-specific expressed sequence tags obtained during preimplantation bovine development by differential display RT-PCR and suppression subtractive hybridization

Differential display RT-PCR (DDRT-PCR) and suppression subtractive hybridization (SSH) were applied in order to detect preimplantation stage-specific expressed sequence tags (ESTs) of bovine embryos. Seventeen ESTs were detected from the differential display RT-PCR approach. All clones but two showed homology to genes or ESTs known in human, cattle or other species. One of the clones similar to H. sapiens mRNA for KIAA1764 protein was used exemplarily to quantify the transcripts by real-time PCR. The result of quantitative differential screening was found to be in agreement with DDRT-PCR banding patterns. In the second approach, a blastocyst-stage enriched cDNA library was constructed using SSH of blastocyst versus morula transcripts. The 71 clones that were analysed represent 33 distinct loci including candidate genes for the regulative processes during differentiation of inner cell mass (ICM) and trophoblast cells and the initial phase of embryo implantation, such as galectin-3 and fibronectin. As revealed by real-time PCR, the mRNA level of galectin-3 was three times higher in the blastocyst stage than in the morula stage. DDRT-PCR and SSH are both powerful tools for the identification of stage-specific expressed gene in preimplantation bovine embryos. Real-time PCR allows to test and confirm the outcome and to add quantitative data of selected transcripts of interest.

Galectins-3 and -7, but not galectin-1, play a role in re-epithelialization of wounds

Disorders of wound healing characterized by impaired or delayed re-epithelialization are a serious medical problem. These conditions affect many tissues, are painful, and are difficult to treat. In this study, using cornea as a model, we demonstrate for the first time the importance of carbohydrate-binding proteins galectins-3 and -7 in re-epithelialization of wounds. In two different models of corneal wound healing, re-epithelialization of wounds was significantly slower in galectin-3-deficient (gal3(-/-)) mice compared with wild-type (gal3(+/+)) mice. In contrast, there was no difference in corneal epithelial wound closure rates between galectin-1-deficient and wild-type mice. Quantitation of the bromodeoxyuridine-labeled cells in gal3(+/+) and gal3(-/-) corneas revealed that corneal epithelial cell proliferation rate is not perturbed in gal3(-/-) corneas. Exogenous galectin-3 accelerated re-epithelialization of wounds in gal3(+/+) mice but, surprisingly, not in the gal3(-/-) mice. Gene expression analysis using cDNA microarrays revealed that healing corneas of gal3(-/-) mice contain markedly reduced levels of galectin-7 compared with those of gal3(+/+) mice. More importantly, unlike galectin-3, galectin-7 accelerated re-epithelialization of wounds in both gal3(-/-) and gal3(+/+) mice. In corresponding experiments, recombinant galectin-1 did not stimulate the corneal epithelial wound closure rate. The extent of acceleration of re-epithelialization of wounds with both galectin-3 and galectin-7 was greater than that observed in most of the published studies using growth factors. These findings have broad implications for developing novel therapeutic strategies for treating nonhealing wounds.

Sweet 'n' sour: the impact of differential glycosylation on T cell responses

The fate and functional activity of T lymphocytes depend largely on the precise timing of gene expression and protein production. However, it is clear that post-translational modification of proteins affects their functional properties. Although modifications such as phosphorylation have been intensely studied by immunologists, less attention has been paid to the impact that changes in glycosylation have on protein function. However, there is considerable evidence that glycosylation plays a key role in immune regulation. We will focus here on examples in which differential glycosylation affects the development, survival or reactivity of T cells.

Galectin-1 is a stromal cell ligand of the pre-B cell receptor (BCR) implicated in synapse formation between pre-B and stromal cells and in pre-BCR triggering

Although preB cell-receptor (pre-BCR) formation and cell-surface expression is essential for B cell development, pre-BCR generation of signal transduction remains elusive. Here, we report that recombinant pre-BCRs and the surrogate light chain bind specifically to the bone marrow stromal cell galectin-1 (GAL1), an S-type lectin. The surrogate light chain/GAL1 association is a direct protein-protein interaction (K(a) = 2 x 10(6) M(-1)), and the NH(2) extra loop of lambda-like is the major binding element. Pre-BCR binding to stromal cells depends upon GAL1 anchoring to glycosylated counter-receptors, and these complexes completely relocalize to form a synapse at the contact zone between preB and stromal cells. This immune developmental synapse is accompanied by the initiation of intracellular tyrosine kinase activity and signal transduction from the pre-BCR.

Analysis of the innate and adaptive phases of allograft rejection by cluster analysis of transcriptional profiles

Both clinical and experimental observations suggest that allograft rejection is a complex process with multiple components that are, at least partially, functionally redundant. Studies using graft recipients deficient in various genes including chemokines, cytokines, and other immune-associated genes frequently produce a phenotype of delayed, but not indefinitely prevented, rejection. Only a small subset of genetic deletions (for example, TCR(alpha) or beta, MHC I and II, B7-1 and B7-2, and recombinase-activating gene) permit permanent graft acceptance suggesting that rejection is orchestrated by a complex network of interrelated inflammatory and immune responses. To investigate this complex process, we have used oligonucleotide microarrays to generate quantitative mRNA expression profiles following transplantation. Patterns of gene expression were confirmed with real-time PCR data. Hierarchical clustering algorithms clearly differentiated the early and late phases of rejection. Self-organizing maps identified clusters of coordinately regulated genes. Genes up-regulated during the early phase included genes with prior biological functions associated with ischemia, injury, and Ag-independent innate immunity, whereas genes up-regulated in the late phase were enriched for genes associated with adaptive immunity.

Galectins and their ligands: amplifiers, silencers or tuners of the inflammatory response?

Recent evidence has implicated galectins and their ligands as master regulators of immune cell homeostasis. Whereas some members of this family, such as galectin-3, behave as amplifiers of the inflammatory cascade, others, such as galectin-1, trigger homeostatic signals to shut off T-cell effector functions. These carbohydrate-binding proteins, identified by shared consensus amino acid sequences and affinity for beta-galactoside-containing sugars, participate in the homeostasis of the inflammatory response, either by regulating cell survival and signaling, influencing cell growth and chemotaxis, interfering with cytokine secretion, mediating cell-cell and cell-matrix interactions or influencing tumor progression and metastasis. The current wealth of new information promises a future scenario in which individual members of the galectin family or their ligands will be used as powerful anti-inflammatory mediators and selective modulators of the immune response.

Shuttling of galectin-3 between the nucleus and cytoplasm

In previous studies, we documented that galectin-3 (M(r) approximately 30,000) is a pre-mRNA splicing factor. Recently, galectin-3 was identified as a component of a nuclear and cytoplasmic complex, the survival of motor neuron complex, through its interaction with Gemin4. To test the possibility that galectin-3 may shuttle between the nucleus and the cytoplasm, human fibroblasts (LG-1) were fused with mouse fibroblasts (3T3). The monoclonal antibody NCL-GAL3, which recognizes human galectin-3 but not the mouse homolog, was used to monitor the localization of human galectin-3 in heterodikaryons. Human galectin-3 localized to both nuclei of a large percentage of heterodikaryons. Addition of the antibiotic leptomycin B, which inhibits nuclear export of galectin-3, decreased the percentage of heterodikaryons showing human galectin-3 in both nuclei. In a parallel experiment, mouse 3T3 fibroblasts, which express galectin-3, were fused with fibroblasts derived from a mouse in which the galectin-3 gene was inactivated. Mouse galectin-3 localized to both nuclei of a large percentage of heterodikaryons. Again, addition of leptomycin B restricted the presence of galectin-3 to one nucleus of a heterodikaryon. The results from both heterodikaryon assays suggest that galectin-3 can exit one nucleus, travel through the cytoplasm, and enter the second nucleus, matching the definition of shuttling.

Developmental aspect of the gonadotropin-releasing hormone system

Gonadotropin-releasing hormone (GnRH) regulates the hypothalamo-pituitary-gonadal (HPG) axis in all vertebrates studied. GnRH neurons that regulate the HPG axis are primarily derived from progenitor cells in the nasal compartment (NC) and migrate along olfactory system derived fibers across the cribriform plate to destinations in the forebrain. Across their long and uncommon migratory route many factors are likely important for their successful development. Several classes of molecules are being studied for their potential influences on migration, including those related to cell surface interactions (membrane receptors, adhesion molecules, extracellular matrix (ECM) molecules, etc.) and those related to communication across distances (neurotransmitters, peptides, chemoattractant or repellent molecules). Of the classes of molecules associated with cell surface interactions, glycoconjugates with terminal galactose, are temporally and spatially expressed on olfactory fibers that guide GnRH neurons and may play role(s) in migration. Of the molecules associated with communication across distances, the neurotransmitter gamma-aminobutyric acid (GABA) is associated with the GnRH migration pathway and influences the position and organization of GnRH neurons in vitro and in vivo. Furthermore, galactose-containing glycoconjugates and GABA are associated with GnRH neurons in species ranging from humans to lamprey. In mice and rats, GABA is found transiently within a subpopulation of GnRH neurons as they migrate through the NC. One of the key elements in considering regulators of GnRH neuron migration is the diversity of GnRH synthesizing cells. For example, only subpopulations of GnRH neurons also contain GABA, specific GABA receptors, or select glycoconjugates. Similarly, treatments that influence GnRH neuronal migration may only affect specific subsets and not the entire population. It is likely that we will not be able to characterize the migration of all GnRH neurons by a single factor. By combining molecular inquiries with genetic models, single cell analyses, and an in vitro migration model, we are beginning to decipher one of the most critical events in the establishment of the reproductive axis.

Galectins as modulators of cell adhesion

The galectins are a family of carbohydrate-binding proteins that are distributed widely in metazoan organisms. Each galectin exhibits a specific pattern of expression in various cells and tissues, and expression is often closely regulated during development. Although these proteins are found mainly in the cell cytoplasm, some are secreted from cells and interact with appropriately glycosylated proteins at the cell surface or within the extracellular matrix. These receptors include cell-adhesion molecules such as integrins, and matrix glycoproteins such as laminin and fibronectin isoforms. Recent studies have increased understanding of the roles of the galectins in regulating cell-cell and cell-matrix adhesion. These interactions are critically involved in modulation of normal cellular motility and polarity and during tissue formation, and loss of adhesive function is implicated in several disease states including tumour progression, inflammation and cystic development in branching epithelia such as kidney tubules. This review discusses recent progress in defining the specificities and mechanisms of action of secreted galectins as multifunctional cell regulators.

Anti-galectin-1 autoantibodies in human Trypanosoma cruzi infection: differential expression of this beta-galactoside-binding protein in cardiac Chagas' disease

The pathogenesis of Chagas' disease has been subject of active research and still remains to be ascertained. Galectin-1 (Gal-1), a member of a conserved family of animal beta-galactoside-binding proteins, localized in human heart tissue, has been suggested to play key roles in immunological and inflammatory processes. In the present study we demonstrated the occurrence of anti-Gal-1 autoAb in sera from patients in the acute and chronic stages of Chagas' disease (ACD and CCD) by means of ELISA and Western blot analysis. We found a marked increase in the level and frequency of Ig E anti-Gal-1 antibodies in sera from patients with ACD, but a low frequency of Ig M anti-Gal-1 immunoreactivity. Moreover, Ig G immunoreactivity to this beta-galactoside-binding protein was found to be correlated with the severity of cardiac damage in CCD, but was absent in nonrelated cardiomyopathies. We could not detect immunoreactivity with Trypanosoma cruzi antigens using a polyclonal antibody raised to human Gal-1 and no hemagglutinating activity could be specifically eluted from a lactosyl-agarose matrix from parasite lysates. Moreover, despite sequence homology between Gal-1 and shed acute phase antigen (SAPA) of T. cruzi, anti-Gal-1 antibodies eluted from human sera failed to cross-react with SAPA. In an attempt to explore whether Gal-1 immunoreactivity was originated from endogenous human Gal-1, we finally investigated its expression levels in cardiac tissue (the main target of Chagas' disease). This protein was found to be markedly upregulated in cardiac tissue from patients with severe CCD, compared to cardiac tissue from normal individuals.

Galectins structure and function--a synopsis

The 20 or so galectins expected to be found in man, and their many possible functional effects promise a rich and fruitful research field in the future. At present, the biomedically most promising areas for use of galectins or their ligands are in inflammation, immunity, and cancer. Many good stories can be formulated, but the field lacks the cohesion of knowing basic galectin function. The only basic common denominators among galectins are beta-galactoside binding, and the unusual combination of intra- and extracellular expression with non-classical secretion in between. Maybe that is all there is, and nature has used these properties for multiple, otherwise unrelated functions. Then again, maybe there is some deeper common function that has so far been overlooked. If it exists, this probably lies somewhere in the detailed integration of galectin activity in the complexities of cell physiology.

Co-stimulation and counter-stimulation: lipid raft clustering controls TCR signaling and functional outcomes

T cell receptor (TCR) antigen recognition induces the formation of a specialized 'immunological synapse' at the T cell : antigen presenting cell (APC) junction. This junction is generated by the recruitment and exclusion of particular proteins from the contact area and is required for T cell activation. We and others have hypothesized that lipid raft/non-raft partitioning provides a molecular basis for protein sorting which organizes the TCR, co-stimulators, signal transducers and the actin cytoskeleton at the T cell : APC interface. Here we discuss the emerging paradigm that co-stimulators induce the directional transport and clustering of lipid rafts at the T cell : APC interface, thus generating platform(s) specialized for processive and sustained TCR signal transduction and T cell activation. We also discuss recent data implicating the involvement of 'counter-stimulators' and other negative regulators which prevent optimal raft clustering at the TCR contact site and, thus, facilitate T cell inactivation and tolerance induction.

Galectin-1 induces partial TCR zeta-chain phosphorylation and antagonizes processive TCR signal transduction

Galectin-1 is an endogenous lectin with known T cell immunoregulatory activity, though the molecular basis by which galectin-1 influences Ag specific T cell responses has not been elucidated. Here, we characterize the ability of galectin-1 to modulate TCR signals and responses by T cells with well defined hierarchies of threshold requirements for signaling distinct functional responses. We demonstrate that galectin-1 antagonizes TCR responses known to require costimulation and processive protein tyrosine phosphorylation, such as IL-2 production, but is permissive for TCR responses that only require partial TCR signals, such as IFN-gamma production, CD69 up-regulation, and apoptosis. Galectin-1 binding alone or together with Ag stimulation induces partial phosphorylation of TCR-zeta and the generation of inhibitory pp21zeta. Galectin-1 antagonizes Ag induced signals and TCR/costimulator dependent lipid raft clustering at the TCR contact site. We propose that galectin-1 functions as a T cell "counterstimulator" to limit required protein segregation and lipid raft reorganization at the TCR contact site and, thus, processive and sustained TCR signal transduction. These findings support the concept that TCR antagonism can arise from the generation of an inhibitory pp21zeta-based TCR signaling complex. Moreover, they demonstrate that TCR antagonism can result from T cell interactions with a ligand other than peptide/MHC.

Identification of oxidized galectin-1 as an initial repair regulatory factor after axotomy in peripheral nerves

Various neurotrophic factors that promote axonal regeneration have been investigated in vivo, but the signals that prompt the axons to send out processes in peripheral nerves after axotomy are not well understood. We have shown using two specific strategies that galectin-1 can play an important role in this initial stage. One used an in vitro nerve regeneration model that allowed us to monitor the initial axon and support cell outgrowth from the proximal nerve stump comparable to the initial stages of nerve repair. The other strategy was to clarify the axonal regeneration-promoting factor from kidney-derived cells. Using these strategies, we discovered that oxidized galectin-1 from the cell (COS1 cell) conditioned media acts as an axonal regeneration-promoting factor without the lectin activity. Oxidized recombinant human galectin-1 (rhGAL-1/Ox) showed the same activity at low concentrations (pg/ml range). A similarly low concentration also effectively promoted axonal regeneration in both transection and crush experiments in vivo. Moreover, the application of functional anti-galectin-1 antibody strongly inhibited the regeneration in vivo. Since galectin-1was shown to be secreted and localized in the regenerating sciatic nerve, this suggests that secreted galectin-1 may be oxidized and change its molecular structure to regulate initial repair after axotomy as a kind of cytokine.

Role of galectin-3 as a receptor for advanced glycosylation end products

The advanced glycosylation end product (AGE)-binding proteins identified so far include the components of the AGE-receptor complex p60, p90 and galectin-3, receptor for advanced glycosylation end products (RAGE), and the macrophage scavenger receptor types I and II. Galectin-3 interacts with beta-galactoside residues of several cell surface and matrix glycoproteins through the carbohydrate recognition domain and is also capable of peptide-peptide associations mediated by its N-terminus domain. These structural properties enable galectin-3 to exert multiple functions, including the modulation of cell adhesion, the control of cell cycle, and the mRNA splicing activity. Moreover, in macrophages, astrocytes, and endothelial cells, galectin-3 has been shown to exhibit a high-affinity binding for AGEs; the lack of a transmembrane anchor sequence or signal peptide suggests that it associates with other AGE-receptor components rather than playing an independent role as AGE-receptor. In tissues that are targets of diabetic vascular complications, such as the mesangium and the endothelium, galectin-3 is not expressed or only weakly expressed under basal conditions, at variance with p90 and p60 but becomes detectable with aging and is induced or up-regulated by the diabetic milieu, which only slightly affects the expression of p90 or p60. This (over)expression of galectin-3 may in turn modulate AGE-receptor-mediated events by modifying the function of the AGE-receptor complex, which could play a role in the pathogenesis of target tissue injury. Up-regulated galectin-3 expression may also exert direct effects on tissue remodeling, independently of AGE ligands, by virtue of its adhesive and growth regulating properties.

Molecular genetics of implantation in the mouse

Embryo implantation is a complex developmental process requiring precise coordination between mother and offspring to ensure success. Implantation failure is clinically relevant to in vitro fertilization programs and to an understanding of diseases of pregnancy like preeclampsia. Basic and clinical research have identified a number of proteins involved in peri-implantation development, but an understanding of the implantation process and its cellular and molecular components is just beginning. This review will focus on the implantation and development of the murine embryo and placenta. The significance of ectopic expression and targeted mutagenesis models to these processes will be discussed.

Mice lacking Bmp6 function

Bmp6, a member of the 60A subgroup of bone morphogenetic proteins (BMPs), is expressed in diverse sites in the developing mouse embryo from preimplantation stages onwards. To evaluate roles for Bmp6 signaling in vivo, gene targeting was used to generate a null mutation at the Bmp6 locus. The resulting Bmp6 mutant mice are viable and fertile, and show no overt defects in tissues known to express Bmp6 mRNA. The skeletal elements of newborn and adult mutants are indistinguishable from wild-type. However, careful examination of skeletogenesis in late gestation embryos reveals a consistent delay in ossification strictly confined to the developing sternum. In situ hybridization studies in the developing long bones and sternum show that other BMP family members are expressed in overlapping domains. In particular we find that Bmp2 and Bmp6 are coexpressed in hypertrophic cartilage, suggesting that Bmp2 may functionally compensate in Bmp6 null mice. The defects in sternum development in Bmp6 null mice are likely to be associated with a transient early expression of Bmp6 in the sternal bands, prior to ossification. These sternal defects are slightly exacerbated in Bmp5/6 double mutant animals.

Blastocyst implantation: the adhesion cascade

This review covers the sequence of cell adhesion events occurring during implantation of the mammalian embryo, concentrating on data from mouse and human. The analogy is explored between initial attachment of trophoblast to the uterine lining epithelium and that of neutrophils to the endothelial lining of blood vessels at sites of inflammation. The possible role of various carbohydrate ligands in initial attachment of the blastocyst is reviewed. The evidence for subsequent stabilization of cell adhesion via integrins or the trophinin-tastin complex is discussed.

Recombinant galectin-1 and its genetic delivery suppress collagen-induced arthritis via T cell apoptosis

Galectin-1 (GAL-1), a member of a family of conserved beta-galactoside-binding proteins, has been shown to induce in vitro apoptosis of activated T cells and immature thymocytes. We assessed the therapeutic effects and mechanisms of action of delivery of GAL-1 in a collagen-induced arthritis model. A single injection of syngeneic DBA/1 fibroblasts engineered to secrete GAL-1 at the day of disease onset was able to abrogate clinical and histopathological manifestations of arthritis. This effect was reproduced by daily administration of recombinant GAL-1. GAL-1 treatment resulted in reduction in anticollagen immunoglobulin (Ig)G levels. The cytokine profile in draining lymph node cells and the anticollagen IgG isotypes in mice sera at the end of the treatment clearly showed inhibition of the proinflammatory response and skewing towards a type 2-polarized immune reaction. Lymph node cells from mice engaged in the gene therapy protocol increased their susceptibility to antigen-induced apoptosis. Moreover, GAL-1-expressing fibroblasts and recombinant GAL-1 revealed a specific dose-dependent inhibitory effect in vitro in antigen-dependent interleukin 2 production to an A(q)-restricted, collagen type 2-specific T cell hybridoma clone. Thus, a correlation between the apoptotic properties of GAL-1 in vitro and its immunomodulatory properties in vivo supports its therapeutic potential in the treatment of T helper cell type 1-mediated autoimmune disorders.

Pathological homeostasis: its meaning, its inferences

The notion of 'pathological homeostasis' (PH) allows a better understanding of the escape phenomena to the effects of a therapy, as suggested by experimental researches. This concept refers to mechanisms we already know as desensitization, mutation, etc. Moreover, it focuses on the following possibility: in a couple of antagonistic agents, the already prevalent one will increase even more so that it could cancel the therapeutic effect of the administered opposite agent. PH is also defined as a change in the norms of the cell regulation or of the great systems of regulation in the body. In order to neutralize this occurrence, the PH notion may open up on new experimental studies and therapeutical strategies.

Efficient gene-specific expression of cre recombinase in the mouse embryo by targeted insertion of a novel IRES-Cre cassette into endogenous loci

Site specific recombinases have provided the experimental strategy necessary to modulate the expression of gene products in the mouse embryo. In this study we have exploited Cre recombinase to develop a widely applicable cell marking system which functions efficiently even at early post-implantation embryonic stages. Importantly, the techniques and reagents derived in this study are generally applicable to any recombinase driven approach, including strategies to temporally and spatially modulate endogenous or ectopic gene expression in the embryo. The cell marking scheme has two essential components which were derived as separate mouse lines. The first line carries a universal conditional lacZ reporter (UCR) locus which was prepared by using gene targeting in a novel approach to modify a ubiquitously expressed retroviral lacZ promoter trap insertion. The UCR locus is silent until it undergoes a Cre mediated DNA rearrangement to restore lacZ expression. To generate the Cre expressing allele, we outline a flexible strategy which requires the introduction of a novel IRES-Cre cassette into exon sequence of an endogenous locus by gene targeting. We successfully demonstrate this approach by generating a Cre expressing allele of the EphA2 gene, an Eph receptor protein tyrosine kinase expressed early in development. Analysis of double heterozygote embryos clearly demonstrates that Cre recombinase is expressed in vivo from the EphA2 IRES-Cre allele, and that the conditional reporter locus is efficiently restored in EphA2-expressing cells as early as 7.5 dpc. This cell marking experiment establishes the feasibility of expressing Cre recombinase from a single copy allele in the embryo and demonstrates the utility of the conditional reporter mouse which can be used in the analysis of any Cre expressing allele.

Specific inhibition of T-cell adhesion to extracellular matrix and proinflammatory cytokine secretion by human recombinant galectin-1

The migration of immune cells through the extracellular matrix (ECM) towards inflammatory sites is co-ordinated by receptors recognizing ECM glycoproteins, chemokines and proinflammatory cytokines. In this context, galectins are secreted to the extracellular milieu, where they recognize poly-N-acetyllactosamine chains on major ECM glycoproteins, such as fibronectin and laminin. We investigated the possibility that galectin-1 could modulate the adhesion of human T cells to ECM and ECM components. T cells were purified from human blood, activated with interleukin-2 (IL-2), labelled, and incubated further with intact immobilized ECM and ECM glycoproteins in the presence of increasing concentrations of human recombinant galectin-1, or its more stable, related, C2-S molecule obtained by site-directed mutagenesis. The presence of galectin-1 was shown to inhibit T-cell adhesion to intact ECM, laminin and fibronectin, and to a lesser extent to collagen type IV, in a dose-dependent manner. This effect was specifically blocked by anti-galectin-1 antibody and was dependent on the lectin's carbohydrate-binding properties. The inhibition of T-cell adhesion by galectin-1 correlates with the ability of this molecule to block the re-organization of the activated cell's actin cytoskeleton. Furthermore, tumour necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) production was markedly reduced when IL-2-activated T cells were incubated with galectin-1 or its mutant. This effect was prevented by beta-galactoside-related sugars. The present study reveals an alternative inhibitory mechanism for explaining the suppressive properties of the galectin-1 subfamily on inflammatory and autoimmune processes.

Galectin-1, an alternative signal for T cell death, is increased in activated macrophages

Galectin-1 belongs to an evolutionarily conserved family of animal beta-galactoside-binding proteins, which exert their functions by crosslinking the oligosaccharides of specific glycoconjugate ligands. During the past decade, attempts to identify the functional role of galectin-1 suggested participation in the regulation of the immune response. Only in the last few years has the molecular mechanism involved in these properties been clearly elucidated, revealing a critical role for galectin-1 as an alternative signal in the generation of T cell death. In the present study we will discuss the latest advances in galectin research in the context of the regulation of the immune response, not only at the central level but also at the periphery. Moreover, we will review the purification, biochemical properties and functional significance of a novel galectin-1-like protein from activated rat macrophages, whose expression is differentially regulated according to the activation state of the cells. The novel role of a carbohydrate-binding protein in the regulation of apoptosis is providing a breakthrough in galectin research and extending the interface between immunology, glycobiology and clinical medicine.

Galectins: a key intersection between glycobiology and immunology

Galectins are a family of evolutionarily conserved animal lectins, widely distributed from lower invertebrates to mammals. They share sequence and structure similarities in the carbohydrate recognition domain and specificity for polylactosamine-enriched glycoconjugates. In the last few years significant experimental data have been accumulated concerning their participation in different biological processes requiring carbohydrate recognition such as cell adhesion, cell growth regulation, inflammation, immunomodulation, apoptosis and metastasis. In the present review we will discuss some exciting questions and advances in galectin research, highlighting the significance of these proteins in immunological processes and their implications in biomedical research, disease diagnosis and clinical intervention. Designing novel therapeutic strategies based on carbohydrate recognition will provide answers for the treatment of autoimmune disorders, inflammatory processes, allergic reactions and tumor spreading.

Galectin-1 Specifically Modulates TCR Signals to Enhance TCR Apoptosis but Inhibit IL-2 Production and Proliferation

Galectin-1 is an endogenous lectin expressed by thymic and lymph node stromal cells at sites of Ag presentation and T cell death during normal development. It is known to have immunomodulatory activity in vivo and can induce apoptosis in thymocytes and activated T cells (1–3). Here we demonstrate that galectin-1 stimulation cooperates with TCR engagement to induce apoptosis, but antagonizes TCR-induced IL-2 production and proliferation in a murine T cell hybridoma and freshly isolated mouse thymocytes, respectively. Although CD4+CD8+ double positive cells are the primary thymic subpopulation susceptible to galectin-1 treatment alone, concomitant CD3 engagement and galectin-1 stimulation broaden susceptible thymocyte subpopulations to include a subset of each CD4−CD8−, CD4+CD8+, CD4−CD8+, and CD4+CD8− subpopulations. Furthermore, CD3 engagement cooperates with suboptimal galectin-1 stimulation to enhance cell death in the CD4+CD8+ subpopulation. Galectin-1 stimulation is shown to synergize with TCR engagement to dramatically and specifically enhance extracellular signal-regulated kinase-2 (ERK-2) activation, though it does not uniformly enhance TCR-induced tyrosine phosphorylation. Unlike TCR-induced IL-2 production, TCR/galectin-1-induced apoptosis is not modulated by the expression of kinase inactive or constitutively activated Lck. These data support a role for galectin-1 as a potent modulator of TCR signals and functions and indicate that individual TCR-induced signals can be independently modulated to specifically affect distinct TCR functions.

Developmental association of the beta-galactoside-binding protein galectin-1 with the nuclear matrix of rat calvarial osteoblasts

The protein composition of the nuclear matrix changes significantly as the osteoblast matures from a proliferating pre-osteoblast to an osteocyte embedded in a mineralized matrix. These matrix protein are the result of developmental stage-specific gene expression during osteoblast differentiation. To isolate nuclear matrix proteins unique to the bone phenotype we analyzed nuclear matrix preparations from cultures of rat calvarial osteoblasts by high resolution two-dimensional gel electrophoresis at two different stages: proliferation (day 3) and differentiation (day 18, mineralized). We characterized one protein (14 kDa; pI 5.0), that was detectable only in the nuclear matrix of differentiated osteoblasts. By mass spectrometry and microsequencing, this protein was identified as the beta -galactoside-binding protein galectin-1. Both immunofluorescence staining of nuclear matrix preparations with the galectin-1 antibody and western blot analysis of subcellular fractions confirmed that galectin-1 is only associated with the nuclear matrix in differentiated osteoblasts as the result of differential retention. Galectin-1 protein and mRNA are present throughout osteoblast differentiation. Galectin-1 is present in the cytoplasmic and nuclear fractions in both proliferating and differentiated osteoblasts. However, its only stable binding is to the nuclear matrix of the differentiated osteoblast; but, in proliferating osteoblasts, galectin-1 is not retained in the nuclear matrix. Taken together, our results suggest that developmental association of galectin-1 with the nuclear matrix reflects differential subnuclear binding of galectin-1 during osteoblast differentiation.

Galectin-7, a marker of all types of stratified epithelia

Galectin-7 is a 14-kDA member of the lectin family we have previously cloned in the human. Its expression was found at all stages of differentiation of the human epidermis and was reduced but not suppressed when oral metaplasia of reconstructed epidermis was induced by retinoic acid. This suggested that galectin-7 could be a marker of both keratinized and non-keratinized stratified epithelia. To ascertain this hypothesis, we cloned the rat and the mouse cDNAs and produced a specific antiserum raised against a synthetic peptide. The distribution of galectin-7 mRNAs and protein was studied by in situ hybridization and immunolabelling of various human, rat and mouse epithelia. Galectin-7 was found to be expressed in interfollicular epidermis and in the outer root sheath of the hair follicle, but not in the hair matrix, nor in the sebaceous glands. It was present in esophagus and oral epithelia, cornea, Hassal's corpuscles of the thymus, but not in simple and transitional epithelia. Galectin-7 can thus be considered as a marker of all subtypes of keratinocytes. In that respect it differs from both "basal-specific" keratins K5-K14 and from "suprabasal-specific" markers such as keratins K1-K10 and involucrin. Galectin-7 also differs from some desmosomal proteins, which are present in all types of epithelia and in myocardium. Galectin-7 was absent from cultured carcinoma cell lines and was reduced both in human carcinomas and in murine tumors produced with the two-stage carcinogenesis protocol.

Activated Rat Macrophages Produce a Galectin-1-Like Protein That Induces Apoptosis of T Cells: Biochemical and Functional Characterization

Galectins, a family of closely related β-galactoside-binding proteins, show specific immunomodulatory properties. We have recently identified the presence of a galectin-like protein in rat peritoneal macrophages by means of a cross-reactivity with a polyclonal Ab raised against a galectin purified from adult chicken liver. Galectin expression was up-regulated in inflammatory and activated macrophages, revealing a significant increase in phorbol ester- and formylmethionine oligopeptide-treated cells. In an attempt to further explore its functional significance, rat macrophage galectin was purified from activated macrophages by a single-step affinity chromatography on a lactosyl-Sepharose matrix. The eluted fraction was resolved as a single protein band of ∼15,000 Da by SDS-PAGE that immunoreacted strongly with the anti-chicken galectin serum. Gel filtration studies revealed that the protein behaved like a dimer under native conditions, and saccharides bearing a β-d-galactoside configuration were able to inhibit the hemagglutinating activity displayed by the purified galectin. In agreement with its isoelectric point of ∼4.8, the amino acid analysis showed a definitive acidic pattern. Internal amino acid sequencing of selected peptides obtained by proteolytic cleavage revealed that this carbohydrate-binding protein shares all the absolutely preserved and critical residues found in other members of the mammalian galectin-1 subfamily. Finally, biochemical and ultrastructural evidence, obtained by genomic DNA fragmentation and transmission electron microscopy, are also provided to show its potential implications in the apoptotic program of T cells. This effect was quantified by using the terminal deoxynucleotidyl transferase-mediated dUTP biotin nick end-labeling assay and was found to be associated to the specific carbohydrate-binding properties of galectin.

Embryonic implantation in galectin 1/galectin 3 double mutant mice

Galectin 1 and galectin 3 are first expressed in the trophectoderm cells of the implanting embryo and have been implicated in the process of implantation. However, we had previously shown that the lack of galectin 1 in galectin 1 null mutant mice is compatible with implantation. In this study, we describe the generation of galectin 3 null mutant mice and show that they are viable and have no overt abnormalities. The importance of galectin 1 and galectin 3 in implantation was assessed by obtaining double mutant mice [gal1 -/-; gal3 -/-]. We find that implantation can still occur in the absence of both galectin 1 and galectin 3. However, we show that galectin 5, a third member of this gene family, is also present in the blastocyst at the time of implantation.

Galectin-1, an endogenous lectin produced by thymic epithelial cells, induces apoptosis of human thymocytes

Galectin-1, a beta-galactoside binding protein, is produced by thymic epithelial cells and binds to human thymocytes. We have previously reported that galectin-1 induces the apoptosis of activated T lymphocytes. Because the majority of thymocytes die via apoptosis while still within the thymus, we tested whether galectin-1 could induce the apoptosis of these cells. We now report that in vitro exposure to galectin-1 induced apoptosis of two subsets of CD4(lo) CD8(lo) thymocytes. The phenotypes of susceptible thymocytes were consistent with that of both negatively selected and nonselected cells. Galectin-1-induced apoptosis was enhanced by preexposure of thymocytes to antibody to CD3, suggesting that galectin-1 may be a participant in T-cell- receptor mediated apoptosis. In contrast, pretreatment of thymocytes with dexamethasone had no effect on galectin-1 susceptibility. We noted that 71% of the cells undergoing apoptosis after galectin-1 treatment had a DNA content greater than 2N, indicating that proliferating thymocytes were most sensitive to galectin-1. We propose that galectin-1 plays a role in the apoptosis of both negatively selected and nonselected thymocytes, and that the susceptibility of thymocytes to galectin-1 is regulated, in part, by entry or exit from the cell cycle.

Animal lectins

Protein and lipid glycosylation is no longer considered as a topic whose appeal is restricted to a limited number of analytical experts perseveringly pursuing the comprehensive cataloguing of structural variants. It is in fact arousing curiosity in various areas of basic and applied bioscience. Well founded by the conspicuous coding potential of the sugar part of cellular glycoconjugates which surpasses the storage capacity of oligonucleotide- or oligopeptide-based code systems, recognition of distinct oligosaccharide ligands by endogenous receptors, i.e. lectins and sugar-binding enzymes or antibodies, is increasingly being discovered to play salient roles in animal physiology. Having inevitably started with a descriptive stage, research on animal lectins has now undubitably reached maturity. Besides listing the current categories for lectin classification and providing presentations of the individual families and their presently delineated physiological significance, this review places special emphasis on tracing common structural and functional themes which appear to reverberate in nominally separated lectin and animal categories as well as lines of research which may come to fruition for medical sciences.

Recombinant galectin-1 recognizes mucin and epithelial cell surface glycocalyces of gastrointestinal tract

Rat gastrointestinal (GI) tract is rich source of galectins, a family of mammalian galactoside-binding lectins. To determine which tissue component is the relevant glycoconjugate ligand for the galectins, we produced recombinant galectin-1 and surveyed its binding sites on tissue sections of rat GI tract. Mucin and epithelial surface glycocalyces of both gastric and intestinal mucosa were intensely stained. This finding raises the possibility that some GI tract galectins known to be secreted by the epithelia may recognize these glycoconjugates and crosslink them into a macromolecular mass. This galectin-ligand complex may play a role in protecting the epithelial surface against luminal contents such as gastric acid, digestive enzymes, and foreign organisms.

Relationship between asymmetric nodal expression and the direction of embryonic turning

Growth factors related to TGF-beta provide important signals for patterning the vertebrate body plan. One such family member, nodal, is required for formation of the primitive streak during mouse gastrulation. Here we have used a nodal-lacZ reporter allele to demonstrate asymmetric nodal expression in the mouse node, a structure thought to be the functional equivalent of the frog and chick 'organizer', and in lateral place mesoderm cells. We have also identified two additional genes acting with nodal in a pathway determining the left-right body axis. Thus we observe in inv mutant embryos that the sidedness of nodal expression correlates with the direction of heart looping and embryonic turning. In contrast, HNF3-beta(+/-) nodal(lacZ/+) double-heterozygous embryos display LacZ staining on both left and right sides, and frequently exhibit defects in body situs. Taken together, these experiments, along with similar findings in chick, demonstrate that elements of the genetic pathway that establish the left-right body axis are conserved in vertebrates.

Purification and molecular characterization of a novel 16-kDa galectin from the nematode Caenorhabditis elegans

In our previous study (Hirabayashi, J., Satoh, M., Ohyama, Y., and Kasai, K. (1992) J. Biochem. (Tokyo) 111, 553-555), two beta-galactoside-binding lectins (apparent subunit molecular masses, 16 and 32 kDa, respectively) were identified in the nematode Caenorhabditis elegans. The subsequent study revealed that the 32-kDa lectin is a member of the galectin family. Since the 32-kDa galectin was found to consist of two homologous domains (approximately 16 kDa), 16-kDa lectin was thought to be a degradation product of the 32-kDa galectin. To clarify this, the 16-kDa lectin was purified by an improved procedure employing extraction with a calcium-supplemented buffer. The purified 16-kDa lectin was found to exist as a dimer (approximately 30 kDa) and showed hemagglutinating activity toward trypsinized rabbit erythrocytes, which was inhibited by lactose. Almost the whole sequence of the 16-kDa polypeptide (approximately 95%, 135 amino acids) was determined after digestion with various proteases. Based on the obtained information, a full-length cDNA was cloned with the aid of RNA-polymerase chain reaction. The clone encoded 146 amino acids including initiator methionine (calculated molecular mass, 15,928 Da). Based on these results, it was concluded that the 16-kDa lectin is a novel member of the galectin family, but not a degradation product of the 32-kDa galectin as had previously thought. However, the 16-kDa galectin showed relatively low sequence similarities to both the N-terminal and the C-terminal domains of the 32-kDa galectin (28% and 27% identities, respectively) and to various vertebrate galectins (14-27%). Nonetheless, all of the critical amino acids involved in carbohydrate binding were conserved. These observations suggest that, in spite of phylogenic distance between nematodes and vertebrates, both the 16-kDa and 32-kDa nematode isolectins have conserved essentially the same function(s) as those of vertebrate galectins, probably through recognition of a key disaccharide moiety, "N-acetyllactosamine."

A requirement for bone morphogenetic protein-7 during development of the mammalian kidney and eye

BMP-7/OP-1, a member of the transforming growth factor-beta (TGF-beta) family of secreted growth factors, is expressed during mouse embryogenesis in a pattern suggesting potential roles in a variety of inductive tissue interactions. The present study demonstrates that mice lacking BMP-7 display severe defects confined to the developing kidney and eye. Surprisingly, the early inductive tissue interactions responsible for establishing both organs appear largely unaffected. However, the absence of BMP-7 disrupts the subsequent cellular interactions required for their continued growth and development. Consequently, homozygous mutant animals exhibit renal dysplasia and anophthalmia at birth. Overall, these findings identify BMP-7 as an essential signaling molecule during mammalian kidney and eye development.

Increasing diversity of animal lectin structures

The number of animal proteins known to recognize carbohydrates and the number of their biological roles continue to increase. Comparisons of primary structures show that some of the newly described lectins are akin to previously investigated lectins, whereas others represent new structural groups. Progress has been made in understanding structure-function relationships for several lectins in both the old and the new categories.

Identification of cells expressing galectin-1, a galactose-binding receptor, in the rat olfactory system

Interactions between carbohydrate ligands and their receptors play an important role in cell adhesion and migration in many tissues. Cell-surface carbohydrates that contain terminal galactose have previously been implicated in primary sensory axon growth in the rodent olfactory system. The aim of the present study was to determine whether galectin-1, a galactose-binding receptor, was expressed within the rat primary olfactory pathway. Immunohistochemical and in situ hybridisation analyses revealed expression of galectin-1 by primary sensory olfactory neurons during the major embryonic period of axonogenesis as well as in maturity. In the adult olfactory bulb, galectin-1 was expressed by both second-order projection neurons and interneurons and was selectively localised to the synaptic neuropil layers. Mitral cells, the principal postsynaptic target of primary olfactory axons, began expressing this lectin soon after genesis and maintained high levels into adulthood. The expression of galectin-1 in the primary olfactory pathway and olfactory bulb neuropil suggests a role for this lectin both in the initial formation and in the subsequent maintenance of neuronal connections between the peripheral and the central olfactory neurons as well as between neurons within the bulb.

Galectin-3 is expressed in the notochord, developing bones, and skin of the postimplantation mouse embryo

The galectins are a family of low molecular weight, calcium-independent mammalian carbohydrate binding proteins that exhibit specificity for beta-galactoside derivatives. We have examined the expression pattern of galectin-3 in the developing mouse embryo by in situ hybridisation and immunohistochemistry. In the embryo proper, galectin-3 message and protein are first detected in notochord, starting from 8.5 days post coitum (dpc), and persist until this structure disappears. Galectin-3 is later found in cartilage primordia and in developing skin from 13.5 dpc. This very restricted and dynamic pattern suggests that galectin-3 may participate in the establishment and/or maintenance of notochord as well as the formation of cartilage and differentiation of skin. Finally, we find that galectin-3, which is identical to the macrophage marker Mac-2, is also expressed in embryonic macrophages.

Glycobiology. The beginning of a sweet tale

The diversity of complex carbohydrates has fascinated and frustrated glycobiologists for years. Now, manipulating oligosaccharide composition in the embryo promises new insights into their developmental functions.

More to learn from gene knockouts

Gene targeting by homologous recombination in mouse embryonic stem cells is a powerful technique to determine the physiological function of any gene product in embryonic and postnatal development and in molecular pathogenesis. Although the technique is very demanding and still in its developing stage several knockout mice carrying disrupted genes, which were once thought important for the development or molecular pathogenesis of certain tissues, have given unexpected results. A gene/function redundancy or superfluous and on-functional theory has been advanced by many investigators to explain the unexpected results. These surprising results may teach us a new lesson and lead to a revision of the strongly held view that highly conserved and abundantly expressed genes have a prominent role and function in cell physiology and development. Additional, they may also support the notion that molecular cross-talk among the genes may play an important role in determining the minimal phenotype.