Genetic defects in Chediak-Higashi syndrome and the beige mouse

Chediak-Higashi syndrome

PURPOSE OF REVIEW

Chediak-Higashi syndrome is a rare autosomal recessive disorder characterized by congenital immunodeficiency, bleeding diathesis, pyogenic infection, partial oculocutaneous albinism, and progressive neurodegeneration. Treatment is hematopoietic stem cell transplantation or bone marrow transplantation; however, this does not treat the neurologic aspect of the disease. Mutations in the lysosomal trafficking regulator (LYST) gene were identified to be causative of Chediak-Higashi, but despite many analyses, there is little functional information about the LYST protein. This review serves to provide an update on the clinical manifestations and cellular defects of Chediak-Higashi syndrome.

RECENT FINDINGS

More recent papers expand the neurological spectrum of disease in CHS, to include hereditary spastic paraplegia and parkinsonism. Granule size and distribution in NK cells have been investigated in relation to the location of mutations in LYST. Patients with mutations in the ARM/HEAT domain had markedly enlarged granules, but fewer in number. By contrast, patients with mutations in the BEACH domain had more numerous granules that were normal in size to slightly enlarged, but demonstrated markedly impaired polarization. The role of LYST in autophagosome formation has been highlighted in recent studies; LYST was defined to have a prominent role in autophagosome lysosome reformation for the maintenance of lysosomal homeostasis in neurons, while in retinal pigment epithelium cells, LYST deficiency was shown to lead to phagosome accumulation.

SUMMARY

Despite CHS being a rare disease, investigation into LYST provides an understanding of basic vesicular fusion and fission. Understanding of these mechanisms may provide further insight into the function of LYST.

Tamoxifen reduces silicone implant capsule formation in a mouse model

Capsular contracture as a result of the foreign body response (FBR) is a common issue after implant-based breast reconstruction, affecting up to 20% of patients. New evidence suggests that tamoxifen may mitigate the FBR. C57BL/6 female mice were treated with daily tamoxifen or control injections and implanted with bilateral silicone implants in the submammary glandular plane. Implants were removed en bloc after 2 weeks and the implant capsules were evaluated histologically. Tamoxifen treatment decreased capsule thickness, decreased the number of αSMA+ cells (477 ± 156 cells/mm control vs 295 ± 121 cells/mm tamoxifen, p = 0.005 unpaired t test), and decreased CD31+ cells (173.9 ± 96.1 cells/mm2 control vs 106.3 ± 51.8 cells/mm2 tamoxifen, p = 0.043 unpaired t test). There were similar amounts of pro- and anti-inflammatory macrophages (iNOS 336.1 ± 226.3 cells/mm control vs 290.6 ± 104.2 cells/mm tamoxifen, p > 0.999 Mann-Whitney test and CD163 136.6 ± 76.4 cells/mm control vs 94.1 ± 45.9 cells/mm tamoxifen, p = 0.108 unpaired t test). Tamoxifen treatment in the mouse silicone breast implant model decreased capsule formation through modulation of myofibroblasts, neovascularization, and collagen deposition. Tamoxifen may be useful for reducing or preventing capsule formation in clinical breast implantations.

Management of albinism: French guidelines for diagnosis and care

Albinism is a worldwide genetic disorder caused by mutations in at least 20 genes, identified to date, that affect melanin production or transport in the skin, hair and eyes. Patients present with variable degrees of diffuse muco-cutaneous and adnexal hypopigmentation, as well as ocular features including nystagmus, misrouting of optic nerves and foveal hypoplasia. Less often, albinism is associated with blood, immunological, pulmonary, digestive and/or neurological anomalies. Clinical and molecular characterizations are essential in preventing potential complications. Disease-causing mutations remain unknown for about 25% of patients with albinism. These guidelines have been developed for the diagnosis and management of syndromic and non-syndromic forms of albinism, based on a systematic review of the scientific literature. These guidelines comprise clinical and molecular characterization, diagnosis, therapeutic approach and management.

Genetics of non-syndromic and syndromic oculocutaneous albinism in human and mouse

Oculocutaneous albinism (OCA) is the most frequent presentation of albinism, a heterogeneous rare genetic condition generally associated with variable alterations in pigmentation and with a profound visual impairment. There are non-syndromic and syndromic types of OCA, depending on whether the gene product affected impairs essentially the function of melanosomes or, in addition, that of other lysosome-related organelles (LROs), respectively. Syndromic OCA can be more severe and associated with additional systemic consequences, beyond pigmentation and vision alterations. In addition to OCA, albinism can also be presented without obvious skin and hair pigmentation alterations, in ocular albinism (OA), and a related genetic condition known as foveal hypoplasia, optic nerve decussation defects, and anterior segment dysgenesis (FHONDA). In this review, we will focus only in the genetics of skin pigmentation in OCA, both in human and mouse, updating our current knowledge on this subject.

Assisted reproduction mediated resurrection of a feline model for Chediak-Higashi syndrome caused by a large duplication in LYST

Chediak-Higashi Syndrome (CHS) is a well-characterized, autosomal recessively inherited lysosomal disease caused by mutations in lysosomal trafficking regulator (LYST). The feline model for CHS was originally maintained for ~20 years. However, the colonies were disbanded and the CHS cat model was lost to the research community before the causative mutation was identified. To resurrect the cat model, semen was collected and cryopreserved from a lone, fertile,  CHS carrier male. Using cryopreserved semen, laparoscopic oviductal artificial insemination was performed on three queens, two queens produced 11 viable kittens. To identify the causative mutation, a fibroblast cell line, derived from an affected cat from the original colony, was whole genome sequenced. Visual inspection of the sequence data identified a candidate causal variant as a ~20 kb tandem duplication within LYST, spanning exons 30 through to 38 (NM_001290242.1:c.8347-2422_9548 + 1749dup). PCR genotyping of the produced offspring demonstrated three individuals inherited the mutant allele from the CHS carrier male. This study demonstrated the successful use of cryopreservation and assisted reproduction to maintain and resurrect biomedical models and has defined the variant causing Chediak-Higashi syndrome in the domestic cat.

Morphological and functional analysis of beige (Chèdiak-Higashi syndrome) mouse mast cells with giant granules

Chèdiak-Higashi syndrome is a rare autosomal recessive disease that causes hypopigmentation, recurrent infections, mild coagulation defects and neurological problems. Beige mice carry a mutation in the lysosome trafficking regulator (LYST) gene and display some of the key characteristics of human Chèdiak-Higashi syndrome, in particular, a high susceptibility to infection due to aberrant natural killer (NK) cell and polymorphonuclear leucocyte function. Morphological analysis of beige mice reveals the presence of enlarged lysosomes in a variety of cell types, including leucocytes, hepatocytes, fibroblasts and renal tubule cells. To examine the process of granule maturation and degranulation in beige mice mast cells, morphological studies have been conducted using a combination of electrophysiological techniques; however, few functional studies have been conducted with mast cells, such as mediator release. The aim of the present study was to determine the morphological and functional characteristics of skin and peritoneal mast cells and bone marrow-derived mast cells of homozygous (bg/bg) and heterozygous (bg/+) beige mice and wild-type (+/+) mice. The histamine concentration was lower in the peritoneal and bone marrow-derived mast cells of bg/bg mice compared with those of bg/+ and +/+ mice, but the histamine release response was potentiated. In vivo studies of passive cutaneous anaphylaxis showed no differences between bg/bg mice and either bg/+ or +/+ mice. Although bg/bg mast cells with enlarged granules display specific exocytotic processes in vitro, the consequences of mast cell activation in beige mice were similar to those of wild-type mice in vivo.

Genetic Depletion or Hyperresponsiveness of Natural Killer Cells Do Not Affect Atherosclerosis Development

Rationale:

Chronic inflammation is central in the development of atherosclerosis. Both innate and adaptive immunities are involved. Although several studies have evaluated the functions of natural killer (NK) cells in experimental animal models of atherosclerosis, it is not yet clear whether NK cells behave as protective or proatherogenic effectors. One of the main caveats of previous studies was the lack of specificity in targeting loss or gain of function of NK cells.

Objectives:

We used 2 selective genetic approaches to investigate the role of NK cells in atherosclerosis: (1) Ncr1 iCre/+ R26 lsl− DTA/+ mice in which NK cells were depleted and (2) Noé mice in which NK cells are hyperresponsive.

Methods and Results:

No difference in atherosclerotic lesion size was found in Ldlr −/− (low-density lipoprotein receptor null) mice transplanted with bone marrow (BM) cells from Ncr1 iCre R26R lsl− DTA , Noé , or wild-type mice. Also, no difference was observed in plaque composition in terms of collagen content, macrophage infiltration, or the immune profile, although Noé chimera had more IFN (interferon)-γ–producing NK cells, compared with wild-type mice. Then, we investigated the NK-cell selectivity of anti–asialoganglioside M1 antiserum, which was previously used to conclude the proatherogenicity of NK cells. Anti–asialoganglioside M1 treatment decreased atherosclerosis in both Ldlr −/− mice transplanted with Ncr1 iCre R26R lsl− DTA or wild-type bone marrow, indicating that its antiatherogenic effects are unrelated to NK-cell depletion, but to CD8 + T and NKT cells. Finally, to determine whether NK cells could contribute to the disease in conditions of pathological NK-cell overactivation, we treated irradiated Ldlr −/− mice reconstituted with either wild-type or Ncr1 iCre R26R lsl− DTA bone marrow with the viral mimic polyinosinic:polycytidylic acid and found a significant reduction of plaque size in NK-cell–deficient chimeric mice.

Conclusions:

Our findings, using state-of-the-art mouse models, demonstrate that NK cells have no direct effect on the natural development of hypercholesterolemia-induced atherosclerosis, but may play a role when an additional systemic NK-cell overactivation occurs.

Physical, Functional and Genetic Interactions between the BEACH Domain Protein SPIRRIG and LIP5 and SKD1 and Its Role in Endosomal Trafficking to the Vacuole in Arabidopsis

Beige and Chediak Higashi (BEACH) domain-containing proteins (BDCPs) are facilitators of membrane-dependent cellular processes in eukaryotes. Mutations in BDCPs cause malfunctions of endosomal compartments in various cell types. Recently, the molecular analysis of the BDCP homolog gene SPIRRIG (SPI) has revealed a molecular function in P-bodies and the regulation of RNA stability. We therefore aimed to analyze, whether SPI has also a role in membrane-dependent processes. In this study, we show that SPI physically interacts with endosomal sorting complex required for transport associated ATPase Suppressor of K⁺-transport growth defect1 (SKD1) and its positive regulator, LYST Interacting Protein 5 (LIP5) and report genetic interactions between SPI and SKD1 and LIP5. We further show that the endosomal transport route of soluble proteins to the lytic vacuole is disturbed in spi lip5 double mutants but not in the single mutants. These vacuolar transport defects were suppressed by additional expression of SKD1. Our results indicate that the BEACH domain protein SPI has in addition to a role in P-bodies a function in endosomal transport routes.

Allogeneic hematopoietic stem cell transplantation for Chediak-Higashi syndrome

The clinical outcome of allogeneic HSCT was retrospectively analyzed in eight patients with CHS. In total, six of these eight patients are alive. Four of five patients transplanted with MAC achieved prompt engraftment, and three of the four patients, including two patients with AP before transplant, are alive without disease. In contrast, three patients transplanted with RIC without active AP disease achieved prompt engraftment and survive long term. RIC-HSCT might be an alternative treatment for CHS similar to other types of HLH, at least for patients without active AP disease.

Primary immunodeficiencies and the control of Epstein-Barr virus infection

Human primary immunodeficiency (PID) states, where mutations in single immune system genes predispose individuals to certain infectious agents and not others, are experiments of nature that hold important lessons for the immunologist. The number of genetically defined PIDs is rising rapidly, as is the opportunity to learn from them. Epstein-Barr virus (EBV), a human herpesvirus, has long been of interest because of its complex interaction with the immune system. Thus, it causes both infectious mononucleosis (IM), an immunopathologic disease associated with exaggerated host responses, and at least one malignancy, EBV-positive lymphoproliferative disease, when those responses are impaired. Here, we describe the full range of PIDs currently linked with an increased risk of EBV-associated disease. These provide examples where IM-like immunopathology is fatally exaggerated, and others where responses impaired at the stage of induction, expansion, or effector function predispose to malignancy. Current evidence from this rapidly moving field supports the view that lesions in both natural killer cell and T cell function can lead to EBV pathology.

The immunology of Epstein-Barr virus-induced disease

Epstein-Barr virus (EBV) is usually acquired silently early in life and carried thereafter as an asymptomatic infection of the B lymphoid system. However, many circumstances disturb the delicate EBV-host balance and cause the virus to display its pathogenic potential. Thus, primary infection in adolescence can manifest as infectious mononucleosis (IM), as a fatal illness that magnifies the immunopathology of IM in boys with the X-linked lymphoproliferative disease trait, and as a chronic active disease leading to life-threatening hemophagocytosis in rare cases of T or natural killer (NK) cell infection. Patients with primary immunodeficiencies affecting the NK and/or T cell systems, as well as immunosuppressed transplant recipients, handle EBV infections poorly, and many are at increased risk of virus-driven B-lymphoproliferative disease. By contrast, a range of other EBV-positive malignancies of lymphoid or epithelial origin arise in individuals with seemingly intact immune systems through mechanisms that remain to be understood.

LYST controls the biogenesis of the endosomal compartment required for secretory lysosome function

Chediak-Higashi syndrome (CHS) is caused by mutations in the gene encoding LYST protein, the function of which remains poorly understood. Prominent features of CHS include defective secretory lysosome exocytosis and the presence of enlarged, lysosome-like organelles in several cell types. In order to get further insight into the role of LYST in the biogenesis and exocytosis of cytotoxic granules, we analyzed cytotoxic T lymphocytes (CTLs) from patients with CHS. Using confocal microscopy and correlative light electron microscopy, we showed that the enlarged organelle in CTLs is a hybrid compartment that contains proteins components from recycling-late endosomes and lysosomes. Enlargement of cytotoxic granules results from the progressive clustering and then fusion of normal-sized endolysosomal organelles. At the immunological synapse (IS) in CHS CTLs, cytotoxic granules have limited motility and appear docked while nevertheless unable to degranulate. By increasing the expression of effectors of lytic granule exocytosis, such as Munc13-4, Rab27a and Slp3, in CHS CTLs, we were able to restore the dynamics and the secretory ability of cytotoxic granules at the IS. Our results indicate that LYST is involved in the trafficking of the effectors involved in exocytosis required for the terminal maturation of perforin-containing vesicles into secretory cytotoxic granules.

Hemophagocytic lymphohistiocytosis (HLH): A heterogeneous spectrum of cytokine-driven immune disorders

Hemophagocytic lymphohistiocytosis (HLH) comprises a group of life-threatening immune disorders classified into primary or secondary HLH. The former is caused by mutations in genes involved in granule-mediated cytotoxicity, the latter occurs in a context of infections, malignancies or autoimmune/autoinflammatory disorders. Both are characterized by systemic inflammation, severe cytokine storms and immune-mediated organ damage. Despite recent advances, the pathogenesis of HLH remains incompletely understood. Animal models resembling different subtypes of HLH are therefore of great value to study this disease and to uncover novel treatment strategies. In this review, all known animal models of HLH will be discussed, highlighting findings on cell types, cytokines and signaling pathways involved in disease pathogenesis and extrapolating therapeutic implications for the human situation.

Drosophila mauve mutants reveal a role of LYST homologs late in the maturation of phagosomes and autophagosomes

Chediak-Higashi syndrome (CHS) is a lethal disease caused by mutations that inactivate the lysosomal trafficking regulator protein (LYST). Patients suffer from diverse symptoms including oculocutaneous albinism, recurrent infections, neutropenia and progressive neurodegeneration. These defects have been traced back to over-sized lysosomes and lysosome-related organelles (LROs) in different cell types. Here, we explore mutants in the Drosophila mauve gene as a new model system for CHS. The mauve gene (CG42863) encodes a large BEACH domain protein of 3535 amino acids similar to LYST. This reflects a functional homology between these proteins as mauve mutants also display enlarged LROs, such as pigment granules. This Drosophila model also replicates the enhanced susceptibility to infections and we show a defect in the cellular immune response. Early stages of phagocytosis proceed normally in mauve mutant hemocytes but, unlike in wild type, late phagosomes fuse and generate large vacuoles containing many bacteria. Autophagy is similarly affected in mauve fat bodies as starvation-induced autophagosomes grow beyond their normal size. Together these data suggest a model in which Mauve functions to restrict homotypic fusion of different pre-lysosomal organelles and LROs.

Exome sequencing identifies NBEAL2 as the causative gene for gray platelet syndrome

Gray platelet syndrome (GPS) is a predominantly recessive platelet disorder characterized by a mild thrombocytopenia with large platelets and a paucity of α-granules; these abnormalities cause mostly moderate but in rare cases severe bleeding. We sequenced the exomes of four unrelated cases and identified as the causative gene NBEAL2, a gene with previously unknown function but a member of a gene family involved in granule development. Silencing of nbeal2 in zebrafish abrogated thrombocyte formation.

Two novel mutations identified in an african-american child with chediak-higashi syndrome

Background. Chediak-Higashi syndrome (CHS) is a rare, autosomal recessive disorder characterized by oculocutaneous albinism, immunodeficiency, coagulopathy and late-onset, progressive neurological dysfunction. It also has an “accelerated phase” characterized by hemophagocytic lymphohistiocytosis (HLH). The disease is caused by mutations in the CHS1/LYST gene located on chromosome 1, which affects lysosome morphology and function. We report the case of an African-American child with CHS in Case. This 16-month old African-American girl presented with fever and lethargy. The proband had pale skin compared to her parents, with light brown eyes, silvery hair and massive hepatosplenomegaly. Her laboratory evaluation was remarkable for pancytopenia, high serum ferritin and an elevated LDH. Bone marrow aspirate revealed large inclusions in granulocytes and erythrophagocytosis consistent with HLH. Genetic evaluation revealed two novel nonsense mutations in the CHS1 gene: c.3622C > T (p.Q1208X) and c.11002G > T (p.E3668X). Conclusions. Our patient is one of the few cases of CHS reported in the African American population. We identified 2 nonsense mutations in the CHS1 gene, the first mutation analysis published of an African-American child with Chediak-Higashi Syndrome. These two mutations predict a severe phenotype and thus identification of these mutations has an important clinical significance in CHS.

A concanavalin A-like lectin domain in the CHS1/LYST protein, shared by members of the BEACH family

CHS1/LYST, the causative protein of the Chediak-Higashi syndrome (CHS), belongs to the BEACH (named after BEige And Chediak-Higashi) family, which includes various large proteins sharing the same C-terminal domain architecture [a PH (Pleckstrin homology)-BEACH domain followed by WD repeats). Members of the BEACH family are generally defined as vesicle-trafficking regulatory proteins, but their functions remain to be determined at the molecular level. Here, using a panel of sensitive methods of sequence analysis, we show that the N-terminal regions of BEACH proteins contain an as yet not described domain, which shares striking similarities with clostridial neurotoxins and defines a novel family within the concanavalin A (ConA)-like lectin superfamily. These results suggest that the BEACH ConA-like lectin domain could be involved in oligosaccharide binding associated with protein traffic and sorting along the secretory pathway, especially in relation with components of the vesicle fusion machinery.

Transcription factor foxq1 controls mucin gene expression and granule content in mouse stomach surface mucous cells

BACKGROUND & AIMS

The gastric mucosa provides a stringent epithelial barrier and produces acid and enzymes that initiate digestion. In this regenerating tissue, progenitors differentiate continually into 4 principal specialized cell types, yet underlying mechanisms of differentiation are poorly understood. We identified stomach-restricted expression of the forkhead transcription factor FOXQ1.

METHODS

We used a combination of genetic, histochemical, ultrastructural, and molecular analysis to study gastric cell lineages with respect to FOXQ1.

RESULTS

Within the developing and adult gastrointestinal tract, Foxq1 messenger RNA (mRNA) is restricted to the stomach and expressed predominantly in foveolar (pit) cells, the abundant mucin-producing cells that line the mucosal surface. Mice carrying Foxq1 coding mutations show virtual absence of mRNA and protein for the backbone of the major stomach mucin MUC5AC. These observations correspond to a paucity of foveolar cell secretory vesicles and notable loss of stomach but not intestinal mucus. Transcriptional profiling identified a surprisingly restricted set of genes with altered expression in Foxq1 mutant stomachs. MUC5AC is a highly tissue-restricted product that similarly depends on FOXQ1 in its other major site of expression, conjunctival goblet cells.

CONCLUSIONS

Taken together, these observations imply that promotion of gastric MUC5AC synthesis is a primary, cell-autonomous function of FOXQ1. This study is the first to implicate a transcription factor in terminal differentiation of foveolar cells and begins to define the requirements to assemble highly specialized organelles and cells in the gastric mucosa.

Genetic resistance of mice to Mycobacterium paratuberculosis is influenced by Slc11a1 at the early but not at the late stage of infection

We have recently described the development of a luminescent Mycobacterium paratuberculosis strain of bovine origin expressing the luxAB genes of Vibrio harveyi. With this luminescent isolate, fastidious and costly enumeration of CFU by plating them on agar can be replaced by easy and rapid luminometry. Here, we have reevaluated the effect of Slc11a1 (formerly Nramp1) polymorphism on susceptibility to M. paratuberculosis, using this luminometric method. A series of inbred mouse strains were infected intravenously with luminescent M. paratuberculosis S-23 and monitored for bacterial replication in spleen, liver, and lungs for 12 weeks. The results indicate that, as for Mycobacterium avium subsp. avium, innate resistance to infection is genetically controlled by Slc11a1. In BALB/c, congenic BALB.B10-H2(b) (BALB/c background; H-2(b)), C57BL/6, and beige C57BL/6(bg/)(bg) mice (all Slc11a1(s)), bacterial numbers in spleen and liver remained unchanged during the first 4 weeks of infection, whereas in DBA/2 and congenic BALB/c.DBA/2 (C.D2) mice (both Slc11a1(r)) and in (C57BL/6 x DBA/2)F(1) mice (Slc11a1(s/r)), the bacterial numbers had decreased more than 10-fold at 4 weeks postinfection in both male and female mice. At later time points, additional differences in bacterial replication were observed between the susceptible mouse strains, particularly in the liver. Whereas bacterial numbers in the liver gradually decreased more than 100-fold in C57BL/6 mice between week 4 and week 12, bacterial numbers were stable in livers from BALB/c and beige C57BL/6(bg/)(bg) mice during this period. Mycobacterium-specific gamma interferon responses developed earlier and to a higher magnitude in C57BL/6 mice than in BALB/c mice and were lowest in resistant C.D2 mice.

Keeping NK cells in highly regulated antiviral warfare

Natural killer (NK) cells use multiple mechanisms to defend against viral infections, and different stimuli can activate these antiviral effects. When engaged, receptors for innate cytokines produced during infections and for ligands on target cells can both induce NK cell cytotoxicity and the production of cytokines. These stimuli use different classes of intracellular signaling pathways to elicit the overlapping responses. What is the advantage of using different roads to the same ends? One answer might be in the nature of the alternative regulatory pathways that are in place to control the respective stimuli. A model of flexibility in accessing NK cell function, in the context of negative regulation of particular intracellular signaling pathways, is proposed here.

When intracellular logistics fails--genetic defects in membrane trafficking

The number of human genetic disorders shown to be due to defects in membrane trafficking has greatly increased during the past five years. Defects have been identified in components involved in sorting of cargo into transport carriers, vesicle budding and scission, movement of vesicles along cytoskeletal tracks, as well as in vesicle tethering, docking and fusion at the target membrane. The nervous system is extremely sensitive to such disturbances of the membrane trafficking machinery, and the majority of these disorders display neurological defects--particularly diseases affecting the motility of transport carriers along cytoskeletal tracks. In several disorders, defects in a component that represents a fundamental part of the trafficking machinery fail to cause global transport defects but result in symptoms limited to specific cell types and transport events; this apparently reflects the redundancy of the transport apparatus. In groups of closely related diseases such as Hermansky-Pudlak and Griscelli syndromes, identification of the underlying gene defects has revealed groups of genes in which mutations lead to similar phenotypic consequences. New functionally linked trafficking components and regulatory mechanisms have thus been discovered. Studies of the gene defects in trafficking disorders therefore not only open avenues for new therapeutic approaches but also significantly contribute to our knowledge of the fundamental mechanisms of intracellular membrane transport.

Secretory lysosomes and their cargo in T and NK cells

Secretory lysosomes are specialized organelles that combine catabolic functions of conventional lysosomes with an inducible secretory potential. They are present in various hematopoietic cell types commonly characterized by the need for rapid mobilization and secretion of effector proteins. As an example, the cytotoxic effector function of T cells and natural killer cells strictly depends on the activation-dependent mobilization of such vesicles to the cytotoxic immunological synapse. This review focuses on some molecules that have been identified as cargo of secretory lysosomes and which play a major role in effector function of CTL and NK cells. We also briefly point to the fact that the dysregulation of formation and transport of secretory vesicles is causative for severe immunodeficiencies and autoimmunity observed in patients and also in mice that have been used as representative model systems to analyze the pathophysiological relevance of secretory vesicles in vivo.

The Slc35d3 gene, encoding an orphan nucleotide sugar transporter, regulates platelet-dense granules

Platelet dense granules are lysosome-related organelles which contain high concentrations of several biologically important low-molecular-weight molecules. These include calcium, serotonin, adenine nucleotides, pyrophosphate, and polyphosphate, which are necessary for normal blood hemostasis. The synthesis of dense granules and other lysosome-related organelles is defective in inherited diseases such as Hermansky-Pudlak syndrome (HPS) and Chediak-Higashi syndrome (CHS). HPS and CHS mutations in 8 human and at least 16 murine genes have been identified. Previous studies produced contradictory findings for the function of the murine ashen (Rab27a) gene in platelet-dense granules. We have used a positional cloning approach with one line of ashen mutants to establish that a new mutation in a second gene, Slc35d3, on mouse chromosome 10 is the basis of this discrepancy. The platelet-dense granule defect is rescued in BAC transgenic mice containing the normal Slc35d3 gene. Thus, Slc35d3, an orphan member of a nucleotide sugar transporter family, specifically regulates the contents of platelet-dense granules. Unlike HPS or CHS genes, it has no apparent effect on other lysosome-related organelles such as melanosomes or lysosomes. The ash-Roswell mouse mutant is an appropriate model for human congenital-isolated delta-storage pool deficiency.

Grey, a novel mutation in the murine Lyst gene, causes the beige phenotype by skipping of exon 25

The murine beige mutant phenotype and the human Chediak-Higashi syndrome are caused by mutations in the murine Lyst (lysosomal trafficking regulator) gene and the human CHS gene, respectively. In this report we have analyzed a novel murine mutant Lyst allele, called Lyst(bg-grey), that had been found in an ENU mutation screen and named grey because of the grey coat color of affected mice. The phenotype caused by the Lyst(bg-grey) mutation was inherited in a recessive fashion. Melanosomes of melanocytes associated with hair follicles and the choroid layer of the eye, as well as melanosomes in the neural tube-derived pigment epithelium of the retina, were larger and irregularly shaped in homozygous mutants compared with those of wild-type controls. Secretory vesicles in dermal mast cells of the mutant skin were enlarged as well. Test crosses with beige homozygous mutant mice (Lyst(bg)) showed that double heterozygotes (Lyst(bg)/Lyst(bg-grey)) were phenotypically indistinguishable from either homozygous parent, demonstrating that the ENU mutation was an allele of the murine Lyst gene. RT-PCR analyses revealed the skipping of exon 25 in Lyst(bg-grey) mutants, which is predicted to cause a missense D2399E mutation and the loss of the following 77 amino acids encoded by exon 25 but leave the C-terminal end of the protein intact. Analysis of the genomic Lyst locus around exon 25 showed that the splice donor at the end of exon 25 showed a T-to-C transition point mutation. Western blot analysis suggests that the Lyst(bg-grey) mutation causes instability of the LYST protein. Because the phenotype of Lyst(bg) and Lyst(bg-grey) mutants is indistinguishable, at least with respect to melanosomes and secretory granules in mast cells, the Lyst(bg-grey) mutation defines a critical region for the stability of the murine LYST protein.

Histological study of granulated metrial gland (GMG) cells in beige (DA-bg/bg) rats

To clarify the roles of granulated metrial gland (GMG) cells for successful pregnancy in rats, GMG cells in beige rats (genotype: DA-bg/bg), whose NK cells show lysosomal dysfunction because of abnormalities in cytoplasmic granules, were examined in mid- and late-pregnancy by light and electron microscopies. The GMG cells of beige rats were significantly less in number than those of the two controls (genotypes: DA-bg/+ and DA-+/+) in mid- and late-pregnancy, and this accompanied a low reproductive performance in the beige rats. The size of intracellular granules in the GMG cells of the beige rats was larger than for the two controls on each corresponding day of pregnancy. These results suggest that the activity of rat GMG cells and peripheral NK cells might be influenced by the beige gene, which is involved in reproductive performance.

Engraftment of human T, B and NK cells in CB.17 SCID/beige mice by transfer of human spleen cells

Models of severe combined immuno-deficient (SCID) mice reconstituted with a competent human immune system represent a valuable tool for the study of human immune responses in vivo. Reconstitution with human cells can be achieved using large numbers of peripheral blood lymphocytes, but levels of engraftment are poor and graft versus host disease (GVHD) frequently occurs. SCID/beige mice are at the same time deficient for adaptive and innate immunity and the objective of this study was to develop a safe and efficient way to achieve human lymphocyte engraftment in these mice using human spleen cells. After institutional authorisations and informed consent of relatives, a piece of spleen was obtained from cadaveric organ donors and the splenocytes were isolated and cryopreserved for later use. Single intraperitoneal injections of 5-100 x10(6) splenocytes were performed into SCID/beige mice. Reconstitution of a human immune system was monitored weekly by the presence of human cells and IgG in peripheral blood. The mice were sacrificed 4 weeks after the injection and the engraftment in lymphoid organs was studied. A reproducible reconstitution was obtained with intraperitoneal injection of 30-40 x10(6) spleen cells. Human T, B and NK cells as well as human IgG were present in peripheral blood. In lymphoid tissues, the same lymphocytic subpopulations were detected and in addition some antigen presenting cells. The reconstitution was functional because graft rejection was observed after transplantation of human allogeneic tissues. When less than 30 x10(6) cells were injected, the reconstitution was variable. When more than 40 x10(6) cells were injected, GVHD occurred with increasing frequency. In conclusion, we show that intraperitoneal injection of 30-40 x10(6) human splenocytes into SCID/beige mice induces a quick and functional engraftment of human T, B and NK cells with no risk of GVHD. This model may be used to study human transplantation immunobiology in vivo.

Expression profile of mouse BWF1, a protein with a BEACH domain, WD40 domain and FYVE domain

We isolated a mouse cDNA encoding a protein that contains a BEACH domain, 5 WD40 repeats and a FYVE domain, which we designated as BWF1. The mRNA is approximately 10 kb in size and encodes a protein consisting of 3508 amino acids with a predicted molecular weight of 385 kDa. BWF1 has 45% homology with the Drosophila protein, blue cheese (BCHS). The BWF1 gene consists of 67 exons, which span 270 kb of genomic sequence, and has been mapped to mouse chromosome 5. Northern blot analysis revealed that it was strongly expressed in the liver, moderately in the kidney and testis, and weakly in the brain of adult mice. During the development of the mouse brain, BWF1 mRNA was abundant on embryonic day (E) 14-16; after birth, the level of BWF1 mRNA expression decreased markedly to reach the adult level at postnatal day 3. In situ hybridization analysis revealed that the expressed BWF1 mRNA was restricted to the marginal region both in E14 and E16 embryonic brain, but became diffuse after birth. Confocal microscopy studies of the epitope-tagged BWF1 protein showed that the protein was a cytoplasmic one.

Crystal Structure of the PH−BEACH Domains of Human LRBA/BGL†

The beige and Chediak-Higashi syndrome (BEACH) domain defines a large family of eukaryotic proteins that have diverse cellular functions in vesicle trafficking, membrane dynamics, and receptor signaling. The domain is the only module that is highly conserved among all of these proteins, but the exact functions of this domain and the molecular basis for its actions are currently unknown. Our previous studies showed that the BEACH domain is preceded by a novel, weakly conserved pleckstrin homology (PH) domain. We report here the crystal structure at 2.4 A resolution of the PH-BEACH domain of human LRBA/BGL. The PH domain has the same backbone fold as canonical PH domains, despite sharing no sequence homology with them. However, our binding assays demonstrate that the PH domain in the BEACH proteins cannot bind phospholipids. The BEACH domain contains a core of several partially extended peptide segments that is flanked by helices on both sides. The structure suggests intimate association between the PH and the BEACH domains, and surface plasmon resonance studies confirm that the two domains of the protein FAN have high affinity for each other, with a K(d) of 120 nM.

Chediak-Higashi syndrome with parkinsonism

Chediak-Higashi syndrome (CHS), typically presents with partial albinism and severe hematological abnormalities. About 10% of the patients have a mild adult form associated with various neurological manifestations. We describe the case of a 24-year-old woman with parkinsonism that responded well to antiparkinsonian drugs.

Elejalde syndrome: report of a case and review of the literature

Elejalde syndrome is a rare autosomal recessive condition, with only 10 reported cases through 2001. It is characterized by silvery hair, pigment abnormalities, and profound central nervous system dysfunction. The differential diagnosis includes Griscelli and Chediak-Higashi syndromes, which present with silvery hair, pigment abnormalities, central nervous system alterations, and severe immunologic dysfunction. We report a 6-year-old girl with Elejalde syndrome and review Elejalde, Griscelli, and Chediak-Higashi syndromes.

Deregulated expression of LRBA facilitates cancer cell growth

LRBA expression is induced by mitogens in lymphoid and myeloid cells. The Drosophila LRBA orthologue rugose/DAKAP550 is involved in Notch, Ras and EGFR pathways. These findings suggest that LRBA could play a role in cell types that have increased proliferative and survival capacity. Here, we show by microarray and real-time PCR analyses that LRBA is overexpressed in several different cancers relative to their normal tissue controls. We also show that LRBA promoter activity and endogenous LRBA mRNA levels are reduced by p53 and increased by E2F1, indicating that mutations in the tumor suppressors p53 and Rb could contribute to the deregulation of LRBA. Furthermore, inhibition of LRBA expression by RNA interference, or inhibition of its function by a dominant-negative mutant, leads to significant growth inhibition of cancer cells, demonstrating that deregulated expression of LRBA contributes to the altered growth properties of a cancer cell. Finally, we show that the phosphorylation of EGFR is affected by the dominant-negative mutant, suggesting LRBA plays a role in the mammalian EGFR pathway. These findings demonstrate that LRBA facilitates cancer cell growth and thus LRBA may represent a novel molecular target for cancer therapy.

Hyperpigmentation in Chediak-Higashi syndrome

We describe a 4 1/2 -year-old Saudi Arabian boy born to consanguineous parents who was initially seen with gradual onset of fever and abdominal distention. The patient was found to have speckled hypopigmentation and hyperpigmentation of the sun-exposed areas. The finding of large cytoplasmic granules in blood and bone marrow leukocytes established the diagnosis of Chediak-Higashi syndrome. We review the literature on this finding, which might be underreported, especially in darkly pigmented races.

Crystal structure of the BEACH domain reveals an unusual fold and extensive association with a novel PH domain

The BEACH domain is highly conserved in a large family of eukaryotic proteins, and is crucial for their functions in vesicle trafficking, membrane dynamics and receptor signaling. However, it does not share any sequence homology with other proteins. Here we report the crystal structure at 2.9 A resolution of the BEACH domain of human neurobeachin. It shows that the BEACH domain has a new and unusual polypeptide backbone fold, as the peptide segments in its core do not assume regular secondary structures. Unexpectedly, the structure also reveals that the BEACH domain is in extensive association with a novel, weakly conserved pleckstrin-homology (PH) domain. Consistent with the structural analysis, biochemical studies show that the PH and BEACH domains have strong interactions, suggesting they may function as a single unit. Functional studies in intact cells demonstrate the requirement of both the PH and the BEACH domains for activity. A prominent groove at the interface between the two domains may be used to recruit their binding partners.

Chediak-Higashi Syndrome: a rare disorder of lysosomes and lysosome related organelles

Chediak-Higashi Syndrome (CHS) is a rare autosomal recessive disorder characterized by severe immunologic defects including recurrent bacterial infections, impaired chemotaxis and abnormal natural killer (NK) cell function. Patients with this syndrome exhibit other symptoms such as an associated lymphoproliferative syndrome, bleeding tendencies, partial albinism and peripheral neuropathies. The classic diagnostic feature of CHS is the presence of huge lysosomes and cytoplasmic granules within cells. Similar defects are found in other mammals, the most well studied being the beige mouse and Aleutian mink. A positional cloning approach resulted in the identification of the Beige gene on chromosome 13 in mice and the CHS1/LYST gene on chromosome 1 in humans. The protein encoded by this gene is 3801 amino acids and is highly conserved throughout evolution. The identification of CHS1/Beige has defined a family of genes containing a common BEACH motif. The function of these proteins in vesicular trafficking remains unknown.

Lymphocyte-mediated cytotoxicity

Virtually all of the measurable cell-mediated cytotoxicity delivered by cytotoxic T lymphocytes and natural killer cells comes from either the granule exocytosis pathway or the Fas pathway. The granule exocytosis pathway utilizes perforin to traffic the granzymes to appropriate locations in target cells, where they cleave critical substrates that initiate DNA fragmentation and apoptosis; granzymes A and B induce death via alternate, nonoverlapping pathways. The Fas/FasL system is responsible for activation-induced cell death but also plays an important role in lymphocyte-mediated killing under certain circumstances. The interplay between these two cytotoxic systems provides opportunities for therapeutic interventions to control autoimmune diseases and graft vs. host disease, but oversuppression of these pathways may also lead to increased viral susceptibility and/or decreased tumor cell killing.

Patterns of engraftment in different strains of immunodeficient mice reconstituted with human peripheral blood lymphocytes

BACKGROUND

Models of immunodeficient mice reconstituted with a competent human immune system would represent an invaluable tool for the study of transplantation immunobiology allergy, autoimmunity, and infectious diseases. Severe combined immune deficiency (scid) mice can be successfully reconstituted with human peripheral blood lymphocytes (PBLs), but rates and levels of engraftment are poor. New strains of mice with diverse immunodeficiencies have been recently characterized or developed, which might prove to be advantageous for in vivo studies of human immune reactivity.

METHODS

We have compared rates and patterns of human PBL engraftment in four available immunodeficient murine strains; scid-beige, nonobese diabetic (NOD)-scid, NOD-scid-beta2 m- and rag-. T- and B-lymphocyte engraftment, phenotype of engrafted cells, and occurrence of graft-versus-host disease (GVHD) were studied and compared.

RESULTS

Successful engraftment of human PBL was readily obtained in the majority of scid-beige, NOD-scid, and NOD-scid-beta2 m- with a single i.p. administration of human PBLs, whereas it was seldom achieved in rag- animals. Human Ig levels were accordingly remarkably low in rag- recipients but, interestingly also in NOD-scid-beta2 m- mice. Engraftment was readily observed not only in peripheral blood but also in spleen and bone marrow of successfully reconstituted animals. Phenotypic analysis of engrafted human cells showed preserved CD4/CD8 ratios and a clear skewing toward an activated phenotype. GVHD was invariably observed in successfully reconstituted animals.

CONCLUSIONS

Our data indicate that a high rate of reconstitution with human lymphocytes can be achieved in scid-beige, NOD-scid, and NOD-scid-beta2 m- mice. Human Ig are produced at high levels, except in NOD-scid-beta2 m-, including xenoreactive natural antibodies. Scid-beige and NOD-scid appear therefore better suited than NOD-scid-beta2 m- or rag- for analysis of human immunoreactivity in vivo. An important caveat is the invariable occurrence of GVHD that precludes long-term studies in this model system.

The winged helix/forkhead transcription factor Foxq1 regulates differentiation of hair in satin mice

Satin (sa) homozygous mice have a silky coat with high sheen arising from structurally abnormal medulla cells and defects in differentiation of the hair shaft. We demonstrate that the winged helix/forkhead transcription factor, Foxq1 (Forkhead box, subclass q, member 1) is mutant in sa mice. An intragenic deletion was identified in the radiation-induced satin mutant of the SB/Le inbred strain; a second allele, identified by an N-ethyl-N-nitrosourea (ENU) mutagenesis screen, has a missense mutation in the conserved winged helix DNA-binding domain. Homozygous mutants of the two alleles are indistinguishable. We show that Foxq1 is expressed during embryogenesis and exhibits a tissue-restricted expression pattern in adult tissues. The hair defects appear to be restricted to the inner structures of the hair; consequently, Foxq1 has a unique and distinct function involved in differentiation and development of the hair shaft. Despite an otherwise healthy appearance, satin mice have been reported to exhibit suppressed NK-cell function and alloimmune cytotoxic T-cell function. We show instead that the immune defects are attributable to genetic background differences.

Identification of a novel lipopolysaccharide-inducible gene with key features of both A kinase anchor proteins and chs1/beige proteins

Mutations in chs1/beige result in a deficiency in intracellular transport of vesicles that leads to a generalized immunodeficiency in mice and humans. The function of NK cells, CTL, and granulocytes is impaired by these mutations, indicating that polarized trafficking of vesicles is controlled by CHS1/beige proteins. However, a molecular explanation for this defect has not been identified. Here we describe a novel gene with orthologues in mice, humans, and flies that contains key features of both chs1/beige and A kinase anchor genes. We designate this novel gene lba for LPS-responsive, beige-like anchor gene. Expression of lba is induced after LPS stimulation of B cells and macrophages. In addition, lba is expressed in many other tissues in the body and has three distinct mRNA isoforms that are differentially expressed in various tissues. Strikingly, LBA-green-fluorescent protein (GFP) fusion proteins are localized to vesicles after LPS stimulation. Confocal microscopy indicates this protein is colocalized with the trans-Golgi complex and some lysosomes. Further analysis by immunoelectron microscopy demonstrates that LBA-GFP fusion protein can localize to endoplasmic reticulum, plasma membrane, and endocytosis vesicles in addition to the trans-Golgi complex and lysosomes. We hypothesize that LBA/CHS1/BG proteins function in polarized vesicle trafficking by guiding intracellular vesicles to activated receptor complexes and thus facilitate polarized secretion and/or membrane deposition of immune effector molecules.

12-year-old male with Elejalde syndrome (neuroectodermal melanolysosomal disease)

Neuroectodermal melanolysosomal disease, also known as Elejalde syndrome, is a rare syndrome characterized by silvery hair, pigment abnormalities, and profound central nervous system dysfunction. It is similar to the Chediak-Higashi and Griscelli syndromes, although these syndromes are associated with severe immunologic dysfunction. We report on a 12-year-old male with Elejalde syndrome and compare the Elejalde, Chediak-Higashi, and Griscelli syndromes.