👤 Val C Sheffield

Salmonella Typhi secretes typhoid toxin that activates cellular DNA damage responses (DDR) during acute typhoid fever. Human infection challenge studies revealed that the toxin suppresses bacteraemia via unknown mechanisms. Using quantitative proteomic analysis on the plasma of bacteraemic participants, we demonstrate that wild-type toxigenic Salmonella induced secretion of lysozyme (LYZ) and apolipoprotein C3 (APOC3). Recombinant typhoid toxin or Salmonella infection recapitulated LYZ and APOC3 secretion in cultured cells, which involved ATM/ATR-dependent DDRs and confirmed observations in typhoid fever. LYZ caused spheroplast formation, inhibited the Salmonella type 3 secretion system, and intracellular infections. LYZ expression was regulated by p53 in a cell type-specific manner and driven by mitochondrial oxidative stress that caused nuclear DDRs and p53-mediated senescence responses. Addition of LYZ inhibited oxidative DNA damage and resulting senescence responses caused by typhoid toxin. Our findings may indicate that toxin-induced DDRs elicit antimicrobial responses, which suppress Salmonella bacteraemia during typhoid fever. Show less

The BBSome is a protein complex consisting of BBS1, BBS2, BBS4, BBS5, BBS7, BBS8, BBS9 and BBS18 that associates with intraflagellar transport complexes and specializes in ciliary trafficking. In primary cilia, ciliary entry requires the fully assembled BBSome as well as the small GTPase, ARL6 (BBS3). Retinal photoreceptors possess specialized cilia. In light of key structural and functional differences between primary and specialized cilia, we examined the principles of BBSome recruitment to photoreceptor cilia. We performed sucrose gradient fractionation using retinal lysates of Bbs2-/-, Bbs7-/-, Bbs8-/- and Bbs3-/- mice to determine the status of BBSome assembly, then determined localization of BBSome components using immunohistochemistry. Surprisingly, we found that a subcomplex of the BBSome containing at least BBS1, BBS5, BBS8 and BBS9 is recruited to cilia in the absence of BBS2 or BBS7. In contrast, a BBSome subcomplex consisting of BBS1, BBS2, BBS5, BBS7 and BBS9 is found in Bbs8-/- retinas and is denied ciliary entry in photoreceptor cells. In addition, the BBSome remains fully assembled in Bbs3-/- retinas and can be recruited to photoreceptor cilia in the absence of BBS3. We compared phenotypic severity of their retinal degeneration phenotypes. These findings demonstrate that unlike primary cilia, photoreceptor cilia admit a partially assembled BBSome meeting specific requirements. In addition, the recruitment of the BBSome to photoreceptor cilia does not require BBS3. These findings indicate that the ciliary entry of the BBSome is subjected to cell-specific regulation, particularly in cells with highly adapted forms of cilia such as photoreceptors. Show less

Bardet-Beidl syndrome (BBS) manifests from genetic mutations encoding for one or more BBS proteins. BBS4 loss impacts olfactory ciliation and odor detection, yet the cellular mechanisms remain unclear. Here, we report that Show less

Bardet-Biedl syndrome (BBS) is a genetically heterogeneous inherited human disorder displaying a pleotropic phenotype. Many of the symptoms characterized in the human disease have been reproduced in animal models carrying deletions or knock-in mutations of genes causal for the disorder. Thinning of the cerebral cortex, enlargement of the lateral and third ventricles, and structural changes in cilia are among the pathologies documented in these animal models. Ciliopathy is of particular interest in light of recent studies that have implicated primary neuronal cilia (PNC) in neuronal signal transduction. In the present investigation, we tested the hypothesis that areas of the brain responsible for learning and memory formation would differentially exhibit PNC abnormalities in animals carrying a deletion of the Bbs4 gene (Bbs4-/-). Immunohistochemical localization of adenylyl cyclase-III (ACIII), a marker restricted to PNC, revealed dramatic alterations in PNC morphology and a statistically significant reduction in number of immunopositive cilia in the hippocampus and amygdala of Bbs4-/- mice compared to wild type (WT) littermates. Western blot analysis confirmed the decrease of ACIII levels in the hippocampus and amygdala of Bbs4-/- mice, and electron microscopy demonstrated pathological alterations of PNC in the hippocampus and amygdala. Importantly, no neuronal loss was found within the subregions of amygdala and hippocampus sampled in Bbs4-/- mice and there were no statistically significant alterations of ACIII immunopositive cilia in other areas of the brain not known to contribute to the BBS phenotype. Considered with data documenting a role of cilia in signal transduction these findings support the conclusion that alterations in cilia structure or neurochemical phenotypes may contribute to the cognitive deficits observed in the Bbs4-/- mouse mode. Show less

Bardet-Biedl syndrome (BBS) is a well-known ciliopathy with mutations reported in 18 different genes. Most of the protein products of the BBS genes localize at or near the primary cilium and the centrosome. Near the centrosome, BBS proteins interact with centriolar satellite proteins, and the BBSome (a complex of seven BBS proteins) is believed to play a role in transporting ciliary membrane proteins. However, the precise mechanism by which BBSome ciliary trafficking activity is regulated is not fully understood. Here, we show that a centriolar satellite protein, AZI1 (also known as CEP131), interacts with the BBSome and regulates BBSome ciliary trafficking activity. Furthermore, we show that AZI1 interacts with the BBSome through BBS4. AZI1 is not involved in BBSome assembly, but accumulation of the BBSome in cilia is enhanced upon AZI1 depletion. Under conditions in which the BBSome does not normally enter cilia, such as in BBS3 or BBS5 depleted cells, knock down of AZI1 with siRNA restores BBSome trafficking to cilia. Finally, we show that azi1 knockdown in zebrafish embryos results in typical BBS phenotypes including Kupffer's vesicle abnormalities and melanosome transport delay. These findings associate AZI1 with the BBS pathway. Our findings provide further insight into the regulation of BBSome ciliary trafficking and identify AZI1 as a novel BBS candidate gene. Show less

Ciliopathies are a group of heterogeneous disorders associated with ciliary dysfunction. Diseases in this group display considerable phenotypic variation within individual syndromes and overlapping phenotypes among clinically distinct disorders. Particularly, mutations in CEP290 cause phenotypically diverse ciliopathies ranging from isolated retinal degeneration, nephronophthisis and Joubert syndrome, to the neonatal lethal Meckel-Gruber syndrome. However, the underlying mechanisms of the variable expressivity in ciliopathies are not well understood. Here, we show that components of the BBSome, a protein complex composed of seven Bardet-Biedl syndrome (BBS) proteins, physically and genetically interact with CEP290 and modulate the expression of disease phenotypes caused by CEP290 mutations. The BBSome binds to the N-terminal region of CEP290 through BBS4 and co-localizes with CEP290 to the transition zone (TZ) of primary cilia and centriolar satellites in ciliated cells, as well as to the connecting cilium in photoreceptor cells. Although CEP290 still localizes to the TZ and connecting cilium in BBSome-depleted cells, its localization to centriolar satellites is disrupted and CEP290 appears to disperse throughout the cytoplasm in BBSome-depleted cells. Genetic interactions were tested using Cep290(rd16)- and Bbs4-null mutant mouse lines. Additional loss of Bbs4 alleles in Cep290(rd16/rd16) mice results in increased body weight and accelerated photoreceptor degeneration compared with mice without Bbs4 mutations. Furthermore, double-heterozygous mice (Cep290(+/rd16);Bbs4(+/-)) have increased body weight compared with single-heterozygous animals. Our data indicate that genetic interactions between BBSome components and CEP290 could underlie the variable expression and overlapping phenotypes of ciliopathies caused by CEP290 mutations. Show less

Bardet-Biedl syndrome (BBS) is a genetically heterogeneous autosomal recessive disorder characterized by obesity, retinal degeneration, polydactyly, hypogenitalism and renal defects. Recent findings have associated the etiology of the disease with cilia, and BBS proteins have been implicated in trafficking various ciliary cargo proteins. To date, 17 different genes have been reported for BBS among which BBS1 is the most common cause of the disease followed by BBS10, and BBS4. A murine model of Bbs4 is known to phenocopy most of the human BBS phenotypes, and it is being used as a BBS disease model. To better understand the in vivo localization, cellular function, and interaction of BBS4 with other proteins, we generated a transgenic BBS4 mouse expressing the human BBS4 gene under control of the beta actin promoter. The transgene is expressed in various tissues including brain, eye, testis, heart, kidney, and adipose tissue. These mice were further bred to express the transgene in Bbs4 null mice, and their phenotype was characterized. Here we report that despite tissue specific variable expression of the transgene, human BBS4 was able to complement the deficiency of Bbs4 and rescue all the BBS phenotypes in the Bbs4 null mice. These results provide an encouraging prospective for gene therapy for BBS related phenotypes and potentially for other ciliopathies. Show less

The pleiotropic features of obesity, retinal degeneration, polydactyly, kidney abnormalities, cognitive impairment, hypertension, and diabetes found in Bardet-Biedl syndrome (BBS) make this disorder an important model disorder for identifying molecular mechanisms involved in common human diseases. To date, 16 BBS genes have been reported, seven of which (BBS1, 2, 4, 5, 7, 8, and 9) code for proteins that form a complex known as the BBSome. The function of the BBSome involves ciliary membrane biogenesis. Three additional BBS genes (BBS6, BBS10, and BBS12) have homology to type II chaperonins and interact with CCT/TRiC proteins and BBS7 to form a complex termed the BBS-chaperonin complex. This complex is required for BBSome assembly. Little is known about the process and the regulation of BBSome formation. We utilized point mutations and null alleles of BBS proteins to disrupt assembly of the BBSome leading to the accumulation of BBSome assembly intermediates. By characterizing BBSome assembly intermediates, we show that the BBS-chaperonin complex plays a role in BBS7 stability. BBS7 interacts with BBS2 and becomes part of a BBS7-BBS2-BBS9 assembly intermediate referred to as the BBSome core complex because it forms the core of the BBSome. BBS1, BBS5, BBS8, and finally BBS4 are added to the BBSome core to form the complete BBSome. Show less

Many signaling proteins including G protein-coupled receptors localize to primary cilia, regulating cellular processes including differentiation, proliferation, organogenesis, and tumorigenesis. Bardet-Biedl Syndrome (BBS) proteins are involved in maintaining ciliary function by mediating protein trafficking to the cilia. However, the mechanisms governing ciliary trafficking by BBS proteins are not well understood. Here, we show that a novel protein, Leucine-zipper transcription factor-like 1 (LZTFL1), interacts with a BBS protein complex known as the BBSome and regulates ciliary trafficking of this complex. We also show that all BBSome subunits and BBS3 (also known as ARL6) are required for BBSome ciliary entry and that reduction of LZTFL1 restores BBSome trafficking to cilia in BBS3 and BBS5 depleted cells. Finally, we found that BBS proteins and LZTFL1 regulate ciliary trafficking of hedgehog signal transducer, Smoothened. Our findings suggest that LZTFL1 is an important regulator of BBSome ciliary trafficking and hedgehog signaling. Show less

Bardet-Biedl syndrome (BBS) is a rare hereditary autosomal recessive disease associated with several features including obesity, hypertension, and renal abnormalities. The underlying mechanisms of renal defects associated with BBS remain poorly defined. We examined the histological, molecular, and functional renal changes in BBS mouse models that have features of the human disorder. Interestingly, obese hypertensive Bbs4(-/-) mice exhibited inflammatory infiltration and renal cysts, whereas the obese normotensive Bbs2(-/-) mice had only minor inflammatory infiltration. Accordingly, the expression level of inducible nitric oxide synthase was elevated in the kidney of both BBS mice with a more marked increase in Bbs4(-/-) mice. In contrast, endothelial nitric oxide synthase expression was decreased in Bbs4(-/-), but not Bbs2(-/-), mice. Similarly, the expression levels of transient receptor potential vanilloid 1 and 4 channels as well as β- and γ-subunits of epithelial Na channel were significantly reduced only in the kidney of Bbs4(-/-) mice. Metabolic studies revealed changes in urine output and urinary concentrations of creatinine, blood urea nitrogen, sodium, and potassium with a more pronounced effect in Bbs4(-/-) mice. Finally, we found that calorie restriction which prevented obesity in BBS mice reversed the morphological and molecular changes found in Bbs2(-/-) and Bbs4(-/-) mice, indicating the kidney abnormalities associated with BBS are obesity related. These findings extend our understanding of the function of BBS proteins and emphasize the importance of these proteins in renal physiology. Show less

Bardet-Biedl syndrome (BBS) is a genetically heterogeneous disorder affecting multiple organ systems and resulting in blindness, obesity, cognitive impairment, and congenital defects. Interest in the etiology of this disorder stems, in part, from the fact that patients with BBS develop common clinical problems, including obesity, diabetes and hypertension. Twelve genes independently causing BBS have been identified. The heterogeneity is explained by the existence of two BBS complexes, the BBSome consisting of seven known BBS proteins, and the BBS chaperone complex consisting of three known BBS proteins. The formation of the BBSome requires the function of the BBS chaperone complex. Both mouse and zebrafish data support a role for BBS genes in cilia function, and in intracellular and intraflagellar trafficking. From the work described here, a common primary function of BBS proteins has emerged, specifically the mediation and regulation of microtubule-based intracellular transport. Show less

Bardet-Biedl syndrome (BBS) is an autosomal recessive disease characterized by retinal dystrophy, polydactyly, obesity, learning disabilities, renal involvement, and male hypogenitalism. BBS is genetically heterogeneous with mutations of 14 genes, accounting for approximately 70% of cases. Triallelic inheritance has been suggested in about 5% of cases. Forty-nine unrelated BBS patients were screened for mutations by DHPLC analysis in BBS1, BBS2, BBS4, BBS6/MKKS, BBS10, and BBS12. The selected genes either account for more than 5% of the mutational load or are commonly reported in triallelic inheritance. Eight patients with only one or no BBS mutation were further investigated by single nucleotide polymorphism (SNP) analysis. In total, mutations were detected in 44 patients. Twenty percent had two mutations in BBS1, 18% in BBS2, 4% in BBS9, 43% in BBS10, and 2% in BBS12. Five patients were heterozygous for a sequence variation in BBS6/MKKS. We found eight patients with three sequence variations in two genes, which could be explained by triallelic inheritance, by the prevalence of heterozygous carriers or the third sequence variations representing rare polymorphisms. All changes found in a second BBS gene were amino acid substitutions. Genotype-phenotype correlations suggest a milder phenotype for BBS1 compared to BBS2 and BBS10, which we ascribe to the hypomorphic p.Met390Arg-mutation. Show less

We report a mouse model of multiple osteochondromas (MO), an autosomal dominant disease in humans, also known as multiple hereditary exostoses (MHE or HME) and characterized by the formation of cartilage-capped osseous growths projecting from the metaphyses of endochondral bones. The pathogenesis of these osteochondromas has remained unclear. Mice heterozygous for Ext1 or Ext2, modeling the human genotypes that cause MO, occasionally develop solitary osteochondroma-like structures on ribs [Lin et al. (2000) Dev Biol 224(2):299-311; Stickens et al. (2005) Development 132(22):5055-5068]. Rather than model the germ-line genotype, we modeled the chimeric tissue genotype of somatic loss of heterozygosity (LOH), by conditionally inactivating Ext1 via head-to-head loxP sites and temporally controlled Cre-recombinase in chondrocytes. These mice faithfully recapitulate the human phenotype of multiple metaphyseal osteochondromas. We also confirm homozygous disruption of Ext1 in osteochondroma chondrocytes and their origin in proliferating physeal chondrocytes. These results explain prior modeling failures with the necessity for somatic LOH in a developmentally regulated cell type. Show less

Obesity is a major public health problem in most developed countries and a major risk factor for diabetes and cardiovascular disease. Emerging evidence indicates that ciliary dysfunction can contribute to human obesity but the underlying molecular and cellular mechanisms are unknown. Bardet-Biedl syndrome (BBS) is a genetically heterogeneous human obesity syndrome associated with ciliary dysfunction. BBS proteins are thought to play a role in cilia function and intracellular protein/vesicle trafficking. Here, we show that BBS proteins are required for leptin receptor (LepR) signaling in the hypothalamus. We found that Bbs2(-/-), Bbs4(-/-) and Bbs6(-/-) mice are resistant to the action of leptin to reduce body weight and food intake regardless of serum leptin levels and obesity. In addition, activation of hypothalamic STAT3 by leptin is significantly decreased in Bbs2(-/-), Bbs4(-/-) and Bbs6(-/-) mice. In contrast, downstream melanocortin receptor signaling is unaffected, indicating that LepR signaling is specifically impaired in Bbs2(-/-), Bbs4(-/-) and Bbs6(-/-) mice. Impaired LepR signaling in BBS mice was associated with decreased Pomc gene expression. Furthermore, we found that BBS1 protein physically interacts with the LepR and that loss of BBS proteins perturbs LepR trafficking. Our data indicate that BBS proteins mediate LepR trafficking and that impaired LepR signaling underlies energy imbalance in BBS. These findings represent a novel mechanism for leptin resistance and obesity. Show less

Bardet-Biedl syndrome (BBS) is a heterogeneous genetic disorder characterized by many features, including obesity and cardiovascular disease. We previously developed knockout mouse models of 3 BBS genes: BBS2, BBS4, and BBS6. To dissect the mechanisms involved in the metabolic disorders associated with BBS, we assessed the development of obesity in these mouse models and found that BBS-null mice were hyperphagic, had low locomotor activity, and had elevated circulating levels of the hormone leptin. The effect of exogenous leptin on body weight and food intake was attenuated in BBS mice, which suggests that leptin resistance may contribute to hyperleptinemia. In other mouse models of obesity, leptin resistance may be selective rather than systemic; although mice became resistant to leptin's anorectic effects, the ability to increase renal sympathetic nerve activity (SNA) was preserved. Although all 3 of the BBS mouse models were similarly resistant to leptin, the sensitivity of renal SNA to leptin was maintained in Bbs4 -/- and Bbs6 -/- mice, but not in Bbs2 -/- mice. Consequently, Bbs4 -/- and Bbs6 -/- mice had higher baseline renal SNA and arterial pressure and a greater reduction in arterial pressure in response to ganglionic blockade. Furthermore, we found that BBS mice had a decreased hypothalamic expression of proopiomelanocortin, which suggests that BBS genes play an important role in maintaining leptin sensitivity in proopiomelanocortin neurons. Show less

Mutations in a group of genes that contribute to ciliary function cause Bardet-Biedl syndrome (BBS). Most studies of BBS have focused on primary, sensory cilia. Here, we asked whether loss of BBS proteins would also affect motile cilia lining the respiratory tract. We found that BBS genes were expressed in human airway epithelia, and BBS2 and BBS4 localized to cellular structures associated with motile cilia. Although BBS proteins were not required for ciliogenesis, their loss caused structural defects in a fraction of cilia covering mouse airway epithelia. The most common abnormality was bulges filled with vesicles near the tips of cilia. We discovered this same misshapen appearance in airway cilia from Bbs1, Bbs2, Bbs4, and Bbs6 mutant mice. The structural abnormalities were accompanied by functional defects; ciliary beat frequency was reduced in Bbs mutant mice. Previous reports suggested BBS might increase the incidence of asthma. However, compared with wild-type controls, neither airway hyperresponsiveness nor inflammation increased in Bbs2(-/-) or Bbs4(-/-) mice immunized with ovalbumin. Instead, these animals were partially protected from airway hyperresponsiveness. These results emphasize the role of BBS proteins in both the structure and function of motile cilia. They also invite additional scrutiny of motile cilia dysfunction in patients with this disease. Show less

Bardet-Biedl syndrome (BBS) is a genetically heterogeneous disorder that results in retinal degeneration, obesity, cognitive impairment, polydactyly, renal abnormalities, and hypogenitalism. Of the 12 known BBS genes, BBS1 is the most commonly mutated, and a single missense mutation (M390R) accounts for approximately 80% of BBS1 cases. To gain insight into the function of BBS1, we generated a Bbs1(M390R/M390R) knockin mouse model. Mice homozygous for the M390R mutation recapitulated aspects of the human phenotype, including retinal degeneration, male infertility, and obesity. The obese mutant mice were hyperphagic and hyperleptinemic and exhibited reduced locomotor activity but no elevation in mean arterial blood pressure. Morphological evaluation of Bbs1 mutant brain neuroanatomy revealed ventriculomegaly of the lateral and third ventricles, thinning of the cerebral cortex, and reduced volume of the corpus striatum and hippocampus. Similar abnormalities were also observed in the brains of Bbs2(-/-), Bbs4(-/-), and Bbs6(-/-) mice, establishing these neuroanatomical defects as a previously undescribed BBS mouse model phenotype. Ultrastructural examination of the ependymal cell cilia that line the enlarged third ventricle of the Bbs1 mutant brains showed that, whereas the 9 + 2 arrangement of axonemal microtubules was intact, elongated cilia and cilia with abnormally swollen distal ends were present. Together with data from transmission electron microscopy analysis of photoreceptor cell connecting cilia, the Bbs1 M390R mutation does not affect axonemal structure, but it may play a role in the regulation of cilia assembly and/or function. Show less

To identify and characterize gene expression changes associated with photoreceptor cell loss in a Bbs4-knockout mouse model of retinal degeneration. Differential gene expression in the eyes of 5-month-old Bbs4(-/-) mice undergoing retinal degeneration were analyzed using gene microarrays (Affymetrix, Santa Clara, CA). Elevated ocular transcripts were confirmed by Northern blotting of RNA from Bbs4(-/-) and three additional mouse models of Bardet-Biedl Syndrome (BBS). TUNEL assays and transmission electron microscopy were used to study cell death and photoreceptor morphology in these mice. Three hundred fifty-four probes were differentially expressed in Bbs4(-/-) eyes compared with controls using a twofold cutoff. Numerous vision-related transcripts decreased because of photoreceptor cell loss. Increased expression of the stress response genes Edn2, Lcn2, Serpina3n, and Socs3 was noted at 5 months of age and as early as postnatal week 4 in the eyes of four BBS mouse model strains. A burst of apoptotic activity in the photoreceptor outer nuclear layer at postnatal week 2 and highly disorganized outer segments by postnatal weeks 4 to 6 was observed in all four strains. The specific loss of photoreceptors in Bbs4(-)(/)(-) mice allows us to identify a set of genes that are preferentially expressed in photoreceptors compared with other cell types found in the eye and is a valuable resource in the continuing search for genes involved in retinal disease. The molecular and morphologic changes observed in young BBS animal model eyes implies that BBS proteins play a critical, early role in establishing the correct structure and function of photoreceptors. Show less

Bardet-Biedl syndrome (BBS) is characterized by obesity, retinopathy, polydactyly, cognitive impairment, renal and cardiac anomalies as well as hypertension and diabetes. The nine known BBS genes do not appear to belong to the same functional category; yet mutation of these genes results in a nearly identical pleiotropic phenotype. Although the precise functions of the BBS proteins have yet to be determined, current data support a role in cilia function and intraflagellar transport. To gain insight into the biological processes controlled by BBS genes, we embarked on studies of six BBS orthologues from zebrafish. Knockdown of zebrafish bbs2, bbs4, bbs5, bbs6, bbs7 or bbs8 results in disruption of Kupffer's vesicle (KV), a ciliated organ thought to play a role in left-right patterning. KV defects are due to a progressive loss of cilia within the vesicle and result in subsequent alterations to organ laterality. We also note a specific defect altering retrograde melanosome transport. These studies are the first to comprehensively compare the diverse group of BBS genes in parallel and demonstrate a common role in intracellular trafficking, indicating that BBS proteins are involved in general organelle trafficking. Show less

McKusick-Kaufman syndrome (MKS) is an autosomal recessive disorder characterized by post-axial polydactyly, congenital heart defects and hydrometrocolpos, a congenital structural abnormality of female genitalia. Mutations in the MKKS gene have also been shown to cause some cases of Bardet-Biedl syndrome (BBS) which is characterized by obesity, pigmentary retinopathy, polydactyly, renal abnormalities and hypogenitalism with secondary features of hypertension and diabetes. Although there is overlap in clinical features between MKS and BBS, MKS patients are not obese and do not develop retinopathy or have learning disabilities. To further explore the pathophysiology of BBS and the related disorder MKS, we have developed an Mkks(-/-) mouse model. This model shows that the absence of Mkks leads to retinal degeneration through apoptosis, failure of spermatozoa flagella formation, elevated blood pressure and obesity. The obesity is associated with hyperphagia and decreased activity. In addition, neurological screening reveals deficits in olfaction and social dominance. The mice do not have polydactyly or vaginal abnormalities. The phenotype of the Mkks(-/-) mice closely resembles the phenotype of other mouse models of BBS (Bbs2(-/-) and Bbs4(-/-)). These observations suggest that the complete absence of MKKS leads to BBS while the MKS phenotype is likely to be due to specific mutations. Show less

Bardet-Biedl syndrome is a genetically heterogeneous multisystem disorder that causes severe visual impairment. Retinitis pigmentosa (RP), hypogonadism, digit and renal anomalies, obesity, and a variable degree of mental retardation characterize the disorder. Eight different loci have been identified on 2q31(BBS5), 3p13 (BBS3), 4q27 (BBS7), 11q13 (BBS1), 14q32 (BBS8), 15q22.3 (BBS4), 16q21 (BBS2), and 20p12 (BBS6). The ocular manifestations of Bardet-Biedl syndrome include an early and severe rod-cone dystrophy causing legal blindness in the second decade. Features of systemic phenotypic variability were proposed to distinguish patients mapped to either the BBS2, BBS3, or BBS4 loci but no phenotype-genotype correlation has been established for the ocular phenotype. We studied the three original families used for the identification of BBS2, BBS3, and BBS4 loci to define the ocular phenotypes of patients (n = 34) and obligate carriers (n = 32) using clinical examination and electroretinography (ERG). RP was severe and early in all cases. Myopia was associated with BBS3 and BBS4, but not BBS2. One patient with Bardet-Biedl syndrome also had iris and chorioretinal colobomata, features suggestive of Biemond syndrome. Show less

Recent discoveries have lead to the hypothesis that ciliary dysfunction is a mechanism underlying the pathogenesis of Bardet-Biedl syndrome (BBS). Here, we describe two individuals with decreased olfaction who are members of an extended family affected with BBS caused by a homozygous deletion (c.77-220del) in the BBS4 gene. These findings correlate with the evidence that several BBS proteins, including BBS4, are expressed in the olfactory epithelium (OE). Although the prevalence and the spectrum of impaired olfaction in BBS are not known, the causal relationship of the BBS4 deletion in this family and the decreased olfaction is corroborated by evidence that Bbs2 and Bbs4 knockout mice have severe olfaction deficits and that also patients with BBS caused by mutations in other BBS genes can have impaired olfaction. This finding broadens the spectrum of clinical manifestations associated with BBS, confirms the role of BBS4 in olfaction, and lends support to the hypothesis that ciliary dysfunction is an important aspect of BBS pathogenesis. Show less

Bardet-Biedl syndrome (BBS) is a heterogeneous, pleiotropic human disorder characterized by obesity, retinopathy, polydactyly, renal and cardiac malformations, learning disabilities, hypogenitalism, and an increased incidence of diabetes and hypertension. No information is available regarding the specific function of BBS2. We show that mice lacking Bbs2 gene expression have major components of the human phenotype, including obesity and retinopathy. In addition, these mice have phenotypes associated with cilia dysfunction, including retinopathy, renal cysts, male infertility, and a deficit in olfaction. With the exception of male infertility, these phenotypes are not caused by a complete absence of cilia. We demonstrate that BBS2 retinopathy involves normal retina development followed by apoptotic death of photoreceptors, the primary ciliated cells of the retina. Photoreceptor cell death is preceded by mislocalization of rhodopsin, indicating a defect in transport. We also demonstrate that Bbs2(-/-) mice and a second BBS mouse model, Bbs4(-/-), have a defect in social function. The evaluation of Bbs2(-/-) mice indicates additional phenotypes that should be evaluated in human patients, including deficits in social interaction and infertility. Show less

The functions of the proteins encoded by the Bardet-Biedl syndrome (BBS) genes are unknown. Mutations in these genes lead to the pleiotropic human disorder BBS, which is characterized by obesity, retinopathy, polydactyly, renal and cardiac malformations, learning disabilities, and hypogenitalism. Secondary features include diabetes mellitus and hypertension. Recently, it has been suggested that the BBS phenotypes are the result of a lack of cilia formation or function. In this study, we show that mice lacking the Bbs4 protein have major components of the human phenotype, including obesity and retinal degeneration. We show that Bbs4-null mice develop both motile and primary cilia, demonstrating that Bbs4 is not required for global cilia formation. Interestingly, male Bbs4-null mice do not form spermatozoa flagella, and BBS4 retinopathy involves apoptotic death of photoreceptors, the primary ciliated cells of the retina. These mutation data demonstrate a connection between the function of a BBS protein and cilia. To further evaluate an association between cilia and BBS, we performed homology comparisons of BBS proteins in model organisms and find that BBS proteins are specifically conserved in ciliated organisms. Show less

Bardet-Biedl syndrome (BBS) is a pleiotropic genetic disorder with the cardinal features of obesity, photoreceptor degeneration, polydactyly, hypogenitalism, renal abnormalities, and developmental delay. Other associated clinical findings in BBS patients include diabetes, hypertension, and congenital heart defects. The clinical diagnosis is based on the presence of at least four of the cardinal symptoms. BBS is recognized to be a genetically heterogeneous autosomal recessive disorder mapping to eight known loci. Positional cloning and candidate gene evaluation have resulted in the identification of six BBS genes. Mutation of one of these genes, BBS6, also causes McKusick-Kaufman syndrome. The BBS6 gene is predicted to code for a protein with sequence similarity to the chaperonin family of proteins. The predicted BBS1, BBS2, BBS4, BBS7, and BBS8 gene products do not seem to be molecular chaperones, on the basis of a lack of sequence similarity to the chaperonin family of proteins. The identification of BBS8 suggests a possible role in cilia function for BBS gene products. It remains to be determined whether the multiple BBS proteins are part of a multisubunit complex or do not directly interact with each other but are part of a common pathway. The study of BBS illustrates the value of using isolated inbred populations for the study of human genetic diseases and suggests strategies for facilitating the study of complex diseases and traits. Show less

Bardet-Biedl syndrome (BBS) is a genetic disorder with the primary features of obesity, pigmentary retinopathy, polydactyly, renal malformations, mental retardation, and hypogenitalism. Patients with BBS are also at increased risk for diabetes mellitus, hypertension, and congenital heart disease. BBS is known to map to at least six loci: 11q13 (BBS1), 16q21 (BBS2), 3p13-p12 (BBS3), 15q22.3-q23 (BBS4), 2q31 (BBS5), and 20p12 (BBS6). Although these loci were all mapped on the basis of an autosomal recessive mode of inheritance, it has recently been suggested-on the basis of mutation analysis of the identified BBS2, BBS4, and BBS6 genes-that BBS displays a complex mode of inheritance in which, in some families, three mutations at two loci are necessary to manifest the disease phenotype. We recently identified BBS1, the gene most commonly involved in Bardet-Biedl syndrome. The identification of this gene allows for further evaluation of complex inheritance. In the present study we evaluate the involvement of the BBS1 gene in a cohort of 129 probands with BBS and report 10 novel BBS1 mutations. We demonstrate that a common BBS1 missense mutation accounts for approximately 80% of all BBS1 mutations and is found on a similar genetic background across populations. We show that the BBS1 gene is highly conserved between mice and humans. Finally, we demonstrate that BBS1 is inherited in an autosomal recessive manner and is rarely, if ever, involved in complex inheritance. Show less

To describe the phenotype of the Bardet-Biedl syndrome in patients with mutations in the BBS4 gene. We examined 3 pairs of siblings with Bardet-Biedl syndrome in whom 3 different mutations in the BBS4 gene were detected, 2 of which were homozygous for the mutation. All patients had an increased body mass index. The obesity varied between families from moderate to severe. All of the males had hypogenitalism. All had brachydactyly and similar dental anomalies. Polydactyly was present in 5 of the 6 patients. The number and location of the extra digits varied even between siblings. The intelligence varied between families and was within the normal range in 4 individuals. One male had spinal stenosis with paraparesis of his legs. Four patients had increased blood pressure, but only 1 had impaired renal function. Severe retinitis pigmentosa with onset in early childhood was present in all patients. There were few abnormal retinal pigmentary deposits even at advanced stages. The phenotype of patients with BBS4 mutations consists of severe retinitis pigmentosa, variable obesity, brachydactyly with variable polydactyly, small or missing teeth, genital hypoplasia, and cardiovascular disease. The combinations of clinical signs are mostly independent of the individual BBS4 mutation and can vary even within pairs of siblings. It is possible that there is a characteristic appearance of the ocular fundus in patients with BBS4 mutations. Show less

Bardet-Biedl syndrome (BBS, OMIM 209900) is a genetic disorder with the primary features of obesity, pigmentary retinopathy, polydactyly, renal malformations, mental retardation and hypogenitalism. Individuals with BBS are also at increased risk for diabetes mellitus, hypertension and congenital heart disease. What was once thought to be a homogeneous autosomal recessive disorder is now known to map to at least six loci: 11q13 (BBS1), 16q21 (BBS2), 3p13 p12 (BBS3), 15q22.3 q23 (BBS4), 2q31 (BBS5) and 20p12 (BBS6). There has been considerable interest in identifying the genes that underlie BBS, because some components of the phenotype are common. Cases of BBS mapping ro BBS6 are caused by mutations in MKKS; mutations in this gene also cause McKusick-Kaufman syndrome (hydrometrocolpos, post-axial polydactyly and congenital heart defects). In addition, we recently used positional cloning to identify the genes underlying BBS2 (ref. 16) and BBS4 (ref. 17). The BBS6 protein has similarity to a Thermoplasma acidophilum chaperonin, whereas BBS2 and BBS4 have no significant similarity to chaperonins. It has recently been suggested that three mutated alleles (two at one locus, and a third at a second locus) may be required for manifestation of BBS (triallelic inheritance). Here we report the identification of the gene BBS1 and show that a missense mutation of this gene is a frequent cause of BBS. In addition, we provide data showing that this common mutation is not involved in triallelic inheritance. Show less

Bardet-Biedl syndrome (BBS, MIM 209900) is a heterogeneous autosomal recessive disorder characterized by obesity, pigmentary retinopathy, polydactyly, renal malformations, mental retardation, and hypogenitalism. The disorder is also associated with diabetes mellitus, hypertension, and congenital heart disease. Six distinct BBS loci map to 11q13 (BBS1), 16q21 (BBS2), 3p13-p12 (BBS3), 15q22.3-q23 (BBS4), 2q31 (BBS5), and 20p12 (BBS6). Although BBS is rare in the general population (<1/100,000), there is considerable interest in identifying the genes causing BBS because components of the phenotype, such as obesity and diabetes, are common. We and others have demonstrated that BBS6 is caused by mutations in the gene MKKS (refs. 12,13), mutation of which also causes McKusick-Kaufman syndrome (hydrometrocolpos, post-axial polydactyly, and congenital heart defects). MKKS has sequence homology to the alpha subunit of a prokaryotic chaperonin in the thermosome Thermoplasma acidophilum. We recently identified a novel gene that causes BBS2. The BBS2 protein has no significant similarity to other chaperonins or known proteins. Here we report the positional cloning and identification of mutations in BBS patients in a novel gene designated BBS4. Show less

Bardet-Biedl Syndrome (BBS) is a heterogeneous, autosomal recessive disorder characterized by mental retardation, obesity, retinitis pigmentosa, syndactyly and/or polydactyly, short stature, and hypogenitalism and is caused by mutations at a number of distinct loci. Using a positional cloning approach for identifying the BBS4 (chromosome 15) gene, we identified and cloned an unconventional myosin gene, myosin IXA (HGMW-approved symbol MYO9A). Since mutations in unconventional myosins are known to cause several human diseases, and since mutations of unconventional myosin VIIa cause retinal degeneration, we evaluated myosin IXA as a candidate for BBS. We exploited PCR-based techniques to clone a 8473-nt cDNA for myosin IXA. A 7644-bp open reading frame predicts a protein with all the hallmarks of class IX unconventional myosins. Human Northern blot analysis and in situ hybridization of mouse embryos reveal that myosin IXA is expressed in many tissues consistent with BBS. Intron/exon boundaries were identified, and myosin IXA DNA and RNA from BBS4 patients were evaluated for mutation. Show less