Human DCTN1: genomic structure and evaluation as a candidate for Alström syndrome

NMR resonance assignment and structure prediction of the C-terminal domain of the microtubule end-binding protein 3

End-binding proteins (EBs) associate with the growing microtubule plus ends to regulate microtubule dynamics as well as the interaction with intracellular structures. EB3 contributes to pathological vascular leakage through interacting with the inositol 1,4,5-trisphosphate receptor 3 (IP₃R3), a calcium channel located at the endoplasmic reticulum membrane. The C-terminal domain of EB3 (residues 200–281) is functionally important for this interaction because it contains the effector binding sites, a prerequisite for EB3 activity and specificity. Structural data for this domain is limited. Here, we report the backbone chemical shift assignments for the human EB3 C-terminal domain and computationally explore its EB3 conformations. Backbone assignments, along with computational models, will allow future investigation of EB3 structural dynamics, interactions with effectors, and will facilitate the development of novel EB3 inhibitors.

Fat aussie--a new Alström syndrome mouse showing a critical role for ALMS1 in obesity, diabetes, and spermatogenesis

Mutations in the human ALMS1 gene are responsible for Alström syndrome, a disorder in which key metabolic and endocrinological features include childhood-onset obesity, metabolic syndrome, and diabetes, as well as infertility. ALMS1 localizes to the basal bodies of cilia and plays a role in intracellular trafficking, but the biological functions of ALMS1 and how these relate to the pathogenesis of obesity, diabetes, and infertility remain unclear. Here we describe a new mouse model of Alström syndrome, fat aussie, caused by a spontaneous mutation in the Alms1 gene. Fat aussie (Alms1 foz/foz) mice are of normal weight when young but, by 120 d of age, they become obese and hyperinsulinemic. Diabetes develops in Alms1 foz/foz mice accompanied by pancreatic islet hyperplasia and islet cysts. Female mice are fertile before the onset of obesity and metabolic syndrome; however, male fat aussie mice are sterile due to a progressive germ cell loss followed by an almost complete block of development at the round-to-elongating spermatid stage of spermatogenesis. In conclusion, Alms1 foz/foz mouse is a new animal model in which to study the pathogenesis of the metabolic and fertility defects of Alström syndrome, including the role of ALMS1 in appetite regulation, pathogenesis of the metabolic syndrome, pancreatic islet physiology, and spermatogenesis.

A mild form of Alstrom disease associated with metabolic syndrome and very high fasting serum free fatty acids: two cases diagnosed in adult age

Alstrom syndrome (ALMS) is a very rare genetic autosomal recessive disease, characterized by early-onset severe abdominal obesity, impaired glucose tolerance or type 2 diabetes with insulin resistance, acanthosis nigricans, hyperlipidemia, childhood progressive retinal degeneration or retinitis pigmentosa and neurosensory hearing loss or deafness, cardiomyopathy, and other endocrine disorders. Genetic studies locate the ALMS gene on chromosome 2p12-13. The aim of this paper is to describe and discuss two unrelated cases of a mild ALMS form diagnosed after the age of 40 and 60, respectively, in adult fertile female patients. These cases showed several features of the disease plus other alterations characteristic of the classic "metabolic syndrome," including hypertension, hyperfibrinogenemia, and thrombotic states. Moreover, the patients had very high fasting serum free fatty acid (FFA) levels (2150 and 1919 micromol/L, respectively), which proved to be sensitive to inhibition by oral glucose tolerance test (OGTT)-induced hyperinsulinemia as well as to caloric restriction. ALMS may have an adverse prognosis and is often underdiagnosed. Its mild form, which allows a long survival, may also be associated with the late complications of the metabolic syndrome, leading to increased vascular risk.

Characterization of functional domains of human EB1 family proteins

EB1 family proteins are evolutionarily conserved proteins that bind microtubule plus-ends and centrosomes and regulate the dynamics and organization of microtubules. Human EB1 family proteins, which include EB1, EBF3, and RP1, also associate with the tumor suppressor protein adenomatous polyposis coli (APC) and p150glued, a component of the dynactin complex. The structural basis for interaction between human EB1 family proteins and their associated proteins has not been defined in detail. EB1 family proteins have a calponin homology (CH) domain at their N terminus and an EB1-like C-terminal motif at their C terminus; the functional importance of these domains has not been determined. To better understand functions of human EB1 family proteins and to reveal functional similarities and differences among these proteins, we performed detailed characterizations of interactions between human EB1 family proteins and their associated proteins. We show that amino acids 1-133 of EB1 and EBF3 and the corresponding region of RP1, which contain a CH domain, are necessary and sufficient for binding microtubules, thus demonstrating for the first time that a CH domain contributes to binding microtubules. EB1 family proteins use overlapping but different regions that contain the EB1-like C-terminal motif to associate with APC and p150glued. Neither APC nor p150glued binding domain is necessary for EB1 or EBF3 to induce microtubule bundling, which requires amino acids 1-181 and 1-185 of EB1 and EBF3, respectively. We also determined that the EB1 family protein-binding regions are amino acids 2781-2820 and 18-111 of APC and p150glued, respectively.

Crystal structure of the cytoskeleton-associated protein glycine-rich (CAP-Gly) domain

Cytoskeleton-associated proteins (CAPs) are involved in the organization of microtubules and transportation of vesicles and organelles along the cytoskeletal network. A conserved motif, CAP-Gly, has been identified in a number of CAPs, including CLIP-170 and dynactins. The crystal structure of the CAP-Gly domain of Caenorhabditis elegans F53F4.3 protein, solved by single wavelength sulfur-anomalous phasing, revealed a novel protein fold containing three beta-sheets. The most conserved sequence, GKNDG, is located in two consecutive sharp turns on the surface, forming the entrance to a groove. Residues in the groove are highly conserved as measured from the information content of the aligned sequences. The C-terminal tail of another molecule in the crystal is bound in this groove.

Evaluation of insulin resistant diabetes mellitus in Alström syndrome: a long-term prospective follow-up of three siblings

Alström syndrome is a rare cause of diabetes mellitus. We studied two generations of a Turkish family in whom four members were affected by Alström syndrome. The natural course of the syndrome in three sisters was followed for 13 yr. The three sisters had short stature and truncal obesity, and developed complete blindness due to retinitis pigmentosa at 10, 5 and 13 yr of age. Two had sensorineural hearing loss and mild mental retardation, while the other developed diabetic ketoacidosis (DKA) at 14 yr and was treated with insulin from onset of diabetes. In the second case, diagnosis of diabetes was made by an OGTT at age 20 yr, and controlled with diet alone for 11 yr, then with a sulphonylurea for 2.5 yr, then with insulin. The third case developed acute hyperglycaemia at 20 yr, and required insulin from onset. Moreover, transitional features of impaired carbohydrate and fat metabolism (severe hyperinsulinaemia and insulin resistance progressing to islet beta cell failure, and hypertriglyceridaemia with fatty liver) were demonstrated, in accord with the literature. Previously unreported findings characteristic of nephro-uropathy with early-onset hypertension were also detected, and included in all cases proteinuria, glomerulopathy, and abnormal locations of the kidneys, narrowed uretero-renal junctions and dilated ureters.

Mutation of ALMS1, a large gene with a tandem repeat encoding 47 amino acids, causes Alström syndrome

Alström syndrome (OMIM 203800) is an autosomal recessive disease, characterized by cone-rod retinal dystrophy, cardiomyopathy and type 2 diabetes mellitus, that has been mapped to chromosome 2p13 (refs 1-5). We have studied an individual with Alström syndrome carrying a familial balanced reciprocal chromosome translocation (46, XY,t(2;11)(p13;q21)mat) involving the previously implicated critical region. We postulated that this individual was a compound heterozygote, carrying one copy of a gene disrupted by the translocation and the other copy disrupted by an intragenic mutation. We mapped the 2p13 breakpoint on the maternal allele to a genomic fragment of 1.7 kb which contains exon 4 and the start of exon 5 of a newly discovered gene (ALMS1); we detected a frameshift mutation in the paternal copy of the gene. The 12.9-kb transcript of ALMS1 encodes a protein of 4,169 amino acids whose function is unknown. The protein contains a large tandem-repeat domain comprising 34 imperfect repetitions of 47 amino acids. We have detected six different mutations (two nonsense and four frameshift mutations causing premature stop codons) in seven families, confirming that ALMS1 is the gene underlying Alström syndrome. We believe that ALMS1 is the first human disease gene characterized by autosomal recessive inheritance to be identified as a result of a balanced reciprocal translocation.

Characterization of the murine Lbx2 promoter, identification of the human homologue, and evaluation as a candidate for Alström syndrome

The murine Lbx2 gene is a member of the ladybird family of homeobox genes, which is expressed in the developing urogenital system, eye, and brain. Using transgenic mice, we demonstrate that 9 kb of the 5' flanking region of mouse Lbx2 is able to direct expression of a reporter gene in a tissue-specific manner recapitulating the endogenous expression pattern. This regulatory region provides a novel reagent allowing for transgenic expression in the developing urogenital ridge. In addition, we describe the identification of the human homologue, LBX2. Comparison of the human LBX2 and mouse Lbx2 sequences upstream of the coding regions reveals sequence conservation suggesting conserved regulatory regions. Both the human LBX2 and the mouse Lbx2 genes have similar genomic structures and are composed of two exons separated by an intron. We mapped the mouse Lbx2 gene to 35 cM on chromosome 6 and the human LBX2 gene to a homologous region of chromosome 2p13. This is a candidate region for several inherited disorders, including Alström syndrome, a disorder that includes ocular, urogenital, and renal abnormalities. Given the expression pattern of Lbx2, the chromosomal location in humans, and the potential function of mammalian ladybird genes, we have begun to analyze patients with ocular disorders and those with Alström syndrome for mutations in LBX2. Although polymorphisms were identified, our results indicate that mutations in the coding region of LBX2 do not account for Alström syndrome in the six kindreds analyzed.