Molecular characterization of a novel tubby gene family member, TULP3, in mouse and humans

Tubby and related proteins are derived from a small family of novel genes. The carboxytermini of this family are highly conserved across a number of species including humans, mice, Caenorhabditis elegans, Arabidopsis, rice, and maize. Splicing defects in both tub and another member of the gene family, TULP1 (tubby-like protein 1), lead to phenotypes of retinal degeneration in mice and humans, respectively. We describe here the isolation of the human and mouse homologs of a new family member, TULP3. The cDNAs code for proteins of 442 and 460 amino acids, respectively. The level of identity between the human TULP3 and the mouse homolog is 69%, lower than that observed for the homologs of the other family members (96% for human and mouse TUB), and is higher at the amino- and carboxytermini than in the central region of the protein. Phylogenetically, TULP3 is the family member most closely related to TUB. Also, like TUB, it has a wider pattern of tissue expression than either TULP1 or TULP2. TULP3 is detected at high levels in human RNA from testis, ovaries, thyroid, and spinal chord. Tulp3 is also highly expressed in mouse RNA from eyes and adipose depots, tissues not tested in the human Northern analysis. We also report that TULP3 maps to human chromosome 12p13. The murine homolog, Tulp3, maps to the telomere of mouse chromosome 6.

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

The human dynactin 1 gene (DCTN1) is positioned on chromosome 2p13, the candidate region for various diseases including Alström syndrome, limb-girdle muscle dystrophy, and Miyoshi myopathy. Here, we report the exon-intron structure of DCTN1 along with characterization of the 5' upstream sequence and alternative splice variants previously identified by Tokito et al. (1996), Mol. Biol. Cell 7: 1167-1180). Knowledge of the genomic structure of DCTN1allowed us to design intronic primers necessary for analyzing mutations in families segregating for diseases linked to this gene. These primers were tested on a French Acadian kindred segregating for Alström syndrome. No mutations were observed within the coding region of DCTN1 in this family. However, the intronic primers should allow for the rapid amplification of the coding region for mutational analysis of additional Alström families and other diseases tightly linked to the DCTN1locus on chromosome 2p13.

Cloning and expression analysis of mouse Cclp1, a new gene encoding a coiled-coil-like protein

Here we describe the nucleotide sequence and expression pattern of a novel gene termed Coiled-coil-like protein 1 (Cclp1). A 2646bp open reading frame encodes a 882 amino acid protein with a predicted coiled-coil domain at the amino terminus. Cclp1 is expressed in a variety of adult tissues and during different stages of embryogenesis. The broad expression pattern suggests a general cellular function of CCLP1.

The atherogenic lipoprotein phenotype is not caused by a mutation in the coding region of the low density lipoprotein receptor gene

The atherogenic lipoprotein phenotype (ALP) is a common heritable trait characterized by a predominance of small, dense low density lipoprotein particles (subclass pattern B), increased levels of triglyceride-rich lipoproteins, reductions in high density lipoproteins, and an increased risk for myocardial infarction. In a previous linkage study of 11 families, evidence for tight linkage of subclass pattern B with the LDL receptor (LDLR) locus on chromosome 19p13.2 was obtained. To test whether a mutation in the structural portion of the LDLR gene could be responsible for the phenotype, we first sequenced the exons of the receptor binding domain for each pair of parents in these 11 pedigrees. For the remaining portion of the LDLR coding region, exons as well as cloned LDLR cDNAs were sequenced for selected members of the pedigrees. No mutations that changed the amino acid sequence of the LDLR were found. We conclude that it is unlikely that a mutant allele of the LDLR protein is responsible for ALP.

Molecular characterization of TUB, TULP1, and TULP2, members of the novel tubby gene family and their possible relation to ocular diseases

Tubby, an autosomal recessive mutation, mapping to mouse chromosome 7, was recently found to be the result of a splicing defect in a novel gene with unknown function. Database searches revealed that sequences corresponding to the C terminus of the tub protein were highly conserved across a number of species including humans, mice, Caenorhabditis elegans, Arabidopsis, rice, and maize, and that tub was a member of a gene family. We describe here, TUB, the human homolog of mouse tub, and two newly characterized family members, TULP1 for tubby like protein 1 and TULP2. These three family members, which differ in the N-terminal half of the protein, share 60-90% amino acid identity across their conserved C-terminal region and have distinct tissue expression patterns. Alternatively spliced transcripts with 5' variable sequences, three of which have been identified for the tubby gene, may mediate tissue specific expression. We also report that TUB, TULP1, and TULP2 map to human chromosomes 11p15.4, 6p21.3, and 19q13.1, respectively. TULP1 and TULP2 map within the minimal intervals identified for retinitis pigmentosa 14 on chromosome 6p21.3 and cone-rod dystrophy on chromosome 19q13.1. TULP1 and TULP2, which are expressed in the retina, make excellent candidates for these ocular diseases as a mutation within the tub gene is known to lead to early progressive retinal degeneration.

Physical and genetic mapping of novel microsatellite polymorphisms on human chromosome 19

We describe here the identification of 11 novel microsatellite polymorphisms on human chromosome 19. These dinucleotide repeat polymorphisms were detected in chromosome 19-specific cosmids that were physically mapped by fluorescence in situ hybridization. For each repeat, flanking oligonucleotide primers were synthesized and the polymerase chain reaction assay was performed on a panel of 100 unrelated individuals to determine the heterozygosity and allele frequencies. To characterize these markers further, genetic and radiation hybrid maps were constructed. These microsatellite polymorphisms will be valuable in further linkage analysis of inherited diseases on chromosome 19p.

A candidate gene for the mouse mutation tubby

A mutation in the tub gene causes maturity-onset obesity, insulin resistance, and sensory deficits. In contrast to the rapid juvenile-onset weight gain seen in diabetes (db) and obese (ob) mice, obesity in tubby mice develops gradually, and strongly resembles the late-onset obesity seen in the human population. Excessive deposition of adipose tissue eventually leads to a twofold increase of body weight. Tubby mice also suffer retinal degeneration and neurosensory hearing loss. The tripartite character of the tubby phenotype shows striking similarity to human obesity syndromes, such as Alström and Bardet-Biedl. Here we report the identification of a G --> T transversion in a candidate gene that abolishes a donor splice site in the 3' coding region and results in a larger transcript containing the unspliced intron. This alteration is predicted to replace the 44-carboxyterminal amino acids with a 20-amino-acid sequence not found in the wide-type protein. Additionally, a second, prematurely truncated transcript with the unspliced intron is observed in testis messenger RNA and a 2-3-fold increase in brain mRNA is observed in tubby mice compared to B6. The phenotype features of tubby mice may be the result of cellular apoptosis triggered by expression of the mutuated tub gene.

Hyperproinsulinaemia in obese fat/fat mice associated with a carboxypeptidase E mutation which reduces enzyme activity

Mice homozygous for the fat mutation develop obesity and hyperglycaemia that can be suppressed by treatment with exogenous insulin. The fat mutation maps to mouse chromosome 8, very close to the gene for carboxypeptidase E (Cpe), which encodes an enzyme (CPE) that processes prohormone intermediates such as proinsulin. We now demonstrate a defect in proinsulin processing associated with the virtual absence of CPE activity in extracts of fat/fat pancreatic islets and pituitaries. A single Ser202Pro mutation distinguishes the mutant Cpe allele, and abolishes enzymatic activity in vitro. Thus, the fat mutation represents the first demonstration of an obesity-diabetes syndrome elicited by a genetic defect in a prohormone processing pathway.

Atherosclerosis in genetically obese mice: the mutants obese, diabetes, fat, tubby, and lethal yellow

Mice with five different mutations conferring an obese or diabetic phenotype were evaluated for fatty streak lesions after consuming an atherogenic diet containing 15% fat and 1.25% cholesterol (wt/wt) for 14 weeks. The five mutations, fat, obese, tubby, diabetes, and lethal yellow, are maintained as congenic strains with C57BL/6J (B6) or C57BL/KsJ (BKs) as genetic backgrounds. None of the mutants exhibited accelerated fatty streak lesion formation; the mutant fat had aortic lesions comparable in size to those of its control strain, and the mutants obese, diabetes, tubby, and lethal yellow had significantly reduced lesion area in comparison to controls. Although B6 and BKs are closely related strains, we observed that the BKs strain was more prone to early-stage atherogenesis. Fatty streak lesion area was twice as large in BKs mice than those found in B6 mice; likewise, in comparison, the mutants obese and diabetes had larger lesions if they were carried as congenic strains in the BKs rather than the B6 genetic background. Plasma triglycerides, total cholesterol, high-density lipoprotein cholesterol (HDL-C), and combined low-density and very-low-density lipoprotein cholesterol (LDL-C and VLDL) levels were also measured in the mice. Lipid profiles differed among the mutant mice, but in general, elevations in plasma total cholesterol, triglycerides, and HDL-C were observed. Whereas the hypertriglyceridemia and hypercholesterolemia are consistent with an atherogenic lipid profile, HDL-C levels, which are normally decreased in individuals with non-insulin-dependent diabetes mellitus, were increased in the mouse mutants.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of dietary fats from animal and plant sources on diet-induced fatty streak lesions in C57BL/6J mice

This study was designed to determine the effects of a variety of naturally occurring saturated fats on aortic lesion formation in C57BL/6J mice that are susceptible to diet-induced fatty streak lesions. Groups of female mice were randomly assigned to one of seven treatment groups and were fed diets containing 15% (w/w) hydrogenated coconut oil, hydrogenated soy oil, hydrogenated palm oil, cocoa butter, lard, tallow, or dairy butter, 1% cholesterol, and 0.5% cholic acid. Plasma lipid levels were measured to determine whether lesion formation was related to specific changes in these parameters. Lesions, which were observed in all groups of mice, ranged from 420 to 3220 microns2/aortic cross section. Lesion area was positively correlated to the percentage of saturated fatty acids contained in the fat sources and the ratio of combined VLDL plus LDL-cholesterol to HDL-cholesterol and inversely correlated to monounsaturated fatty acids content and to HDL-cholesterol levels. Results from this study demonstrate that inbred mice may provide a good model for dissecting the genetic basis for the differential atherogenic responses to diet-induction and for studying the effects of dietary factors on aortic lesion development.

Strain distribution pattern in AXB and BXA recombinant inbred strains for loci on murine chromosomes 10, 13, 17, and 18

Strain distribution patterns (SDPs) of selected loci previously mapped to murine Chromosomes (Chrs) 10, 13, 17, and 18 are reported for the AXB, BXA recombinant inbred (RI) strain set derived from the progenitor strains A/J (A) and C57BL/6J (B). The loci included the simple sequence length polymorphisms (D10Nds1, D10Mit2, D10Mit10, D10Mit14, D13Mit3, D13Nds1, D13Mit10, D13Mit13, D13Mit7, D13Mit11, D17Mit18, D17Mit10, D17Mit20, D17Mit3, D17Mit2, D18Mit17, D18Mit9, and D18Mit4), the restriction fragment length polymorphisms Pdea and Csfmr, and the biochemical marker AS-1. These loci were chosen because they map to genomic regions that had few or no genetic markers in the AXB, BXA RI set. Several of these loci also were typed in backcross progeny of matings of the (AXB)F1 to strain A or B. The strain distribution patterns for chromosomes 10, 13, 17, and 18 are reported, and the gene order and map distances determined from the backcross data. The addition of these markers to the AXB, BXA RI strain set increases the genomic region over which linkage for new markers can be detected.

Linkage of atherogenic lipoprotein phenotype to the low density lipoprotein receptor locus on the short arm of chromosome 19

The atherogenic lipoprotein phenotype (ALP) is a common heritable trait characterized by a predominance of small, dense low density lipoprotein (LDL) particles (subclass pattern B), increased levels of triglyceride-rich lipoproteins, reductions in high density lipoprotein, and a 3-fold increased risk of myocardial infarction. Significant two-point linkage was found between ALP and the LDL receptor locus on the short arm of chromosome 19 in 51 relatives of nine probands with ALP pattern B. The maximum logarithm of odds (LOD) score of 4.07 was observed at a recombination fraction of 0.04, assuming 100% penetrance of ALP pattern B, and 4.27 at a recombination fraction of zero, assuming 90% penetrance of pattern B. Haplotyping data and multipoint linkage analysis suggest that the gene [named ATHS for atherosclerosis susceptibility (lipoprotein-associated)] responsible for ALP is located distal to D19S76 near or at the LDL receptor locus. This result suggests the possibility that genetic variation at the LDL receptor locus or a closely linked locus on chromosome 19 may be responsible for metabolic alterations in ALP pattern B that account for a substantial proportion of the familial predisposition to coronary artery disease in the general population.

PCR assay for a polymorphic PvuII site in the LPL gene

Images