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Ikeda S, Ikeda A, Naggert JK, Nishina PM. Towards understanding the function of the tubby gene family in the retina. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2004; 533:309-14. [PMID: 15180278 DOI: 10.1007/978-1-4615-0067-4_38] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/29/2023]
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77
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Mehalow AK, Kameya S, Smith RS, Hawes NL, Denegre JM, Young JA, Bechtold L, Haider NB, Tepass U, Heckenlively JR, Chang B, Naggert JK, Nishina PM. CRB1 is essential for external limiting membrane integrity and photoreceptor morphogenesis in the mammalian retina. Hum Mol Genet 2003; 12:2179-89. [PMID: 12915475 DOI: 10.1093/hmg/ddg232] [Citation(s) in RCA: 272] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Mutations within the CRB1 gene have been shown to cause human retinal diseases including retinitis pigmentosa and Leber congenital amaurosis. We have recently identified a mouse model, retinal degeneration 8 (rd8) with a single base deletion in the Crb1 gene. This mutation is predicted to cause a frame shift and premature stop codon which truncates the transmembrane and cytoplasmic domain of CRB1. Like in Drosophila crumbs (crb) mutants, staining for adherens junction proteins known to localize to the external limiting membrane, the equivalent of the zonula adherens in the mammalian retina, is discontinuous and fragmented. Shortened photoreceptor inner and outer segments are observed as early as 2 weeks after birth, suggesting a developmental defect in these structures rather than a degenerative process. Photoreceptor degeneration is observed only within regions of retinal spotting, which is seen predominantly in the inferior nasal quadrant of the eye, and is caused by retinal folds and pseudorosettes. Photoreceptor dysplasia and degeneration in Crb1 mutants strongly vary with genetic background, suggesting that the variability in phenotypes of human patients that carry mutations in CRB1 may be due to interactions with background modifiers in addition to allelic variations. The Crb1rd8 mouse model will facilitate the analysis of Crb1 function in the neural retina and the identification of interacting factors as candidate retinal disease genes.
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Ikeda S, Cunningham LA, Boggess D, Hawes N, Hobson CD, Sundberg JP, Naggert JK, Smith RS, Nishina PM. Aberrant actin cytoskeleton leads to accelerated proliferation of corneal epithelial cells in mice deficient for destrin (actin depolymerizing factor). Hum Mol Genet 2003; 12:1029-37. [PMID: 12700171 DOI: 10.1093/hmg/ddg112] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Corneal disease is the most common cause of bilateral blindness in the world. Visual loss in this condition is often due to changes in morphology and function of the corneal epithelial surface. Corneal disease-1 (corn1) and corn1(2J) are spontaneous mouse mutants that develop irregular thickening of the corneal epithelium, similar to that observed in human corneal surface disease. These autosomal-recessive mutations cause an increase in the rate of proliferation of the corneal epithelial cells. Here, we report that the phenotypes in both mutants are caused by mutations within the destrin gene (also known as actin-depolymerizing factor). By positional cloning, we identified a deletion encompassing the entire coding sequence of the destrin gene in corn1 mice, and a point mutation (Pro106Ser) in the coding sequence of destrin in corn1(2J) mice. In situ analysis showed that destrin is highly expressed in the corneal epithelium. Consistent with the cellular roles for destrin, an essential regulator of actin filament turnover that acts by severing and enhancing depolymerization of actin filament, we observed that the corn1 mutations increased the content of filamentous actin in corneal epithelial cells. Our results suggest an in vivo connection between remodeling of the actin cytoskeleton and the control of cell proliferation, and a new pathway through which an aberrant actin cytoskeleton can cause epithelial hyperproliferation.
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Kim JH, Taylor PN, Young D, Karst SY, Nishina PM, Naggert JK. New leptin receptor mutations in mice: Lepr(db-rtnd), Lepr(db-dmpg) and Lepr(db-rlpy). J Nutr 2003; 133:1265-71. [PMID: 12730408 DOI: 10.1093/jn/133.5.1265] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Three new spontaneous recessive mouse mutations in the leptin receptor gene (Lepr), Lepr(db-rtnd), Lepr(db-dmpg) and Lepr(db-rlpy), originated in the CBA/J (CBA), B10.D2-H8(b)(57N)/Sn (B10) and NU/J strains, respectively. Lepr(db-rtnd) and Lepr(db-dmpg) were maintained on C57BL/6J (B6), resulting in congenic lines of B6.CBA-Lepr(db-rtnd) and B6.B10-Lepr(db-dmpg). Lepr(db-rtnd) was also maintained on CBA post F1 generation of a cross between the B6 and the CBA, generating the congenic line CBA.B6CBA-Lepr(db-rtnd). Lepr(db-rlpy) was maintained as a coisogenic strain. The aims of this study were to determine the molecular bases for these new Lepr mutations and to characterize the new mutant stocks, with respect to obesity and diabetes. Mutations were analyzed by Southern blot analysis, reverse transcriptase-polymerase chain reaction and sequencing. Body weights and plasma glucose and insulin levels were measured, and the histology of the pancreas was carried out. Lepr(db-rtnd) contained one G deletion in exon 4 of Lepr, introducing a frameshift and premature termination. Lepr(db-dmpg) had a deletion in the extracellular domain of LEPR: Lepr(db-rlpy) exhibited a large DNA deletion, leading to a complete lack of LEPR: All three mutations led to morbid obesity and diabetes. It is noteworthy that Lepr(db-rtnd) caused milder hyperglycemia accompanied by higher plasma and pancreatic insulin contents on B6 compared to that on CBA backgrounds. In summary, we discovered three new mutations of Lepr, providing new mouse models for obesity and diabetes. Furthermore, our mutant stocks will be useful in elucidating the effects of the genetic background on the Lepr mutations and in testing the specificity of antibodies to LEPR.
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Kameya S, Hawes NL, Chang B, Heckenlively JR, Naggert JK, Nishina PM. Mfrp, a gene encoding a frizzled related protein, is mutated in the mouse retinal degeneration 6. Hum Mol Genet 2002; 11:1879-86. [PMID: 12140190 DOI: 10.1093/hmg/11.16.1879] [Citation(s) in RCA: 86] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The autosomal recessive mouse mutation retinal degeneration 6 (rd6) causes small, white retinal spots and progressive photoreceptor degeneration similar to that observed in human flecked retinal diseases. Using a positional cloning approach, we determined that rd6 mice carry a splice donor mutation in the mouse homolog of the human membrane-type frizzled-related protein (Mfrp) gene that results in the skipping of exon 4. We found that mRNA of Mfrp is predominantly expressed in the eye, and at a lower level in the brain. To determine where in the eye Mfrp is expressed, in situ hybridization was done and showed that Mfrp is expressed specifically in the retinal pigment epithelium (RPE) and ciliary epithelium of the eye. The deduced amino acid sequence of MFRP contains a region with similarities to the cysteine-rich domain (CRD) of frizzled, a gene originally found in Drosophila that controls tissue polarity. The CRD is essential for Wnt binding and signaling. Wnt signaling has been shown to be involved in the control of gene expression, cell adhesion, planar polarity, proliferation and apoptosis. We also observed the localization of Wnt family proteins in the apical membrane of the RPE. Our results provide genetic evidence for an involvement of the Mfrp gene expressed by RPE in the degeneration of photoreceptors.
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81
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Abstract
The identification of 'disease genes' and the mutations within them has greatly enhanced our understanding of normal function in the eye and ear. At the same time, it has become clear that these single-gene mutations must reside in a permissive genetic background for a disease phenotype to manifest. Segregating background genes can also modify the age of onset, rate of progression or severity of these diseases. These background genes that interact with the disease mutation and that are responsible for the specific phenotypes observed are commonly called genetic modifiers. Identification of these modifier genes may define the biological pathways that lead from the primary genetic defect to the aberrant phenotype. Once the identities of modifier genes that suppress vision or hearing loss become known, the door opens to new potential therapeutic targets, since these modifier genes may be more amenable to treatment than the primary mutant gene.
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82
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Collin GB, Marshall JD, Ikeda A, So WV, Russell-Eggitt I, Maffei P, Beck S, Boerkoel CF, Sicolo N, Martin M, Nishina PM, Naggert JK. Mutations in ALMS1 cause obesity, type 2 diabetes and neurosensory degeneration in Alström syndrome. Nat Genet 2002; 31:74-8. [PMID: 11941369 DOI: 10.1038/ng867] [Citation(s) in RCA: 251] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Alström syndrome is a homogeneous autosomal recessive disorder that is characterized by childhood obesity associated with hyperinsulinemia, chronic hyperglycemia and neurosensory deficits. The gene involved in Alström syndrome probably interacts with genetic modifiers, as subsets of affected individuals present with additional features such as dilated cardiomyopathy, hepatic dysfunction, hypothyroidism, male hypogonadism, short stature and mild to moderate developmental delay, and with secondary complications normally associated with type 2 diabetes, such as hyperlipidemia and atherosclerosis. Our detection of an uncharacterized transcript, KIAA0328, led us to identify the gene ALMS1, which contains sequence variations, including four frameshift mutations and two nonsense mutations, that segregate with Alström syndrome in six unrelated families. ALMS1 is ubiquitously expressed at low levels and does not share significant sequence homology with other genes reported so far. The identification of ALMS1 provides an entry point into a new pathway leading toward the understanding of both Alström syndrome and the common diseases that characterize it.
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Abstract
Mice that carry the recessive mutation tub develop neurosensory defects including retinal and cochlear degeneration, as well as maturity-onset obesity associated with insulin resistance. The biological function of the gene and the mechanism by which it induces its phenotypes are still unclear. In order to elucidate the pathways through which tub functions, in the current study, QTL modifiers were identified in an F2 intercross between (C57BL/6J- tub/tub and AKR/J-+/+) F1 hybrids (AKR intercross). The thickness of the outer nuclear layer of the retina and the number of photoreceptor nuclei were assessed in F2 mice homozygous for the tub mutation. A genome-wide scan revealed a significant linkage on chromosome 11 (named motr1) and two suggestive linkages on chromosomes 2 and 8. Interestingly, the same chromosome 2 region identified for the hearing modifier of tubby, the moth1 locus, showed a peak lod score of 2.3 for protection from retinal degeneration. This result suggests that the gene responsible for the QTL on chromosome 2 might be involved in a common pathway through which retinal and cochlear degeneration are induced in tubby mice.
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84
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Ikeda A, Zheng QY, Zuberi AR, Johnson KR, Naggert JK, Nishina PM. Microtubule-associated protein 1A is a modifier of tubby hearing (moth1). Nat Genet 2002; 30:401-5. [PMID: 11925566 PMCID: PMC2862212 DOI: 10.1038/ng838] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Once a mutation in the gene tub was identified as the cause of obesity, retinal degeneration and hearing loss in tubby mice, it became increasingly evident that the members of the tub gene family (tulps) influence maintenance and function of the neuronal cell lineage. Suggested molecular functions of tubby-like proteins include roles in vesicular trafficking, mediation of insulin signaling and gene transcription. The mechanisms through which tub functions in neurons, however, have yet to be elucidated. Here we report the positional cloning of an auditory quantitative trait locus (QTL), the modifier of tubby hearing 1 gene (moth1), whose wildtype alleles from strains AKR/J, CAST/Ei and 129P2/OlaHsd protect tubby mice from hearing loss. Through a transgenic rescue experiment, we verified that sequence polymorphisms in the neuron-specific microtubule-associated protein 1a gene (Mtap1a) observed in the susceptible strain C57BL/6J (B6) are crucial for the hearing-loss phenotype. We also show that these polymorphisms change the binding efficiency of MTAP1A to postsynaptic density molecule 95 (PSD95), a core component in the cytoarchitecture of synapses. This indicates that at least some of the observed polymorphisms are functionally important and that the hearing loss in C57BL/6J-tub/tub (B6-tub/tub) mice may be caused by impaired protein interactions involving MTAP1A. We therefore propose that tub may be associated with synaptic function in neuronal cells.
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MESH Headings
- Adaptor Proteins, Signal Transducing
- Alleles
- Animals
- Cell Line
- Cloning, Molecular
- DNA, Complementary/metabolism
- Disks Large Homolog 4 Protein
- Gene Library
- Genetic Markers
- Guanylate Kinases
- Immunoblotting
- Insulin/metabolism
- Intracellular Signaling Peptides and Proteins
- Membrane Proteins
- Mice
- Mice, Inbred C57BL
- Mice, Transgenic
- Microscopy, Fluorescence
- Microtubule-Associated Proteins/genetics
- Microtubule-Associated Proteins/metabolism
- Microtubule-Associated Proteins/physiology
- Models, Genetic
- Nerve Tissue Proteins/genetics
- Nerve Tissue Proteins/metabolism
- Nerve Tissue Proteins/physiology
- Neurons/metabolism
- Phenotype
- Polymorphism, Genetic
- Precipitin Tests
- Protein Binding
- Protein Structure, Tertiary
- Proteins/genetics
- Quantitative Trait, Heritable
- Reverse Transcriptase Polymerase Chain Reaction
- Signal Transduction
- Synapses/metabolism
- Transcription, Genetic
- Transgenes
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85
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Ikeda A, Nishina PM, Naggert JK. The tubby-like proteins, a family with roles in neuronal development and function. J Cell Sci 2002; 115:9-14. [PMID: 11801719 DOI: 10.1242/jcs.115.1.9] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The identification of a mutation at the tubby (Tub) locus, which causes obesity and neurosensory degeneration, led to the discovery of the tubby-like proteins (TULPs). Tub and the genes that encode three tubby-like proteins (TULP1- TULP3) form a novel, small gene family that plays an important role in maintenance and function of neuronal cells during development and post-differentiation. Although exploration of the molecular function of these genes is still in its infancy, recent biochemical studies have provided ‘entry points’ into pathways whose elucidation will further our understanding of TULP action. In addition, mRNA expression and translocation of the TUB protein have been shown to be regulated by thyroid hormone and by G-protein-coupled receptor signaling, respectively. These latter findings may help to link the cellular function of TUB to known mechanisms for energy homeostasis.
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86
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Haider NB, Naggert JK, Nishina PM. Excess cone cell proliferation due to lack of a functional NR2E3 causes retinal dysplasia and degeneration in rd7/rd7 mice. Hum Mol Genet 2001; 10:1619-26. [PMID: 11487564 DOI: 10.1093/hmg/10.16.1619] [Citation(s) in RCA: 135] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The rd7 mouse is a model for hereditary retinal degeneration characterized clinically by retinal spotting throughout the fundus and late onset retinal degeneration, and histologically by retinal dysplasia manifesting as folds and whorls in the photoreceptor layer. This study demonstrates that the rd7 phenotype results from a splicing error created by a genomic deletion of an intron and part of an exon. Hematoxylin/eosin staining of rd7 tissue shows that the whorls in the outer nuclear layer of the retina do not appear during embryonic development but manifest by postnatal day 12.5 (P12.5). Furthermore, in situ hybridization data indicates that the Nr2e3 message is first present at barely discernable levels at embryonic day 18.5, becomes abundant by P2.5, and reaches maximal adult levels by P10.5. Results from these experiments indicate that Nr2e3 message is expressed prior to the development of S-cones. This data coincides with studies in humans showing that mutations in Nr2e3 result in a unique type of retinal degeneration known as enhanced S-cone syndrome, where patients have a 30-fold increase in S-cone sensitivity compared to normal. Immunohistochemical staining of cone cells demonstrates that rd7 retinas have an increased number of cone cells compared to wild-type retinas. Thus, Nr2e3 may function by regulating genes involved in cone cell proliferation, and mutations in this gene lead to retinal dysplasia and degeneration by disrupting normal photoreceptor cell topography as well as cell-cell interactions.
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87
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Bronson RT, Donahue LR, Samples R, Kim JH, Naggert JK. Mice with mutations in the mahogany gene Atrn have cerebral spongiform changes. J Neuropathol Exp Neurol 2001; 60:724-30. [PMID: 11444801 DOI: 10.1093/jnen/60.7.724] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
A new mutation characterized by mahogany coat color, sprawling gait, tremors, and severe vacuolization of cerebrum, brainstem, granular layer of cerebellum and spinal cord was discovered in a stock of Mus castaneus mice. Tests for allelism using mice homozygous for 2 known mahogany attractin (Atrnmg) mutants showed that the new mutation was an allele of Atrnmg. Northern analysis showed no expression of Atrn in the new mutants. Southern analysis strongly suggested that the new mutation deleted most of the Atrn gene, but was not large enough to affect flanking genes including the prion gene, Prnp, located 1.1 cM from Atrn on Chromosome 2. Histopathological analysis of brains from each of the 2 known Atrnmg mutants showed that they also have severe spongiform changes. This finding was surprising and raises questions about the mechanism by which mahogany controls appetite and metabolic rate, as recently reported.
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88
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Kim JH, Sen S, Avery CS, Simpson E, Chandler P, Nishina PM, Churchill GA, Naggert JK. Genetic analysis of a new mouse model for non-insulin-dependent diabetes. Genomics 2001; 74:273-86. [PMID: 11414755 DOI: 10.1006/geno.2001.6569] [Citation(s) in RCA: 114] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The TallyHo (TH) mouse strain is a newly established model for non-insulin-dependent diabetes mellitus (NIDDM). TH mice show obesity, hyperinsulinemia, hyperlipidemia, and male-limited hyperglycemia. A genetic dissection of the diabetes syndrome has been carried out using male backcross 1 progeny obtained from crosses between (C57BL/6J x TH)F1 and TH mice or (CAST/Ei x TH)F1 and TH mice. A genome-wide scan reveals three quantitative trait loci (QTLs), Tanidd1-3 (TH-associated NIDDM) linked to hyperglycemia. The major QTL (common in both crosses), Tanidd1, maps to chromosome (Chr) 19. Additionally, gene-gene interactions contributing to hyperglycemia have been observed between Tanidd1 and a locus on Chr 18 as well as between Tanidd2 and a locus on Chr 16. The overt hyperglycemia in TH mice is, therefore, likely due to a mutation in a major diabetes susceptibility locus on Chr 19, which interacts with additional genes to lead to an observable phenotype.
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89
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Ikeda A, Ikeda S, Gridley T, Nishina PM, Naggert JK. Neural tube defects and neuroepithelial cell death in Tulp3 knockout mice. Hum Mol Genet 2001; 10:1325-34. [PMID: 11406614 DOI: 10.1093/hmg/10.12.1325] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The tubby-like protein 3 (Tulp3) gene has been identified as a member of a small novel gene family which is primarily neuronally expressed. Mutations in two of the family members, tub and tulp1, have been shown to cause neurosensory disorders. To determine the in vivo function of Tulp3, we have generated a germline mutation in the mouse Tulp3 gene by homologous recombination. Embryos homozygous for the Tulp3 mutant allele exhibit failure of neural tube closure, and die by embryonic day 14.5. Failure of cranial neural tube closure coincided with increased neuroepithelial apoptosis specifically in the hindbrain and the caudal neural tube. In addition, the number of betaIII-tubulin positive cells is significantly decreased in the hindbrain of Tulp3(-/-) embryos. These results suggest that disruption of the Tulp3 gene affects the development of a neuronal cell population. Interestingly, some Tulp3 heterozygotes also manifest embryonic lethality with neuroepithelial cell death. Our results demonstrate that the Tulp3 gene is essential for embryonic development in mice.
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90
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He W, Ikeda S, Bronson RT, Yan G, Nishina PM, North MA, Naggert JK. GFP-tagged expression and immunohistochemical studies to determine the subcellular localization of the tubby gene family members. BRAIN RESEARCH. MOLECULAR BRAIN RESEARCH 2000; 81:109-17. [PMID: 11000483 DOI: 10.1016/s0169-328x(00)00164-9] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The tubby gene family consists of four members, TUB, TULP1, TULP2 and TULP3, with unknown function. However, a splice junction mutation within the mouse tub gene leads to retinal and cochlear degeneration, as well as maturity onset obesity and insulin resistance. Mutations within human TULP1 have also been shown to co-segregate in several cases of autosomal recessive retinitis pigmentosa (RP) and TULP1 deficiency in mice leads to retinal degeneration. The primary amino acid sequences of the tubby family members do not predict a likely biochemical function. As a first step in defining their function, we present a detailed characterization of the cellular and subcellular localization of the human (TUB) and mouse (tub) homologous gene products. We report the isolation of TUB splice variants which have different subcellular localizations (nuclear versus cytoplasmic) and which define a nuclear localization signal. In addition, using green fluorescent protein (GFP) tags, we observe a nuclear localization for TULP1, similar to TUB splicing forms TUB 561 and TUB 506. Finally, we report tubby expression in mouse brain by in situ hybridization and by immunohistochemistry with polyclonal antibodies. Protein was found in both the hypothalamic satiety centers and in a variety of other CNS structures including the cortex, cerebellum, olfactory bulb and hippocampus. Both nuclear and cytoplasmic signals were detected with a series of independently generated polyclonal antibodies, consistent with the presence of multiple alternatively spliced isoforms within the CNS.
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91
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Ikeda S, Shiva N, Ikeda A, Smith RS, Nusinowitz S, Yan G, Lin TR, Chu S, Heckenlively JR, North MA, Naggert JK, Nishina PM, Duyao MP. Retinal degeneration but not obesity is observed in null mutants of the tubby-like protein 1 gene. Hum Mol Genet 2000; 9:155-63. [PMID: 10607826 DOI: 10.1093/hmg/9.2.155] [Citation(s) in RCA: 88] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The tub gene is a member of a small, well conserved neuronal gene family of unknown function. Mutations within this gene lead to early-onset blindness and deafness, as well as late-onset obesity and insulin resistance. To test the hypothesis that mutations within other members of this gene family would lead to similar phenotypes as observed in tubby mice, and hence have similar functional properties, we have generated null mutants of the tubby-like protein ( Tulp ) 1 gene by homologous recombination. Similarly to tubby mice, Tulp1 (-/-)mice exhibit an early-onset retinal degeneration with a progressive, rapid loss of photoreceptors, further supporting the notion that previously identified mutations within the human TULP1 gene are indeed causative of retinitis pigmentosa. However, in contrast to tubby mice, Tulp1 (-/-)mice exhibited normal hearing ability and, surprisingly, normal body weight despite the fact that both TUB and TULP1 are expressed in the same neurons within the hypothalamus in areas known to be involved in feeding behavior and energy homeo stasis. However, TUB and TULP1 show a distinctly different staining pattern in the nucleus of these neurons, perhaps explaining the difference in body weight between the Tulp1 (-/-)and tubby mutant mice.
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92
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Collin GB, Marshall JD, Boerkoel CF, Levin AV, Weksberg R, Greenberg J, Michaud JL, Naggert JK, Nishina PM. Alström syndrome: further evidence for linkage to human chromosome 2p13. Hum Genet 1999; 105:474-9. [PMID: 10598815 DOI: 10.1007/s004390051133] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Alström syndrome is a rare autosomal recessive disorder characterized by retinal degeneration, sensorineural hearing loss, early-onset obesity, and non-insulin-dependent diabetes mellitus. The gene for Alström syndrome (ALMS1) has been previously localized to human chromosome 2p13 by homozygosity mapping in two distinct isolated populations - French Acadian and North African. Pair-wise analyses resulted in maximum lod (logarithm of the odds ratio) scores of 3.84 and 2.9, respectively. To confirm these findings, a large linkage study was performed in twelve additional families segregating for Alström syndrome. A maximum two-point lod score of 7.13 (theta = 0.00) for marker D2S2110 and a maximum cumulative multipoint lod score of 9.16 for marker D2S2110 were observed, further supporting linkage to chromosome 2p13. No evidence of genetic heterogeneity was observed in these families. Meiotic recombination events have localized the critical region containing ALMS1 to a 6.1-cM interval flanked by markers D2S327 and D2S286. A fine resolution radiation hybrid map of 31 genes and markers has been constructed.
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93
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Ikeda S, He W, Ikeda A, Naggert JK, North MA, Nishina PM. Cell-specific expression of tubby gene family members (tub, Tulp1,2, and 3) in the retina. Invest Ophthalmol Vis Sci 1999; 40:2706-12. [PMID: 10509669] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/14/2023] Open
Abstract
PURPOSE The family of tubby-like proteins (TULPs), consisting of four family members, are all expressed in-the retina at varying levels. Mutations within two members, tub and TULP1, are known to lead to retinal degeneration in mouse and humans, respectively, suggesting the functional importance of this family of proteins in the retina. Despite a high degree of conservation in the carboxy-terminal region (e.g., putative functional domain of the genes) among family members, they are unable to compensate for one another. The purpose of this study was to provide a rationale for this lack of compensation by investigating the spatial distribution of tubby gene family members in the retina and to investigate the mechanism of photoreceptor cell death in tubby mice. METHODS In situ hybridization using riboprobes specific for each tubby gene family member and immunohistochemistry for TUB and TULP1 were performed to determine their expression patterns in the retina of tubby and wild-type control mice. The terminal dUTP nick-end labeling (TUNEL) assay was performed to detect apoptotic cells in the retina of tubby and wild-type control mice. RESULTS tub mRNA was found to be expressed throughout the retina, with highest expression in the ganglion cell layer (GCL) and photoreceptor cells. In contrast, Tulp1 expression was observed only in photoreceptor cells and Tulp3 mRNA was expressed at a moderate level only in the inner nuclear layer (INL) and GCL. The results of the immunohistochemical analysis paralleled those observed in the in situ studies. TUB immunoreactivity was most highly concentrated in the GCL, in the inner and outermost regions of the INL, in the outer plexiform layer (OPL), and in the inner segments of photoreceptor cells. Similarly, TULP1 immunoreactivity was observed in the OPL and inner segments of the photoreceptor cells. No differences in expression at the mRNA or protein level were observed for any of the molecules tested in tubby or wild-type mice. TUNEL-positive cells were detected in the ONL of tubby mice, whereas very few were seen in the same layer of age-matched control mice. CONCLUSIONS Although all tubby gene family members are expressed in the retina, they each have different cell-specific expression patterns, which may account in part for their inability to compensate for the loss of one family member. The photoreceptor cell death in tubby mice occurs through an apoptotic mechanism, which is known to be the common final outcome of other forms of retinal degeneration.
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94
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Ikeda A, Zheng QY, Rosenstiel P, Maddatu T, Zuberi AR, Roopenian DC, North MA, Naggert JK, Johnson KR, Nishina PM. Genetic modification of hearing in tubby mice: evidence for the existence of a major gene (moth1) which protects tubby mice from hearing loss. Hum Mol Genet 1999; 8:1761-7. [PMID: 10441341 PMCID: PMC3249642 DOI: 10.1093/hmg/8.9.1761] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Quantitative trait locus (QTL) analysis of genetic crosses has proven to be a useful tool for identifying loci associated with specific phenotypes and for dissecting genetic components of complex traits. Inclusion of a mutation that interacts epistatically with QTLs in genetic crosses is a unique and potentially powerful method of revealing the function of novel genes and pathways. Although we know that a mutation within the novel tub gene leads to obesity and cochlear and retinal degeneration, the biological function of the gene and the mechanism by which it induces its phenotypes are not known. In the current study, a QTL analysis for auditory brainstem response (ABR) thresholds, which indicates hearing ability, was performed in tubby mice from F(2)intercrosses between C57BL/6J- tub / tub and AKR/J-+/+ F(1)hybrids (AKR intercross) and between C57BL/6J- tub / tub and CAST/Ei.B6- tub / tub F(1)hybrids (CAST intercross). A major QTL, designated asmodifieroftubbyhearing1 ( moth1 ), was identified on chromosome 2 with a LOD score of 33.4 ( P < 10(-33)) in the AKR intercross (181 mice) and of 6.0 ( P < 10(-6)) in the CAST intercross (46 mice). This QTL is responsible for 57 and 43% of ABR threshold variance, respectively, in each strain combination. In addition, a C57BL/6J congenic line carrying a 129/Ola segment encompassing the described QTL region when made homozygous for tubby also exhibits normal hearing ability. We hypothesize that C57BL/6J carries a recessive mutation of the moth1 gene which interacts with the tub mutation to cause hearing loss in tub / tub mice. A moth1 allele from either AKR/J, CAST/Ei or 129/Ola is sufficient to protect C57BL/6J- tub / tub mice from hearing loss.
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95
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Mu JL, Naggert JK, Svenson KL, Collin GB, Kim JH, McFarland C, Nishina PM, Levine DM, Williams KJ, Paigen B. Quantitative trait loci analysis for the differences in susceptibility to atherosclerosis and diabetes between inbred mouse strains C57BL/6J and C57BLKS/J. J Lipid Res 1999; 40:1328-35. [PMID: 10393218] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/13/2023] Open
Abstract
Mice from the inbred strain C57BLKS/J (BKS) exhibit increased susceptibility to both diabetes and atherosclerosis compared to C57BL/6J (B6) mice. To determine whether the differences in diabetes and atherosclerosis are related, we carried out a cross between B6-db/db and BKS. We selected 99 female F2-db/db progeny, tested the progeny for plasma lipids, plasma glucose, and fatty-streak lesions, and used quantitative trait loci (QTL) analysis to identify the chromosomal regions associated with these phenotypes. No major QTL were found for total cholesterol, VLDL-cholesterol, or triglycerides. Two suggestive QTL were found for HDL-cholesterol (LOD scores of 2. 7 and 2.8), and two suggestive loci were found for plasma glucose (LOD scores of 2.3 and 2.0). Lesion size was not correlated with plasma lipid levels or glucose. Lesion size was determined by a locus at D12Mit49 with a LOD score of 2.5 and a significant likelihood ratio statistic. The gene for apolipoprotein apoB lies within the region, but apoB levels were similar in strains B6 and BKS. The QTL on Chr 12 was confirmed by constructing a congenic strain with BKS alleles in the QTL region on a B6 genetic background. We conclude that susceptibilities to diabetes and atherosclerosis are not conferred by the same genes in these strains and that a major gene on Chr 12, which we name Ath6, determines the difference in atherosclerosis susceptibility.
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96
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Mu JL, Naggert JK, Svenson KL, Collin GB, Kim JH, McFarland C, Nishina PM, Levine DM, Williams KJ, Paigen B. Quantitative trait loci analysis for the differences in susceptibility to atherosclerosis and diabetes between inbred mouse strains C57BL/6J and C57BLKS/J. J Lipid Res 1999. [DOI: 10.1016/s0022-2275(20)33495-7] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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97
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York B, Truett AA, Monteiro MP, Barry SJ, Warden CH, Naggert JK, Maddatu TP, West DB. Gene-environment interaction: a significant diet-dependent obesity locus demonstrated in a congenic segment on mouse chromosome 7. Mamm Genome 1999; 10:457-62. [PMID: 10337618 DOI: 10.1007/s003359901023] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
Abstract
We have previously reported suggestive evidence for a locus on Chromosome (Chr) 7 that affects adiposity in F2 mice from a CAST/Ei x C57BL/6J intercross fed a high-fat diet. Here we characterize the effect of a high-fat (32.6 Kcal% fat) diet on male and female congenic mice with a C57BL/6J background and a CAST/Ei-derived segment on Chr 7. Adiposity index (AI) and weights of certain fat pads were approximately 50% lower in both male and female congenic mice than in control C57BL/6J mice, and carcass fat content was significantly reduced. The reduction of fat depot weights was not seen, however, in congenic animals fed a low-fat chow diet (12 Kcal% fat). The congenic segment is approximately 25 cM in length, extending from D7Mit213 to D7Mit41, and includes the tub, Ucp2 and Ucp3, genes, all of which are candidate genes for this effect. Some polymorphisms have been found on comparing c-DNA sequences of the Ucp2 gene from C57BL/6J and CAST/Ei mice. These results suggest that one or more genes present in the congenic segment modulate the susceptibility to fat deposition on feeding a high-fat diet. We were unable to show any significant difference between the energy intakes of the congenic and the control C57BL/6J mice on the high-fat diet. Also, measurements of energy expenditure in male mice at 6 weeks of age, during the first 2 weeks of exposure to the high-fat diet, failed to show any differences between control and congenic animals.
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98
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Kim JH, Nishina PM, Naggert JK. Genetic models for non insulin dependent diabetes mellitus in rodents. J Basic Clin Physiol Pharmacol 1999; 9:325-45. [PMID: 10212842 DOI: 10.1515/jbcpp.1998.9.2-4.325] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Efforts to identify human genes with major effects on insulin resistance and type II diabetes have yet to be successful because of the technical difficulties associated with the analysis of complex traits in humans. Animal models, particularly the rodent models with their well developed genetic tools, and their genetic similarity to humans, offer an alternate approach to access genes important in the etiology of diabetes. This approach is validated by the remarkable progress that has been made in the identification and characterization of the genes mutated in five monogenic mouse models of obesity. Identification of these genes has led to new insights into the etiology of obesity and provided promising targets for therapeutic intervention. Arguably, genetic animal models could do the same for our understanding of diabetes. In this brief review, we introduce rodent models of type II diabetes and report on the state of their genetic analyses.
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99
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Leiter EH, Kintner J, Flurkey K, Beamer WG, Naggert JK. Physiologic and endocrinologic characterization of male sex-biased diabetes in C57BLKS/J mice congenic for the fat mutation at the carboxypeptidease E locus. Endocrine 1999; 10:57-66. [PMID: 10403572 DOI: 10.1385/endo:10:1:57] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/06/1998] [Revised: 11/04/1998] [Accepted: 11/05/1998] [Indexed: 12/26/2022]
Abstract
The fat gene in mice represents a recessive mutation at the carboxypeptidase E (Cpe) locus. The mutant allele (Cpe(fat)) encodes a highly unstable enzyme and produces an obesity phenotype characterized by attenuated processing of prohormones such as proinsulin that require this exopeptidase for full maturation. This article presents a preliminary physiologic and endocrinologic characterization of the stock of C57BLKS/LtJ-Cpe(fat)/Cpe(fat) mice at the backcross generation (N10) currently distributed by The Jackson Laboratory. Although previously reported not to be diabetogenic at N5, an additional five backcrosses to the C57BLKS/J background resulted in a male-biased development of both obesity and diabetes. Major differences distinguishing this mutant stock from the phenotypes produced by either the diabetes (Lepr(db)) or obese (Lep(ob)) mutations on the same inbred strain background are lack of hyperphagia and hypercorticism, sensitivity of diabetic males to exogenous insulin, and a milder and male-biased diabetes syndrome that is not associated with widespread beta-cell necrosis and islet atrophy, and that often remits with age.
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100
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Collin GB, Marshall JD, Naggert JK, Nishina PM. TGFA: exon-intron structure and evaluation as a candidate gene for Alström syndrome. Clin Genet 1999; 55:61-2. [PMID: 10066034 DOI: 10.1034/j.1399-0004.1999.550111.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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