Conserved linkage of early growth response 4, annexin 4, and transforming growth factor alpha on mouse chromosome 6

Global gene expression profiling of somatic motor neuron populations with different vulnerability identify molecules and pathways of degeneration and protection

Different somatic motor neuron subpopulations show a differential vulnerability to degeneration in diseases such as amyotrophic lateral sclerosis, spinal muscular atrophy and spinobulbar muscular atrophy. Studies in mutant superoxide dismutase 1 over-expressing amyotrophic lateral sclerosis model mice indicate that initiation of disease is intrinsic to motor neurons, while progression is promoted by astrocytes and microglia. Therefore, analysis of the normal transcriptional profile of motor neurons displaying differential vulnerability to degeneration in motor neuron disease could give important clues to the mechanisms of relative vulnerability. Global gene expression profiling of motor neurons isolated by laser capture microdissection from three anatomical nuclei of the normal rat, oculomotor/trochlear (cranial nerve 3/4), hypoglossal (cranial nerve 12) and lateral motor column of the cervical spinal cord, displaying differential vulnerability to degeneration in motor neuron disorders, identified enriched transcripts for each neuronal subpopulation. There were striking differences in the regulation of genes involved in endoplasmatic reticulum and mitochondrial function, ubiquitination, apoptosis regulation, nitrogen metabolism, calcium regulation, transport, growth and RNA processing; cellular pathways that have been implicated in motor neuron diseases. Confirmation of genes of immediate biological interest identified differential localization of insulin-like growth factor II, guanine deaminase, peripherin, early growth response 1, soluble guanylate cyclase 1A3 and placental growth factor protein. Furthermore, the cranial nerve 3/4-restricted genes insulin-like growth factor II and guanine deaminase protected spinal motor neurons from glutamate-induced toxicity (P < 0.001, ANOVA), indicating that our approach can identify factors that protect or make neurons more susceptible to degeneration.

Genetic linkage of Welander distal myopathy to chromosome 2p13

Welander distal myopathy (WDM) is an autosomal dominant myopathy with late-adult onset characterized by slow progression of distal muscle weakness. The disorder is considered a model disease for hereditary distal myopathies and is almost only seen in Sweden and some parts of Finland. A genomewide screening has been performed in initially two Swedish families with 400 highly polymorphic microsatellite markers. We report here that the disease is linked to chromosome 2p13. Seven additional nonrelated families have subsequently been mapped to the same area where a maximum two-point LOD score of 17.97 was obtained with the marker D2S2113 at 0.0 recombination fraction. The region has been restricted by recombinations and the finding of a common shared haplotype through all analyzed families. This restricts the gene locus region to 2.4 cM. These findings provide evidence for the involvement of a single locus for WDM. The WDM region overlaps with the linkage region for Miyoshi myopathy and limb-girdle muscular dystrophy 2B. The dysferlin gene responsible for these disorders is considered a primary candidate gene for WDM.

Integrated radiation hybrid map of human chromosome 2p13: possible involvement of dynactin in neuromuscular diseases

The genes for the human neuromuscular diseases limb-girdle muscular dystrophy type 2B (LGMD2B) and Miyoshi myopathy are located on chromosome 2p13-p14, and two neuromuscular mutations of the mouse have been mapped to regions homologous to human chromosome 2p13 by conserved synteny, wobbler (wr) on proximal Chr 11 and motor neuron degeneration 2 (mnd2) on Chr 6. Neither one is a mouse homologue of LGMD2B. Recently the gene DCTN1, coding for the large subunit of the cytoskeletal protein dynactin, was shown by FISH to be located in this region and therefore should be considered a candidate for all these disease genes. Here we present mapping data based on radiation hybrid and physical mapping that more precisely define the location of nine genetic markers in the critical region and the homology relationship of human chromosome 2p with mouse proximal Chr 11 and Chr 6. The human dynactin gene was mapped between markers TGFA and D2S1394, implying that the mouse dynactin gene Dctn1 is located on Chr 6, distal to mnd2. Thus DCTN1/Dctn1 is a candidate for LGMD2B but not for mnd2 or wr.

Mapping of the taurine transporter gene to mouse chromosome 6 and to the short arm of human chromosome 3

Transport proteins have essential functions in the uptake of neurotransmitters and neuromodulators. We have mapped the gene encoding the taurine transporter, Taut, to the central region of mouse chromosome 6. Analysis of a cross segregating the neurological mutant mnd2 excluded Taut as a candidate gene for this closely linked mutation. To map the human taurine transporter gene, TAUT, a sequence-tagged site (STS) corresponding to the 3' untranslated region of the human cDNA was developed. TAUT was assigned to human chromosome 3 by typing this STS on a panel of somatic cell hybrids. Further analysis of a hybrid panel containing defined deletions of chromosome 3 suggested that TAUT maps to 3p21-p25. These data extend a conserved linkage group on mouse chromosome 6 and human chromosome 3p. Deletion of TAUT might contribute to some phenotypic features of the 3p- syndrome.

The mouse waved-2 phenotype results from a point mutation in the EGF receptor tyrosine kinase

Mice harboring the waved-1 (wa-1) and waved-2 (wa-2) mutations exhibit skin and eye abnormalities that are strikingly similar to those of TGF-alpha-deficient mice, and wa-1 and TGF-alpha were recently shown to be allelic. Because the wa-2 mutation was mapped previously to the vicinity of the EGF/TGF-alpha receptor (EGFR) gene on mouse chromosome 11, we hypothesized that the wa-2 phenotype might result from a defect in either the expression or activity of EGFR, or both. In the present report, we show that EGFR mRNA and protein of normal size are expressed in wa-2 liver and skin at levels that are comparable to those in the corresponding normal tissues, and that the ability of wa-2 EGFR to bind ligand is unaltered. However, ligand-dependent autophosphorylation of wa-2 EGFR is diminished 5- to 10-fold in vitro, and the ability of wa-2 EGFR to phosphorylate an exogenous substrate is reduced by > 90% compared with that of the control receptor. EGF-induced tyrosine phosphorylation, including that of EGFR itself, is also diminished in skin, particularly at lower dose of exogenous EGF. To establish the nature of the wa-2 mutation, we determined the nucleotide sequence of the coding region of normal and wa-2 murine EGFR cDNAs. A comparison of these sequences revealed a single-nucleotide transversion resulting in the substitution of a glycine for a conserved valine residue near the amino terminus of the tyrosine kinase domain. The importance of this mutation was confirmed by showing that its introduction into an otherwise normal EGFR markedly reduced the receptor's tyrosine kinase activity in transfected Chinese hamster ovary cells. Finally, in situ hybridization analysis demonstrated expression of EGFR predominantly in the outer root sheath of active hair follicles in neonatal mice. As we previously localized TGF-alpha mRNA to the inner root sheath, this pattern of EGFR expression is consistent with the effect of the wa-2 mutation on hair structure, and together with our previous characterization of TGF-alpha-deficient mice, reveals a critical role for signaling by this ligand/receptor system in skin.