Regulated expression and RNA processing of transcripts from the Srp20 splicing factor gene during the cell cycle

Eukaryotic splicing factors belonging to the SR family are essential splicing factors consisting of an N-terminal RNA-binding region and a C-terminal RS domain. They are believed to be involved in alternative splicing of numerous transcripts because their expression levels can influence splice site selection. We have characterized the structure and transcriptional regulation of the gene for the smallest member of the SR family, SRp20 (previously called X16). The mouse gene encoding SRp20, termed Srp20, consists of one alternative exon and six constitutive exons and was mapped to a 2-centimorgan interval on chromosome 17. When cells are transfected with SRp20 genomic DNA, both standard and alternatively spliced transcripts and corresponding proteins are produced. Interestingly, in starved (G0) cells, the amount of SRp20 mRNA containing the alternative exon is large, whereas the amount of the standard SRp20 mRNA without the alternative exon is small. When starved cells are stimulated with serum, the alternative form is lost and the standard form is induced. These results suggest that splicing could be regulated during the cell cycle and that this could be, at least in part, due to regulated expression of SR proteins. Consistent with this, experiments with synchronized cells showed an induction of SRp20 transcripts in late G1 or early S. We have also characterized the promoter of SRp20. It lies within a GC-rich CpG island and contains two consensus binding sites for E2F, a transcription factor thought to be involved in regulating the cell cycle. These motifs may be functional since reporter constructs with the SRp20 promoter can be stimulated by cotransfection with E2F expression plasmids.

cDNA isolation, expression, and chromosomal localization of the mouse survival motor neuron gene (Smn)

Spinal muscular atrophy (SMA) is a frequent autosomal recessive disease in human characterized by degeneration of motor neurons of the spinal cord. The genomic region containing the defective gene (5q13) is particularly unstable and prone to large-scale deletions whose characterization led to the identification of the survival motor neuron (SMN) gene, the SMA determining gene encoding a hitherto unknown protein. As an initial step toward the generation of a murine model for SMA, we identified and characterized a full-length murine Smn cDNA. The coding sequence of the mouse Smn gene was found to be 82% identical, at the amino acid level, with the human SMN coding sequence. The Smn locus was mapped to the segment of mouse chromosome 13 exhibiting conservation of synteny with human chromosome 5q11-q23, which contains the SMN gene. However, no evidence for a duplication of the Smn gene was found in the mouse, suggesting that the duplication reported in human is a recent evolutionary event.

[Animal models of hereditary diseases]

A large number of genetic diseases are found both in humans and in one or several animal species. The mouse is a species of choice since, in addition to hundreds of spontaneous mutations which have been described, it is now possible to produce at will a mutation in any gene. This strategy has been used to generate genetically engineered mice which carry genetic defects found in human molecular pathology. Animal models are an invaluable tool to study the pathophysiology of diseases and to test new therapies. However, they are rarely exact replicates of the human disease. Possible origins for these differences are discussed in detail.

Modulation of mRNA levels in the presence of thymocytes and genome mapping for a set of genes expressed in mouse thymic epithelial cells

Modulation of gene expression in mouse thymic epithelium upon culture in the presence of thymocytes (coculture) was studied by comparison of hybridization signatures on a set of nearly 5000 mouse thymus cDNA clones. Forty-nine differentially expressed clones (usually down-regulated in coculture) were characterized by tag sequencing. Many of them corresponded to entities that had not been described previously in the mouse, and were further characterized by genome mapping. This set of genes appears to be involved in growth regulation and differentiation within the thymus.

Rbt (Rabo torcido), a new mouse skeletal mutation involved in anteroposterior patterning of the axial skeleton, maps close to the Ts (tail-short) locus and distal to the Sox9 locus on chromosome 11

Rbt (Rabo torcido) is a new semidominant mouse mutant with a variety of skeletal abnormalities. Heterozygous Rbt mutants display homeotic anteroposterior patterning problems along the axial skeleton that resemble Polycomb group and trithorax gene mutations. In addition, the Rbt mutant displays strong similarities to the phenotype observed in Ts (Tail-short), indicating also a homeotically transformed phenotype in these mice. We have mapped the Rbt locus to an interval of approximately 6 cM on mouse Chromosome (Chr) 11 between microsatellite markers D11Mit128 and D11Mit103. The Ts locus was mapped within a shorter interval of approximately 3 cM between D11Mit128 and D11Mit203. This indicates that Rbt and Ts may be allelic mutations. Sox9, the human homolog of which is responsible for the skeletal malformation syndrome campomelic dysplasia, was mapped proximal to D11Mit128. It is, therefore, unlikely that Ts and Rbt are mouse models for this human skeletal disorder.

A rat mutation producing demyelination (dmy) maps to chromosome 17

A recessive mutation exhibiting severe myelin breakdown, mainly at the level of the lumbar segments of the spinal cord and without any associated inflammation, was discovered in a partially inbred rat colony. Analysis of the segregation patterns of a set of polymorphic microsatellite markers in two inter-strain crosses allowed the mapping of this autosomal recessive mutation to rat Chromosome (Chr) 17, very close to the prolactin (Prl) locus, in a region homologous to human Chr 6p21.2-22.3 and mouse Chr 13. The pathology of the demyelination process and the chromosomal localization indicate that this mutation has no known equivalent in either mouse or human.

The mouse mutation sarcosinemia (sar) maps to chromosome 2 in a region homologous to human 9q33-q34

The autosomal recessive mouse mutation sarcosinemia (sar), which was discovered segregating in the progeny of a male whose premeiotic germ cells had been treated with the mutagen ethylnitrosourea, is characterized by a deficiency in sarcosine dehydrogenase activity. Using an intersubspecific cross, we mapped the sar locus to mouse chromosome 2, approximately 15-18 cM from the centromere. The genetic localization of this locus in the mouse allows the identification of a candidate region in human (9q33-q34) where the homologous disease should map.

Lanceolate hair (lah): a recessive mouse mutation with alopecia and abnormal hair

A new autosomal recessive mutation of the house mouse developed generalized alopecia associated with breakage of abnormal hair shafts. This mutation, named 'lanceolate hair' (symbol: lah), arose in a mutagenesis experiment using ethylnitrosourea. Hair shafts were short with a focal degeneration at the breakpoint characterized by a pronounced enlargement at the apex, resembling a lance head. Plucked hair fibers were 2.0 to 3.5 mm in length with a normal base, suggesting that there was a synchronized developmental defect. Histologic examination of anagen follicles revealed abnormal cornification of the matrix region with degeneration resulting in the focal hair shaft deformity. Catagen follicles showed pronounced follicular dystrophy but telogen follicles were almost normal. There was a marked, persistent thickening of the epidermis associated with a non-scarring, relatively non-inflammatory ichthyosiform dermatitis. These features are found in the Netherton's syndrome of the human, for which this mouse mutation may represent a model. The lah mutation has been localized to the centromeric end of mouse Chromosome 18.

Nucleotide sequence, chromosomal assignment and mRNA expression of mouse hypoxia-inducible factor-1 alpha

The heterodimeric hypoxia-inducible transcription factor HIF-1 is involved in the oxygen-regulated transcription of several genes including erythropoietin. Cloning and sequencing of the alpha-subunit of mouse HIF-1 cDNA revealed a 90% overall homology to human HIF-l alpha but lack of any similarity in the 5' untranslated region and translational start site. Mouse HIF-1 alpha is encoded by an evolutionary conserved single-copy gene located on chromosome 12. We found a widespread constitutive expression of mouse HIf-1 alpha mRNA which was particularly high in lung and kidney. Despite a strong erythropoietin induction, HIF-1 alpha mRNA concentrations were not upregulated in hypoxic mouse tissues.

Murine acariasis: I. Pathological and clinical evidence suggesting cutaneous allergy and wasting syndrome in BALB/c mouse

We describe here a disease related to mite-associated ulcerative dermatitis in BALB/c mice, a strain previously classified as resistant to this condition. The disease was recognized by pruritic cutaneous pathology and wasting. Pathologic studies showed a marked allergic-type inflammation in the skin. The dominant histologic feature was extensive mast cell infiltration in cutaneous lesions and in lymphoid tissues, associated with a greatly elevated serum IgE concentration. The disease was secondary to infestation with an acarian ectoparasite Myocoptes musculinus, and seemed to represent an allergic reaction to the parasite-derived substances, with an associated wasting syndrome. This condition may be a useful experimental model for allergic diseases.

A high-resolution genetic map of mouse chromosome 15 encompassing the Dominant megacolon (Dom) locus

Dominant megacolon (Dom) is one of four mutations in the mouse that can produce a phenotype similar to Hirschsprung disease in human. The Dom gene product is not known, and no candidate region has been defined for a possible human homolog. In this publication we report mapping the Dom locus with high definition, using several intra-and interspecific crosses and a set of 16 Chr 15-specific microsatellites flanking this locus.

The mouse mutation progressive motor neuronopathy (pmn) maps to chromosome 13

Analysis of polymorphic markers segregating in both intra- and interspecific crosses has allowed us to map the autosomal recessive mutation progressive motor neuronopathy (pmn) to mouse Chr 13. Although this mutation, based on its histological description, was reported as a model for infantile spinal muscular atrophy of the Werdnig-Hoffmann type, its localization to a region that is not homologous with human 5q makes it unlikely to be a homologue to SMA. The presence of the Extra-toe (Xt) locus in proximity to pmn will help in the detection of affected progenies before the onset of the degenerative process.

Transient and restricted expression during mouse embryogenesis of Dll1, a murine gene closely related to Drosophila Delta

The Drosophila Delta (Dl) gene is essential for cell-cell communication regulating the determination of various cell fates during development. Dl encodes a transmembrane protein, which contains tandem arrays of epidermal-growth-factor-like repeats in the extracellular domain and directly interacts with Notch, another transmembrane protein with similar structural features, in a ligand-receptor-like manner. Similarly, cell-cell interactions involving Delta-like and Notch-like proteins are required for cell fate determinations in C. elegans. Notch homologues were also isolated from several vertebrate species, suggesting that cell-to-cell signaling mediated by Delta- and Notch-like proteins could also underlie cell fate determination during vertebrate development. However, in vertebrates, no Delta homologues have yet been described. We have isolated a novel mouse gene, Dll1 (delta-like gene 1), which maps to the mouse t-complex and whose deduced amino acid sequence strongly suggests that Dll1 represents a mammalian gene closely related to Drosophila Delta. Dll1 is transiently expressed during gastrulation and early organogenesis, and in a tissue-restricted manner in adult animals. Between day 7 and 12.5 of development, expression was detected in the paraxial mesoderm, closely correlated with somitogenesis, and in subsets of cells in the nervous system. In adult animals, transcripts were detected in lung and heart. Dll1 expression in the paraxial mesoderm and nervous system is strikingly similar to the expression of mouse Notch1 during gastrulation and early organogenesis. The overlapping expression patterns of the Dll1 and Notch1 genes suggest that cells in these tissues can communicate by interaction of the Dll1 and Notch1 proteins. Our results support the idea that Delta- and Notch-like proteins are involved in cell-to-cell communication in mammalian embryos and suggest a role for these proteins in cellular interactions underlying somitogenesis and development of the nervous system.

The mouse Fau gene: genomic structure, chromosomal localization, and characterization of two retropseudogenes

The Fau gene is the cellular homolog of the fox sequence of the Finkel-Biskis-Reilly murine sarcoma virus (FBR-MuSV). FBR-MuSV acquired the Fau gene by transduction in a transcriptional orientation opposite to that of the genomic Fau gene. The genomic structure of the mouse Fau gene (MMFAU) and its upstream elements have been determined and are similar to those of the human FAU gene. The gene consists of five exons and is located on chromosome 19. The first exon is not translated. The promoter region has no well-defined TATA box but contains the polypyrimidine initiator flanked by regions of high GC content (65%) and shows all of the characteristics of a housekeeping gene. The 5' end of the mRNA transcript was determined by 5' RACE analysis and is located, as expected, in the polypyrimidine initiator site. Furthermore, the sequences of two retropseudogenes (Fau-ps1 and Fau-ps2) are reported. Both pseudogenes are approximately 75% identical to the Fau cDNA, but both are shorter due to a deletion at the 5' end and do not encode a functional protein. Fau-prs is interrupted by an AG-rich region of about 350 bp within the S30 region of the Fau cDNA. Fau-ps1 was localized on chromosome 1 and Fau-ps2 on chromosome 7.

Etl2, a novel putative type-I cytokine receptor expressed during mouse embryogenesis at high levels in skin and cells with skeletogenic potential

The regulatory effects of signaling proteins like hormones, growth factors, and cytokines are mediated by specific cell surface receptors which are grouped into distinct families on the basis of structural criteria. Here we report on the isolation and embryonic expression of a novel mouse gene, Etl2 (enhancer trap locus 2) which, based on its deduced amino acid sequence, constitutes a new member of the cytokine type-I receptor family. Among type-I receptors Etl2 is most similar to the alpha subunits of the human ciliary neurotrophic factor (CNTF) receptor and the mouse interleukin-6 (IL6) receptor with 32 and 30% identical amino acids, respectively. From Day 9 p.c. (postcoitum) onward low levels of Etl2 mRNA were detected in mesenchymal cells throughout the embryo and in parts of the nervous system, in particular in the ependymal linings of the spinal cord and the developing brain vesicles and in the neuronal layer of the retina. Highest levels of Etl2 expression were found on Day 12.5 p.c. in the craniofacial mesenchyme and during subsequent development in mesenchymal cells around all developing cartilages. At later stages, Etl2 transcripts were abundant in the dental papilla, the dermis, and hair follicles, as well as in the perichondrium and periost, i.e., in regions containing chondro and osteo progenitor cells. Etl2 mRNA was not detected, however, in mature odontoblasts, chondroblasts, osteoblasts, chondrocytes, and osteocytes. Our results suggest that Etl2 is a new orphan receptor belonging to the type-I cytokine receptor family and that Etl2 might have regulatory functions, particularly in the control of proliferation and/or differentiation of skeletogenic progenitor and other mesenchymal cells.

A high-resolution genetic map of mouse chromosome 5 encompassing the reeler (rl) locus

Using interspecific crosses between BALB/c and Mus spretus (SEG) mice, the murine reeler (rl) gene was mapped to the proximal region of chromosome 5 between the hepatocyte growth factor gene (Hgf) and the D5Mit66 microsatellite. The following order was defined: (centromere)-Cchl2a/Hgf-D5Mit1-D5Nam1/D5-Nam2 -rl/D5Mit61-D5Mit72-Xmv45-Htr5a- Peplb-D5Nam3-D5Mit66. Estimated distances between reeler and the nearest flanking markers D5Nam1 and D5Mit72 are 1.5 and 1.0 cM, respectively (95% confidence level), suggesting that the region could be physically mapped using a manageable number of YAC clones.

The spastic mouse: aberrant splicing of glycine receptor beta subunit mRNA caused by intronic insertion of L1 element

Mice homozygous for the spastic mutation (spa) suffer from a complex motor disorder resulting from reduced CNS levels of the adult glycine receptor isoform GlyRA, which is composed of ligand-binding alpha 1 and structural beta polypeptides. The beta subunit-encoding gene (Glyrb) was mapped near the spa locus on mouse chromosome 3. In spa/spa mice, aberrant splicing of the beta subunit pre-mRNA strikingly diminishes the CNS contents of full-length transcripts, whereas truncated beta subunit mRNAs accumulate. This is a result of exon skipping, which causes translational frameshifts and premature stop codons. Intron 5 of the spa Glyrb gene contains an L1 transposable element that apparently is causal for the aberrant splicing of beta subunit transcripts.

Human inositol 1,4,5-trisphosphate type-1 receptor, InsP3R1: structure, function, regulation of expression and chromosomal localization

We have isolated cDNA clones encoding an inositol 1,4,5-trisphosphate receptor type 1 (InsP3R1) from human uteri and a leukaemic cell line, HL-60. Northern-blot analysis showed that approx. 10 kb of InsP3R1 mRNA is expressed in human uteri, oviducts and HL-60 cells. The predicted amino acid sequence of human InsP3R1 (2695 amino acids) has 99% identity with that of the mouse SI-/SII- splicing counterpart. Western-blot analysis with anti-(mouse InsP3R1) antibodies showed that InsP3R1 protein of human uteri and oviducts of approx 220 kDa is immunostained. Northern-blot analysis of HL-60 cell differentiation along the neutrophilic lineage induced by retinoic acid or dimethylsulphoxide showed an accompanying enhanced expression of InsP3R1 mRNA. Immunohistochemical analysis of the cerebella of spinocerebellar degeneration patients showed a variable loss of Purkinje cells with an altered pattern of immunostaining. The InsP3R1 gene (Insp3r1) was localized to the 3P25-26 region of human chromosome 3. The data presented here clearly show that InsP3R1 exists widely in human tissues and may play critical roles in various kinds of cellular functions.

Msx1 is close but not allelic to either Hm or Hx on mouse chromosome 5

The Msx1 homeobox locus has been mapped in relation to the mutations hammer-toe (Hm) and hemimelic extra toes (Hx). Msx1 is expressed in the developing limb, while limb development is affected by the Hm and Hx mutations. Hm and Hx are very tightly linked loci. In interspecific crosses, the segregation of either mutation was followed in relation to polymorphic alleles of Msx1, Il6, and En2, to give a fine map around the mutant loci. Our results show that Msx1 is not allelic to either of the mutations, but is located about 3 cM from them. Il6 did not recombine with either Hm or Hx and, therefore, provides a point of access for the analysis of these mutations at the molecular level.