FVB.Cg-Grm7^{Tg(SMN2)89Ahmb} Smn1^tm1Msd Tg(SMN2*delta7)4299Ahmb/J

Stock number: 005025
Product name: FVB.SMNΔ7;SMN2;Smn- , Moderate Type II SMA , Delta 7 mouse incipient congenic
Strain synonyms: Moderate Type II SMA mice, SMNdelta7;SMN2;Smn-/-
Research areas: Developmental Biology Research, Neurobiology Research, Research Tools

Description

Mice that are homozygous for the Smn targeted mutant lacZ reporter allele and homozygous for the two transgenic alleles exhibit symptoms and neuropathology similar to patients afflicted with proximal spinal muscular atrophy (SMA). Triple homozygous mice on the FVB/N genetic background are noticeably smaller than normal littermates at birth and show progressive muscle weakness.

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Detailed description

This triple mutant mouse harbors two transgenic alleles and a single targeted null mutant. The Tg(SMN2*delta7)4299Ahmb transgene consists of a SMA cDNA lacking exon 7 whereas the Tg(SMN2)89Ahmb transgene consists of the entire human SMN2 gene. The Smn targeted mutant lacZ reporter allele replaces endogenous Smn expression with lacZ expression.

Triple homozygous mice exhibit symptoms and neuropathology similar to patients afflicted with proximal spinal muscular atrophy (SMA). At birth, triple homozygotes are noticeably smaller than normal littermates. By day 5, signs of muscle weakness are apparent and become progressively more pronounced over the following week as the mice display an abnormal gait, shakiness in the hind limbs and a tendency to fall over. In 2006, mean survival was originally reported to be ~13 days. Cohorts tested at The Jackson Laboratory in 2013 show death by ~15-22 days (mean survival of 17.7 days).

Immunocytochemical analysis indicates that dystrophin expression is normal, however fibers isolated from the gastrocnemius muscle of a 14 day old triple mutant clearly show evidence of atrophy.

The Jackson Laboratory maintains this strain by breeding mice together that are homozygous for both transgenes (Δ7SMN^+/+;SMN2^+/+) and either heterozygous for the null allele (Smn^+/-) or wildtype at the Smn1 locus (Smn^+/+). These breeding pairs are phenotypically normal and do not exhibit symptoms of neuropathology.

In 2021, a cohort of breeders homozygous for both transgenes and heterozygous for the null allele were examined for inheritance data. 17 of 26 breeding units produced offspring (65.4%), with average litter size of ~7 pups. Of the 251 pups genotyped at 5 days of age, 56 were homozygous (22.3%).

Importation of this model was supported by the Spinal Muscular Atrophy Foundation. Creation and development was supported by the National Institutes of Health, the Deutsche Forschungsgemeinschaft to M.S., Families of SMA, the Preston fund, the Madison fund, the Mathew fund and the Muscular Dystrophy Association of America.

Development

The targeted mutant allele was created in the laboratory of Dr. Michael Sendtner at the University of Wurzburg, Germany. Exon 2 of the endogenous mouse Smn gene was disrupted by employing a targeting vector encoding a neomycin cassette and a lacZ gene fused to the first 40 nucleotides of the disrupted exon to permit expression of the lacZ gene in tissues where Smn is normally expressed. The construct was electroporated into 129P2/OlaHsd-derived E14Tg2a-IV embryonic stem (ES) cells. Correctly targeted ES cells were injected into C57BL/6 blastocysts and chimeric animals obtained. Chimeric animals were crossed to C57BL/6 for an unspecified number of generations.
The transgenic alleles were created in the laboratory of Dr. Arthur Burghes at Ohio State University. A 35.5 kb BamHI genomic fragment encoding the human SMN2 promoter and gene (derived from genomic clone PAC215P15) was injected into fertilized FVB/N mouse oocytes and founder animal 89 was obtained. Similarly, a human SMN2 cDNA (SMNdelta7) lacking exon 7 under the control of the human SMN2 promoter was microinjected into fertilized FVB/N oocytes and founder animal 4299 was obtained. Founder animal 89 was mated to mice heterozygous for the targeted mutation of the endogenous mouse Smn gene. These double mutants were in turn mated with mice bearing the SMNdelta7 transgenic allele. The triple mutant was then backcrossed to FVB/N for at least 6 generations.

Allele

Symbol: Tg(SMN2*delta7)4299Ahmb
Name: transgene insertion 4299, Arthur H M Burghes
MGI accession ID: MGI:3056918
Generation method: Transgenic
Attributes: Inserted expressed sequence; Humanized sequence
Marker symbol: Tg(SMN2*delta7)4299Ahmb
Marker name: transgene insertion 4299, Arthur H M Burghes
Chromosome: UN
Strain of origin: FVB/N
Expressed genes: SMN2,survival of motor neuron 2, centromeric,human
Site of expression: Tg(SMN2*delta7)4299Ahmb
Molecular note: The transgene contains a human SMN2 promoter and a human SMN2 cDNA (SMNdelta7) that lacks exon 7. There are 14 copies of this allele integrated into the genome.

Allele

Symbol: Smn1^tm1Msd
Name: targeted mutation 1, Michael Sendtner
MGI accession ID: MGI:2183946
Generation method: Targeted
Attributes: Reporter; Null/Knockout
Marker symbol: Smn1
Marker name: survival motor neuron 1
Chromosome: 13
Strain of origin: 129P2/OlaHsd
Expressed genes: lacZ,beta-galactosidase,E. coli
Site of expression: The expression of the lacZ gene in tissues where Smn is normally expressed was noted.
Molecular note: A lacZ-neo cassette was inserted into exon 2 by homologous recombination resulting in an in-frame fusion of lacZ to exon 2. Homozygous mutant embryos were identified up to 80 hours post coitum. The expression of the lacZ gene in tissues where Smn is normally expressed was noted.

Allele

Symbol: Grm7^{Tg(SMN2)89Ahmb}
Name: transgene insertion 89, Arthur H M Burghes
MGI accession ID: MGI:2448989
Generation method: Transgenic
Attributes: Hypomorph; Inserted expressed sequence; Humanized sequence
Marker symbol: Grm7
Marker name: glutamate receptor, metabotropic 7
Chromosome: 6
Strain of origin: FVB/N
Expressed genes: SMN2,survival of motor neuron 2, centromeric,human
Site of expression: Human SMN2 protein is expressed in the tissues examined (brain, liver, spinal cord) [Stock No. 005024].
Molecular note: A 35.5 kb genomic fragment containing the human survival motor neuron 2 (SMN2) gene and promoter was used for the transgene. The transgene is ubiquitously expressed in all tissues examined by Northern blot analysis. Line 89 carries 1 copy of the transgene integrated into intron 4 of the gene. RT-PCR confirmed reduced expression of the gene the transgene is integrated into.