Homozygous C9orf72 null mice exhibit lysosomal accumulation, altered immune responses in macrophages and microglia, as well as age-related neuro-inflammation similar to human C9orf72 amyotrophic lateral sclerosis (ALS). These mice may be useful in studying human ALS and frontotemporal dementia.
Robert H Baloh, Cedars Sinai Medical Center
Cathleen Lutz, The Jackson Laboratory
Genetic Background | Generation |
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|
Allele Type | Gene Symbol | Gene Name |
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Endonuclease-mediated (Null/Knockout) | C9orf72 | C9orf72, member of C9orf72-SMCR8 complex |
The most common genetic mutation associated with human amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) is a hexanucleotide repeat expansion in a non-coding region of the chromosome 9 open reading frame 72 gene (C9orf72). Decreased expression of C9orf72 is seen in expansion carriers, suggesting loss of function may play a role in disease. The mouse 3110043O21Rik locus is the orthologue of human C9orf72.
The F12 C9orf72 null allele has a 79 bp deletion in exon 2 of the 3110043O21Rik locus (deletion extends from 38 nt upstream of ATG start codon in exon 2 to 38 nt downstream of the start codon [May 2020]). While mRNA expression levels from the mutant allele are similar to wildtype, western blot of brain lysates shows homozygous null F12 mice had complete loss of full-length C9orf72 protein. The presence/absence of proteins from any alternate transcripts identified more recently (e.g., transcript C9orf72-202 bypasses exon 2 and encodes a smaller 314 amino acid protein) has not been characterized to date (May 2020).
Homozygous mice are viable, fertile and develop normally, with no evidence of motor neuron disease or histological neurodegeneration through advanced age (17 months). Instead, C9orf72 null mice develop progressive splenomegaly and lymphadenopathy with accumulation of engorged macrophage-like cells. C9orf72 expression is normally highest in myeloid cells, and loss of C9orf72 in these C9orf72 null mice leads to lysosomal accumulation and altered immune responses in macrophages and microglia, with age-related neuroinflammation similar to C9orf72 ALS but not sporadic ALS patient tissue. The only histologic abnormalities exhibited in the nervous system of homozygous mice are rare chromatolytic structures in gray and white matter of the spinal cord, that did not increase with age or show reactive gliosis. Homozygotes exhibit no abnormalities in weight gain, lifespan, sensorimotor coordination, limb strength, muscle electrophysiology and femoral motor and sensory axon counts. [May 2016]
The F12 C9orf72 null allele (exon 2 deletion; 3110043o21Rikem5Lutzy) was created by Dr. Cat Lutz (The Jackson Laboratory) and Dr. Robert Baloh (Cedars-Sinai) using zinc finger nuclease (ZFN)-mediated genome editing in C57BL/6J mouse zygotes (Stock No. 000664).
Specifically, the 3110043O21Rik locus on chromosome 4 (orthologue of human C9orf72) was targeted by two ZFNs at the TGTTGC sequence located immediately downstream of the exon 2 ATG (GRCm38:4:35,218,827). Both ZFNs were microinjected in fertilized C57BL/6J oocytes and the live born were screened for deletions by loss-of-allele (LOA) assays designed with probes covering the respective cutting sites. Founders positive in the LOA screens were mated with wildtype C57BL/6J mice for germline transmission, and the progeny were sequenced at the locus targeted by the ZFN to map the deletions. The resulting F12 C9orf72 null mice have a 79 bp deletion in exon 2 (deletion extends from 38 nt upstream of ATG start codon in exon 2 to 38 nt downstream of the start codon [May 2020]). These mice were maintained on a C57BL/6J genetic background.
Expressed Gene | C9orf72, C9orf72, member of C9orf72-SMCR8 complex, mouse, laboratory |
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Site of Expression |
Allele Name | endonuclease-mediated mutation 5, Cathy Lutz |
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Allele Type | Endonuclease-mediated (Null/Knockout) |
Allele Synonym(s) | C9Orf72 null |
Gene Symbol and Name | C9orf72, C9orf72, member of C9orf72-SMCR8 complex |
Gene Synonym(s) | |
Expressed Gene | C9orf72, C9orf72, member of C9orf72-SMCR8 complex, mouse, laboratory |
Strain of Origin | C57BL/6J |
Chromosome | 4 |
Molecular Note | The locus is targeted by two zinc finger nucleases (ZFNs) at the TGTTGC sequence located immediately downstream of the exon 2 ATG (GRCm38:4:35,218,827) resulting in a 79 bp deletion in exon 2 (38 bp upstream of the start codon and 38 bp downstream), which maps to mm10/GRCm38:4:35,218,896-35,218,822. Western blot of brain lysates shows homozygous null mice have complete loss of full-length protein, however, mRNA expression levels from the mutant allele are similar to wild type. |
When maintaining a live colony, homozygous mice may be bred together.
When using the C9Orf72 null mouse strain in a publication, please cite the originating article(s) and include JAX stock #027068 in your Materials and Methods section.
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Heterozygous for 3110043021Rik<em5Lutzy> |
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