Species: Mouse
Genes: Tardbp
Mutations: Tardbp M323K
Modification: Tardbp: Other
Disease Relevance: Frontotemporal Dementia, Amyotrophic Lateral Sclerosis
Strain Name: Tardbp M323K
Genetic Background: DBA/2J x C57BL/6J
Availability: Mice from original founders, on a hybrid DBA/2J x C57BL/6J background, are available from the RIKEN BioResource Center, BRC# GD000110.

Summary

LCDmut mice harbor the p.M323K mutation within the C-terminal low complexity domain (LCD) of the endogenous mouse Tardp gene. This line was generated after screening DNA archives from two large-scale chemical mutagenesis projects (Acevedo-Arozena et al., 2008; Gondo et al., 2010) for mutations in Tardbp. Mice express TDP-43 at physiological levels, under the control of its natural regulatory elements. Homozygous LCDmut mice exhibit a progressive motor phenotype, accompanied by p62- and ubiquitin-positive inclusions. Studies of cells and tissues derived from these mice reveal that the p.M323K mutation in TDP-43 results in a gain of splicing function, so that there is more exon skipping (i.e., skipping of specific conserved exons that are normally constitutively expressed). Although the p.M323K mutation has not been identified in human ALS or FTD patients, similar skipped exons have been found in fibroblasts from ALS patients with disease-causing mutations in the LCD of TDP-43 (Fratta et al., 2018).

When homozygous, the p.M323K mutation is embryonic lethal on a congenic C57BL/6J background.  However, homozygous LCDmut mice are viable on a mixed C57BL6J;DBA/2J background. The remainder of this description refers to mice on a hybrid C57BL/6J;DBA/2J background.

Homozygous LCDmut mice exhibit a progressive motor phenotype, but do not exhibit paralysis or premature death, at least until 24 months of age. Grip strength in both male and female mice begins to decline at 12 months of age. By 24 months, there is a nearly 40 percent reduction in force measured in tibialis anterior muscles, a 15 percent reduction in motor units innervating the extensor digitorum muscle, and a 28 percent reduction in the number of motor neurons in the sciatic motor neuron pool, compared with non-transgenic littermates.  At 18 months of age, p62- and ubiquitin-positive inclusions are found in the ventral regions of the spinal cord, although these inclusions do not appear to be located in the cytoplasm of motor neurons. TDP-43 was normally localized to the nucleus in 12-month mice.

TDP-43 levels are similar in LCDmut and wild-type mouse embryonic fibroblasts (MEFs). RNAseq revealed transcriptome-wide splicing changes in MEFs from LCDmut homozygotes compared with wild-type littermate MEFs, which were opposite of the changes seen when shRNA was used to knock down TDP-43 expression in wild-type MEFs. RNAseq analysis of spinal cords from year-old mice revealed novel exon-skipping events: 47 “skiptic” exons, skipped exons that are normally constitutively expressed, from 44 genes were identified, five of which were within genes related to the ubiquitin-proteasome pathway. iCLIP analysis performed on brains of adult LCDmut homozygotes showed that p.M323K TDP-43 maintained normal RNA binding specificity.

Modification Details

DNA archives from two large-scale chemical mutagenesis projects (Acevedo-Arozena et al., 2008; Gondo et al., 2010) were screened for mutations in Tardbp. Founder mice were produced using the mutagenesis projects’ archived sperm (on a hybrid C57BL/6J;DBA/2J  background), and backcrossed for at least five generations to place the Tardbp mutation on congenic C57BL/6J and DBA/2J backgrounds and eliminate other potential mutations. Subsequently, the two congenic lines were crossed to produce C57BL/6J; DBA/2J F1 homozygotes.

Availability

Mice from original founders, on a hybrid DBA/2J x C57BL/6J background, are available from the RIKEN BioResource Center, BRC# GD000110. C57BL/6J and DBA/2J congenic lines are in the process of being deposited at RIKEN and the European Mouse Mutant Archive (EMMA).

Phenotype Characterization

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References

Paper Citations

2. Gondo Y, Fukumura R, Murata T, Makino S. ENU-based gene-driven mutagenesis in the mouse: a next-generation gene-targeting system. Exp Anim. 2010;59(5):537-48. PubMed.
3. Fratta P, Sivakumar P, Humphrey J, Lo K, Ricketts T, Oliveira H, Brito-Armas JM, Kalmar B, Ule A, Yu Y, Birsa N, Bodo C, Collins T, Conicella AE, Mejia Maza A, Marrero-Gagliardi A, Stewart M, Mianne J, Corrochano S, Emmett W, Codner G, Groves M, Fukumura R, Gondo Y, Lythgoe M, Pauws E, Peskett E, Stanier P, Teboul L, Hallegger M, Calvo A, Chiò A, Isaacs AM, Fawzi NL, Wang E, Housman DE, Baralle F, Greensmith L, Buratti E, Plagnol V, Fisher EM, Acevedo-Arozena A. Mice with endogenous TDP-43 mutations exhibit gain of splicing function and characteristics of amyotrophic lateral sclerosis. EMBO J. 2018 Jun 1;37(11) Epub 2018 May 15 PubMed.

External Citations

1. RIKEN BioResource Center
2. RIKEN BioResource Center

Further Reading

No Available Further Reading