The human TAR DNA binding protein (TARDBP or TDP-43) is an ubiquinated, DNA/RNA-binding protein localized to the nucleus of cells. TDP-43 mutations in the amyloidogenic core region (residues 311-360) and the glycine-rich, flexible C-terminal region are associated with the development of amyotrophic lateral sclerosis (ALS or Lou Gehrig's disease) and frontotemporal dementia (FTD or frontotemporal lobar degeneration). The TDP-43 methionine-to-valine (M337V) missense mutation is associated with increased low molecular weight aggregates and neuronal dysfunction.
The TDP-43M337V BAC allele has a loxP-flanked, full-length human TARDBP genomic locus with M337V mutation in exon 6 and C-terminal fluorescent tag, all inserted into the Gt(ROSA)26Sor locus. Exposure to Cre recombinase leads to deletion of the TDP-43M337V BAC sequences. The phenotype of TDP-43M337V BAC mice prior to Cre recombinase is described below.
In contrast to transgene overexpression models, this Gt(ROSA)26Sor knock-in TDP-43M337V BAC allele exhibits stable, single-copy, low-level expression of TDP-43M337V-Ypet driven by the endogenous human promoter. Both homozygous and heterozygous mice of both sexes recapitulate many of the key features of ALS/FTD; including progressive motor deficits in conjunction with neuromuscular junction (NMJ) abnormalities and reduced survival.
At 12 months of age, despite a clear neuromuscular phenotype, homozygotes and heterozygotes do not demonstrate cytoplasmic mislocalization/accumulation of TDP-43 - the key pathological hallmark of ALS in the CNS.
Reduced survival is observed in both sexes (homozygotes ~500 days; heterozygotes ~650 days). The phenotype is dose-dependent: homozygous mice have an earlier age-of-onset and are more severely affected than heterozygous littermates.
In addition, cultured spinal cord motor neurons derived from heterozygous embryos show a characteristic phenotype of reduced survival, translocation of TDP-43 from nucleus to cytoplasm and reduced stress granule formation.
Homozygous and heterozygous mice are viable and fertile, with no apparent deficits in fertility or litter size compared to controls. Human TDP-43M337V-Ypet is expressed at low levels in all tissues examined in the expected pattern of cellular distribution, with no significant expression level differences reported between heterozygous or homozygous mice (cortex and spinal cord). In heterozygous mice, the TDP-43M337V-Ypet expression level is ~40% of endogenous levels.
The donating investigator reports that C-terminal Ypet tag is suitable for immunostaining via antibody directed against GFP, but not for direct fluorescence.
