Likewise, in ALS, a third molecular class exists without clear TDP-43 or FUS pathology, ALS-SOD, which is observed in ALS patients with a SOD1 mutation (76).
Analysis of TDP-1 binding in genes with increased dsRNA structure/stability in tdp-1 mutants (as assayed by J2-IP enrichment) showed about 40% of these genes contained clear TDP-1 binding sites (P = 1 × 10−21, hgd).
Score "++" means the nucleus is mostly clear of TDP-43 staining and strong, diffuse cytoplasmic staining is evident.
It has become clear that TDP-43 is a dosage-sensitive protein (76, 77) that plays an important role during development (146– 148) and in adulthood (149, 150).
Thus, although it is clear that TDP-43 plays a crucial and central role in ALS pathology many questions remain about its pathological mechanisms in ALS.
We did not observe TDP-43 binding to G4C2 repeats or mislocalization in our cellular models as has been described in C9ORF72 mutant ALS and FTD cases, and it is not yet clear whether TDP-43 misaccumulation is mechanistic in these cases.
Evidence of "nuclear clearing" of TDP-43 from neurons containing cytoplasmic inclusions, similar to that seen in two-thirds of surviving aggregate containing cells in the TDP-43WTxQ331K animals, has been reported in ALS and FTLD patients [ 4, 5] and in other mouse models [ 32, 38].
Despite lack of clear evidence for TDP-43 overexpression in ALS and FTLD patients, certain pathogenic mutations in TDP-43 showed longer half-lives of mutant protein which correlated with an earlier disease onset (82, 151).
Quantitative assessment of TDP-43 pathology was carried out by rating each ventral horn MN in examined sections according to a 5-point scale as follows: 0, no cytosolic TDP-43; 1, faint diffuse cytosolic label; 2, some granularity of cytosolic labeling with no clear aggregate; 3, some clear cytosolic TDP-43 aggregation; and 4, large and dense cytosolic TDP-43 aggregates.
Although there are clear pathologic distinctions in FTLD-TDP, the molecular pathways which underlie its progression are still mostly undefined.
How the EGFP was produced from the construct is not clear but by immunostaining using an anti-TDP-43 antibody, TDP-43 was predominantly nuclear in cells transfected with construct 1 (Fig. 3B), thus indicating that the TDP-43-EGFP fusion protein is predominantly distributed in nucleus, consistent with the literature [33], [34].
