Figure 5
From: Assessing average somatic CAG repeat instability at the protein level
MSD signal ratio for mHTT by total HTT, corresponding to the average polyQ length, correlates with average CAG repeat length. (a) Striatal homogenates from 14 homozygous HdhQ140 KI mice of different ages were analyzed by MSD assay for average polyQ length quantification (MSD signal ratio MW1/MAB5492 corresponding to mHTT/Total HTT). Results were plotted as a function of average CAG repeat length determined by PCR method in DNA extracted from the contralateral striatum of each animal (see Methods, Quantification of average CAG repeat length). It is unclear why there is more variability (larger SDs) in raw MSD signals for samples between ~108 and 124 CAG repeats than for other samples. All samples were processed at the same time and in the same manner, so it is likely that variation may be from pipetting. (b) Homogenates prepared from postmortem cortex of HD patients were analyzed by MSD assay for average polyQ length quantification (MSD signal ratio for mHTT by total HTT). Results were plotted as a function of average CAG repeat length determined by PCR method from the same sample lysates (see Methods, Quantification of average CAG repeat length). Light blue sample was below the level of detection (background + 3 SD) for total HTT assay and was not used for correlation. Mean values ± propagated SD (1 σ) of duplicates of a single experiment are shown. Please note that the MSD signal is normalized using the following MSD signal ratio (MSD of mHTT/MSD of Total HTT; plotted on y-axis in the figure). The MSD signal for total HTT is solely dependent on protein concentration and does not depend on polyQ length.
