All three MutL complexes are required for repeat expansion in a human stem cell model of CAG-repeat expansion mediated glutaminase deficiency
This article has been Reviewed by the following groups
Listed in
- Evaluated articles (Arcadia Science)
Abstract
The Repeat Expansion Diseases (REDs) arise from expansion of a disease-specific short tandem repeat (STR). Different REDs differ with respect to the repeat involved, the cells that are most expansion prone and the extent of expansion and whether these diseases share a common expansion mechanism is unclear. To date, expansion has only been studied in a limited number of REDs. Here we report the first studies of the expansion mechanism in induced pluripotent stem cells derived from a patient with a form of the glutaminase deficiency disorder known as Global Developmental Delay, Progressive Ataxia, And Elevated Glutamine (GDPAG; OMIM# 618412) caused by the expansion of a CAG-STR in the 5’ UTR of the glutaminase ( GLS ) gene. We show that alleles with as few as ∼100 repeats show detectable expansions in culture despite relatively low levels of R-looped formed at this locus. Additionally, using a CRISPR-cas9 knockout approach we show that PMS2 and MLH3, the constituents of MutLα and MutLψ, the 2 mammalian MutL complexes known to be involved in mismatch repair (MMR), are essential for expansion. Furthermore, PMS1, a component of a less well understood MutL complex, MutLβ, is also important, if not essential, for repeat expansion in these cells. Our results provide insights into the factors important for expansion and lend weight to the idea that, despite some differences, many, if not all, REDs likely expand via in very similar ways.
Article activity feed
-
Rather it may be a general feature of expansion in the REDs
I'm really excited by this hypothesis! Do you know how well conserved these mismatch repair proteins are? We recently used comparative genomics to find repeat expanded proteins across diverse organisms, but didn't look into mismatch repair proteins at all. If there's an evolutionary link between the presence/variant of mismatch proteins and repeat expansions that would provide strong evidence for your hypothesis!
-
The number of repeats in the PMS2 and MLH3 null lines did not change over the same period (Fig 5 - 6), consistent with the idea that MutLα and MutLψ are both required for expansion in these cells.
It's very compelling that no matter which mismatch repair protein you knock-out you can basically stop expansion in these cells compared to the original culture! Rather than just comparing to the original culture, could you show the repeat length for an unedited culture to the knock out culture over time? It might be particularly nice if the unedited culture also got CRISPR treatment but with a scrambled guide RNA as a negative control!
-
∼1 repeat/day or ∼1 expansion event/day
Wow, how interesting! Do you have data for the in vivo expansion rate for patient P2 to compare this in vitro rate to? Or alternatively, how does this rate compare with the estimated rate of somatic mutation for GDPAG patients in general?
-
-