Introduction
Human pluripotent stem cells (hPSC), either embryonic stem cells (hESC) or induced pluripotent stem cells (iPSC) are a powerful tool to model repeat instability in DM1.
Mismatch repair genes, especially Msh2, play an important role in inducing repeat instability in DM1 as shown in knock out mouse models. Also, human cell models with a downregulation of MSH2 induced by shRNA indicate MSH2 as a possible instability modifier. However, remaining MSH2 protein levels in down regulation experiments in human cell models and methods to measure instability with a limited resolution probably only yielded partial answers.

Methods
To fully understand the role of MSH2 in repeat instability in human models, we knocked out MSH2 in three DM1 hESC lines and two hiPSC lines derived from two different DM1 patients using CRISPR/Cas9 systems. Repeat instability in hPSCs was measured by PacBio sequencing of long range PCR fragments spanning the repeat, allowing accurate and complete assessment of the TNR length.

Results
Our preliminary data shows that the first MSH2 wild type DM1 hESC line has a wide repeat size distribution compared to its MSH2 mutant line in which the repeat lengths are less heterogeneous and cluster around a particular CTG expansion. Our results suggest that MSH2 drives repeat instability in DM1 hPSCs and that a lack of MSH2 could stabilize the CTG repeat. However, our other MSH2 knock-out hPSC lines still need to be analysed and could probably strengthen this first observation.

Discussion
We show that hPSC are excellent models for DM1, as we have reiterated the previously observed role of MSH2 in TNR instability. Differentiation of our MSH2 knock-out hPSC lines into disease-relevant tissues or manipulation of other instability modifiers will expand the model.

Grant support
FWO grant G02315N, Chair Mireille Aerens and Methusalem grant to K. Sermon, Association Belge contre les Myopathies neuroMusculaires (ABMM).

Original languageEnglish
StateUnpublished - 5 Sep 2017
EventIDMC-11 conference - San Fransisco, California, United States
Duration: 5 Sep 20179 Sep 2017

Conference

ConferenceIDMC-11 conference
CountryUnited States
CityCalifornia
Period5/09/179/09/17

ID: 35107089