CTG repeat expansion (CTGexp) is associated with aberrant
alternate splicing that contributes to cardiac dysfunction in
myotonic dystrophy type 1 (DM1). Excision of this CTGexp
repeat using CRISPR-Cas resulted in the disappearance of
punctate ribonuclear foci in cardiomyocyte-like cells derived
from DM1-induced pluripotent stem cells (iPSCs). This was
associated with correction of the underlying spliceopathy as
determined by RNA sequencing and alternate splicing analysis.
Certain genes were of particular interest due to their role in cardiac
development, maturation, and function (TPM4, CYP2J2,
DMD, MBNL3, CACNA1H, ROCK2, ACTB) or their association
with splicing (SMN2, GCFC2, MBNL3). Moreover, while
comparing isogenic CRISPR-Cas9-corrected versus non-corrected
DM1 cardiomyocytes, a prominent difference in the
splicing pattern for a number of candidate genes was apparent
pertaining to genes that are associated with cardiac function
(TNNT, TNNT2, TTN, TPM1, SYNE1, CACNA1A, MTMR1,
NEBL, TPM1), cellular signaling (NCOR2, CLIP1, LRRFIP2,
CLASP1, CAMK2G), and other DM1-related genes (i.e.,
NUMA1, MBNL2, LDB3) in addition to the disease-causing
DMPK gene itself. Subsequent validation using a selected
gene subset, including MBNL1, MBNL2, INSR, ADD3, and
CRTC2, further confirmed correction of the spliceopathy
following CTGexp repeat excision. To our knowledge, the present
study provides the first comprehensive unbiased transcriptome-
wide analysis of the differential splicing landscape in
DM1 patient-derived cardiac cells after excision of the CTGexp
repeat using CRISPR-Cas9, showing reversal of the abnormal
cardiac spliceopathy in DM1