Aberrant splicing in transgenes containing introns, exons, and V5 epitopes: lessons from developing an FSHD mouse model expressing a D4Z4 repeat with flanking genomic sequences.
The DUX4 gene, encoded within D4Z4 repeats on human chromosome 4q35, has recently emerged as a key factor in the pathogenic mechanisms underlying Facioscapulohumeral muscular dystrophy (FSHD). This recognition prompted development of animal models expressing the DUX4 open reading frame (ORF) alone or embedded within D4Z4 repeats. In the first published model, we used adeno-associated viral vectors (AAV) and strong viral control elements (CMV promoter, SV40 poly A) to demonstrate that the DUX4 cDNA caused dose-dependent toxicity in mouse muscles. As a follow-up, we designed a second generation of DUX4-expressing AAV vectors to more faithfully genocopy the FSHD-permissive D4Z4 repeat region located at 4q35. This new vector (called AAV.D4Z4.V5.pLAM) contained the D4Z4/DUX4 promoter region, a V5 epitope-tagged DUX4 ORF, and the natural 3' untranslated region (pLAM) harboring two small introns, DUX4 exons 2 and 3, and the non-canonical poly A signal required for stabilizing DUX4 mRNA in FSHD. AAV.D4Z4.V5.pLAM failed to recapitulate the robust pathology of our first generation vectors following delivery to mouse muscle. We found that the DUX4.V5 junction sequence created an unexpected splice donor in the pre-mRNA that was preferentially utilized to remove the V5 coding sequence and DUX4 stop codon, yielding non-functional DUX4 protein with 55 additional residues on its carboxyl-terminus. Importantly, we further found that aberrant splicing could occur in any expression construct containing a functional splice acceptor and sequences resembling minimal splice donors. Our findings represent an interesting case study with respect to AAV.D4Z4.V5.pLAM, but more broadly serve as a note of caution for designing constructs containing V5 epitope tags and/or transgenes with downstream introns and exons.
University of Mons, Research Institute for Health Sciences and Technology, Laboratory of Molecular Biology, Mons, Belgium.
Eugénie
E
Ansseau
Center for Gene Therapy, The Research Institute at Nationwide Children's Hospital, Columbus, OH, United States of America.
Jacqueline S
JS
Domire
Center for Gene Therapy, The Research Institute at Nationwide Children's Hospital, Columbus, OH, United States of America.
Lindsay M
LM
Wallace
Center for Gene Therapy, The Research Institute at Nationwide Children's Hospital, Columbus, OH, United States of America.
Jocelyn O
JO
Eidahl
Center for Gene Therapy, The Research Institute at Nationwide Children's Hospital, Columbus, OH, United States of America.
Susan M
SM
Guckes
Center for Gene Therapy, The Research Institute at Nationwide Children's Hospital, Columbus, OH, United States of America; Biomedical Sciences Graduate Program, The Ohio State University, Columbus, OH, United States of America.
Carlee R
CR
Giesige
Center for Gene Therapy, The Research Institute at Nationwide Children's Hospital, Columbus, OH, United States of America.
Nettie K
NK
Pyne
University of Mons, Research Institute for Health Sciences and Technology, Laboratory of Molecular Biology, Mons, Belgium.
Alexandra
A
Belayew
Center for Gene Therapy, The Research Institute at Nationwide Children's Hospital, Columbus, OH, United States of America; Biomedical Sciences Graduate Program, The Ohio State University, Columbus, OH, United States of America; Department of Pediatrics, The Ohio State University College of Medicine, Columbus, OH, United States of America.
Scott Q
SQ
Harper
D000818:Animals; D004195:Disease Models, Animal; D000939:Epitopes / Q000235:genetics*; D005091:Exons; D007438:Introns; D051379:Mice; D020391:Muscular Dystrophy, Facioscapulohumeral / Q000235:genetics*; D022821:RNA Splice Sites; D019076:Transgenes
D000939:Epitopes; D022821:RNA Splice Sites