GSE134528
CRISPR/Cas9/AAV9-sgRNA Mediated In Vivo Genome Editing  Reveals the Indispensability of Myc During Muscle Stem Cells Activation by Remodeling the 3D Chromatin [Deep-seq(dose)]
Skeletal muscle satellite cells (SCs) are muscle stem cells responsible for muscle development and injury induced muscle regeneration. The pace of SC related study, however, is constrained partially by the technological limitations in generating genetically modified mice. Although the ease of use of CRISPR-Cas9 in genome manipulation has been documented in many cell lines and various species, its application in endogenous SCs remains elusive. In this study, we generated muscle-specific Cas9-expressing mice and achieved robust in vivo genome editing in juvenile SCs at the postnatal stage through AAV9 mediated short guide RNAs (sgRNAs) delivery. We also found adult quiescent SCs are reluctant to CRISPR/Cas9 editing despite efficient AAV9 transduction. To edit juvenile SCs in vivo, as a proof-of-concept, we delivered sgRNAs targeting MyoD, a key gene critical for muscle physiology and showed an efficient editing at MyoD locus, resulting in accumulation of SCs and defects in SCs differentiation which resembled the phenotypes reported in MyoD knockout mice. Further application of this system on potential key transcription factors (TFs) involved in SC fate transition, Myc, Bcl6 and Pknox2, unveiled their distinct functions in the early stage of SC activation and injury induced muscle regeneration. In addition, we revealed that Myc orchestrated SCs activation through impinging on 3D chromatin architecture. Altogether we established a robust muscle restricted CRISPR/Cas9-based gene editing platform in endogenous SCs and elucidated the functionality of key factors governing SC activities. Overall design: Pax7Cas9 mice were administrated with different doses of single AAV-sgMyoD (high: 5×1011 vg/mouse; middle; 1×1011 vg/mouse; low: 0.2×1011 vg/mouse) virus intramuscularly at P10. Pax7Cas9 mice administrated with a high (5×1011 vg/mouse) dose of AAV9 virus containing pAAV9-sgRNA backbone without any sgRNA insertion were used as control. Muscle stem cells were isolated 4 weeks after injection and sgMyoD targeted locus was amplified from genomic DNA in freshly isolated satellite cells and subjected to deep sequencing.