An analysis of MyoD-dependent transcription using CRISPR/Cas9 gene targeting in Xenopus tropicalis embryos

• MyoD regulates specific sets of genes prior to skeletal muscle differentiation
• CRISPR-Cas9 gene editing used to target MyoD in Xenopus resulted in highly mosaic founder (F0) embryos
• Transcriptomic analysis of F0 embryos identified genes that require MyoD activity during gastrula stages

Myogenic regulatory factors (MRFs) are known to have essential roles in both the establishment and differentiation of the skeletal muscle cell lineage. MyoD is expressed early in the Xenopus mesoderm where it is present and active several hours before the activation of muscle differentiation genes. Previous studies in cultured cells and in Xenopus laevis have identified sets of genes that require MyoD prior to differentiation of skeletal muscle. Here we report results from experiments using CRISPR/Cas9 to target the MyoD gene in the diploid frog Xenopus tropicalis, that are analysed by RNA-seq at gastrula stages. We further investigate our data using cluster analysis to compare developmental expression profiles with that of MyoD and α-cardiac actin, reference genes for skeletal muscle determination and differentiation. Our findings provide an assessment of using founder (F0) Xenopus embryos from CRISPR/Cas9 protocols for transcriptomic analyses and we conclude that although targeted F0 embryos are genetically mosaic for MyoD, there is significant disruption in the expression of a specific set of genes. We discuss candidate target genes in context of their role in the sub-programs of MyoD regulated transcription.