(A) Embryos injected at the one-cell stage with mRNA or Cas9 + gRNAs for endoderm master regulator sox32. in situ hybridization at shield stage, dorsal to the right. Expression of aplnrA, fn1a and ta decrease slightly or do not change in the presence of excess endoderm and increase in the absence of endoderm. (B–C) PCR of a genomic locus (B: sox32; C: cxcr4a) in wild-type embryos, wild-type embryos injected with Cas9 or wild-type embryos injected with Cas9 and sox32 gRNAs. Each lane represents an individual 2-day-old embryo that was injected at the one-cell stage. (B) Evidence of various large deletions in the genomic sox32 locus in response to injection of Cas9 and sox32 gRNAs. (C) The locus of a non-targeted gene, cxcr4a, is unaffected by injection of Cas9 and sox32 gRNAs.