Collection of definitive endoderm from E8.0–8.5 mouse embryo. (A) Dissection procedure and germ layer separation process. After trypsin treatment, ectoderm and endoderm can be separated (indicated by the red line). After the somites and mesoderm were removed, enriched ectoderm and endoderm can be obtained. (B) Photographs of the intact dissected endoderm at the indicated somite stage. Somite 0–6 endoderm pieces were pooled for the early whole endoderm library. Somite 8–12 endodermal portions were separated into foregut and hindgut portions (indicated by the red line). So: somite; end: endoderm; ect: ectoderm; F: foregut; H: hindgut.