What cells are in the endoderm?

The endoderm is one of the germ layers – aggregates of cells that organize early during embryonic life and from which all organs and tissues develop. During the early stages of gastrulation, a group of cells called the mesoendoderm expresses sets of endoderm and mesoderm and defines genes. Cells in the mesoendoderm have the ability to differentiate into mesoderm or endoderm, depending on their position among the surrounding cells. Scientists have found mesoentoderm in many invertebrates as well as some vertebrates.