It takes guts: Development of the embryonic and juvenile zebrafish digestive system

Endoderm is specified around the blastula margin followed by migration to the midline. Endoderm organizes into individual digestive organs that later connect to form a patent tube. Few cells are specified as endoderm early in embryogenesis requiring extensive proliferation through the first 3days of embryogenesis. Proliferation is driven by at least three major pathways (Epidermal Growth Factor Insulin-like Growth Factor (IGF), and Wnt) demonstrated to promote proliferation in other vertebrates. Epithelial proliferation becomes restricted to the interfold base by the end of embryogenesis. At the end of embryogenesis, a functional digestive system has formed. Although the digestive system is functional at the end of embryogenesis, with cell types and organs common to other vertebrates, it takes another 4weeks to mature to the adult form. At 4weeks postembryogenesis, the proliferation pattern matures into the adult form with the progeny of asymmetric stem cell divisions differentiating as they migrate up the fold to undergo apoptosis at the tips.