Studies on the morphogenesis of the stomach of the chick embryo

The development of the chicken stomach, particularly its asymmetrical and glandular morphogenesis is poorly understood. From a straight epithelial tube the gizzard endoderm evaginates dorsally to form the basic asymmetrical shape. It is suggested that evagination might be brought about by contractile elements in the dorsal bulging epithelium. The cell proliferation rate, examined by tritiated thymidine autoradiography, decreased in the bulging epithelium. Thus cell proliferation was not responsible for evagination morphogenesis. Expansion of the gizzard dorsally was achieved by differential localization of cell proliferation to the dorsal-most epithelium. There was also differential localized cell proliferation to the dorsal-most mesenchyme. The morphogenesis of the proventricular exocrine tubular glands was described using transmission electron microscopy and tritiated thymidine autoradiography. Development began by numerous evaginations in the rapidly dividing endoderm in which population pressure might have been developing. Evaginations were also brought about by cell shape changes which were thought to be caused by contractile elements. Localization of cell proliferation to the distal expanding tubule was the mechanism by which the glands expanded. The morphogensis of the gizzard tubular glands was also examined using light and electron microscopy. From columnar cells the epithelium became stratified in morphology and penetrated the underlying tunica propria. Deep in the stratified layer, microlumina formed between the cells which were delineated with junctional complexes. These were similar to the apical junctional complexes. The microlumina coalesced, expanded, and eventually opened up to the main lumen. A changing pattern of mitotic figures was noted. The pits developed by cell detachment and invasion by the underlying mesenchymal papilla. Epithelial cells from the transient stratified stage were examined in tissue culture. They mimicked their in vivo behaviour and managed to form small microlumina when plated on gizzard fibroblasts of the same age