Anteroposterior Patterning in Avian Wing Bud Development: Positional Signalling and Positional Memory.

A model for the positionally-related control of cartilage differentiation in the developing avian wing was used to investigate positional memory at the cellular level. Freshly dissociated anterior mesodermal cells from quail wing buds elicit the formation of supernumerary cartilaginous structures in a high percentage of cases when they are grafted to posterior slits in host chick wing buds. This indicates that positional memory is a function of the individual cells and does not depend upon the integrity of the donor mesoderm. The donor cells do not need to be in constant contact with one another and the extracellular matrix does not need to be maintained continuously to retain this positional property. Positional memory is retained by mesodermal cells that have been cultured in vitro away from the influence of the limb field as a high-density monolayer (20 hours) or as a pellet of dissociated cells (1-2 days). Polarized supernumerary digits or rods of supernumerary cartilage develop when Hensen's nodes from stage 4-6 quail or chick embryos are grafted to anterior slits in chick wing buds. No supernumerary digits developed when tissues that have limb-inducing activity (chick otic vesicle, frog (Rana pipiens) lung and kidney) or that can act as heteroinductors in primary embryonic induction (rat kidney, lung, submaxillary gl and and urinary bladder; mouse liver and submaxillary gl and ) were grafted to anterior slits in chick wing buds. Supernumerary digits also failed to develop following preaxial grafts of chick optic vesicles. These results support the hypothesis that a universal signal may provide positional information in different embryonic fields. Hensen's node may be the source of one signal that can act as an "organizer" in establishing the primary body axis and as a "polarizer" if it is grafted to the anterior side of a developing wing. Alternatively, the polarizing signal that is found at later stages in the zone of polarizing activity (ZPA) in the wing bud may originate in Hensen's node and move into the ZPA during development.PhDBiologyZoologyUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/161726/1/8801423.pd