Early embryonic birth of gemmal cells in the prehatching chick

This autoradiographic study in the chick embryo tested whether one possible source of cells comprising early-developing taste bud primordia arose from gemmal cell precursors, or their progeny, born during the first week of incubation. Following single in ovo injections of [ 3 H]thymidine on embryonic day (E) 2, E4 or E6, labeled gemmal cells were identified in developing, anterior lower beak taste buds on E19, which is 2 days after the first sign of bud primordium formation and 2 days before hatching. The greatest number of labeled cells/bud occurred after the E2 injection. Thus the embryonic gustatory peripheral receptor, in common with developing auditory, vestibular and retinal sensory receptor epithelia, contains at least postmitotic and/or quiescent cells whose precursors proliferated during the first week of gestation. These early pre-bud precursors could serve as tropic targets for local epithelial cells in the formation of bud primordia as well as guiding growing distal processes of the gustatory sensory ganglia whose neurons are already postmitotic by E5.