Cell proliferation in the embryonic quail uropygial gland during placode stage to lumen formation

The uropygial gland is one of the epidermal derivatives in birds. In the beginning of the morphogenesis of the uropygial gland of the quail embryo, placode formation occurs: Epidermal basal cells remain cuboidal until day 7 of incubation. At day 8 they begin to elongate, become columnar, and develop placode-like structure at day 9. To examine the proliferative activity of the epidermal basal cells, we recorded positions of [3H]-thymidine-labelled nuclei in serial sections by autoradiography (ARG) using a digitizer and a microcomputer. The distribution pattern of labelled nuclei was reconstituted and redisplayed on the cathode ray tube (CRT) as two-dimensional computer graphics. Three-dimensional reconstitution of the same serial sections revealed that cuboidal basal cells in the presumptive uropygial placode became columnar. Unlike the feather and scale placodes, the uropygial placode possessed no resting period of DNA synthesis. The labelling index of the uropygial placode increased considerably compared with that of nonplacode epidermis. No dermal condensation was observed beneath the uropygial placode.