CELL-CYCLE OF NEURAL CREST CELLS IN THE EARLY MIGRATORY STAGE IN-VIVO

The fact that directional migration of neural crest cells (NCC) in viv o occurs in narrow pathways at high cell density, together with our pr eliminary results showing their high proliferative behaviour, supports the view that a 'population pressure' could be an important factor in the mechanism of early dispersion of NCC. The purpose of this work wa s to establish the cranial proliferative pattern of chick embryo NCC d uring their early migratory stage in vivo. Growth rates and parameters of cell cycle were obtained from cell populations at several cephalic levels by means of autoradiography after labelling with [H-3]dT. The labelled cell index of NCC (Forebrain, 0.288; Midbrain, 0.206; and Hin dbrain, 0.134) was significantly greater than in other cells populatio ns (e.g. for the neural tube cells: 0.085, 0.030, and 0.031, respectiv ely). The cell generation time was the shortest in NCC (16 h), compare d to ectoderm (33 h), mesoderm (58 h) and endoderm (72 h). The duratio n of the cell cycle phases for NCC were: M, 0.29 h; G(1), 11.23 h; S, 3.40 h; and GZ, 1.02 h These quantitative results show that NCC have t he greatest proliferative rate in young chick embryos. In relation to cranial regions, the data are consistent with the idea that, in the ea rly migratory phase of this cell population in vivo, migration is in p art driven by population pressure.