MOUSE-CHICK CHIMERA - A DEVELOPMENTAL MODEL OF MURINE NEUROGENIC CELLS

Chimeras were prepared by transplanting fragments of neural primordium from 8- to 8.5- and 9-day postcoital mouse embryos into 1.5- and 2-da y-old chick embryos at different axial levels. Mouse neuroepithelial c ells differentiated in ovo and organized to form the different cellula r compartments normally constituting the central nervous system. The g raft also entered into the development of the peripheral nervous syste m through migration of neural crest cells associated with mouse neuroe pithelium. Depending on the graft level, mouse crest cells participate d in the formation of various derivatives such as head components, sen sory ganglia, orthosympathetic ganglionic chain, nerves and neuroendoc rine glands. Tenascin knockout mice, which express lacZ instead of ten ascin and show no tenascin production (Saga, Y., Yagi, J., Ikawa, Y., Sakakura, T. and Aizawa, S. (1992) Genes and Development 6, 1821-1838) , were specifically used to label Schwann cells lining nerves derived from the implant. Although our experiments do not consider how mouse n eural tube can participate in the mechanism required to maintain myoge nesis in the host somites, they show that the grafted neural tube beha ves in the same manner as the chick host neural tube. Together with ou r previous results on somite development (Fontaine-Perus, J., Jarno, V ., Fournier Le Ray, C., Li, Z. and Paulin, D. (1995) Development 121, 1705-1718), this study shows that chick embryo constitutes a privilege d environment, facilitating access to the developmental potentials of normal or defective mammalian cells. It allows the study of the histog enesis and precise timing of a known structure, as well as the implica tion of a given gene at all equivalent mammalian embryonic stages.