DEVELOPMENTAL BIOLOGY 121,220-236 (1987) Neural Crest Cell Migratory Pathways in the Trunk of the Chick Embryo J. F. LORING AND C. A. ERICKSON Department of Zoology, University of California, Davis, California 95616 Received July 7, 1986; accepted in revised form December 15, 1986 Neural crest cells migrate during embryogenesis to give rise to segmented structures of the vertebrate peripheral nervous system: namely, the dorsal root ganglia and the sympathetic chain. However, neural crest cells arise from the dorsal neural tube where they are apparently unsegmented. It is generally agreed that the somites impose segmentation on migrating crest cells, but there is a disagreement about two basic questions: (1) exactly what pathways do neural crest cells use to move through or around somites, and (2) do neural crest cells actively migrate or are they passively dispersed by the movement of somite cells? The answers to both questions are critically important to any further understanding of the mechanisms underlying the precise distribution of the neural crest cells that develop into ganglia. We have done an exhaustive study of the locations of neural crest cells in chick embryos during early stages of their movement, using antibodies to neural crest cells (HNK-l), to neural filament-associated protein in growing nerve processes (E/CS), and to the extracellular matrix molecule laminin. Our results show that (1) Some neural crest cells invade the extracellular space between adjacent somites, but the apparent majority move into the somites themselves along the border between the dermatome/myotome (DM) and the sclerotome. (2) Neural crest cells remain closely associated with the anterior half of the DM of developing somites as they travel, suggesting that the basal lamina of the DM may be used as a migratory substratum. Supporting this idea is our observation that the development of the DM basal lamina coincides in time and location with the onset of crest migration through the somite. (3) The leading front of neural crest cells advance through the somite while the length of the DM pathway remains constant, suggesting active locomotion, at least in this early phase of development. (4) Neural crest cells leave the DM at a later stage of development to associate with the dorsal aorta, where sympathetic ganglia form, and to associate with newly emerging fibers of the ventral root nerve, where they presumably give rise to neuronal supportive cells. Thus we propose that the establishment of the segmental pattern of the peripheral ganglia and nerves depends on the timely development of appropriate substrata to guide and distribute migrating neural crest cells during the early stages of embryogenesis. o 1987 Academic Press, Inc. INTRODUCTION The peripheral nervous system in the trunk of ver- tebrate embryos is segmented. Although the origin and control of this segmentation during development is un- known, embryonic structures such as the somites are thought to be important in producing the pattern of the peripheral nervous system. Early studies by Lehmann (1927) showed that removal of somites produces a loss of sensory ganglia at the axial level of ablation, whereas Detwiler (1937) found that addition of extra somites re- sults in duplicated spinal nerves and ganglia. Recently, the somites have been shown to have a role in the pattern of outgrowth of segmented motor nerves as well (Keynes and Stern, 1984,1985). The development of the segmented pattern of spinal nerves and ganglia is presumably generated during mi- gration and localization of the progenitor cells and their axons. Because most of the peripheral nervous system of the trunk is derived from the neural crest (for review, see Le Douarin, 1982; Erickson, 1986), we were interested in knowing what environmental features regulate the migratory pathways of the trunk neural crest cells. In particular, we wanted to map the pathways of migration through or around the somites, since there has been considerable controversy in the literature concerning the precise movement of neural crest cells during the earliest stages of their migration (Weston, 1963; Thiery et al., 1982). The recent development of an antibody that rec- ognizes migrating neural crest cells (NC-l, HNK-1: Vin- cent et al., 1983; Vincent and Thiery, 1984; Tucker et al., 1984) has allowed us to observe the distribution of neural crest cells in embryonic sections and whole embryos and, by examining embryos of differing ages, to infer the pathways of crest cell migration. We did not have to perturb normal development, as is required with other marking techniques (Weston, 1963; Le Douarin and Teillet, 1974). Our studies suggest that timely develop- mental changes in other embryonic tissues, including the somites and central nervous system axons, provide substrata that pattern the migration of neural crest cells and ultimately the locations of neural crest-derived ganglia and nerves. MATERIALS AND METHODS Tissue Culture Neural tubes associated with the last five somites and the segmental plate were cut from 22-somite chick em- 0012-1606/87 $3.00 Copyright 0 1987 by Academic Press, Inc. All rights of reproduction in any form reserved. 220