![]() Usually, cranial neural crest (arch crest, red) cells cannot give rise to cartilage when grafted to the trunk. (C) Heterotopic grafts were used to explore the role of tissue interactions during neural crest chondrogenesis. When grafted into other species, pigment cells continued to form patterns characteristic of the donor, indicating that pigment distribution is dependent on the intrinsic ability of neural crest cells to migrate and aggregate. To understand whether patterning information is intrinsic to neural crest cells or imparted by the environment, trunk neural crest was reciprocally exchanged between two species: T. (B) Neural crest cells give rise to melanophores. In the chimeric animal, the gill arch skeleton on the transplanted side was larger than that on the host side owing to different growth rates between the two species, demonstrating that the gill arch skeleton originates from hindbrain neural crest. tigrinum) was transplanted to another host. After migration, the pharyngeal wall (outlined in red) containing neural crest cells from the donor ( Amb. (A) A neural crest contribution to the gill arch skeleton was mapped by interchanging hindbrain and ectoderm (arch crest, red) between Amb. Understanding neural crest development through transplantation experiments. A caveat of such interspecific grafts, however, is that they may alter normal tissue interactions, thus modulating signaling and timing events between donor and host tissues in unpredictable ways ( Hörstadius, 1950). He discovered that grafted cells undergo migratory patterns characteristic of the donor, indicating that intrinsic properties of the pigment cells, rather than the environment, affected cell migration ( Twitty, 1945) ( Fig. 1B). The migratory properties of neural crest cells were examined in a similar way by Victor Twitty, who interchanged trunk neural crest cells between two species of salamander, Triturus rivularis and Trogulus torosus, with distinct pigment patterns. ![]() Gill size in the resulting chimera matched that of the donor on the transplanted side, suggesting that intrinsic information in the neural crest contributed to the arch skeleton ( Harrison, 1935) ( Fig. 1A). In this way, only branchial neural crest cells were derived from the donor. After neural crest cells had migrated to the arch, the branchial arch itself – including both donor and host cells – was transplanted to another host of the same species. tigrinum or mexicanum, the gill arches of which vary in size. To understand whether neural crest cells contribute to the gill arch skeleton, Harrison exchanged hindbrain regions between two amphibian species, Amblystoma punctatum and Amb. One lineage-tracing experiment Hörstadius addressed as ‘exceedingly beautiful’ was performed by Ross Harrison in 1935. For example, how do migrating neural crest cells interact with each other, both molecularly and mechanically? How are lineage decisions coupled with migration, and how do neural crest cells interact with the rapidly developing surrounding tissue? As neural crest cells have stem cell properties, what is their degree of fate restriction versus multipotency to form diverse cell types? How does this vary along the rostrocaudal body axis? In the adult, do neural crest-derived cells participate in tissue repair? How and why do things go wrong, resulting in neural crest-derived tumor formation? These questions require the means to indelibly label the progeny of single cells or specific groups of neural crest cells in vivo, while enabling assessment of their transcriptomic landscape, spatial characteristics and cellular dynamics. Thus, there are many interesting unanswered questions about neural crest development. ![]() Although experimental embryologists over the past century have mapped neural crest cells at all of these axial levels, recent studies using refined tools have revealed previously unrecognized neural crest derivatives and behaviors. ![]()
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