The neural crest: in Xenopus and Avian models
Developmental Biology And Genetics
The Bronner laboratory is concerned with analyzing the cellular and molecular events underlying the formation, cell lineage decisions and migration of neural crest cells. The neural crest is a population of migratory cells, arising from the ectoderm of vertebrate embryos, which gives rise to a diverse range of cell types. Following neurulation, neural crest cells emerge from the neural tube and undergo extensive movements along pathways that often are characteristic of their axial level of origin. After migration, these assume one of a number of possible fates, ranging from neurons and glia of the peripheral nervous system to pigment cells and cells of the facial skeleton. What dictates the cell lineage decisions of these cells into one of numerous possible derivatives and what controls the precise and stereotypic pattern of neural crest migration? These areas represent the focus of my research. It has been classically assumed that the neural crest is a segregated population in the early ectoderm, lying between the neural plate and presumptive epidermis. However, our recent studies on avian embryos show that individual precursor cells within the "neural folds" can form neural tube (central nervous system), neural crest (peripheral nervous system) and epidermal derivatives. This led us to explore the interactions that impart the potential to form the neural crest. Interestingly, we found that neural crest cells are generated when epidermis and neural plate are juxtaposed--a classical type of embryonic induction. Our current goal is to characterize the inductive interactions that lead to formation of the neural crest and to examine how regional differences arise in the neural crest populations along the rostrocaudal axis.
With respect to neural crest migrations, we are examining the mechanisms controlling cell movement by manipulating the environment using reagents that block specific cell-cell and cell-matrix interactions as well as ectopic expression of molecules of interest by retrovirally-mediated gene transfer. We can directly observe the effects of disrupting cell interactions on neural crest cell guidance by preparing trunk explants of living embryos in which neural crest cells are labeled with a membrane intercalating dye. Importantly, we have found that inhibitory cues inherent to the somites and notochord prevent neural crest cells from entering these domains. In addition, cell-matrix interactions mediated by integrins and extracellular matrix molecules are required for normal neural crest cell migration. Our goal is to identify interactions that are important for cell migration that subsequently leads to segmentation of the peripheral nervous system. These studies shed important light on the mechanisms of neural crest formation and migration. Because neural crest cells are involved in a variety of birth defects and cancers such as neurofibromatosis, melanoma, neuroblastoma, our results on the normal mechanisms of neural crest development provide important clues regarding the mistakes that may lead to abnormal development or loss of the differentiated state