Roles for Tgfß1 in Chick Embryo Cell Transformation
Early embryonic development is characterized by the occurrence of sequential epithelial-to-mesenchymal and mesenchymal-to-epithelial cell transformations, each of which results in the appearance of a novel cell population. The factors that trigger and influence these early cell transformations are unknown, but may rely on changes in the complement of receptors at the cell surface, changes in the surrounding extracellular matrix, or changes in the influence of local soluble factors. Such events are well-illustrated by the differentiation of the various divisions of the early mesoderm in the avian embryo (Sanders, 1989; 1991). In this sequence, cells of the epithelial epiblast are first transformed into mesenchyme by passage through the primitive streak -- a region in which as yet undisclosed cell events result in localized phenotypic transformation (Bellairs, 1986; Sanders, 1986). After emergence from the primitive streak, the mesodermal cells align paraxially to form the transient segmental plate from which, by mesenchymal-to-epithelial transformation, somites form (Bellairs, 1979). Further differentiation of this tissue necessitates dispersal of its ventromedial portion into sclerotome, as a result of a transformation back into the mesenchymal phenotype. Nothing is known of the factors that precipitate this dispersal.
KeywordsChick Embryo Embryonic Axis Mesenchymal Phenotype Primitive Streak Mesoderm Cell
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