Hormone Receptors and Malformations

Abstract

Differentiation may be considered as an orderly progression of various morphological, cellular, and biochemical events which occur temporally and spatially during development in specific cell types. During embryogenesis, an array of cellular interactions are proceeding along genetically and epigenetically defined pathways. These interactions can be direct cell-cell-or tissue-tissue interactions such as occur between the epithelium and adjacent mesenchyme in the developing pancreas, thyroid, salivary glands, lung, intestine, kidney, mammary gland, and secondary palate (Salomon and Pratt 1979; Kratochwil 1972; Saxén 1972; Le Douarin 1970), as mediated by the extracellular matrix (Grobstein 1975). Alternatively, indirect interactions perform equally important roles during development. These interactions occur between adjacent or distant cell types and are mediated by extracellular or intracellular chemical messengers (hormones, growth factors, and cyclic nucleotides). Hormones are compounds which are specific products of one or more groups of cells (endocrine tissue) that are transported in the vascular system to other groups of cells (target tissue) which are capable of responding in a specific physiologic and biochemical manner. Cells of one tissue may also produce growth factors locally which affect an adjacent, but different, cell type (paracrine) without entering the vascular system. There is also evidence for autocrine growth regulation in which a cell which is producing a growth factor can also respond to that same growth factor (Sporn and Todaro 1980). Paracrine or autocrine regulation of growth and/or differentiation could play an important role during development under circumstances where one cell type is locally influencing the differentiation of a second cell type (Salomon et al. 1981; Saxén 1972).