Molecular Events Accompanying Morphogenesis
Morphogenesis, the development of shape, can be discussed both at the organismal level and the cellular level. Within a multicellular embryo several distinct morphogenetic processes occur simultaneously. First, differential mitosis results in selective stimulation of the growth of certain cell types relative to others. Selective growth can be due to any one of several cellular or extracellular factors, or to the localization of a cell type within a part of the embryo: (1) differential nutrient supplies or differential abilities of the cell types to transport and accumulate nutrients; (2) the presence of cell-specific hormones and growth factors which stimulate (or inhibit) growth of those cells that possess the requisite receptor proteins; or (3) bioelectric activities, due to the presence of ion selective channel proteins in the plasma membranes of certain cells, which may influence growth rate either by controlling the cytoplasmic ion composition or by creating a transcellular electrical potential. Second, programmed cell death plays an important role in morphogenetic processes during embryogenesis. In the developing tadpole, the Rohan-beard cells, which are important constituents of the nervous system, are programmed to die at a certain developmental stage so that other conducting cells can replace them. Loss of the tadpole tail, loss of the webbing between the fingers of the developing human hand, and regression of the Mullerian or Wolfian duct in developing male or female mammals, respectively, represent other examples of programmed cell death allowing embryonic morphogenesis. Third, cell migration and changes in cell shape occur continuously during development.
KeywordsNeurospora Crassa Nurse Cell Swarmer Cell Mycelial Morphology Membrane Whorl
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