. Biological structure and function; proceedings. Biochemistry; Cytology. CELL DIFFERENTIATION 523 micro-en\ironment such that "outside"cells now find themselves" inside" as in the case with buried neural tissue that once was external epithelium. The three germ layers of the embryo, in fact, represent the outside and inside of a hollow sphere respectively, together with those most anaero- bically placed, the mesoderm that is literally sandwiched between its epidermal and endodermal neighbours. A picture of sequential pro- gramming thus arises, the order of the programming b
. Biological structure and function; proceedings. Biochemistry; Cytology. CELL DIFFERENTIATION 523 micro-en\ironment such that "outside"cells now find themselves" inside" as in the case with buried neural tissue that once was external epithelium. The three germ layers of the embryo, in fact, represent the outside and inside of a hollow sphere respectively, together with those most anaero- bically placed, the mesoderm that is literally sandwiched between its epidermal and endodermal neighbours. A picture of sequential pro- gramming thus arises, the order of the programming being vital in that exposure to high-then-low levels of micro-environmental pCOo should. morphogenetic movement differentiation Fig. 6. Diagram to illustrate tht interrelatiuns between growth, morphogenetic movement, and cellular differentiation (from Bonner [14]). cause a ditferent type of differentiated cell from one that has been exposed to low-then-high. As in the education of a young man, exposure to different environments can produce different final results. Why do cells move from one location to another within the developing embryo ? One answer may be that they become positively or negatively chemotactic to pCOo. Thus, Chlamydomonas cells are known to be chemo- tactic to pCO., [15] and even the acrasin phenomenon in slime moulds may be due to the mutual attraction of the washed amoebae owing to their positive chemotaxis towards a high pCO., such as that generated by their neighbours. Preliminary experiments in our laboratory have shown that. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original IUB/IUBS International Symposium (1st : 1960 : Stockholm); International Union of Biochemistry; International Union of Biological Sciences; Goodwin, T. W. (Trevor Walworth); Lindberg, Olov, 1914-. London, New York, Ac
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