Cell patterning.

  • Symposium on Cell Patterning (1974 : London, England)
Date:
1975
Catalogue details

Licence: Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)

Credit: Cell patterning. Source: Wellcome Collection.

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    membrane, but in general it is possible to imagine molecular components undergoing exchange in and out of the membrane while the pattern within the membrane persists. Brenner: All these models face certain difficulties which will have to be resolved. Here we have a piece of communication machinery different from those which have been previously considered, and which has many possibilities for generating variation. Are the models logically consistent and are they in detail biochemically plausible? Kauffman: In your model 3 with only 1000 or 2000 different enzymes you can generate a million different glycoproteins combinatorially by the sequential operation of enzymes, but how is the recognition of the million glycoproteins going to be done in this combinatorial kind of way without having a million distinct receptors? Roth: One thing that I did not state in these models, but for which we for tunately have evidence, is that there is not a stoichiometrical one-to-one relationship between enzyme and substrate. There must be a vast excess of substrates compared with enzymes, so the enzymes are the limiting factors. You will end up with an enzyme distribution exactly as in the second model; the point is that there is a gradient of completion of one polysaccharide chain as you go further in one direction. Hunt pointed out (p. 329) that this particular model was not really consistent with the fact that fibres seem to go to the right place. This would only be valid if they go to the middle in the absence of competition. Kauffman: So you have to add the enzymes in some sort of temporal sequence to get them to generate the distinct glycoprotein spatial map. If you add them all at once it would not necessarily do that. Roth: I do not agree. Wolpert: In the sort of model that you have described with the special labels, do you imply that molecules stick best to their complementary molecule? How do they stick to the one next door to it? 1 cannot see that cells from opposite ends would ever adhere. Roth: They do because the nature of oligosaccharide biosynthesis could be summed up in one word, sloppy. It is impossible to build a strictly qualitative model, a third model—it would have to be quantitative also. No one has ever got a glycoprotein or a glycolipid to be homogeneous in the sense that it always has five sugars. These components exist with between five and zero sugars and that is why they are looked on as heterogeneous and are so hard to work with. The number of variables you can throw into those models is immense and we really had to fight to weed it down to three. Wolpert: Is there any example in the whole of developmental biology which