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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    ventral tectum halves more readily than they do to dorsal halves. For the next three hours, ventral retina cells adhere significantly more rapidly to dorsal tecta while their rate of attachment to ventral tecta declines drastically. The overall result is that, after six hours, more ventral retina cells are adhering to dorsal tecta than to ventral tecta. There is, therefore, a preferential adhesion, that is easily measurable, of both dorsal and ventral retina cells to their physiologically matching tectal half six hours after the retina cells have been trypsinized. Similar results with optic tecta uninnervated by retina show that the observed specificity is not just a result of retinal cells adhering to their own axons on the surface of the tectum. As a further control, labelled cell suspensions are prepared from liver, cerebellum or brain stem of comparably aged chick embryos. No preferential adhesion to either tectal half is seen. Similar ex periments have been conducted under a wide variety of conditions, the results of which will be presented in detail elsewhere (Barbera, in preparation). These experiments show that adhesive specificity between retinal and tectal cells in the developing chick embryo correlate well with the final projection of the retina on the tectum. Cells from the dorsal half of the retina adhere prefer entially to the ventral half of the tectum and vice versa. It is possible, therefore, that these differential affinities are the cause of the orderly arrangement of the retinal ganglion termini over the expanse of the tectum. These data are best explained by the presence of relatively permanent, cell surface molecules that mediate selective intercellular adhesion. The molecules should vary either quantitatively or qualitatively across the retina and tectum so that physiol ogically connected areas of these tissues show the highest degree of adhesion. In these respects, these experiments support Sperry’s hypothesis of neuronal specificity. MOLECULAR MODELS We have constructed three models that attempt to translate the hypothetical specificity-conferring entities of Sperry’s theory into molecules known to exist on cell surfaces and linked to selective adhesion in other systems. As was the original hypothesis of neuronal specificity, the models are presented with reference to the retinotectal projection of lower vertebrates. Sperry himself made no speculations as to the chemical identity of the molecules involved. Barondes (1970) presented a model in which the sugar composition of the macromolecules on the surface of the retinal and tectal cells determined the adhesive specificity. He proposed that varying lengths of sugar chains along one axis coupled with varying numbers of negatively charged residues along the other axis could yield the final retinotectal pattern.