Showing papers by "Stuart A. Newman published in 1997"

Biological Physics of the Developing Embryo

Abstract: Introduction 1. The cell: fundamental unit of developmental systems 2. Cleavage and blastula formation 3. Cell states: stability, oscillation, differentiation 4. Cell adhesion, compartmentalization and lumen formation 5. Epithelial morphogenesis: gastrulation and neurulation 6. Mesenchymal morphogenesis 7. Pattern formation: segmentation, axes and asymmetry 8. Organogenesis 9. Fertilization: generating one living dynamical system from two 10. Evolution of developmental mechanisms Glossary References Index.

Genetic Evolution of Morphology

Abstract: Two commentaries in the 4 July issue, by their contrast, inadvertently point to a missing element in most discussions of the evolution of animal form. In his Perspective “Which came first, the hypha or the yeast?” ([p. 52][1]), P. T. Magee draws the lesson from a report by B. R. Braun and A. D. Johnson ([4 July, p. 105][2]) that the existence of a simple genetic switch between the budding yeast and the thread-like hypha morphologies of Candida albicans suggests that “there is no ‘default’ form for this organism.” This seems reasonable: C. albicans is thought of as polymorphic, with numerous forms being consistent with a single genetic constitution. The choice between alternative forms in such cases may depend on epigenetic or environmental factors, although, in principle, heritable genetic change could bias such choices, leading to distinct morphological varieties. This view may be compared with one presented in the Special News Report by Elizabeth Pennisi and Wade Roush “Developing a new view of evolution” ([4 July, p. 34][3]), in which they discuss, among other things, recently published evidence that a gene called manx distinguishes a species of tunicates whose larvae lack tails from a related species whose larvae develop them (B. J. Swalla and W. R. Jeffery, Reports, 15 Nov., 1996 p. 1205). We are told in the News article that the result “raises the possibility that a single genetic change could be responsible for the innovation that led to a tail in primitive vertebrates.” The attribution of ineffable creative power to individual genes is not an isolated instance, but can be traced back at least to the erroneous “unit character” model of Mendelism propounded by some early geneticists ([1][4]) and lives on in some precincts of developmental and evolutionary biology (Letters, C. Nielsen, [5 Sept., p. 1422][5]). Investigators of the regulation of morphogenesis of protists and bacteria seem relatively resistant to this form of mystification, as exemplified by the recent work on C. albicans [see also ([2][6])]. Genetic absolutism does not take into account that the correspondence of a given genotype to a nearly unique morphological phenotype seen in modern animals may itself be a product of evolution: in the absence of more recently evolved redundancies and other back-up mechanisms, the earliest animals may have been as polymorphic, or more so, as C. albicans . If true, this would imply that once the metazoa emerged, the genetic evolution of morphology would have been implemented not so much by the origination of novelty as by the selective stabilization of particular forms from those within the ancestral animals' morphological repertoire ([3][7]). 1. [↵][8]L. C. Dunn, A Short History of Genetics (McGraw-Hill, New York, 1965). 2. [↵][9]J. T. Bonner, Life Cycles: Reflections of an Evolutionary Biologist (Princeton Univ. Press, Princeton, NJ, 1993). 3. [↵][10]1. S. A. Newman , J. Evol. Biol. 7, 467 (1994). [OpenUrl][11][CrossRef][12][Web of Science][13] [1]: /lookup/doi/10.1126/science.277.5322.52 [2]: /lookup/doi/10.1126/science.277.5322.105 [3]: /lookup/doi/10.1126/science.277.5322.34 [4]: #ref-1 [5]: /lookup/doi/10.1126/science.277.5331.1421 [6]: #ref-2 [7]: #ref-3 [8]: #xref-ref-1-1 "View reference 1 in text" [9]: #xref-ref-2-1 "View reference 2 in text" [10]: #xref-ref-3-1 "View reference 3 in text" [11]: {openurl}?query=rft.jtitle%253DJ.%2BEvol.%2BBiol.%26rft.volume%253D7%26rft.spage%253D467%26rft_id%253Dinfo%253Adoi%252F10.1046%252Fj.1420-9101.1994.7040467.x%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [12]: /lookup/external-ref?access_num=10.1046/j.1420-9101.1994.7040467.x&link_type=DOI [13]: /lookup/external-ref?access_num=A1994NX82300005&link_type=ISI