Early embryology; not wholly guided by DNA (Introduction)

by David Turell , Saturday, February 11, 2017, 23:32 (2842 days ago) @ David Turell

Membranes form axes and contain formation information. DNA does not contain this information:

http://bio-complexity.org/ojs/index.php/main/article/view/BIO-C.2014.2/BIO-C.2014.2

"Abstract: Embryo development (ontogeny) depends on developmental gene regulatory networks (dGRNs), but dGRNs depend on preexisting spatial anisotropies that are defined by early embryonic axes, and those axes are established long before the embryo’s dGRNs are put in place. For example, the anterior-posterior axis in Drosophila and the animal-vegetal axis in Xenopus and echinoderms are initially derived from the architecture of the ovary through processes mediated by cytoskeletal and membrane patterns rather than dGRNs. This review focuses on plasma membrane patterns, which serve essential ontogenetic functions by providing targets and sources for intracellular signaling and transport, by regulating cell-cell interactions, and by generating endogenous electric fields that provide three-dimensional coordinate systems for embryo development. Membrane patterns are not specified by DNA sequences. Because of processes such as RNA splicing, RNA editing, protein splicing, alternative protein folding, and glycosylation, DNA sequences do not specify the final functional forms of most membrane components. Still less does DNA specify the spatial arrangements of those components. Yet their spatial arrangements carry essential ontogenetic information. The fact that membrane patterns carry ontogenetic information that is not specified by DNA poses a problem for any theory of evolution (such as Neo-Darwinism) that attributes the origin of evolutionary novelties to changes in a genetic program—whether at the level of DNA sequences or dGRNs. This review concludes by suggesting that relational biology and category theory might be a promising new approach to understanding how the ontogenetic information in membrane patterns could be specified and undergo the orchestrated changes needed for embryo development.

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"biological membranes are patterned in complex ways. Those patterns serve important functions in cells, tissues and embryos. The following sections summarize the roles of plasma membrane patterns in (a) providing targets and sources for intracellular transport and signaling, (b) regulating cell-cell interactions by means of a “sugar code,” and (c) generating endogenous electric fields that provide three-dimensional coordinate systems for ontogeny.

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"So membrane patterns—the three-dimensional arrangements of membrane-associated proteins, lipids and carbohydrates, as they change over time—carry essential ontogenetic information. Yet (as I demonstrate below) the information carried by membrane patterns cannot be reduced to sequence information in DNA, for at least two reasons. First, the vast majority of proteins in eukaryotes are not completely specified by DNA sequences. Second, even if DNA sequences completely specified all proteins, DNA would not specify their spatiotemporal arrangements in membranes.

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"Thus, according to Cavalier-Smith, the idea that the genome contains all the information needed to make an organism “is simply false. Membrane heredity, by providing chemically specific two-dimensional surfaces with mutually conserved topological relationships in the three spatial dimensions, plays a key role in the mechanisms that convert the linear information of DNA into the three-dimensional shapes of single cells and multicellular organisms. Animal development creates a complex three-dimensional multicellular organism not by starting from the linear information in DNA... but always starting from an already highly complex three-dimensional unicellular organism, the fertilized egg, which membrane and DNA heredity together have perpetuated”.

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"In embryo development, however, membrane heredity cannot be the whole story. During ontogeny many new membrane patterns arise that cannot be traced back to patterns in pre-existing membranes. The new patterns do not arise haphazardly; they are highly specified. Yet there is no evidence that they—any more than the patterns that precede them—are determined by a program in the organism’s DNA. Whether membrane patterns are templated or form de novo, they carry ontogenetic information that is specified independently of DNA sequences. This fact has serious implications both for evolutionary theory and for our understanding of ontogeny.

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" In the 1950s, mathematical biologists Nicholas Rashevsky and Robert Rosen introduced a new approach they called “relational biology” [432−434]. Unlike Newtonian biology, which gives ontological priority to matter (i.e., molecules), relational biology (as the name implies) gives ontological priority to the relations that constitute an organized system. Although molecular biology has been successful at a certain level, its methods involve discarding the organization of a cell while keeping the matter. Yet the former, once discarded, cannot be recovered from the latter—and living things are fundamentally characterized by their organization."

Comment: This paper says DNA does not wholly control the embryo formation, but that membranes, like the walls of a house, organizes areas and rooms in a coordinated whole. DNA makes proteins, not spatial relations