Before programs: The physical origination of multicellular forms

Abstract

By examining the formative role of physical processes in modern-day developmental systems, we infer that although such determinants are subject to constraints and rarely act in a "pure" fashion, they are identical to processes generic to all viscoelastic, chemically excitable media, non-living as well as living. The processes considered are free diffusion, immiscible liquid behavior, oscillation and multistability of chemical state, reaction-diffusion coupling and mechanochemical responsivity. We suggest that such processes had freer reign at early stages in the history of multicellular life, when less evolution had occurred of genetic mechanisms for stabilization and entrenchment of functionally successful morphologies. From this we devise a hypothetical scenario for pattern formation and morphogenesis in the earliest metazoa. We show that the expected morphologies that would arise during this relatively unconstrained "physical" stage of evolution correspond to the hollow, multilayered and segmented morphotypes seen in the gastrulation stage embryos of modern-day metazoa as well as in Ediacaran fossil deposits of 600 Ma. We suggest several ways in which organisms that were originally formed by predominantly physical mechanisms could have evolved genetic mechanisms to perpetuate their morphologies.

Dynamical patterning modules: a "pattern language" for development and evolution of multicellular form

“…The utilization of homologous transcription factors in seemingly analogous organ systems across the range of metazoan phyla (the apparent molecular homology-analogy paradox; Wilkins, 2002;Newman, 2006) is, in our view, presumptive evidence for the facile interconvertibility of disparate metazoan body plans once multicellularity had been achieved, but before canalizing evolution (Waddington, 1942;Schmalhausen, 1949) had locked phylotypic differences into place (Newman, 2006;Newman et al, 2006). This implies that a comparative genomic analysis of the origination of metazoan form that does not take into account the generic self-organizing properties of multicellular aggregates (e.g., Ruiz-Trillo et al, 2007) cannot be entirely successful.…”

“…Rather, DPMs, by mediating adhesion and tissue multilayering, the generation of spatially nonuniform and temporally periodic cell states, and cell polarity (with resulting tissue topological and shape transformations), were required in order to turn pre-metazoan multicellular aggregates into metazoan body plans (Newman, 1994;Newman and Müller, 2000;Newman et al 2006). These physical-genetic patterning modules, acting relatively independently and combinatorially during the early stages of metazoan evolution, provide a plausible basis for the rapid generation of morphological diversity evidenced in the fossil record of the early Cambrian.…”

¿Es el lenguaje (complejo) el resultado de una transferencia genética entre neandertales y humanos modernos?

“…), al condicionar la actuación de los restantes elementos reguladores implicados (proteínas, ARNs, hormonas, etc. ), pueden ser responsables per se de dimensiones básicas de los procesos de desarrollo, como la regionalización o la aparición de regularidades morfológicas (Newman y Comper 1990;Newman et al 2006). En último término, todo proceso de desarrollo resulta de una interacción azarosa entre el conjunto de moléculas implicadas, por lo que dos sistemas de desarrollo idénti-cos (y por inclusión dos genotipos idénticos), situados en ambientes también idénticos, pueden dar lugar, sin embargo, a fenotipos diferentes (Balaban 2006).…”

Genotype–phenotype mapping and the end of the ‘genes as blueprint’ metaphor

“…Given this conceptual framework, it is no wonder that developmental biology was famously left out of the Modern Synthesis, and that it has (partially) re-emerged only recently within the so-called 'evo-devo' approach (e.g. Amundson 2005;Minelli & Fusco 2005;Love 2006;Newman et al 2006;Carroll 2008).…”