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

摘要

This article considers the role played by a core set of "dynamical patterning modules"(DPMs) in the origination, development and evolution of complex organisms. These consist of theproducts of a subset of the genes of what has come to be known as the "developmental-genetictoolkit" in association with physical processes they mobilize. The physical processes are thosecharacteristic of chemically and mechanically excitable mesoscopic systems like cell aggregates:cohesion, viscoelasticity, diffusion, spatiotemporal heterogeneity based on activator-inhibitorinteraction, and multistable and oscillatory dynamics. We focus on the emergence of the Metazoa,and show how toolkit gene products and pathways that pre-existed the metazoans acquired novelmorphogenetic functions simply by virtue of the change in scale and context inherent tomulticellularity. We propose that DPMs, acting singly and in combination with each other,constitute a "pattern language" capable of generating all metazoan body plans and organ forms.This concept implies that the multicellular organisms of the late Precambrian-early Cambrianwere phenotypically plastic, fluently exploring morphospace in a fashion decoupled from bothfunction-based selection and genotypic change. The relatively stable developmental trajectoriesand morphological phenotypes of modern organisms, then, are considered to be products ofstabilizing selection. This perspective solves the apparent "molecular homology-analogy para-dox," whereby widely divergent modern animal types utilize the same molecular toolkit duringdevelopment, but it does so by inverting the neo-Darwinian principle that phenotypic disparitywas generated over long periods of time in concert with, and in proportion to genotypic change.