Speed Regulation and Gradual Enhancer Switching Models as Flexible and Evolvable Patterning Mechanisms

Abstract

Short AbstractUsing simple animations, mathematical formulations, and computational implementation in Matlab, we present a newly devised embryonic patterning mechanism: the Speed Regulation model, and its molecular realization: the Gradual Enhancer Switching model. We show how our models shed light on the phenomenology of insect development and evolution.Long AbstractPartitioning an initially homogeneous group of cells into different fates is a common problem in development. A curious case is the anterior-posterior (AP) fate specification during early embryogenesis in insects. The AP fates of most insects are specified in two different phases: (i) the blastoderm, where the AP axis does not undergo any axial elongation, and (ii) the germband, where the AP axis undergoes gradual axis elongation. Throughout evolution, insects show remarkable flexibility in the number of fates specified in the blastoderm vs germband. This hints that AP specification in insects relies on a flexible mechanism that can pattern both non-elongating embryonic structures (like the blastoderm) and elongating tissues (like the germband). Here we describe the ‘Speed Regulation’ model, a recently suggested patterning mechanism, that can pattern both elongating and non-elongating tissues and ensures the evolvability between them. The model is successful in reproducing the phenomenology of AP axis specification and evolution in insects. In addition, it explains the temporal-based patterning of other embryonic structures like the AP axis of vertebrates and the dorsoventral axis of vertebrate neural tube. The Speed Regulation model is phenomenological in its formulation, in the sense that it does not specify a particular molecular realization. We then present the ‘Gradual Enhancer Switching’ model, in which we describe a specific molecular implementation of the Speed Gradient model that incorporates a novel scheme of cis-regulation within gene regulatory networks. The paper is linked to two videos on YouTube referred to below.Linked VideosVideo I: https://youtu.be/YcGotl8OdYwVideo II: https://youtu.be/f-JnjF2aNLw