Vertebrate Hourglass

What are the molecular features that limit diversification in embryogenesis and how did they evolve?

The developmental mechanisms generating diverse phenotypes are remarkably conserved – at least at the gene level – and are critical for the development of both conserved and derived features. Across species, embryos exhibit the greatest morphological similarity midway through embryogenesis during the ‘phylotypic period’ with greater interspecific variation earlier and later in embryogenesis. Some recent comparative transcriptomic analyses supports this “hourglass model” of development suggesting that this phenomenon is exhibited at different hierarchical levels of the phenotype; however, the root mechanisms and evolutionary forces that give rise to the hourglass pattern are unknown. My work integrates developmental systems biology and in silico developmental and evolutionary approaches to: (1) determine to which extent pleiotropic constraint on gene regulatory networks underlies the gene expression patterns that characterize the phylotypic period. (2) Define the developmental and evolutionary requirements for emergence of a phylotypic period in silico. Digital evolution and computational modeling are powerful tools for the study of evolutionary processes and for hypothesis generation, although these approaches have yet to harnesses to answer questions related to the evolution of development. With my collaborators (Arend Hintze and Heather Goldsby), we successfully designed a computational system that evolves developing tissues and is evolvable to a variety of morphological targets.