Title: A unified, mechanistic framework for developmental and evolutionary change,
Abstract: The two most fundamental processes describing change in biology -development
and evolution- occur over drastically different timescales, difficult to
reconcile within a unified framework. Development involves a temporal sequence
of cell states controlled by a hierarchy of regulatory structures. It occurs
over the lifetime of a single individual, and is associated to the gene
expression level change of a given genotype. Evolution, by contrast entails
genotypic change through the acquisition or loss of genes, and involves the
emergence of new, environmentally selected phenotypes over the lifetimes of
many individ- uals. Here we present a model of regulatory network evolution
that accounts for both timescales. We extend the framework of boolean models of
gene regulatory network (GRN)-currently only applicable to describing
development-to include evolutionary processes. As opposed to one-to-one maps to
specific attractors, we identify the phenotypes of the cells as the relevant
macrostates of the GRN. A pheno- type may now correspond to multiple
attractors, and its formal definition no longer require a fixed size for the
genotype. This opens the possibility for a quantitative study of the phenotypic
change of a genotype, which is itself changing over evolutionary timescales. We
show how the realization of specific phenotypes can be controlled by gene
duplication events, and how successive events of gene duplication lead to new
regulatory structures via selection. It is these structures that enable control
of macroscale patterning, as in development. The proposed framework therefore
provides a mechanistic explanation for the emergence of regulatory structures
controlling development over evolutionary time.