The evolution of transcription regulatory networks governing cell-type specification

Transcription regulatory networks are an important source of evolutionary novelty. My thesis work describes the molecular details of two examples of evolution of gene regulation in mating type regulation in yeast. First, I uncovered an example in which a new tier of transcription regulation was intercalated into an ancestral network along the lineage to K. lactis. The intercalation of Rme1 maintained the ancestral expression pattern but also added novelty. As a result of this change mating in K. lactis is regulated by nutrient availability as well as cell type. Second, I investigated how a set of co-regulated genes switched from being positively regulated to negatively regulated. This work has illustrated the important role of molecular exploitation and stepwise changes in evolution and provided evidence for the flexibility and reversibility of transcription regulatory networks.