Evolutionary change in gene regulation

Ohio State University Research Foundation -Do Not Use, Columbus OH

Investigators

Abstract

Evolutionary change in gene regulation The molecular mechanisms that allow species to evolve morphological and physiological diversity are not well characterized, and identifying them remains an important challenge for evolutionary biology. Recent work indicates that one important mechanism is alteration to the transcriptional regulation of key developmental genes. In nematodes, novel transcription of the lin-48/ovo gene in the excretory duct cell of C. elegans confers innovative excretory system features on this species compared to others in the Caenorhabditis genus. Comparative study within this genus will clarify the specific molecular changes responsible for the expression difference, as well as clarify how increased regulatory complexity can evolve in the context of existing gene features. Previous results show that multiple changes in the cis-regulatory sequences of Cel-lin-48 enhance its expression in the excretory duct cell, and that one altered regulatory sequence corresponds to the binding site for a bZip transcription factor heterodimer composed of CES-2 and ATF-2. However, these results also indicate that there are multiple changes in both cis-acting sequences and trans-acting factors, and that the key change responsible for selective advantage of lin-48 expression in C. elegans may not yet be identified. Therefore, the overall objective of this proposal is to dissect the changes responsible for the evolution of Cel-lin-48 transcriptional regulation using molecular and genetic strategies. Genetic studies indicate that lin-48 mediates at least two separable functions in the C. elegans excretory system. Thus a first objective is to dissect these functions using altered transgenes, and to characterize the role of trans-acting factors in mediating these functions. Since preliminary results show that changes in unidentified factors also contribute to the evolution of Cel-lin-48 transcription, two additional objectives rely on genetic approaches for discovery of new excretory system genes. A genetic screen has identified a mutation in C. elegans that shares the excretory system defects seen in lin-48 mutants, but that maps to a different locus. Thus a second objective is the functional characterization of the gene affected by this mutation. A genetic screen in C. briggsae has likewise identified mutants that exhibit excretory system features normally found only in C. elegans. A third objective is to characterize these mutants. Analysis of these mutants may identify new genes important for excretory system structure and function, as well as explore the capacity of genomes to evolve innovative traits. Finally, achieving these objectives will incorporate training of graduate and undergraduate students in laboratory research technique and in communicating research results. To facilitate this training process, a fourth objective is to coordinate local and regional research meetings, with a focus on providing a range of research forums in which trainees participate. It is anticipated that this combination of research and training goals will achieve the scientific objective to identify the molecular changes that contribute to the evolution of gene expression patterns and to clarify how regulatory modules can evolve. The intellectual merit of the proposal is that the research will establish the specific molecular changes that can contribute to the evolution of gene transcription patterns as a mechanism for the evolution of organisms. The broader impact of the proposal is that it will contribute to the training of undergraduate and graduate student scientists, and that it will foster scientific community at the local and regional level. The intellectual merit and broader impacts of the proposal are interconnected. The first three objectives focus on research, but the work will serve as a platform for research training. The fourth objective focuses on providing training and networking opportunities and the development of research community.