The incredible diversity of life arose through evolutionary acquisition of novel traits ranging from fundamental shifts in body plans to superficial changes in fur color. Although research has revealed some causative genetic mutations, the manner in which these mutations ripple through different scales of biological organization to produce new traits remain poorly understood. Key questions include – 1) How do mutations impact the networks of interacting genes that control embryological development? 2) How do shifts in gene networks impact cell behaviors in developing embryos? 3) How do shifts in cell behaviors during development lead to anatomical or physiological changes in adult organisms? The proposed research will address these questions through the comparative study of two sea squirts (a group of marine organisms closely related to humans and other vertebrates). In particular, this research will focus on a very poorly characterized group of sea squirts called the doliolids. Doliolids have acquired a number of highly divergent traits including the ability to produce three distinct body types specifically designed for feeding, dispersal or reproduction. The relative simplicity of sea squirt genomes and the low number of cells in sea squirt embryos will facilitate rigorous analysis of the evolutionary acquisition of new traits across multiple biological scales. This project will also provide a diverse group of trainees, including those that identify with groups underrepresented in the biological sciences, the opportunity to participate in cutting-edge research spanning computational, molecular, cellular, developmental, ecological and evolutionary biology.
The acquisition of new traits encompasses changes across multiple scales. Although numerous studies have identified causative mutations in protein coding DNA or in non-coding regulatory elements associated with novel traits, productively examining the impact of these mutations on intervening scales including developmental gene regulatory networks (GRNs) and embryonic cell lineages is extremely challenging. This project aims to overcome these challenges through comparative analysis of a historically neglected chordate taxa, the doliolids. These highly divergent, poorly characterized organisms are uniquely suited for in-depth, multi-scale analyses of cell lineage re-deployment and gene network rewiring. This research effort will focus specifically on comparisons of heart development in the pelagic tunicate Dolioletta gegenbauri and the primary tunicate model species, Ciona intestinalis. These organisms were selected for comparative analysis because – 1) the Ciona heart progenitor lineage and underlying gene network have been comprehensively mapped, 2) comparative analysis indicates that tunicate heart lineages and associated GRNs have been rigorously conserved across a range of tunicates spanning ~400 million years of divergence, 3) the compactness and resulting lack of redundancy in tunicate genomes will facilitate the identification of discrete shifts in network architecture associated with changes in doliolid heart development. To initiate this project, the researchers will pursue the following aims – 1) establish stable cultures of D. gegenbauri, 2) develop basic embryological techniques for characterization of D. gegenbauri heart development, 3) assemble and annotate the D. gegenbauri genome and 4) establish essential techniques (transgenesis, in situ hybridization and CRISPR) required for characterizing the D. gegenbauri heart GRN.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
