Molecular Analysis of Development and Evolution

Our collective goal is to understand the evolution of the chordate body plan, a complex problem that requires interdisciplinary research. We combine methods and approaches in phylogenetics, development, ecology and evolution to study the evolution of this unique body plan from a deuterostome ancestor. We believe that the deuterostome ancestor was a burrowing worm, with gill slits and a cartilaginous skeleton.

One of our projects utilizes two closely related species of ascidians, M. occulta and M. oculata, to continue to isolate and characterize genes important for specifying the chordate body plan during development. Subtractive hybridization between these two species allowed the isolation of five novel genes, manx, lynx, cymric, p58 and bobcat. Two of these genes, lynx and cymric are maternal and experiments are underway to see what their roles are in development . In contrast, manx, p58 and bobcat are expressed both maternally and zygotically in the tailed species, and antisense experiments suggest a role for these genes in specifying the body plan during development. We are interested in characterizing the vertebrate homologs of these genes and where and when they are expressed during development. One of these genes, bobcat, is expressed in the neural tube of chordate embryos. We are now extending our analysis to the non-chordate deuterostomes.

The second major research project is aimed at isolating transcription factors and signalling molecules known to be important in developmental processes in vertebrate embryos and looking at the expression and regulation of these genes in ascidian embryos. Two of the genes we have cloned and are studying are brachyury T, which is expressed in the notochord in ascidian embryos and nodal, which is a signalling molecule that is part of the TGFß superfamily. Both of these genes appear to be downstream of manx, and mRNA expression levels of these genes are directly correlated with manx expression.

The third major project in my laboratory is aimed at understanding the evolution of chordates. We began with sequencing 18S rDNA from urochordates and hemichordates in order to understand phylogenetic relationships of the different families in these groups. Because the phylogenetic analysis suggests that enteropneust worms may be basal hemichordates, we are studying a complex of Saccoglossus worms in the Pacific Northwest in an effort to understand the evolution of the chordate body plan. We are specifically focusing on the nature of the hemichordate cartilage matrix.

Finally, we've started a new project to study the evolution of coloniality in ascidians. We have identified a clade of stolidobranch ascidians that contains species with solitary, social and colonial lifestyles. We are looking at the molecular basis of coloniality by examining genes that are turned on during metamorphosis. One set of genes that is activated at metamorphosis are the innate immunity genes. The innate immune system appears to be critical for remodelling the body plan during metamorphosis. We are also examining the role of these genes in bud formation in colonial larvae.