The origin of animals represents one of the pivotal transitions in life’s history, and one of its greatest unsolved mysteries. While the fossil record remains silent regarding the rise of multicellularity, the genetic and developmental foundations of animal origins may be deduced from shared elements among extant animals and their protozoan relatives, the choanoflagellates. To better understand the origin and evolution of animals, our goals are to:

1. determine the minimal genomic complexity of the unicellular progenitors of animals
2. elucidate the ancestral functions of genes required for animal development
3. characterize choanoflagellate cell and developmental biology
4. investigate the evolution of new modes of gene regulation and intron splicing in the animal lineage

Current Projects

Using comparative genomics to investigate the ancestral animal genome

A key question in the origin of animals concerns how and when the “toolkit” of animal genes was assembled. To test whether genes required for animal development evolved before the origin of animal multicellularity, we are comparing sets of genes expressed by choanoflagellates, animals, Fungi, Plants, and unicellular eukaryotes. Genes shared only by choanoflagellates and animals were likely present in their common ancestor and may shed light on the transition to multicellularity. This work has already provided evidence for the expression in choanoflagellates of protein families (e.g. receptor tyrosine kinases, cadherins, and C-type lectins) required for animal cell signaling and adhesion. Our current goals are to characterize the diversity of genes encoding transcription factors and cytoskeletal components in choanoflagellates, and to examine the history of certain protein families prior to the origin of animals.

Assaying the ancient functions of genes required for multicellular development

The finding of signaling and adhesion gene homologs (e.g. cadherins and receptor tyrosine kinases) in choanoflagellates raises questions about how these genes functioned in the unicellular common ancestor of choanoflagellates and animals, and what role they played in the origin of multicellularity. To determine the function of specific genes in choanoflagellates, we will develop techniques for manipulating gene activity in vivo. Inferences about gene function in diverse choanoflagellates provide an important reference point for studies of gene family evolution in animals.

Cell and developmental biology of choanoflagellates

The mechanisms by which choanoflagellates form colonies, establish cell polarity, and reproduce may provide crucial insights into the transition to multicellularity, but little is known about their cell biology or natural history. Therefore, we will examine the life cycles of diverse choanoflagellates using techniques ranging from classical protistology to microscopy to bioinformatics.