Yi-Hsien Su

Talk Title: Tracing the evolutionary origin of the gastrula organizer-derived notochord in non-chordate deuterostomes

My research focuses on understanding how animal body plans are formed. My lab uses sea urchin and hemichordate as models, which are close relatives of chordates, to study commonality and divergence of developmental mechanisms and genomic features inferring conditions of their common ancestor and identifying lineage-specific evolutionary changes leading to different body plans of deuterostomes. 

One of the central mysteries in biology is how diverse forms of animals develop and originated on this planet. From the perspective of a developmental biologist, this question can be addressed by deciphering how gene regulatory networks (GRNs) that are encoded in the genome regulate the formation of a specific body plan. On the other hand, an evolutionary developmental biologist may answer this question by comparing the developmental mechanisms of two or more extant animal groups. The combination of these approaches in Evolutionary Developmental Biology (EvoDevo) enables researchers to first reconstruct possible ancestral conditions. Based on this information, lineage-specific changes in developmental mechanisms and GRN architectures that deviate from ancestral conditions can then be decoded. Identification of such changes often provides insights into how distinct body forms could have originated during evolution. Taking our own phylum Chordata as an example, all chordates possess several phylum-specific characters, such as a hollow neural tube and a notochord. The two closest relatives of chordates are the phyla Echinodermata and Hemichordata, which constitute the superclade Ambulacraria. These animals lack chordate-specific traits and exhibit other uniquely evolved body plans that define each animal group. The three phyla belong to the deuterostomes, which is one of the two major branches of Bilateria (i.e., animals with bilateral symmetry). My lab investigates developmental mechanisms of sea urchin (Echinoderm) and acorn worm (Hemichordate) embryos to reconstruct the ancestral conditions of ambulacrarians and deuterostomes. We also address questions regarding how phylum-specific traits are originated from common ancestors. Results from our study contribute to a mechanistic understanding of deuterostome evolution and provide insights into the evolution of morphological novelties.