Ascidian Module

Ascidians are the largest group within the tunicates. Tunicates are invertebrate chordates and are the sister group to vertebrates. Ascidians are marine animals and they have a long history as an experimental model system for development.  Edwin Grant Conklin followed the cell lineage of the ascidian Stylela canopus during studies at the Marine Biological Laboratory and published his results in a 1905 monograph. The embryos of Styela have naturally pigmented cytoplasms that are segregated into specific cell lineages during development.  Today, most laboratories that study ascidian development have focused on a few model species including Ciona robusta, C. savignyi, Halocythia roretzi and Botryllus schlosseri.  The genomes of about a dozen species have been, or are currently being, sequenced.  Many of the experimental tools utilized in other systems, CRISPR/Cas-9, RNA-SEQ, and gene knock-downs have been adapted to ascidians.  One of the significant advantages of ascidians is the ability to generate transgenic embryos using a simple electroporation process.  The ability to manipulate gene function in these animals makes them well-suited for studying the molecular mechanisms of development, including the characterization of gene regulatory networks that govern tissue-specific patterns of cell differentiation.

With rare exceptions, tunicates are usually self-sterile hermaphrodites and fertilization occurs between the mixing of gametes from two or more individuals.  As tunicates are marine animals, they are broadcast spawners with gametes being freely shed into sea water.  Many species of ascidians have been spread throughout temperate ocean waters in large part because the adults can grow on the bottoms of cargo ships. When in port, adults attached to the ships release gametes and new generations of animals can gain footholds in the new environments.  In some species, the block to self-fertilization is less restrictive, so even small numbers of adults can initiate new populations of animals.

In this module, students will learn about different species of ascidians, how to spawn the animals and how to generate transgenic embryos.  Additionally, students will learn more classically-oriented experiments including the dissection of early embryos into specific sets of cells.  Students will have an opportunity to examine cells lineages by using a variety of fluorescent protein transgene constructs and mis-express transcription factors and signaling proteins to alter cell fate. Lastly, students will be able to use the CRISPR/Cas9 system to both knock-out genes of interest and to knock genes into the genome.