We study Botryllodies leachii as a model animal to identify and functionally characterize the molecular pathways behind whole body regeneration.
B. leachii provides a fantastic opportunity to study the regeneration phenomenon in a chordate system. Botrylloid colonies consist of adult squirts (zooids) sharing a common vascular system embedded in a gelatinous matrix called a tunic. These versatile animals can reproduce either sexually or asexually. Zooids are hermaphrodites that release sperm into the water, which can then enter the incurrent siphons of nearby zooids to fertilize the internal egg. After fertilization the embryo develops inside a brood pouch within the zooid until it reaches a tadpole stage. All zooids are in unison embryo development and release tadpole larva at similar times. These larvae swim to find suitable substrates to attached to and then undergo metamorphosis into an adult sea squirt. Once an adult forms, they reproduce asexually to establish a clonal colony. Asexual reproduction is by budding that occurs on a weekly basis. The adult zooid forms a primary bud which itself forms a second bud before completing morphogenesis into an adult this is followed by absorption of the original bud. This cycle of budding and absorption allows the colony to expand rapidly and once large enough the sexual cycle begins. The adults of a colony are organised into rows and connected to each other through a blood vessel network. The blood vessels terminate in termini ampullae that are separate to the adult and it is minute fragments of this vasculature containing only a few hundred blood cells are capable of regenerating a whole functional adult organism within 8 days. Only loss of all the zooids results in regeneration response but very little is known about what triggers regeneration, rather than healing or degeneration in the absence of a colony adult.
Check out some short movies of this excellent regeneration model we made in our laboratory on our youtube page.
We have assembled de novo a set of 8 separate transcriptomes for B. leachi including for key stages of the regeneration process, a intact whole colony and a embryo transcriptome (Fig. below)
For more about husbandry of the animal model - click here: Colonial sea squirt : model system
We have also sequenced the genome for B. leachi. Genome Browser coming soon!!!