Tunicate (Ciona intestinalis) 

Ciona adult

Transgenic Ciona embryo, revealing the heart lineage

The C. intestinalis embryo and tadpole has been used for classical studies in animal development since 1886.  It provided the first evidence for the existence of localized determinants, or substances in the egg that program cells to follow specific pathways of development.  C. intestinalis possesses a number of favorable features for the molecular analysis of animal development.  First, it has a small compact genome that is only 5% the size of the human genome, even though it is a chordate.  Second, the tapdole is constructed from simple, well-defined cell lineages.   Third, it is possible to introduce transgenic DNA into developing embryos using simple electroporation methods.  These features have led to the elucidation of a complete blueprint for the early Ciona embryo.  This blueprint should provide a foundation for understanding more complex processes in vertebrate embryos.