As an example, the brachyury gene and the homolog of the PAX2 gene both play a similar role in the development of tunicates as they do in vertebrates.
Activation of various secreted factors (Vg1, Nodal, Wnt8C, FGF8 and Chordin) and transcription factors (Brachyury and Goosecoid) adjacent to the site of streak formation is required for this process.