Vasa protein expression is restricted to the small micromeres of the sea urchin, but is inducible in other lineages early in development.
Voronina E, Lopez M, Juliano CE, Gustafson E, Song JL, Extavour C, George S, Oliveri P, McClay D, Wessel G. Dev Biol. 2008 Feb 15; 314(2):276-86. Epub 2008 Jan 14.