Marseille Cancer Research Center 1 article published in JoVE Developmental Biology Expression of Fluorescent Proteins in Branchiostoma lanceolatum by mRNA Injection into Unfertilized Oocytes Estelle Hirsinger1, João Emanuel Carvalho2, Christine Chevalier1,3, Georges Lutfalla4, Jean-François Nicolas1, Nadine Peyriéras5, Michael Schubert2 1Département de Biologie du Développement et Cellules Souches, Institut Pasteur, 2Laboratoire de Biologie du Développement de Villefranche-sur-Mer (UMR7009 CNRS/UPMC Univ Paris 06), Sorbonne Universités, 3Equipe Epigenetic Control of Normal and Pathological Hematopoiesis, Centre de Recherche en Cancérologie de Marseille, 4Unité de Dynamique des Interactions Membranaires Normales et Pathologiques, CNRS UMR5235/DAA/cc107/Université Montpellier II, 5Plateforme BioEmergences IBiSA FBI, CNRS-NED, Institut de Neurobiologie Alfred Fessard We report here the robust and efficient expression of fluorescent proteins after mRNA injection into unfertilized oocytes of Branchiostoma lanceolatum. The development of the microinjection technique in this basal chordate will pave the way for far-reaching technical innovations in this emerging model system, including in vivo imaging and gene-specific manipulations.