Expression of vitellogenin and transforming growth factor β genes in follicle cells of the developing Botryllus schlosseri oocyte

Abstract

is a colonial marine invertebrate chordate that utilizes both sexual and asexual modes of reproduction. Colonies of Botryllus can fuse and exchange cells via the bloodstream, including mobile stem cells that are capable of parasitizing the soma and germ line. We use Botryllus as a model for investigating the molecular mechanisms of stem-cell competition and the interaction between the germ line and germ-line support cells.The embryonic and post-embryonic origins of follicle cells are still unclear in Botryllus. Shown here is a fluorescence double-in situ hybridization detecting the transcripts of vitellogenin (red) and transforming growth factor ␤ (green) genes in the follicle cells surrounding a developing Botryllus oocyte; nuclei are visualized by DAPI staining (blue). Interior to the follicle cells are the nuclei of the test cells, an accessory cell type that is retained around the Botryllus embryo following fertilization. Vitellogenin and other yolk proteins secreted by follicle cells play an evolutionarily conserved role in nourishing the developing embryo, and are expressed by Botryllus follicle cells during the final phase of oogenesis, termed vitellogenesis. Oocytes mature outside of the body chamber of developing Botryllus buds in a gonadal niche that may also contain maturing testes. Once the oocyte is fully grown, the outer layer of follicle cells is shed and the egg is ovulated into the body chamber for fertilization.