The involvement of three signal transduction pathways in botryllid ascidian astogeny, as revealed by expression patterns of representative genes
Developmental Expression Pattern | Published: 12 March 2015
Amalia Rosner*,1, Gilad Alfassi1,2, Elizabeth Moiseeva1, Guy Paz1, Claudette Rabinowitz1, Ziva Lapidot1, Jacob Douek1, Abraham Haim2 and Baruch Rinkevich1
1Israel Oceanographic and Limnological Research, National Institute of Oceanography, Haifa, Israel and 2Department of Evolutionary & Environmental Biology, Faculty of Natural Sciences, University of Haifa, Mount Carmel, Haifa, Israel
The patterning of the modular body plan in colonial organisms is termed astogeny, as distinct from ontogeny, the development of an individual organism from embryo to adult. Evolutionarily conserved signaling pathways suggest shared roots and common uses for both ontogeny and astogeny. Botryllid ascidians, a widely dispersed group of colonial tunicates, exhibit an intricate modular life form, in which astogeny develops as weekly, highly synchronized growth/death cycles termed blastogenesis, abiding by a strictly regulated plan. In these organisms both astogeny and ontogeny form similar body structures. Working on Botryllus schlosseri, and choosing a representative gene from each of three key Signal Transduction Pathways (STPs: Wnt/β-catenin; TGF-β, MAPK/ERK), we explored and compared gene expression at different stages of ontogeny and blastogenesis. Protein expression was studied via immunohistochemistry, ELISA and Western blotting. Five specific inhibitors and an activator for the selected pathways were used and followed to assess their impact during the blastogenic cycle and the development of distinctive phenotypes. Outcomes show that STPs are activated and function (while not necessarily co-localized) during both ontogeny and astogeny. Cellular patterns in blastogenesis, such as colony architecture, are shaped by these STPs. These results are further supported by administering Wnt agonist and anatagonist, TGF-β receptor antagonists and inhibitors of Mek1/Mek2. Independent of their expression during ontogeny, some of the spatiotemporal patterns of STPs developed within short blastogenic windows. The results support the notion that while the same molecular machinery is functioning in Botryllus schlosseri astogeny and ontogeny, astogenic development is not an ontogenic replicate.