Meeting Abstract
P3.51 Wednesday, Jan. 6 A conserved role of the homeobox transcription factor Tinman during heart development of the bobtail squid Euprymna scolopes NÖDL, Marie T.*; DE COUET, H. Gert; Department of Theoretical Biology, University of Vienna, Austria; Department of Zoology, University of Hawaii at Manoa couet@hawaii.edu
The heart is a key morphological innovation in the evolution of animals. Despite differences in morphology and function of blood pumping systems, the basic molecular mechanisms involved in early patterning of the heart appear to be conserved in bilaterian taxa. The conserved homeodomain transcription factor Tinman is crucial for early patterning of the mesoderm giving rise to the heart. Loss of tinman function leads to loss of dorsal mesodermal structures, including cardioblasts and pericardial cells in the fly, and a dominant-negative variant of the orthologous Nkx2-5 protein blocks cardiogenesis in frog embryos. Cephalopods posses a remarkably effective, closed circulatory system capable of maintaining a high blood pressure. In addition to the systemic heart two accessory branchial hearts function to move blood through the gills and ensure that all blood leaving the systemic heart is oxygenated. In order to understand the mechanisms that led to the evolution of this unique circulatory system within the mollusks we examined the expression of a tinman ortholog during the development of E. scolopes by in situ hybridization. Expression was first observed in the dorsal mesoderm, restricted to the systemic as well as both branchial hearts. Surprisingly, during later developmental stages tinman was also expressed within most major blood vessels of the circulatory system. Our data support the idea that the homologies between blood pumping organs exist at the level of myocytes that underlie organ function, and which are patterned by conserved developmental genes such as tinman. In addition, E. scolopes Tinman has apparently been co-opted for the formation of the vascular system in the squid.
