Charting Deep Time - Evolutionary Physiology of Vertebrate O2 Transport Systems

Abstract

Haemoglobin (Hb) inside red blood cells plays a crucial role in the transport of O₂ from the environment to respiring tissues of vertebrates. Together with myoglobin (Mb), Hb was the first protein whose detailed structure was revealed in Nobel Prize winning work and it has become a paradigm for molecular adaptation to the environment, such as in high altitude hypoxia, and to blood parasite infection such as in malaria. Whereas the properties of muscle O₂ storing Mb appear similar in all vertebrates, Hb function also differs profoundly between major vertebrate groups and even between subgroups of mammals for as yet poorly understood reasons. Here I present comparative data on Hb and red blood cell function across vertebrate groups from fish to human and map the evolution of traits such as the Bohr effect, Hb acid-buffering capacity, red cell sickling and red cell stress response onto a vertebrate phylogeny. The results reveal the dynamics of independent gains and losses of these traits and their association with environmental and lifestyle changes like the transition from water to air-breathing, giving new insights into the evolutionary physiology of vertebrate O₂ transport systems over the last 450 million years. In the second part of this talk I will present our on-going work on the adaptive molecular evolution of Mb in hypoxia tolerant fishes, like the common carp, and in diving mammals, from water shrews to whales, which challenges the view of conserved Mb function across vertebrates.

Michael Berenbrink
Institute of Integrative Biology, Department of Functional & Comparative Genomics, The University of Liverpool

References:

• Berenbrink M. et al. (2005). Evolution of oxygen secretion in fishes and the emergence of a complex physiological system. Science 307: 1752-1757.
• Koldkjaer P. & Berenbrink M (2007). In vivo red blood cell sickling and mechanism of recovery in whiting, Merlangius merlangus. J. Exp. Biol. 210: 2290-2299.
• Cossins A. R. & Berenbrink M. (2008). Myoglobin’s new clothes (News & Views). Nature 454: 416-417)
• Helbo S. et al. (2011). Functional differentiation of myoglobin isoforms in the hypoxia-tolerant carp indicates tissue-specific protective roles. Am. J. Physiol. Reg. Integr. Comp. Physiol. (in press: doi: 10.​1152/​ajpregu.​00501.​2011).