For several upcoming blog posts, I plan to discuss topics on the evolution of cellular life, ranging from abiogenesis to complexification. First though, I wish to establish how I feel evolution impacts my study of cell adhesion and migration, which my PhD advisor’s postdoctoral mentor, Richard O. Hynes, expressed so well in a 2000 paper on the “Evolution of Cell Adhesion”:
Multicellular organisms clearly require mechanisms for intercellular communication and, perhaps even more basically, for intercellular cohesion. The most primative sponges and coelenterates depend on cell adhesion for their organismal organization; so do insects, nematodes and vertebrates. What molecules and mechaisms are common among these different phyla and which ones differ and why?
As you may guess, I’ve become intimately familiar with the many ways in which cell adhesion, and particularly the dynamic and directed aspects of it in cell migration, which play important roles in all aspects of embryonic development, in homeostasis and pathogen surveillance in the adult organism, and in diseases ranging from cancer to atheroschlerosis to rheumatoid arthritis. Above all though, cell adhesion and migration plays the most dynamic role in a defining feature of most multicellular or metazoan life: the mesoderm – the middle cell layer that forms between the inner and outer cell layers during gastrulation to form the coelom, or body cavity, where organs can freely move, grow, and develop independently of the body wall while fluid cushions and protects them from shocks. It’s generally thought that the coelom, and thus the mesoderm, evolved from gastrovascular cavities of cnidarian ancestors (a family represented today by corals, sea anemones and jellyfish). Tissues derived from the mesoderm include bones, most of the vascular system including the heart, connective tissues, muscles, the gastrointestinal tract, and the reproductive system, thus covering a lot of territory in the body.
These characteristics arose, and are ubiquitously conserved by all animals of greater complexity than cnidarians, along with a wide array of other cellular functions – exemplified by the diversity and functions of the kinome superfamily of signaling proteins. Knowing these facts about the evolutionary origins of cell adhesion and the inter-relatedness of adhesion dynamics in multi-cellular organisms helps us to put more pieces of the puzzle together – rather than simply dissecting humans to understand our physiology and basis for disease, we can examine similar processes in simpler animals and gain knowledge about animal physiology and development at large.
…and suddenly, the massive body of scientific study over the last century – in Drosophila, Dictyostelium, Zebrafish, C. elegans, Xenopus, mouse, and more – falls into place and greatly expands our understanding of medicine and of life. (For more, read Sean Carroll’s Endless Forms Most Beautiful: The New Science of Evo-Devo)
Check back over the coming week for topics on earlier stages of cellular evolution.
- The Evolution of Cell Adhesion. Hynes RO and Zhao Q. J Cell Biol. 2000 Jul 24; 150(2):F89-96.
- Early evolution of animal cell signaling and adhesion genes. Nichols SA, Dirks W, Pearse JS, King N. Proc Natl Acad Sci U S A. 2006 Aug 15; 103(33):12451-6.