In today’s Academic Minute, Michael Levin of Tufts University explains the process that determines organ placement as an embryo develops.
Michael Levin is Professor and Director of the Tufts Center for Regenerative and Developmental Biology at Tufts University. His research is focused on understanding morphological and behavioral information processing in living systems. He holds a Ph.D. in genetics from Harvard Medical School.
About Dr. Levin
Dr. Michael Levin, Tufts University – Embryonic Development and Organ Placement
Most problems in biology and medicine come down to the question of shape. During embryonic development, a single fertilized egg cell self-assembles into a complex organism in which internal organs arrange in a consistent left-right asymmetrical pattern—heart and stomach to the left, liver and appendix to the right.
Mistakes in this process occasionally result in birth defects but most of the time a complex 3-dimensional structure, such as a plant or animal body, is correctly created. Understanding this process could yield insight into the prevention and repair of birth defects that result from abnormal placement of organs.
Our research points to the critical role played by a class of proteins, called tubulin proteins. Cells have an internal framework or skeleton, called a cytoskeleton. One important component of the cellular cytoskeleton is tubulin protein. Earlier experiments had shown that tubulin mutations affected the left-right asymmetry of a small plant that is widely used as a model organism in plant biology called Arabidopsis.
In our experiment, we injected the same mutated tubulins into early frog embryos. While the embryos developed into tadpoles, their internal organs were randomly placed on either the right or left side. Subsequent experiments by our collaborators found that mutated tubulins had the same effect on neuronal placement in nematodes and even on the left-right asymmetry of human cells in culture.
Additional experiments indicated that these mutant proteins function at the earliest stages of embryogenesis. The discovery that at least some embryos can tell their left from their right shortly after fertilization, together with the finding that the same molecular process initiates asymmetry in organisms as diverse as plants, nematodes, amphibians, and human cells, strongly revises our current understanding of how asymmetry evolved and is implemented by embryos.