As organisms develop, their internal organs arrange in a consistent asymmetrical pattern -- heart and stomach to the left, liver and appendix to the right. But how does this happen?
Biologists at Tufts University have produced the first evidence that a class of proteins that make up a cell's skeleton -- tubulin proteins -- drives asymmetrical patterning across a broad spectrum of species, including plants, nematode worms, frogs, and human cells, at their earliest stages of development.
Up to now, scientists have identified cilia -- rotating hair-like structures located on the outside of cells -- as having an essential role in determining where internal organs eventually end up. Scientists hypothesized that during later stages of development, cilia direct the flow of embryonic fluid which allows the embryo to distinguish its right side from its left. But it is known that many species develop consistent left-right asymmetry without cilia being present, which suggests that asymmetry can be accomplished in other ways.
The researchers pinpointed tubulin proteins, an important component of the cell's skeleton, or cytoskeleton. Tubulin mutations are known to affect the asymmetry of a plant called Arabidopsis, and previous work suggested the possibility that laterality is ultimately triggered by some component of the cytoskeleton. Further, this mechanism could be widely used throughout the tree of life and could function at the earliest stages of embryonic development. Importantly, mutated tubulins perturbed asymmetry only when they were introduced immediately after fertilization, not when they were injected after the first or second cell division. This suggested that a normal cytoskeleton drives asymmetry at extremely early stages of embryogenesis, many hours earlier than the appearance of cilia.
Via Dr. Stefan Gruenwald