My research has focused on questions of embryonic cell rearrangements. As an embryo develops from a fertilized egg, cells are constantly dividing, migrating, differentiating and rearranging. Time-lapse video microscopy reveals these movements and allows analysis of the cellular mechanisms driving these transformations. My embryo of choice is that of the killifish, Fundulus heteroclitus, and I have been focusing on the rearrangements of a group of epithelial cells that form the first embryonic skin. These embryos are large and transparent, and are ideal for microscopy. To make the invisible visible individual embryonic cells are labeled with fluorescent lipids. Fluorescence and confocal microscopy can be used to watch an individual epithelial cell in vivo, as the entire sheet of cells rearranges and spreads to cover the large yolk sac. These films document that individual cells are extremely dynamic, sending and retracting long protrusions that underlap neighboring cells.
This system can also be used to study membrane turnover in epithelial cells. All cells are constantly adding new material to their membranes, and internalizing regions of surface membrane. This turnover has tremendous ramifications for most cell behaviors. The Fundulus embyronic epithelial cells are remarkable in that many of these fluorescent lipids are immobile in the plane of the membrane, allowing long-term (1-5 days) observation of membrane turnover. This turnover is accelerated near sites of cell-cell contact. The most exciting part of this work is that membrane turnover is accelerated when the cells are under mechanical tension. That is, cells actively rearranging turn over their marginal domains faster than cells that are not under mechanical stress.
I am also involved in making research video footage available for teaching, and have published two compilations of movies. A Dozen Eggs: Time-Lapse Microscopy of Normal Development was published by Sinauer Associates under the auspices of the Society for Developmental Biology. CELLebration was published by Sinauer Associates and the American Society for Cell Biology. Currently I am compiling sequences filmed by my undergraduate students for use in a web-based project to introduce younger audiences to the wonderful world of cells and embryos. At any time in my lab students might be filming fern sperm release, cell movements in hydra, sea urchin gastrulation and/or keratocyte locomotion.
