Sutherland, Ann E.
Associate Professor, Cell Biology
- BA, Biology, Wellesley College
- PhD, Anatomy, University of California
Cell behavior and morphogenesis during early mouse development.
The research in my lab focuses primarily on the cellular mechanisms of implantation and gastrulation in the mouse embryo. In particular , we have been investigating the regulation of motility in the trophoblast cells of the implanting mouse blastocyst, and the cell behaviors leading to axial elongation in the mid-gestation embryo.
We discovered that amino acids are signaling molecules that regulate the onset of invasive behavior of the trophoblast cells of the mouse blastocyst that is required for it to implant into the uterus. In particular, arginine and leucine are each necessary, and together they are sufficient, to induce the trophoblast cells to become motile. They regulate motility through activation of the serine/threonine kinase mTOR, which acts through an unknown downstream effector to activate Rac1, thus promoting protrusive activity. It is likely that this signaling system acts during development to coordinate the development of the embryo with the receptivity of the uterus, and we are currently examining this question by assaying concentrations of amino acids and ions in uterine fluid during the preimplantation stages of pregnancy. We are also examining the transport mechanisms responsible for uptake of leucine and arginine, and how the amino acids affect the activity of mTOR.
We found that the trophoblast cells encounter a new array of extracellular matrix components as they invade into the uterus, and that two of the most prominent proteins are laminin-111 and laminin-521. These two laminins have vastly different effects on cell behavior; laminin-111 is a repulsive substrate leading to cell rounding and boundary formation, while laminin-521 is a very adhesive substrate and promotes spreading. The distribution of laminin-111 vs. laminin-521 suggests that trophoblast cell invasive behavior is limited in the direction of the embryo by laminin-111, and directed into the uterine stroma by laminin-521. We have tested this hypothesis by examining the behavior of trophoblast cells in embryos lacking laminin-111, and in mice where laminin -521 is knocked out in the uterus. The results support our hypothesis, and show that the extracellular matrix composition in the uterine storm has a profound effect on the ability of the embryo to implant. Currently we are working on defining the signaling pathways within trophoblast cells that lead to the different responses to the two laminin isoforms.
In collaboration with Drs. Xiaowei Lu (Cell Biology), Ray Keller (Biology), Ammasi Periasamy (Keck Center for Cellular Imaging), and Carol Burdsal (Bucknell University), we have undertaken a study of cell behavior during gastrulation in the mid-gestation mouse embryo. We worked out techniques for in vitro culture of the embryos and for long-term (6-8 hours) time-lapse confocal imaging, using transgenic animals that express fluorescent reporter proteins (EGFP and Tomato fluorescent protein). With this we have obtained high-resolution imaging of individual cell behavior in the mouse embryo, enabling us to describe the cell behaviors that drive elongation of the primary axis of the embryo, and to extend the analysis to embryos lacking proteins of the planar cell polarity (PCP) signaling system, which exhibit both a shortened primary axis and neural tube closure defects. We have found that one of these PCP proteins, PTK7, normally promotes polarization of mesodermal cells and neural cells, leading to intercalation behavior that drives convergence and extension of the axial and paraxial tissues (somites, notochord, neural plate). In the absence of this protein, neural and mesodermal cells do not polarize their rearrangement, and the axis does not lengthen. Mutations in a different protein, Vangl2, also lead to failure of axial elongation, but affect the efficiency of cell intercalation rather than its polarity. We are now examining the specific effects of each protein on cell behavior in more detail to determine what their function is at the subcellular level.