Professor of Biology
B.A., Kansas State University
Ph.D., University of California, San Francisco
Member of: Institute of Molecular Biology
Office: Streisinger Hall Room 375E
Lab: Streisinger Hall Room 375
- Meiotic and Mitotic Spindle Assembly and Function, and Cytokinesis, in the early Caenorhabditis elegans embryo
- Cell Polarity in the early elegans embryo
The Bowerman lab uses genetics, molecular biology, and microscopy to studycytoskeletal regulation and function in the early Caenorhabditis elegans embryo. Beginning with the first mitotic cell division, the early embryo undergoes a sequence of five asymmetric cleavages. The sequence of confocalfluorescent images images of fixed embryos on the left of this page was provided by Ed Munro, and shows the dyna mics of the first mitotic division during embryogenesis. A time-lapse videomicrograph of the cortical microfilament cytoskeleton during the first division of a live embryo is shown on the movies page.
Many of the early divisions in the C. elegans embryo are asymmetric and are largely responsible for establishing the pattern of cell fates required for normal embryonic development. These asymmetric divisions, with their stereotyped timing and mitotic spindle positioning, provide a rich context in which to use the powerful genetics of C. elegans to investigate cytoskeletal function.
To the right is a time-lapse videomicrograph (aka movie) of the first two mitotic divisions during embryogenesis in C. elegans, beginning with a one-cell stage embryo that has completed the second meiotic division and is beginning the first embryonic mitosis. Meiosis I and II are completed after fertilization of an oocyte by a sperm; movies of meiosis must be made “in utero” inside live and immobilized worms). This movie ends partway through the 4-cell stage. Microtubules are shown in green and detected by virtue of a transgene in which tubulin is fused to the Green Fluorescent Protein (GFP). Chromosomes are shown in red, by virtue of a transgene in which a histone if fused to mCherry, a variant of GFP. The movie was made using a spinning disk confocal microscope. These kinds of movies of live embryos provide a very powerful tool for analyzing cell division and gene requirements in the early embryo. C. elegans embryos are about 50 microns in length, and are contained within a tough chitinous eggshell that is somewhat flattened out by mounting of the embryos for videomicroscopy.
The actomyosin cytoskeleton, including the non-muscle myosin II called NMY-2 (in red in the late anaphase mitotic one-cell stage embryo in the image to the right), is localized predominantly at the cell cortex. The actomyosin cytoskeleton is important both for generating anterior-posterior polarity, and for the execution of cytokinesis.Microtubules (shown in green; DNA is in blue) form the meiotic and mitotic spindles, which capture and segregate chromosomes. During mitosis, astral microtubules contact the cell cortex and are important for proper spindle positioning. See the movies page for more information on these early cell divisions. The images to the left show dynamic changes in non-muscle myosin II distribution over time, beginning early in the one cell stage on the top and proceeding to the first cytokinesis in the middle image, and to the two-cell stage in the bottom two images (all courtesy of Edwin Munro).