Mike Danilchik

Ph.D. University of Washington, 1983
Professor -- Biological Structure & Function

Cytoskeletal interactions and membrane dynamics in cell division

One of the most fascinating problems in biology is the mechanism of cell division. Cleavage of large eggs, such as those of amphibians, has long served in cell biology as a convenient model of general cytokinetic mechanisms, while the geometry, timing, and completeness of cleavage are recognized in developmental biology as fundamental morphogenetic forces critical for transforming eggs into multicellular embryos. For many years, holoblastic cleavage in echinoid eggs has served as the archetypal model for cytokinesis in animal cells, and has shaped our understanding of the basic mechanisms of cleavage-plane specification and development of the actin-myosin contractile ring. This familiar cytokinetic model is often contrasted with a rather different mechanism employed in higher plants, in which cell wall materials are deposited in a cell plate between daughter cells. In the past decade, however, numerous variations on these two basic themes have emerged from studies of a wide variety of organisms, and attempts are now under way to unify the two disparate mechanisms.

My lab’s present focus is on understanding the functions of the cytoskeleton in terminal phases of cytokinesis. In amphibian embryos, cell division is accompanied by the insertion of a new domain of basolateral plasma membrane in the cleavage plane -- a process with some similarities to compaction in morula-stage mammalian embryos. A few years ago, we discovered an unusual array of microtubules in the base of cleavage furrows of early Xenopus embryos. Recently, homologous microtubule-containing structures have been identified in other organisms as well. We hypothesized that this furrow microtubule array serves to direct basolaterally targeted post-Golgi vesicle traffic toward a localized exocytotic site during the membrane expansion of cleavage, and there is now evidence from a variety of in vivo and in vitro experiments that this idea is at least partly correct: for example, interfering with microtubules blocks membrane expansion, while experimentally placing microtubules in ectopic sites under the egg surface results in ectopic membrane addition. Interestingly, however, furrow microtubules also appear to be involved in stabilizing or propagating the actomyosin contractile ring. Present lab aims are to learn the role of microtubules in directing exocytotic vesicles to the growing basolateral surface at the cleavage plane, to understand the details of cytoskeletal assembly in the furrows of living embryos, and to investigate the relationship between furrowing and several dynamic membrane activities that appear to be important for completion of cell division. We are presently using various GFP-tagged constructs to carry out real-time and timelapse confocal analysis of these processes in living embryos.

Recent publications

Danilchik, M.V., Funk, W.C., Brown, E.E., and Larkin, K. (1998) Requirement for microtubules in new membrane formation during cytokinesis of Xenopus embryos. Developmental Biology 194: 47-60.

Mayerhofer, A., Smith, G. D., Danilchik, M., Levine, J., Wolf, D. P., Dissen, G. A., and Ojeda, S. R. (1998) Oocytes are a source of catecholamines in the primate ovary: Evidence for a novel cell-cell regulatory loop. Proc. Natl. Acad. Sci. USA 95: 10990-10995.

Larkin, K. and Danilchik, M. (1999). Microtubules are required for completion of cytokinesis in sea urchin eggs. Developmental Biology 214: 215-226.

Larkin, K. and Danilchik, M. V. (1999) Ventral Cell Rearrangements Contribute to Anterior-Posterior Axis Lengthening between Neurula and Tailbud Stages in Xenopus laevis. Developmental Biology 216: 550 560.

Danilchik, M.V. (2000). Gravity effects on early cytoplasmic movements and cleavage. NASA ISLSWG Developmental Biology Workshop Proceedings.

Larkin, K. and Danilchik, M. (2001). Three-dimensional analysis of laser scanning confocal microscope sections reveals an array of microtubules in the cleavage furrow of sea urchin eggs. Microscopy & Microanalysis 7: 265-275.

To contact Dr. Danilchik directly: danilchi@ohsu.edu