CAREER: Investigating the Role of Clonal Cell Competition in Zebrafish Neural Development using in Vivo Multicolor Imaging

Lewis And Clark College, Portland OR

Investigators

Abstract

The remarkable function of the brain requires proper growth and formation in the embryo. First, a small cluster of cells increases dramatically in number, then transforms into an exquisitely organized organ with a complicated pattern of connections. Most of the time, this process results in brains that are perfectly normal, with the right number of nerve cells. Surprisingly little is known, though, about how the growing brain decides how many cells to produce. This research project will look at the control of cell number in the growing brains of transparent living zebrafish during the first few days of life. The PI has developed techniques for watching clusters of dividing cells over time in special zebrafish embryos whose brain cells glow with unique combinations of colors (called "Brainbow"). This coloring allows new cells to be followed as they divide off from their mother cell. So far it appears that families of cells (mother cell with her set of daughter cells) compete with other families to survive in the growing brain. This type of competition has not been seen before in the brain, and may be responsible for controlling growth - not only in the brain, but in other organs as well. The PI will test which genes are important for cell families to survive this competition. The work will generate a number of new research tools that will be shared with the scientific community. Undergraduate students will perform and analyze the experiments themselves, providing rich opportunities for research training early in developing scientists' careers. By also transforming the data they have personally collected into an interactive, educational website, students will learn various digital media approaches to making scientific material understandable to traditional and non-traditional audiences. The colorful images produced by this research have great appeal to both scientists and non-scientists, making it easier for students to learn how to engage the public with their work. To study dynamic cellular behavior in the living brain, the PI has developed an approach using in vivo time-lapse confocal imaging and multicolor fluorescent protein (Brainbow) expression in zebrafish. Using this technique, the PI has shown that programmed cell death occurs non-randomly in the living brain, with specific neural progenitor cells and their neuronal progeny (entire clones) undergoing cell death in a coordinated manner, while neighboring clones appear normal. If whole clones of dividing cells are in fact competing with one another, increases or decreases in cellular fitness should influence a clone's competitive edge. The planned research will use a mosaic approach to alter gene expression in individual cells, coupled with global Brainbow expression to simultaneously follow dynamics within multiple clones of dividing cells. Cellular fitness will be targeted via both cell-intrinsic mechanisms (cell cycle, c-myc activity) and cell-extrinsic mechanisms (access to extracellular BMP signaling). These experiments will test directly whether cellular fitness influences a clone?s ability to survive in the developing brain. Overall this may support the hypothesis that competition among clones of dividing cells helps regulate neuronal production and growth in the developing nervous system.