Structural Reorganization of Nuclear Proteins During Mitosis

Iowa State University, Ames IA

Investigators

Abstract

Scientific Research: A mitotic spindle is present in all known eukaryotic cells and its function is essential for chromosomal segregation and cell division to occur. Although much work has been directed toward understanding mitotic spindle apparatus structure and function, it is still unclear how chromosome separation is achieved on a microtubule-based structure that is itself in constant flux. The discovery that microtubules assemble and disassemble at both ends of the spindle fiber and of the constant treadmilling of tubulin dimers toward the poles makes it difficult to envision how forces are generated to actually move the chromosomes on such a metastable structure that is not anchored in place. For these reasons and based on theoretical considerations of the requirement for force production at the spindle the concept of a spindle matrix has long been proposed. In its simplest formulation a spindle matrix is hypothesized to provide a stationary or elastic molecular substrate that provides a backbone or strut for motor molecules to interact with during force generation and microtubule sliding. Such a matrix could also have the added properties of helping to organize and stabilize the microtubule spindle. Four nuclear proteins in Drosophila exhibiting properties consistent with a spindle matrix have been identified and will be cytologically and functionally analyzed to test the spindle matrix hypothesis. State-of-the-art fluorescent imaging techniques will be used to determine these proteins' dynamic properties, newly generated mutants will be analyzed to gauge functional consequences of alteration or loss of these proteins, and potential interactions with microtubules and/or an essential motor protein will be probed to assess potential connections between the spindle matrix, the microtubule spindle, and motor proteins essential for mitotic spindle function. Broader Impacts: The broader impacts from the project activities will accrue at several different levels. 1) Advancing discovery with a potential to achieve paradigm-shifting results. The demonstration of a spindle matrix will fundamentally alter the molecular understanding of spindle function. Thus, this project has the potential to change textbook descriptions of mitosis. 2) Incorporation of experimental aims into training projects at the graduate, undergraduate, and high school levels. The PI has mentored 25 graduate students, 34 undergraduates and 4 high school students over the years with 8 undergraduates serving as coauthors on papers. Among the undergraduates, 11 have entered graduate schools, 8 have pursued veterinary or medical training (2 in M.D./Ph.D. programs), and 2 have chosen scientific-related fields (forensics, lab technician). This level of mentoring will be continued under the proposed project. 3) Recruitment of underrepresented groups. During her career, the PI has trained 35 women, including 6 African-Americans, and 1 African-American man. 4) Establishment of international partnerships. As part of this project, a collaboration has been initiated with a group in Portugal that has obtained funding from FLAD to send a student to the PI's laboratory for training. 5) Development of research-based educational materials. The PI has been active in incorporating research methodology into her cell biology class in order to encourage problem-solving approaches. She has developed a set of PowerPoint slides that are available to other Biol 314 instructors that is continually updated. 6) Participation in mentoring programs. The PI has participated as a faculty mentor in a number of different programs, including "Preparing Future Faculty" (advising graduate students on future academic/research careers), "Project Assist" (a program that recruits minority students to Iowa to work in a corporate research setting for academic credit), the "Honors Mentor Program" (a freshman lab orientation program for one-semester research projects for honors students), the BEST (Biology Education Success Teams) program (a living/learning program for orientation of incoming biology students), and Ames High School Partnerships for Biological Sciences program (to mentor high school students on research projects.) The PI has also been very active in making presentations to undergraduate clubs (such as Tribeta, the honors biology club) and area undergraduate colleges on different topics, including her research work or on career prospects in research-related fields. These mentoring activities will be continued.