Cell Differentiation and the Cell Cycle

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During the development of multicellular organisms, cell differentiation is tightly coordinated with cell division. In animals, loss of control of cell division leads to cancer. In some cell types, a modified cell cycle occurs during differentiation in which the DNA is replicated without concomitant cell division, resulting in an increase in nuclear DNA content. This process is called endoreplication; in plants, important examples of endoreplicated cell types include cereal endosperm, cotton fibers, and nitrogen-fixing symbiotic nodules in legumes. The coordination of this modified cell cycle with cell differentiation remains poorly understood. Previous work using Arabidopsis leaf hairs (trichomes) as a model for cell differentiation demonstrated that the SIAMESE (SIM) gene encodes a cell cycle regulator necessary for the suppression of mitosis during establishment of endoreplication in trichomes. The goal of the proposed work is to test a proposed mechanism for the establishment of endoreplication. The proposed work is expected to shed light on the establishment of the endocycle, and on the integration of the cell cycle with development. The proposed role for SIM focuses on a stage of the cell cycle that is not well-understood in any organism; thus the proposed work may also shed light on the mitotic cycle in both plants and animals. Additionally, the proposed work will play a role in the education of graduate students, undergraduates, and high school students from a wide diversity of backgrounds.