Document Type



Doctor of Philosophy


Biology, Molecular and Cellular Biology

Date of Defense


Graduate Advisor

James Umen, PhD


Wendy Olivas, PhD

Lon Chubiz, PhD

Sam Wang, PhD


Size homeostasis is achieved by a balance between cell growth and cell division, but the underlying mechanisms are yet fully understood. Green alga Chlamydomonas reinhardtii (Chlamydomonas) is a unique model for size control. Instead of the canonical binary fission cell cycle, Chlamydomonas uses a multiple fission cell cycle where a prolonged G1 phase is followed by rapid alternative n rounds of S/M (DNA synthesis and mitosis) cycles to produce 2n daughter cells. Two size checkpoints show size-dependence: the Commitment checkpoint governs a minimum size for a cell to divide at least once, and the S/M checkpoint governs the division number to ensure uniformly sized new-born daughters. A conserved retinoblastoma (RB) tumor suppressor is known to be the master regulator for cell cycle progression in animal cells and higher plants. Previous studies support the idea that the RB pathway in Chlamydomonas regulates the S/M checkpoint. I established microscopy-based mathematic models to explain the mitotic behaviors in the multiple fission cell cycle of Chlamydomonas and characterized additional sizer proteins functioning in the Chlamydomonas RB pathway. I related the molecular mechanisms for size control in yeast, higher plants, and animal early embryogenesis, and further concluded that size sensing in eukaryotes can be explained by general titration mechanisms where cell cycle inhibitors titrate against DNA(/genome) to govern the cell cycle progression.

Available for download on Friday, November 28, 2025