Growth-Dependent Signals Link Cell Cycle Entry to Cell Growth
Cell growth and its coupling to cell division is a fundamental yet underappreciated aspect of life. It is astonishing that the field studying the regulation of growth and size is relatively new as the first cells must have evolved mechanisms that ensured cell growth and division were coordinated to ensure survival and evolutionary fitness. The mechanisms that coordinate cell growth with cell division are most likely fundamental processes that are conserved from bacteria to multicellular eukaryotes. In the following chapters, I have investigated how cells coordinate growth with cell cycle entry by studying the most upstream activator, the early G1 cyclin Cln3, and how this cyclin is regulated by overall growth, growth rate, and by nutrient availability. I also investigate the role of Cln3’s reported target Whi5, which prevents cell cycle entry from occurring in early and mid-G1. Later in chapter III, I investigate possible mechanisms that could play a role in activating Cln3 in late G1 to cell cycle entry occurs at the appropriate size based on the growth rate. We have many years ahead of us before we may truly understand the great mystery of how cells regulate their size.