A growing problem: The many unsolved mysteries of cell growth.

Growth is the essential vital process that drives life forward and always occurs within cells. Cell growth fuels the cell divisions that drive proliferation of single-celled organisms and growth of multicellular organisms. Mechanisms that control the extent and location of growth within cells generate the extraordinary diversity of cell sizes and shapes seen across the tree of life and within the human body, and nearly all cancers show profound defects in control of cell growth that lead to severe aberrations in cell size and shape. Yet we know little about how cell growth occurs or how it is controlled. For decades we have known how basic building blocks such as amino acids and lipids are built, but an enormous gap has always remained in our understanding of how these building blocks are used to build out cells of highly diverse sizes and shapes under varying environmental conditions and in diverse developmental contexts. Given the fundamental importance of growth in biology and cancer, our minimal understanding of cell growth is a growing problem. Here, a few of the intriguing and important questions about cell growth are considered.