Cell Growth & Division
Not only do we begin our lives as single cells - but we are cells. For that reason, the story of our own growth and development is actually a cellular story. In this chapter, we began by considering why cells cannot increase in size indefinitely - even though there are some really big cells in nature, such as the green alga Caulerpa, which can grow to several feet in length. Reproduction occurs at thge cellular level, too, whether that process is sexual or asexual. That's why we've tried to present each step of the process of mitosis (in eukaryotes) in this chapter, emphasizing the careful way in which cells duplicate and then separate each of their chromosomes. Part and parcel of this is the Cell Cycle, the orderly series of events through which cells progress between one division and the next. Over the last two decades, it's become apparent that control of the cell cycle is one of the most critical processes for all living things. A loss of cell cycle control is the basic mechanism behind cancer, for example! Finally, we decided that this chapter was the best place to bring students up to date on some of the most recent breakthroughs in Stem Cell research. In addition to describing the role that stem cells play in development. we wanted to highlight the work of Shinya Yamanaka (co-recipient of the Nobel Priize in 2012) for the development of iPS cells.
iPS cells and Regenerative Medicine
As most students know, ethical issues swirling around embryonic stem cell research have made it one of the most contentious areas of biological research in recent years. Some politicians have sought to ban the research, and many governments, including our own, have restricted the work from time to time. Against that backdrop, the work of Shinya Yamanaka is particularly significant. His lab, at the University of Kyoto, developed a "recipe" for converting ordinary body cells into ones that mimic nearly all of the characteristics of embryonic stem cells, quite possibly doing away with the need to extract cells from human embryos. His work has opened up a whole new field in which biologists have begun to unravel the signals that cause cells to differentiate into one cell type or another. Understanding such signals is the key to repairing or replacing cells damaged by a wide variety of diseases, and it seems as though the door is now open to a "regenerative" medicine in which broken body parts and tissues can be routinely replaced. We are indeed entering a new world of medicine, and today's students may be among the first beneficiaries of this work.
