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Developmental timing and oscillating gene expression
Kageyama, Ryoichiro Institute for Virus Research, Kyoto University, Kyoto, Japan.
Niwa, Yasutaka Institute for Virus Research, Kyoto University, Kyoto, Japan.
Shimojo, Hiromi Institute for Virus Research, Kyoto University, Kyoto, Japan.
- Somite segmentation clock
- Neural stem cells
- Related Primary Literature
Our bodies are derived from a single cell, the fertilized egg. This cell divides and proliferates extensively, with progeny differentiating into a variety of cell types destined to form many different organs. The whole process from fertilization to birth is called embryogenesis. During embryogenesis, many events occur at predictable times. For example, in the mouse, brain and limb formation starts around 8 and 9.5 days after fertilization, respectively, and it takes about 20 days to complete embryogenesis. In each organ, cells proliferate until they reach the proper number. If proliferation continues beyond this point, the body and organs will grow disproportionately large and change shape. How embryos or the cells in embryos detect the right time is a major issue for developmental biology, and it has been suggested that some “biological clocks” serve as controllers of developmental processes. The best-known biological clock is the circadian (meaning “approximately one day”) clock, which regulates day and night activities in our bodies. During embryogenesis, however, clocks with shorter time frames such as hours are required, because so many things happen in embryos in a day. The nature of such clocks remains largely unknown with one exception, the somite segmentation clock, which regulates periodic somite formation.
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