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Cell fate determination
Within the field of developmental biology one goal is to understand how a particular cell (or embryo) develops into the final cell type (or organism), essentially how a cell’s fate is determined. Within an embryo, 4 processes play out at the cellular and tissue level to essentially create the final organism. These processes are cell proliferation, cell specialization, cell interaction and cell movement. Each cell in the embryo receives and gives cues to its neighboring cells and retains a cell memory of its own cell proliferation history. Almost all animals undergo a similar sequence of events during embryogenesis and have, at least at this developmental stage, the three germ layers and undergo gastrulation. While embryogenesis has been studied for more than a century, it was only recently (the past 15 years or so) that scientists discovered that a basic set of the same proteins and mRNAs are involved in all of embryogenesis. This is one of the reasons that model systems such as the fly (''Drosophila melanogaster''), the mouse (Muridae), and the leech (Helobdella), can all be used to study embryogenesis and developmental biology relevant to other animals, including humans. What continues to be discovered and investigated is how the basic set of proteins (and mRNAs) are expressed differentially between cells types, temporally and spatially; and whether this is responsible for the vast diversity of organisms produced. This leads to one of the key questions of developmental biology of how is cell fate determined.
==Cell Fate==
In the past 15 years or so, the development of new molecular tools (see GFP) and major advances in optical microscopy (see microscopy) have made cell lineageication in the C. elegans embryo.〔Dev Dyn 2010, 239:1315-1329. 〕〔Zernicka-Goetz M: First cell fate decisions and spatial patterning in the early mouse embryo. Semin Cell Dev Biol 2004, 15:563-572.〕 This technique is used to study cells as they are differentiating into their final cell fates. Merely observing a cell as it becomes differentiated (see Cell differentiation) during embryogenesis provides no indication of the mechanisms that drive the specification. Therefore, the addition of molecular manipulation techniques, including gene and protein knock downs, knock outs and overexpression, along with live cell imaging techniques has been transformational in understanding what mechanisms are involved with cell fate determination.〔Artavanis-Tsakonas S, Rand MD, Lake RJ: Notch signaling: cell fate control and signal integration in development. Science 1999, 284:770-776.〕〔Schuurmans C, Guillemot F: Molecular mechanisms underlying cell fate specification in the developing telencephalon. Curr Opin Neurobiol 2002, 12:26-34.〕〔Rohrschneider MR, Nance J: Polarity and cell fate specification in the control of Caenorhabditis elegans gastrulation. Dev Dyn 2009, 238:789-796. 〕〔Segalen M, Bellaiche Y: Cell division orientation and planar cell polarity pathways. Semin Cell Dev Biol 2009, 20:972-977. 〕〔Fazi F, Nervi C: MicroRNA: basic mechanisms and transcriptional regulatory networks for cell fate determination. Cardiovasc Res 2008, 79:553-561. 〕 Transplantation experiments are commonly used in conjunction with the genetic manipulation and lineage tracing. Transplantation experiments are the only way to determine what state the cell is in on its way to being differentiated.
For a number of cell cleavages (the specific number depends on the type of organism) all the cells of an embryo will be morphologically and developmentally equivalent. This means, each cell has the same development potential and all cells are essentially interchangeable, thus establishing an equivalence group. The developmental equivalence of these cells is usually established via transplantation and cell ablation experiments.
The determination of a cell to a particular fate can be broken down into two states where the cell can be specified (committed) or determined. In the state of being committed or specified, the cell type is not yet determined and any bias the cell has toward a certain fate can be reversed or transformed to another fate. If a cell is in a determined state, the cell’s fate cannot be reversed or transformed. In general, this means that a cell determined to differentiate into a brain cell cannot be transformed into a skin cell. Determination is followed by differentiation, the actual changes in biochemistry, structure, and function that result in specific cell types. Differentiation often involves a change in appearance as well as function.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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