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Source: http://www.liacs.nl/~kyan/

Cell Fate
A cell’s fate can be described as what the cell will become over the course of normal development. It can be discovered and tracked by labeling the cell with a marker and observing how the cell changes and forms in relation to its specialization. Cells have what is known as developmental potential; they have a range of cell types that they can develop into. This developmental decreases overtime as the cell becomes more and more specialized (programmed to perform a specific function). Cells start of in a totipotent form, this means that they have the capability to turn into any cell type. As they develop they become pluripotent; determination occurs which limits the range of potential to a particular area of specialty. Differentiation occurs as the cell becomes fully mature, becoming a fully specialized cell. This plan arises from a selection of genes chosen to be expressed from the genetic makeup of the cell.

Cell Memory
Multi cellular organisms have evolved a way to form an array of highly specialized cells. Once the cell type is chosen the cell will not be able to differentiate again and will maintain this form through future generations. These cells thus remember the gene expression and the changes that result from it. This phenomenon is known as cell memory. Cells only express a fraction of their genes, in turn different cell types arrive because different sets of genes are expressed. Different cell types synthesize different sets of proteins (ie. Hemoglobin that is only present in and thus produced in blood cells) even though all cells actually contain all of the information necessary to construct the entire organism it is a part of.

Mechanisms
Mechanisms that are utilized to guide cell determination are very intricate and elaborate in design. In some cases, determination happens because of the asymmetric segregation of cellular determinants; however most cases occur from inductive signaling between cells. Asymmetric segregation is based on localization of cytoplasmic molecules, usually in the form of mRNA or proteins, before the cell divides. This would cause one daughter cell to receive more of the DNA during cell division. Two different daughter cells with different gene expression (passed down from cell memory) will arise from this process. Inductive signaling utilizes diffusible signals. These signals are sent through extracellular space and are received by receptors that are present on the membrane of the cell. These signals cause secondary signaling to occur within the cell, telling what genes to express and ultimately what to become. Signals can be transmitted through direct contact or through gap junctions. Transmembrane proteins located on cell surfaces of cells in direct contact are able to transmit information to one another. This information yields a response in the cell that often leads to specialization of the cell. Gap junctions (present only in mammalian cells) form between two cells and are primarily for communication. Small molecules and ions are often allowed to pass between one another. Plasmodesmata are essentially gap junctions that form in plants. These, however, are cytoplasmic connections that connect two plant cells together and are more complex than their mammalian cell counterpart. It utilizes a central tubule that joins the endoplasmic reticulum of the two cells together. This would increase the ability of the plant cells that are directly connected to produce what they need relatively quickly and in high amounts to in response to the signals that had been transmitted to it priorly.

Tissue Formation
Through these elaborate relationships common cell types come together to form tissues. Tissues that are found in plants are categorized into thre systems, the epidermis, ground tissue, and vascular tissue. The epidermis is composed of the cells that form the outer surface of the plant. Vascular tissues are the main transportation system utilized in the plant and are composed of the xylem phloem. Ground tissues are responsible for manufacturing nutrients and storing those that are in excess for later usage.

Conducting Tissue in Plants
Conducting tissue that is used for transportation in vascular plants is composed of more than one cell type. Cells that are seen in this system are often long and very slender, similar in structure to a pipe that is used to transfer a substance from point a to point b. The xylem and phloem are separated by the vascular cambium. Overtime the vascular cambium’s cells differentiate to form additional cells to become a part of either the xylem of phloem, enabling growth and constant reparation.

Techniques and Developments
One major technique used to see how cells develop and specialize is the tracking of the cells. In the past it had been done with markers to see how where the cell moved. They could thus observe cell fate, however this method leaves out part of the entire story. It would be difficult to actually see how the cell transformed and changed in order to fit its specialized job. With recent developments in technology it is now possible to photograph the cell which allows one to actually watch the process take place. Tracking software can operate in multiple ways. Some take multiple photographs over designated intervals of time, once put together these pictures form a frame-by-frame stop motion picture. Individual cells or groups can be selected for viewing and the program will track the progress and development of that particular cell or cells (Kwak, Hong & Park, 2010). Programs are still being developed that only advance the capabilities of this type of tracking. TADOR, developed by Kurokawa et al., is a multi-target cell tracking program. It has the ability of backwards tracing and also has a set of user functions that can be used to specifically direct the program. The addition of these user controlled inputs allow this program to run in autopilot, with the researcher only needing to input commands if they want to precisely track a particular cell present on their feed (Kurokawa, Noda, Sugiyama, Sakaue-Sawano, Fukami & Miyawaki, 2010). This technique has been especially useful in many biomedical applications (Chatterjee, Ghosh, Chowdhury & Ray, 2013). It can be used to track migration, mitosis, inactivity and the many process that go into apoptosis as well as reconstruction of cell lineages. Stem cell research avidly uses this technique as well as those who reconstruct tissues, oncology, and many other fields considering the composition of organisms is composed of the very cells that are being tracked. Manual tracking often is tedious and time consuming; the cells that are tracked are alive and thus require to be constantly watched. With the invention of automated trackers scientists have a bit more freedom and don’t have to worry as much about human error. There are different tracking types available based on the research being done, and some of these include sequential tracking, detection based associations, and model based tracking. Each one offers particular insight that, when looked at as a whole, can enable the mechanisms behind cell fate to be better understood.


Development of techniques in cell tracking are still being fine-tuned and ever expanding. By associating types of tracking it is possible to get an overall view of how the cell’s fate is determined as well as check data provided from a different type of tracking for validation purposes. Understanding the development of the cell is essential to understanding how the body works especially in relation to its immediate surroundings. This research, especially if developed further, can allow insights to diseases and other disorders that may have been not well understood earlier. With genetic modification techniques, these two systems could be combined to track faulty growth in cells, determine the factor causing it, and then silencing the expression in order to alleviate symptoms or disrupt the disorder altogether. The opportunities are limitless.

Bibliography

  1. Chatterjee, R., Ghosh, M., Chowdhury, A., & Ray, N. (2013). Cell tracking in microscopic video using matching and linking of bipartite graphs. Computer Methods and Programs in Biomedicine,
  2. Kurokawa, H., Noda, H., Sugiyama, M., Sakaue-Sawano, A., Fukami, K., & Miyawaki, A. (2012). Software for precise tracking of cell proliferation. Biochemical and Biophysical Research Communications, 417(3), 1080-1085. Retrieved from http://www.sciencedirect.com.ezproxy.oswego.edu:2048/science/article/pii/S0006291X11023096
  3. Kwak, Y. H., Hong, S. M., & Park, S. S. (2010). A single cell tracking system in real-time. Cellular Immunology, 265(1), 44-49. Retrieved from http://www.sciencedirect.com.ezproxy.oswego.edu:2048/science/article/pii/S0008874910001760
  4. Alberts, B., Johnson, A., Lewis, J., Raff, M., Roberts, K., & Walter, P. (2008). Molecular biology of the cell. (5 ed., p. 411, 454-477 ). New York, NY: Garland Science.