February 2013 Archives

In early embryo, cell specification is an essential process that determines the formation of different tissues and organs. As mentioned in the article, morphogens have been established as major developmental factors that determine cell fates. Prior works has shown that morphogens provide developmental instruction to cells by its distribution gradient. Cells in different gradient of a specific morphogens have different identity. The authors bring up an important quest. Besides the identification of each cell, many cells such as epithelial cells have to determine their orientation or polarity, and simple diffusion of morphogens seems insufficient to determine the entire cell's fate. In order to give some basis of evaluation on morphogens, the authors introduce two conditions of positional information: precision and robustness. Precision is the measure of how accurate the positional information the morphogens provide to the cells. Robustness is the reliability of morphogens to direct the cells despite of chemical backgrounds or varying diffusion environment. A study is cited in which the gene product has higher precision than the regulating morphogen, Bicoid. This implies that morphogen alone can't provide all of the precision that the cells need. When discussion about roburstness, there are several problems morphogens have to overcome to reliably provide positional information. First, both morphogens and receptors are dilute, and their binding is hinder by the extracellular matrix, which can trap the morphogens. The endocytosis of morphogens and the 3D structure of the tissue further complicate robustness. Other mechanisms responsible for precision and robustness were discussed. I found the distribution of morphogen receptors very interesting. This is kind of unexpected because I only had the mindset that the morphogens are the one that has a gradient of distribution. Also, cell-cell communication and interaction was mentioned. Cell that is activated early by morphogens communicate with its neighbor, which modifies them for different interpretation of similar morphogens concentration. In conclusion, the authors propose that morphogens general effects on cells are fine-tuned by many different mechanisms.

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