I kind of knew that storing food or drink in plastic container was not good. However, I didn't know exactly why. Heidi has a nice blog post about plastic material and their BSA content. The molecular mechanism is very interesting. According to her review, BSA increases MECP2 expression. MECP2 inhibits Kcc2 which code for a chloride pump that is very important to neural development. BSA can leak from plastic container into water or food. An interesting fact that Heidi has in her post is that women are more susceptible to BSA than men.
Last week in class we had some discussion about which type of mutation would be the most important to evolution. We were debating about whether mutation in the regulatory, the cis mutation, or mutation in the gene, the trans mutation, would give rise to new traits.
The cis compartment of a gene is an DNA untranslated region located in the 5' position (upstream) to that gene. The cis regulatory region is very important in turning a gene on/off or the level of expression. A lot of different traits in the animal kingdom are the result of different regulation of the same gene. Take the arm as an example, most vertebrate has very similar arm structure: one bone, two bones, a bunch of little bones and digits. The genes for these bones are similar, but different level of expression caused them to have different size and thus a different shape. Mutation in the regulatory sequence can cause changes in the organism's final form without causing a different protein structure.
The gene is the DNA sequence that actually codes for the proteins. Mutation in the gene gives rise to new proteins. Evolutionary, new proteins are very important in the appearance of new traits. RuBisCO, for example, is a protein originate from changes in the protein structure. This protein allows organism to fix CO2 and do photosynthesis producing O2. This is a very important historical event because the oxygen produced could be used in cellular respiration producing a lot of energy. And multicellular organisms require a lot of energy to maintain their system.
RuBisCO 3D ribbon structure
There were many argument for both sides, cis and trans. For the important of trans mutation, one can say that without the actually gene codes for the protein, there would be no traits. The counter argument would be that without the regulation sequence, the promotor, the gene would not be expressed. In addition a lot of morphological traits are actually derived from the changes in expression of the same genes, not the changes in the genes themselves. On the contrary, the binding protein in the regulatory elements are actually the product of the trans elements.
Cis and trans do not work without the other. A gene without a promoter is not expressed. A promoter without a gene would cause expression of a nonsense protein. It seems like they are equally important. Rather asking which one influenced evolution greater, we should spend our time studying and expanding the knowledge of how cis and trans interact.
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.
In the first week of Developmental Biology, we learnt how to use the microscope and a computer program to take digital images of the slides. These are some photos that I took on Thursday (1/17/13).
Figure 1: The overall image of Nematocera Eclosion was contructed by 6 overlapping images at 5x objectives
Figure 2: The overall image of Staphylindae was contructed by 6 overlapping images at 5x objectives