March 2013 Archives

Week 10: March 25th-29th

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In the book "Endless Forms Most Beautiful," by Sean Carroll the process by which genetic information is stored, copied, and decoded is related to the analogy of modern computer technology. DNA is comparable to the information stored on a computer's hard disk-drive; it is like a long term hard copy of genetic information. It is universal and is the basis of all kingdoms of life, from a tiny microscopic bacterium to a 6 ton elephant in Africa. DNA is the beginning of the central dogma. The central dogma is describing the process of protein production; from DNA to RNA to protein. To continue with our computer analogy, RNA is similar to the information stored in a cache because the lifetime of RNA is much shorter than that of DNA. RNA is simply used as a "messenger" to relay the genetic information for protein production, and the proteins are in essences the "programs" of the computer.
In complex organisms like humans, we have cells that perform different functions. For example we have red blood cells that carry oxygen, and these cells are different from our muscle cells. However, even though these cells have completely different structures and functions they are based upon an identical DNA sequence. How is this possible? Well, it is in the regulation of these genes and differential protein production that allows these cells to perform different roles in our bodies. The genetic information found in DNA is essentially "decoded" in two steps to produce different proteins. DNA is made up of two strands that consist of nucleotides with four distinct bases; complimentary base pair bonding is what holds the two strands together. Each "gene" occupies a certain region along the DNA strand. The gene is decoded in two steps, the first called transcription. During transcription a polymerase produces an RNA strand that is based on the DNA template. This RNA transcript is single stranded, based on the complimentary sequence of the DNA template and is termed "messenger RNA." In the second decoding step the messenger RNA (mRNA) is directly translated into an amino acid sequence that forms a protein. The amino acid sequence corresponds directly with the original DNA sequence, and that determines the specific folding, structure, and chemical properties of the protein which determines the protein's function. Although I am no computer expert, using Sean Carroll's metaphor, this decoding process can be related to the "decoding" of the information put into computer. The information or "code" is given to the computer, and the sequence of that code will be processed by multiple mechanisms in the computer and a "result" will be produced.

Week 9: March 11-15

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This week in class we explored a paper written by Chris J. Cretekos et al. The article was called "Regulatory divergence modifies limb length between mammals," and looked at the limb-specific transcriptional enhancer Prx1 found in mice and compared it to the orthologous gene found in bats. What they found was that when the bat sequence of Prx1 was inserted into the mice, transcript levels in developing forelimbs was much higher and that the forelimbs themselves were also longer compared to the controls. It was also found that when the Prx1 gene was deleted in mice normal forelimbs developed. Overall, this article supports the claim that cis-regulatory are important in generating morphological differences between species.

Week 8: March 4-8

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This week I would like to return to a topic that I discussed in week 6; Mosaicism vs. Regulation. After reading Chelsae's Blog I decided it's worth discussing which of these processes is "more important" or the "right way." To elaborate I do not think either of these mechanism is more important or "better" than the other but rather they both play an important role in development. It is a combination of all these process that contribute to the complexity of development. For Weismann's theory about nuclear determinates, there are developmentally important proteins/RNA's that are unevenly distributed during cell division that lead to the fates of the daughter cells. These factors were termed cytoplasmic determinates. Now the term "mosaic" refers to eggs/embryos that develop as if their pattern of development was determined very early by the differential distribution of different molecules. This determines cell fate at an early stage. Examples that have a significant amount of mosaic development are Caenorhabditis and ascidian embryos. The biggest difference between regulative and mosaic embryos in the importance/amount of cell-cell interactions. In regulative development the cell-cell interactions are absolutely necessary to recognize and restore "the missing cell".
In conclusion, I feel that it is nearly impossible to sum up the phenomenon of development with just one of these terms because the development of an embryo is a complex process in itself and is regulated by even more complex processes.

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