Friday, April 10, 2009
Icefish "antifreeze"
On pages 19-27, Carroll discusses the uniqueness of bloodless icefish and their invention of "antifreeze" proteins. These proteins lower the temperature at which water freezes. Using what we know of genetic engineering, specifically our class experiment in which we recombined bacterial DNA to include a jellyfish gene to cause the bacteria to glow in UV light and to be resistant to ampicillin, how might this unique icefish gene be an advantage in another organism? What adaptations does this organism have that allow it to survive without the antifreeze gene?
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First of all, to be fair, the antifreeze gene is not unique for just icefish; it's also present in many organism that live in subzero environments. For example, fish such as cod that live in subzero polar waters have also evolved to avoid freezing to death by using special antifreeze proteins that work by binding to ice crystals to prevent the crystals growing larger and causing problems (source: http://www.underwatertimes.com/news.php?article_id=54171063092).Therefore, the antifreeze gene would definitely be a selective advantage for any organism that lives in subzero temperatures because it would allow them to survive and reproduce. By that, I mean that they may be able to avoid predators that, unlike them, are unable to withstand the extreme cold.
ReplyDeleteIf the organism did not have the antifreeze gene, it would be very difficult, maybe even next to impossible for them to survive in a subzero environment. Major adaptations would include either migrating to a warmer surrounding or to somehow evolve heating mechanisms that would have to be constantly functioning in order to counter the freezing waters.
Other sources:
http://www.scienceblog.com/community/older/archives/C/archsf623.html
http://en.wikipedia.org/wiki/Notothenioidei
In the book, Carroll also discusses Artic and Antarctic fish. These fish also have an anti-freeze made up of proteins with a repeating code made up of either threonine-alanine-alanine or threonine-proline-alanine. Their antifreeze functions so that their blood does not freeze from the ice water in which they live. By comparing these antifreeze proteins to a digestive enzyme, it could be stated that the antifreeze arose from a piece of DNA encoding part of the enzyme and part of the neighboring cells. There are many selective advantages to having this antifreeze which allows them to reproduce and survive. The fish can then live in this water temperature which many other fish can’t survive in. This allows them to escape predators and have an open environment to live in. This gene could be a great advantage to any organism living in cold temperatures and organisms that may suffer from freezing. But, the antifreeze found in the ice fish are quite different and wouldn’t be much help to other organisms, ice fish do not have red blood cells to transfer oxygen throughout the body, but instead oxygen travels through the blood plasma. Without the antifreeze genes and functions, the fish would freeze to death from the subzero temperatures. The fish would need to move to a different location which could open up opportunities for predators. But, without moving the fish would have a very slim chance of survival, they may try to stay closer to the surface so light may cause warmth. They ay need to move quicker or have adaptations to make their blood circulate and stay warm.
ReplyDeletehttp://www.aad.gov.au/default.asp?casid=1539
The unique icefish gene prevents the freezing of cells by lowering the temperature threshold at which ice crystals can grow (Carroll 25). The ice fish gene could become a selective advantage for not only fishes and marine animals that live in subzero environments, but also other land animals and vertebrates that have to hibernate to prevent freezing to death. The polar bear, for example, are found along the northern most coasts of the northern hemisphere. They live in generally cold environment with lots of snow and ice. In the winter, the Polar Bear lives on the frozen tundra and in the summer they are on the permanent ice of the north pole. In the winter time, the polar bears hibernate during the winter to prevent freezing and starving to death. The antifreeze gene, when developed by polar bears, would reduce the need for polar bears to grow much of their fur and decrease the need for polar bears to hibernate. The antifreeze gene would eliminate the need for polar bears to grow fur and the need for mechanisms that maintain their body temperature. Keeping their body warm in such a cold environment dissipates a lot of energy that could be used for other activities such as hunting and mate-searching for the greater survival rate of the polar bears. The polar bears also would not have to hibernate during the freezing winter, since they have antifreeze proteins that prevent cells from freezing and decreasing cell activity. They can still roam around and hunt for their food for survival. If polar bears were genetically engineered, however, the gene insertion would not be successful. The recombination of DNA into foreign cells is possible when there are a limited number of cells. The polar bear, made up of tons of cells, would not be able to take up the antifreeze gene for the selective advantage of the species. There are too many cells in the polar bear’s body to alter the gene expression and DNA sequence of the species. Also, the insertion of this gene may induce other mutations for natural selection that may be harmful or beneficial. Since no one has ever tested inserting antifreeze genes into polar bears, the effects are unknown and may be risky. The insertion of the gene may provide a selective advantage or a selective disadvantage, since we do not know the effects of the inserted gene in an actual polar bear.
ReplyDeleteThe polar bears, which do not have antifreeze genes for antifreeze proteins, have thick fur and hibernation as a means to survive in cold environments. They hibernate over the winter when the food is scarce and the weather is harsh. The polar bears’ thick white fur provides insulation and also provides a selective advantage for hunting with a camouflage effect with snow and ice.
http://www.thewildones.org/SFC/Seana/ryan.html
As Chris has already stated, the antifreeze protein is not unique to the icefish. It in fact exists in many non-homologous fish living in near freezing waters around the globe. I would first off like to explain the dynamics of the antifreeze proteins (AFPs) that have developed in these various organisms. Normally, in a freezing solution, when ice touches water that is just above the freezing temperature, the water molecules bind to the ice lattice and expand the ice front. Any particles in the solution are just pushed ahead by the “front”, thus allowing the ice to continue its expansion (if the temperature is low enough). However, the structure of the AFPs is unique in that instead of being pushed ahead by the ice, it actually binds to the growing front. This fusion of multiple AFPs to the ice front stops its growth, until enough AFPs have surrounded the areas of frozen water to contain it permanently. This is why AFPs are responsible for lowering the freezing point of the liquid they are in (1).
ReplyDeleteThese proteins would be ideal for animals that inhabit year-round cold areas. It would not be necessary for an animal such as a polar bear, however, because these animals are not subject to the freezing temperatures that exist below the water’s surface. On the land, even in the coldest areas, there are always periods of time when the sun is out even for a little while, and these sunny spurts actually provide warmth to all terrestrial animals. And even without the AFPs, animals that spend time above water in the arctic or any other cold environment have developed dense coats of fur and/or fat to insulate them. Even seals, which spend a lot of time in the water, are capable of “sunbathing” above the ice in order to cool their internal body temperature. The animals that must beware of actually freezing are the ones that exist below the sun’s reach, far under the ice level, where it is absolutely necessary to have a component inside of them to keep them from freezing. Besides the icefish, other fish that contain the antifreeze protein are the winter flounder, smelt, sea ravens, herring, and some types of eelpouts. However, AFP existence is not limited to the Kingdom Animalia. Some plants utilize this protein too. One such overwintering plant is the Secale cereale or winter rye. This plant does not utilize the AFPs in the same way as the ice fish do however. Instead of using the AFPs to stop the formation of ice crystals, the winter rye utilizes the AFPs unique structure to actually form ice crystals into a specific shape that will benefit the plant. One such benefit might be to prevent re-crystallization, a unique reforming of ice crystals that can lead to tissue loss or dehydration (2). Another group of organisms that contain AFPs is in the phylum arthropoda, of the kingdom Animalia. Whereas the arctic fish exhibited a method of freeze avoidance in their use of AFPs and the winter rye used them for freeze tolerance, some insects have adapted in such a way that they use the AFPs for both methods of sub-zero survival (3). One study done on Alaskan insects which produce AFPs turned up some very interesting specimens. The most interesting, I thought, was in the larvae of the beetle Cucujus clavipes. What is interesting about this substance is that after the larvae metamorphasizes into a full grown beetle, it stops synthesizing the protein. This is because the matured beetle has a much thicker exoskeleton capable of providing enough insulation where the insect has no need for “warming” proteins, while the larvae has no exoskeleton at all (4).
To answer the part about in what organisms that currently have no AFPs would it be beneficial to genetically engineer their DNA to have a gene coding for it, I answer that there probably are none. Currently, any animals that exist in cold enough environments where it would be necessary to have the AFPs for survival all ready have the AFPs. If they did not, then they would literally freeze to death, and the species would cease to exist. If an animal has not developed an AFP, then it is likely that it is because they live in an environment where it is not necessary to have such for survival. In other words, it is not cold enough for the organism’s insides to freeze; therefore they have no need for an antifreeze protein. However, this is not to say that a change might come about in the environment where previously temperate environments turn drastically cold, and evolution would not work fast enough to save all the life in that area. It is in cases like these, where an organism that is prepared one day and not the next, that it might be necessary to provide them with an antifreeze protein to ensure survival.
1. Peter L. Davies, Jason Baardsnes, Michael J. Kuiper and Virginia K. Walker.
Structure and Function of Antifreeze Proteins. Philosophical Transactions: Biological Sciences, Vol. 357, No. 1423, Coping with the Cold: The Molecular and Structural . Biology of Cold Stress Survivors (Jul. 29, 2002), pp. 927-935. The Royal Society. April 14, 2009. http://www.jstor.org/stable/3066911
2. Mervi Antikainen, Marilyn Griffith, Jing Zhang, Wai-Ching Hon, Daniel S. C. Yang and Kaarina Pihakas. Immunolocalization of Antifreeze Proteins in Winter Rye Leaves, Crowns, and Roots by Tissue Printing. Plant Physiology, Vol. 110, No. 3 (Mar., 1996), pp. 845-857. American Society of Plant Biologists. April 14, 2009. http://www.jstor.org/stable/4277059
3. John G. Duman, Ding Wen Wu, Lei Xu, Donald Tursman and T. Mark Olsen. Adaptations of Insects to Subzero Temperatures. The Quarterly Review of Biology, Vol. 66, No. 4 (Dec., 1991), pp. 387-410. The University of Chicago Press. April 14, 2009. http://www.jstor.org/stable/2831325.
4. Barnes, Brian M. Collaborative Research: Studies of Antifreeze Proteins in Arctic and Neararctic Insects. U of Alaska, Fairbanks, Institute of Arctic Biology. (2003). April 14, 2009. http://www.polar.ch2m.com/arlss_reports/arlss_projectsdetail.aspx?cbpropnum=0117104