User:Msamodee

Marcus Samodee

Seminar in Physiology UWO Winter 2012

Article options for review

The first section I would like to address is the section on the arctic ground squirrel. One area that is lacking in information is the behavioral section from the article. Insightful information that should be included is hibernation behavior and a brief outline how Non-Shivering Thermogenesis(NST) allows for regulation of body temperature.

The next section I would like to update is the section on anhydrobiosis. Trehalose is mentioned as being important but many of the factors that influence its production are not mentioned such as the behavioral strategies necessary during dehydration survival, and the importance of the rate of evaporative water in successful anhydrobiosis. Furthermore, neither of the two central hypotheses common in anhydrobiotic research are mentioned and are vital to understanding the underlying mechanism that allows for the physiological strategy of anhydrobiosis.

The final section I would like to address is the section on protein catabolism. Currently there is a small section present that contains very little information, besides a basic overview. This article could be enhanced by the addition of a section on endogenous water production. This strategy is used by various animals during water restriction to produce water. It could also use some examples of animals that utilize this strategy.

Anhydrobiosis Article Edits

Article to review: Anhydrobiosis

Critique

The section on anhydrobiosis provides a good general overview of the topic. However, research in the field concerning desiccation tolerant animals is constantly advancing and warrants the addition of some of these newer findings. The addition of these new findings will provide greater depth of knowledge into some of the key aspects of how anhydrobiosis is being used as a survival strategy and allow for a comprehensive understanding of the complete mechanisms involved in anhydrobiosis. I have chosen to only focus on three key additions that I feel will enrich the section on anhydrobiosis:

Firstly, the article briefly mentions and with only minimal elaboration, that contracting into a smaller shape occurs during anhydrobiosis. This requires further clarity because it eludes to mention if this contraction is a consequence of dehydration after losing cellular water or an actual behavioral adaption that precedes successful anhydrobiosis, known as tun formation and found in tardigrades. I feel it is necessary to elaborate on this point because by clarifying this distinction it would provide the opportunity to outline some of the behavioral strategies that accompany the ability to accomplish successful anydrobiosis. These strategies include, coiling in nematodes, the ability to form a tun in tardigrades, and tubular nests in the larvae of Polypedilium vanderplanki. Likewise, all of these animal species are mentioned in the introductory paragraph in the anhydrobiosis section, but there is no further discussion into how they may differ as anhydrobiotic organisms. Thus, I feel it is necessary to emphasize that even though the cryptobiotic state experienced by these animal is physiologically very similar, the induction into these states are controlled by different behavioral strategies varying from one anhydrobiotic species to the next and by habitat. Furthermore, even though trehalose is mentioned as a necessary component for anhydrobiosis, one of the most important factors connected to the ability to produce sufficient amounts of trehalose for survival is neglected in this article, specifically the rate of evaporative water loss and the factors that influence it. An important point that should be mentioned is that it is these behavioral strategies(tun formation, coiling, tubular nests, etc)that allow anhydrobiotes to control the rate of evaporative water and in some anhydrobiotes it is an absolutely necessary step for the proper induction of anhydrobiosis.

The Kikawada et al. 2005 paper examined the factors involved in successful anhydrobiosis and the behavioral strategy used by larvae of Polypedilium vanderplanki. Some points of support are:

• The time available from the triggering of trehalose synthesis to the complete desiccation of the organism is an important factor, such that a slower rate of evaporative water loss works to facilitate the induction of anhydrobiosis by prolonging the time for trehalose synthesis
• Rate of evaporative water loss is more important than the duration of desiccation stress
• Tun formation is seen in tardigrade species in response to dehydration stress
• Coiling and aggregation is seen in nematodes, which is a behavioral strategy that works to decreases cuticular permeability to reduce the rate of water loss to the air
• Tubular nests which are constructed from a mixture of saliva, detritus and soil are seen in chironomid Polypedilum vanderplanki larvae and provide a physical barrier around larvae that slow evaporative water loss

Second, trehalose is briefly mentioned in the anhydrobiosis section as playing a role in the protection of the organism from desiccation damage during dehydration. However, it provides no further insight into what may be happening at the cellular level, which is the basis for understanding the mechanism for how anhydrobiosis works. Two central hypotheses in desiccation tolerance research include: the water replacement hypothesis and the vitrificaion hypothesis. Both hypotheses were formulated based on evidence of desiccation tolerance in plant seeds and more recent research has provided support for an application of these hypotheses to anhydrobiotic animals as well. I feel that the mentioning of these two crucial hypotheses provide the foundation necessary to understand how trehaolse/other underlying processes assist in the protection of the membrane during desiccation. The second reason is that these hypotheses are no longer just exclusive to desiccated plants but also now current research has extrapolated these findings to animal anhydrobiotes. There has been an extensive focus on trehalose production in anhydrobiotic research due to its identification in the majority of anhydrobitoic species and it is no longer just something of speculation or co-relational. I feel that the anhydrobiosis section does not provide enough evidence to support the importance that has been put on trehalose. So the addition of the findings from a study that has identified this sugar in an anhydrobiotic animal, that is not just speculative, but has measured the presence of trehalose in response to desiccation stress, would be a welcome addition to the article. One or two citation from a study like this would provide evidence that builds a case for trehalose’s importance and signifies the necessity of trehalose in animal anhydrobiotes as well.

Sakurai et al. 2008 using techniques such as FTIR and IR spectra identified an animal anhydrobiote in which the physiological changes visualized support the theory that both water replacement and vitrification are occurring and provide insight into the physiological processes that are occur during anhydrobiosis. Some points of support are:

• Slowly dehydrated larvae of Polypedilium vanderplanki have concentrations of trehalose of up to 18% of dry body weight
• Vitrification: mixture of non reducing sugars and hydrophilic proteins form into a glass-like state during dehydration thereby immobilizing membranes in the cytoplasm, protecting them from denaturation, coagulation, and disintegration
• Water replacement: hydrophilic molecules in the membrane interact with membrane macromolecules, through hydrogen bonding and take the place of water
• Using Fourier-transform infrared microspectroscopy(FTIR) an alpha-alpha 1,1 linkage, exclusive to the sugar trehalose (no other disaccharide has this linkage) was identified in slowly desiccated larvae of Polypedilium vanderplanki

Finally, the bdelloid rotifer has been an important animal model to the understanding of anhydrobiosis due to its inability to produce trehalose and survive desiccation. This has lead to the proposition of other possible substances playing a role, as mentioned in the anhydrobiosis section. However, there is no further discussion from that point to outline what these other candidates could be. I feel since more recent research has identified a host of possible candidates that they should be mentioned since the direction of the research has begun to shift towards these new directions. One possible candidate identified across many anhydrobiotic species that should be mentioned is the late embryonic abundant (LEA) proteins. I feel a brief mention of these proteins to the section would be important, since these proteins have been present in response to desiccation stress, have been postulated as having many functions, and implicated in having an important role in the capability to undergo anhydrobiosis in both trehalose and non-tehalose producing species.

The Boschetti et al. 2011 study examined and characterized the genome of the bdelloid rotifer aiming to identify how these non-trehalose producing anhydrobiotes could provide insight into other molecules involved in accomplishing anhydrobiosis. Some points of support are:

• Several other candidates responsible for anhydrobiosis include; late embryogenesis abundant proteins(LEA), molecular chaperones, amphiphiles, or antioxidants
• LEA proteins which were first discovered in plant seeds during dehydration stress but later identified in invertebrates in response to desiccation stress, suggesting a conserved response to desiccation stress
• Belong to a diverse class of proteins that exhibit versatility in function, known as Intrinsically Disordered Proteins(IDP)
• Hydrophilic LEA’s may have functions ranging from molecular shields/ chaperones, membrane protectants, ion sinks, hydration buffers and antioxidants

References

1)Boschetti, C., Pouchkina-Stantcheva, N., Hoffmann, P. and Tunnacliffe, A. (2011) Foreign genes and novel hydrophilic protein genes participate in the desiccation response of the bdelloid Rotifer Adineta ricciae. Journal of Experimental Biology 214: 59-68

2)Kikawada, T., Minakawa, N., Watanabe, M. and Okuda, T. (2005) Factors inducing successful anhydrobiosis in the African chironomid Polypedilum vanderplanki: significance of the larval tubular nest. Integrative and Comparative Biology 45: 710-714

3)Sakurai, M., Furuki, T., Akao, K.I., Tanaka, D., Nakahara, Y., Kikawada, T., Watanabe, M. and Okuda, T. (2008) Vitrification is essential for anhydrobiosis in an African chironornid, Polypedilum vanderplanki. Proceedings of the National Academy of Sciences of the United States of America 105: 5093-5098