BioUpdates for July, 2002

by Andrew Tolley

Skin Cells and Heat Sensitivity

New Species

Cellular Signaling

Tomato Heat Tolerance

Alzheimer Advances

Skin Cells and Heat Sensitivity

We have known for some time that humans and other vertebrates can sense cold temperatures through specialized neurons in the spinal cord that are connected by long axons to the skin and organs. Now, work of scientists at The Scripps Institute and the Genomics Institute of the Novartis Research Foundation, led by Ardem Patapoutian, has demonstrated for the first time that skin cells also appear to be sensitive to warm temperature. Building on earlier work that identified a molecule, TRPM8, which helps the body sense cold temperatures, the researchers concluded that other molecules must sense warm temperatures. Their work has led to location and identification of a specific gene that makes a membrane protein called TRPV3. This protein responds to temperature by allowing ions to pass through the membrane, causing the brain to be signaled. The researchers have found this protein, which is sensitive to temperatures 33°C and above, present in keratinocytes, the predominant skin cell. Furthermore, the similarity between this protein channel and those found on temperature-sensitive neurons confirms the belief that TRPV3 is a "molecular thermometer." Although keratinocytes are not neurons, the team suspects the skin cells are able to communicate information to the brain because of their adjacency to nerve fibers located in the skin.

References:

Patapoutian, Ardem et al (2002). A Heat-Sensitive TRP Channel Expressed in Keratinocytes. Science 296(Jun14):2046

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Patapoutian Lab

http://www.scripps.edu/cb/patapoutian/

http://www.scripps.edu/cb/patapoutian/Sci2002.pdf
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New Species

Two recent announcements demonstrate that there are still many species to be discovered. It is still easy to imagine new species of insects and smaller organisms being discovered, but it is more surprising to learn that larger species still await discovery by modern science. But that would appear to be the case. Conservation International has just announced, in the journal Neotropical Primates, the discovery of two new species of monkeys in the Amazon rainforest, making a total of 24 new monkey species reported since 1990. The two species, Callicebus bernhardi and Callicebus stephennashi are types of titi monkey about the size of small cats. Both live in the dense understory of the rainforests and are distinguished by very colorful markings. So far 28 species of titi monkeys have been identified. Mark van Roosmalen, the leading primatologist revealing the new species to the world hopes that these new species will help him convince the Brazilian government to create nature reserves in the areas where the monkeys were discovered.

In addition, a marine survey has just described to science at least twelve new species of fish and coral inhabiting reefs off the coast of Madagascar. Three new damselfish of the Pomacentridae family and nine coral species have been identified by the survey conducted by Conservation International’s Center for Applied Biodiversity Science. From the perspective of Conservation International, these discoveries underline the importance of its Marine Rapid Assessment Program and the need to protect coral reefs. Together these new species remind us that the rate of extinction may also be underestimated; just how many species are disappearing before we even know they ever existed?

Visit:

Conservation International

http://www.conservation.org/xp/CIWEB/newsroom/press_releases/051002.xml
http://www.conservation.org/xp/CIWEB/newsroom/press_releases/062402.xml

Conservation International - Center for Applied Biodiversity Science

http://www.biodiversityscience.org

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Cellular Signaling

The process of cellular communication is complex. Researchers at Johns Hopkins and Harvard Universities have now revealed a further level of complexity while at the same time increasing our understanding of cellular mechanisms. Examining the role of the two most common cellular second messengers, calcium and cyclic adenosine monophosphate (cAMP), the researchers have demonstrated that a cell decides which second messenger to use based on the presence or absence of a protein called sodium/hydrogen exchanger regulatory factor 2 (NHERF2). Investigating how the cell surface receptor for parathyroid hormone and parathyroid hormone-related protein signals the cell interior, the team discovered that the presence or absence of NHERF2 determines whether calcium or cAMP delivers the message. This is an important consideration because the two second messengers elicit very different responses from their target protein. From this study it is apparent that even at receptor binding, the beginning of cellular signaling, switches are being triggered which determine the nature of the signal generated. The researchers are hopeful that their work will contribute to further understanding and therapy for the many common diseases connected to faulty cellular signaling, including cancer and diabetes.

References:

M.J. Mahon et al (2002). Na+/H+ exchanger regulatory factor 2 directs parathyroid hormone 1 receptor signaling. Nature 417(Jun 20): 858-861

Visit:

Nature

http://www.nature.com/cgi-taf/dynapage.taf?file=/nature/journal/v417/n6891/abs/nature00816_fs.html

Author Page at John Hopkins

http://www.hopkinsmedicine.org/graduateprograms/cmm/donowitz.html

Tomato Heat Tolerance

Heat plays an important role in determining how a plant thrives. Unlike animals, plants cannot move to avoid heat. Consequently, they have evolved complex mechanisms to tolerate heat stress. Now, Dr. Lutz Nover of Johann Wolfgang Goethe-Universitat Frankfurt am Main in Germany have discovered that the protein HsfA1 appears to lie at the foundation of the tomato’s mechanism for tolerating heat stress. The team subjected tomato plants engineered for either excess or deficient HsfA1 to various experiments. The results were conclusive. Deficient plants, when subjected to high temperatures, either died or were unable to ripen. Conversely, plants with higher levels of HsfA1 were more resistant to heat than unmodified plants. Nover’s work demonstrates that of all the various heat stress transcription factors found in tomatoes, HsfA1 has emerged as the most significant. Although controversy abounds when it comes to genetically modified crops, it seems inevitable that this kind of research is going to play a vital role in allowing agriculture to feed a hungry world. Developing heat-resistant crops could be crucial to improving yields in a world growing warmer each day.

References:

Mishra, Shravan Kumar et al (2002). In the complex family of heat stress transcription factors HsfA1 has a unique role as master regulator of thermotolerance in tomato. Genes and Development 16 (Jun 15):1555-1567

Visit:

Genes and Development

http://www.genesdev.org/cgi/content/abstract/16/12/1555
http://www.sp.uconn.edu/~hightowe/noverbiosketch.html

Alzheimer Advances

New evidence from a team of neuroscientists at Northwestern University may be key to unlocking the mysteries of Alzheimer’s disease. Strong links have been established between beta-amyloid plaques and the disease, but understanding of the mechanisms leading to plaque development has been lacking. This latest research now points to the protein tau as a key factor leading to the beta-amyloid induced degeneration of neurons. Comparisons were made between neurons containing normal amounts of tau and neurons prepared to lack tau. The neurons containing tau degenerated in the presence of beta-amyloid while those without tau did not. Further investigation of the neurons lacking tau indicated that these cells had more rapid turnover of microtubules (structures within the cell that help maintain its integrity), a process that creates resistance to degeneration. The research indicates that expanding our knowledge of tau and how it may be manipulated may lead to new therapeutic options for treating Alzheimer’s disease. The researchers also suggest that influencing the dynamic behavior of microtubules could be another possible avenue of treatment.

References:

Rapoport, Mark et al (2002). Tau is essential to _-amyloid-induced neurotoxicity. Proceedings of the National Academy of Sciences 99(April 30);6364-6369

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Proceedings of the National Academy of Sciences

http://www.pnas.org/cgi/content/abstract/99/9/6364