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Progress Report 2007
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Sense and Body Function

Advanced technology has allowed scientists to peer deeper than ever before into the inner workings of the brain, expanding our understanding of the complex relationship between the brain, the senses, and body function. This vast area extends from specialized genomic tools to explore the mechanics of rapid-eye-movement sleep to studies of the influence of circadian clocks on feeding, as well as identifying a section of the brain devoted solely to face recognition. Other studies in 2006 revealed new information about hearing, smell, taste, and sight, answering old questions and raising new ones.

Hearing: Regenerating Hair Cells in Mammals

Sensorineural hearing loss, currently an irreversible condition, is the most common type of deafness in the United States. It is caused by damage to specialized inner-ear hair cells, from  aging, exposure to loud noises, and side effects from certain medications. Scientists interested in developing new therapies for certain types of hearing loss got a boost in 2006 from research that suggests that these specialized hair cells, vital to hearing, may be able to regenerate. 
Although damaged sensory cells in the inner ear, or cochlea, of birds and other lower vertebrates can regenerate, cells in cochlea in mammals, including humans, cannot. Hair cells have long been a target of research aimed at developing new treatments for sensorineural hearing loss. In a study reported in Nature, Neil Segil, Andy Groves, and colleagues at the House Ear Institute in Los Angeles discovered that a gene known as p27Kip1 prevents cell division in the inner ear.1

The researchers studied mouse sensory cells in culture. They found that this gene was switched off in newborn mice, allowing the supporting cells to proliferate and differentiate into hair cells. Studies of cultures from two-week-old mice, however, revealed that this gene, p27 for short, was now switched on, halting cell division. However, cells from two-week-old mice genetically altered to lack the p27 gene were able to make hair cells, suggesting that by silencing the gene, researchers may be able to stimulate inner ear hair cell growth to restore hearing.

Hair cell 
Hear, hair: An image of a hair cell from a high-power scanning electron microscope shows hair bundles projecting from the surface of the cell. Researchers have found in mice that silencing a gene allows hair cell growth that could restore hearing.  (Image courtesy of the House Ear Institute) 

While this process has been shown only in mouse cultures, the work holds promise for the development of new therapeutics to reverse deafness in humans. 

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References

1. White PM, Doetzlhofer A, Lee YS, Groves AK, and Segil N. Mammalian cochlear supporting cells can divide and trans-differentiate into hair cells. Nature 2006 441(7096):984–987.
2. Tsao DY, Freiwald WA, Tootell RB, and Livingstone MS. A cortical region consisting entirely of face-selective cells. Science 2006 311(5761):670–674.
3. Liberles SD and Buck LB. A second class of chemosensory receptors in the olfactory epithelium. Nature 2006 442(7103):645–650.
4. Lu J, Sherman D, Devor M, and Saper CB. A putative flip-flop switch for control of REM sleep. Nature 2006 441(7093):589–594.
5. Gooley JJ, Schomer A, and Saper CB. The dorsomedial hypothalamic nucleus is critical for the expression of food-entrainable circadian rhythms. Nature Neuroscience 2006 9(3):398–407.
6. Mieda M, Williams SC, Richardson JA, Tanaka K, and Yanagisawa M. The dorsomedial hypothalamic nucleus as a putative food-entrainable circadian pacemaker. Proceedings of the National Academy of Sciences USA 2006 103(32):12150–12155.
7. Huang AL, Chen X, Hoon MA, Chandrashekar J, Guo W, Trankner D, Ryba NJ, and Zuker CS. The cells and logic for mammalian sour taste detection. Nature 2006 442(7105):934–938.
8. Ishimaru Y, Inada H, Kubota M, Zhuang H, Tominaga M, and Matsunami H. Transient receptor potential family members PKD1L3 and PKD2L1 form a candidate sour taste receptor. Proceedings of the National Academy of Sciences USA 2006 103(33):12569–12574.
9. Lund RD, Wang S, Klimanskaya I, Holmes T, Ramos-Kelsey R, Lu B, Girman S, Bischoff N, Sauve Y, and Lanza R. Human embryonic stem cell-derived cells rescue visual function in dystrophic RCS rats. Cloning and Stem Cells 2006 8(3):189–199.
10. MacLaren RE, Pearson RA, MacNeil A, Douglas RH, Salt TE, Akimoto M, Swaroop A, Sowden JC, and Ali RR. Retinal repair by transplantation of photoreceptors precursors. Nature 444(7116):203-207.