The new study at Columbia University Medical Center ( CUMC ) has shown the role of the semaphorins in identifying the correct taste . The taste-system of mice with engineered semaphorins perceived sweet stimuli as bitter tastes, and vice versa. This finding provides new insights into how the tongue keeps its sense of taste despite the rapid turnover of the cells in its taste buds.The study was published in the online edition of Nature .
Charles S. Zuker, PhD, professor of biochemistry and molecular biophysics and neuroscience from CUMC said, "All of the tastes we experience are a combination of some or all of the five basic taste qualities, so there's little room for error. survival can depend on its ability to distinguish attractive tastes like sweet from aversive ones like sour and bitter. "
Taste buds each contain 50-100 taste cells which rely on receptors that detect each type of taste including sweet, bitter, sour, salty, or umami, and further transfer this information to the brain.
Co-lead author, Hojoon Lee from CUMC stated, "Most portions of the brain circuits that govern taste are hardwired at birth, except in the tongue, where the cells in our taste buds- taste receptor cells- connect to taste neurons." It's a highly dynamic process, taste cells are replaced rapidly and randomly, new taste receiver cell is produced each time which requires the connection with the brain, "I added. Thus the researchers assumed that when the receptor cells are produced, the cells express the molecular signals in order to attract the right complement of taste neurons.
The CUMC team compared the gene expression of taste receptor cells (bitter and sweet) to identify these signals. It was found that these 2 types of taste cells significantly differed in their expression of semaphorins . Bitter receptors expressed large amounts of the Semaphorin 3A variant and sweet receptors expressed Semaphorin 7A .
To elucidate the role of semaphorins in taste receptor-to-neuron connectivity, the CUMC team genetically engineered two types of mice: one in which bitter receptors expressed Semaphorin 7A, and a second in which sweet receptors were modified to express Semaphorin 3A. It was assumed that the bitter receptors in the first model would activate sweet neurons and vice-versa in the second model.
Dr. Lee Reported MICE When Whose That bitter receptors Were engineered to express the sweet semaphorin Were presented With water and bitter Both plain-tasting water; mice consumed bitter water which confirmed that the receptors had been rewired in the brain by switching the semaphorins.
Dr. Zuker said, "The taste system gives us a unique opportunity to explore how connections between taste cells and neurons are wired and preserved, in the face of the random turnover of our sensory cells." Step-by-step studies like this one are helping us decipher the wiring rules of one of our most basic of our senses. "