生物谷報道：最近,，布朗大學的一個研究組的研究人員發(fā)現(xiàn)一種叫做黑視素（melanopsin）的蛋白對眼睛中的一種叫做ipRGCs（注：intrinsically photosensitive retinal ganglion cells）的細胞的內(nèi)部工作很重要。這項研究公布在近期的《自然》雜志上,。研究首次給出證據(jù)證明黑視素是一種功能性感光色素,。
研究人員發(fā)現(xiàn)黑視素能吸收光并引發(fā)一種使細胞給大腦發(fā)出光信息的生化級聯(lián)反應。通過這些信號,，ipRGCs能夠根據(jù)日出日落校準身體律節(jié),。這種生理節(jié)律控制著警戒、睡眠,、激素產(chǎn)生,、體溫和器官功能。這個研究組在2002年發(fā)現(xiàn)了ipRGCs,，他們的研究表明桿狀細胞和錐狀細胞并不是僅有的感光眼細胞,。
這項研究表明黑視素能吸收光并開啟細胞中的一個化學反應鏈，從而引起電勢反應。研究還表明黑視素在結節(jié)細胞光受體中扮演一定的角色——它能幫助細胞給大腦發(fā)送一種強烈的信號并讓大腦知道是白天還是黑夜,。
實驗中,，研究組將黑視素插入到培養(yǎng)的腎細胞中。正常情況下,，這些細胞沒有感光功能,。但是當加入了黑視素時，這些細胞竟變成了光受體,。事實上,，這些腎臟細胞對光的反應方式基本上與ipRGCs相同。這一點也證實了黑視素是結節(jié)細胞光受體的感光色素,。
研究人員還發(fā)現(xiàn)由黑視素開啟的生化級聯(lián)與無脊椎動物如果蠅的眼睛細胞中的反應很相似,。這些結果可能告訴我們在進化中，這是一種極其古老的系統(tǒng),，而且我們的眼睛可能還保留著一點無脊椎動物的特征,。
由神經(jīng)學科學家David Berson領導的布朗大學研究組近日發(fā)現(xiàn)一種對眼睛中類似蜘蛛細胞的內(nèi)部功能起著重要作用的黑視素蛋白，也被稱為內(nèi)在感光視網(wǎng)膜中心細胞（ipRGCs）,。黑視素吸收光線并引發(fā)產(chǎn)生一個生化通道,，允許細胞發(fā)送光線的信號。通過這些信號,，ipRGCs同身體的日常節(jié)奏,，日升日落保持一致，以24小時為周期控制人體的警覺,，睡眠,，激素量，體溫和器官功能,。
布朗大學研究組并驚人地發(fā)現(xiàn)了桿細胞和錐形細胞不是唯一的感光眼細胞,。像桿細胞和錐形細胞一樣,，ipRGCs將光能轉換成電子信號,。但是桿細胞和錐形細胞靠探測物體，顏色和移動來幫助視覺,，而ipRGCs卻能夠測量全部光強,，僅僅計算數(shù)百萬的眼細胞中1,000至2,000個 ipRGCs，會發(fā)現(xiàn)它們是截然不同的,。它們與大腦有直接的聯(lián)系,，將信息輸送至一個控制與光和黑暗環(huán)境有關的生物鐘很小的區(qū)域，同時也調(diào)控眼睛瞳孔的收縮,。Berson說,，這是眼睛中通用的一個光檢測系統(tǒng)。他的研究目的就在于提供這個系統(tǒng)如何運作更多的細節(jié)信息。
已發(fā)表在近期的自然雜志上的這項研究結果,，驗證了黑視素是具有功能性的視覺感光色素,，這種蛋白能吸收光，引起細胞中一系列的化學反應,，從而引發(fā)一個電子回應,。研究也表明，黑視素對中心細胞的光接受器有作用,，有助于它們發(fā)送一個強信號到大腦以指示白天或者黑夜,。
研究小組將黑視素插入從腎臟中提取和體外培養(yǎng)的細胞中發(fā)現(xiàn)了這個結果。這些正常情況下對光不敏感的細胞,，在黑視素浸泡中,，被轉入光感受器。實際上,，這些腎臟細胞對光的反應幾乎與ipRGCs一致,，證明了黑視素是中心細胞光感受器的感光色素。
Berson說,，這解決了一個關于這些細胞功能的重要問題,。Berson和他的研究小組也有另外一個非常有趣的發(fā)現(xiàn)，由黑視素激發(fā)的生化通道,，相對于如老鼠,，猴子和人等脊椎動物而言，更靠近那些果蠅和魷魚等無脊椎動物的眼細胞,。這個結果也可能表示這是一個極其古老的無脊椎動物系統(tǒng)（http://www.bioon.com/）,。
Brown Scientists Uncover Inner Workings of Rare Eye Cells
Melanopsin, they found, absorbs light and triggers a biochemical cascade that allows the cells to signal the brain about brightness. Through these signals, ipRGCs synchronize the body's daily rhythms to the rising and setting of the sun. This circadian rhythm controls alertness, sleep, hormone production, body temperature and organ function.
Brown researchers, led by neuroscientist David Berson, announced the discovery of ipRGCs in 2002. Their work was astonishing: Rods and cones aren't the only light-sensitive eye cells.
Like rods and cones, ipRGCs turn light energy into electrical signals. But while rods and cones aid sight by detecting objects, colors and movement, ipRGCs gauge overall light intensity. Numbering only about 1,000 to 2,000 out of millions of eyes cells, ipRGCs are different in another way: They have a direct link to brain, sending a message to the tiny region that controls the body clock about how light or dark the environment is. The cells are also responsible for narrowing the pupil of the eye.
"It's a general brightness detection system in the eye," said Berson, the Sidney A. Fox and Dorothea Doctors Fox Professor of Ophthalmology and Visual Sciences. "What we've done now is provide more details about how this system works."
The research, published in the current issue of Nature, provides the first evidence that melanopsin is a functional sensory photopigment. In other words, this protein absorbs light and sets off a chain of chemical reactions in a cell that triggers an electrical response. The study also showed that melanopsin plays this role in ganglion-cell photoreceptors, helping them send a powerful signal to the brain that it is day or night.
The team made the discovery by inserting melanopsin into cells taken from the kidneys and grown in culture. These cells, which are not normally sensitive to light, were transformed into photoreceptors when flooded with melanopsin. In fact, the kidney cells responded to light almost exactly the way ipRGCs do, confirming that melanopsin is the photopigment for ganglion-cell photoreceptors.
"This resolves a key question about the function of these cells," Berson said. "And so little is known about them, anything we learn is important."
Berson and his team made another intriguing finding: The biochemical cascade sparked by melanopsin is closer to that of eye cells in invertebrates like fruit flies and squid than in spined animals such as mice, monkeys or humans.
"The results may well tell us that this is an extremely ancient system in terms of evolution," Berson said. "We may have a bit of the invertebrate in our eyes."
The research team from Brown included lead author and post-doctoral research associate Xudong Qiu and post-doctoral research associate Kwoon Wong, both in the Department of Neuroscience, as well as graduate students Stephanie Carlson and Vanitha Krishna in the Neuroscience Graduate Program. Tida Kumbalasiri and Ignacio Provencio from the Uniformed Services University of the Health Sciences also contributed to the research.
The National Institutes of Health funded the work.
Source: Brown University
