Wisconsin Researchers Identify Sleep Gene

04/27/05 -- Zeroing in on the core cellular mechanisms of sleep, researchers at University of Wisconsin Medical School have identified for the first time a single gene mutation that has a powerful effect on the amount of time fruit flies sleep.

In its normal state, the Drosophila (fruit fly) gene, called Shaker, produces an ion channel that controls the flow of potassium into cells, a process that critically affects, among other things, electrical activity in neurons. A handful of recent studies suggest that potassium channels are also involved in the generation of sleep in humans.

Reported in the April 28 issue of Nature, the finding points to novel approaches to treating sleep irregularities in humans-from promoting restorative sleep to prolonging wakefulness.

"This research offers the possibility of developing a new class of compounds that could affect potassium channels in the brain rather than other brain chemical systems targeted currently," says lead author Dr. Chiara Cirelli, assistant professor of psychiatry at UW Medical School.

UW-Madison genetics professor Barry Ganetsky, likely the world expert on the Shaker gene, was a collaborator on the study. Dr. Giulio Tononi, UW Medical School professor of psychiatry, was the senior author on the paper.

Most people sleep seven to eight hours a night, and if they are deprived of sleep, their cognitive performance suffers greatly. However, a few people do well with just three or four hours of sleep-a trait that seems to run in families.

"We wanted to determine which genes underlie this phenomenon in order to shed light on the mechanisms and functions of sleep," Tononi says.

The Wisconsin study focuses on factors that control sleep duration as opposed to the timing of when sleep occurs, which is regulated by the circadian system, Tononi notes. "The key molecular mechanisms controlling the circadian timing of sleep are well understood, but details about the homeostatic mechanism that regulates the amount of sleep have been unclear," he says.

In a four-year, round-the-clock search, researchers screened 9,000 mutated fruit flies, many of them supplied by Ganetsky's lab, and found one line of them that slept one-third the amount of normal flies. Put through a series of tests, the short-sleeping flies, named minisleep (mns), were found to perform normally and did not appear to be impaired by sleep deprivation. The mns flies, however, did have shorter life spans.

Following the testing, the researchers noticed shaking in the flies' legs as the insects recovered from anesthesia. The observation led the team to focus on the Shaker gene, which produces this effect. Nevertheless, Shaker's main job in flies-and in its equivalent in humans--is to control the excitability of cell membranes.

Genetic analysis of the mns flies, conducted by Daniel Bushey, a post-doctoral fellow working with the Tononi team, revealed that their Shaker genes contained a single amino-acid mutation. Because of the mutation, a functional ion channel could not be formed on the cell membrane and potassium therefore could not flow through it.

When the researchers first tested flies with the Shaker gene, they found that some of them with other mutations were normal sleepers. But these flies became short sleepers when the researchers removed genetic modifiers from their genome.

"This told us that genetic forces push hard against this phenotype to make it ineffective," Cirelli says. "Being a short sleeper is probably not a good thing. We know that the mns mutation affects mortality, but we're not sure how."

In earlier studies, Tononi's team discovered that fruit flies do, in fact, sleep.

"The more behaviors we look at, in terms of sleep, the more we find that sleep in fruit flies is very, very similar to sleep in mammals," Cirelli says.

Like humans, fruit flies generally are quiet and immobile for between six and 12 hours each night and lose most of their ability to respond to stimuli, the researchers found. When deprived of sleep, humans and their winged counterparts rebound on the following night by sleeping longer and more deeply. Flies also sleep more in their youth than later in life, when their sleep is fragmented, as with humans.

In other studies, the scientists also observed that caffeine has the same stimulating effects on human and fly sleep, and that similar genes are expressed in both species when they are awake and asleep. Tononi's team also conducted EEGs on the flies and found evidence of the same electrophysiological changes occurring during sleep and wakefulness as in humans.

"The electrical changes in humans look different that they do in flies because our brains are organized differently," Cirelli says. "But the EEGs showed electrophysiological changes signifying that the flies were asleep and awake."

In mammals the changes produce hallmark waves, or oscillations of groups of neurons, easily detected by EEG. The waves are slower during deep sleep and faster during waking times. One way of getting from the faster to the slower state is by opening ion channels, allowing potassium to flow through them.

"Our hypothesis is that if you don't have potassium channels, you won't get slow waves," Cirelli says. "The cell membrane will remain activated, preventing long periods of deep, non-REM sleep."

The researchers say that the fly research translates to humans even more than they thought it would. "Humans have the same kind of genes and potassium channels. And we know that slow waves must be generated by changes in the excitability of neuron cell membranes," Cirelli says.

"Potassium changes may have a huge affect on sleep in humans."

Sleep is a highly complex activity and probably involves many genes, some of which are more influential than others, says Cirelli. "We believe this gene is very powerful because it acts on the final common pathway and has the ability to change the excitability of neurons."

Source: University of Wisconsin-Madison

    美國(guó)科學(xué)家在28日出版的《自然》雜志上報(bào)告說,，他們發(fā)現(xiàn)如果果蠅的某個(gè)基因發(fā)生變異,，就會(huì)導(dǎo)致其睡眠減少。由于果蠅基因構(gòu)成和睡眠特征與人相似,，該發(fā)現(xiàn)將有助于研究和解決人類睡眠問題,。

    美國(guó)威斯康星大學(xué)科學(xué)家在報(bào)告中說，他們對(duì)果蠅的1．4萬多個(gè)基因進(jìn)行了研究,。結(jié)果發(fā)現(xiàn),，如果果蠅的“沙克爾”基因發(fā)生變異，其睡眠時(shí)間至少比正常果蠅少三分之一,。通常果蠅每天睡眠10到12小時(shí),，而基因變異的果蠅每天只需要3到4小時(shí)的休息。實(shí)驗(yàn)證明,，睡眠減少并不會(huì)立即對(duì)基因變異果蠅造成任何影響,，在24小時(shí)無休息的情況下,，它們?cè)谟龅揭u擊時(shí)的躲避反應(yīng)與平常相當(dāng),，而正常果蠅的反應(yīng)明顯放慢。不過,，變異果蠅的壽命比普通果蠅短三分之一,。

    科學(xué)家進(jìn)一步發(fā)現(xiàn)，“沙克爾”基因控制果蠅體內(nèi)產(chǎn)生一種蛋白質(zhì),，這種蛋白質(zhì)能夠促使鉀離子進(jìn)入神經(jīng)細(xì)胞,。“沙克爾”基因發(fā)生變異，果蠅體內(nèi)的鉀離子就無法進(jìn)入神經(jīng)細(xì)胞,，這可能是導(dǎo)致睡眠減少的原因,。

    果蠅的基因構(gòu)成與人類相似，一直被當(dāng)作研究人體的生物模型,。它的睡眠特征,，比如睡眠不足導(dǎo)致反應(yīng)遲鈍等都與人類相似。而人體內(nèi)也存在“沙克爾”基因,，它的作用也與果蠅的類似,。因此，研究人員認(rèn)為,，該研究結(jié)果有助于更好地理解和解決人類睡眠問題,。

　　生物網(wǎng)4月27日?qǐng)?bào)道，美國(guó)威斯康辛醫(yī)學(xué)院的科研工作者致力于研究動(dòng)物細(xì)胞的睡眠機(jī)理,。他們發(fā)現(xiàn)基因突變可以影響果蠅睡眠時(shí)間的長(zhǎng)短,。

　　正常狀態(tài)下，果蠅的特有基因?qū)⒖刂萍?xì)胞中碳酸氫鉀的活動(dòng),，這種活動(dòng)主要發(fā)生在果蠅的神經(jīng)元細(xì)胞中,?？茖W(xué)家們發(fā)現(xiàn)人類的睡眠過程也存在這種活動(dòng)機(jī)理。此發(fā)現(xiàn)可能為失眠患者找到能延長(zhǎng)睡眠的方法,。

　　華盛頓大學(xué)醫(yī)學(xué)院的精神病學(xué)助理教授Chiara Cirelli說,，該研究結(jié)果表明，科學(xué)家可以制造出一種化合物來影響碳酸氫鉀在人腦神經(jīng)元中的活動(dòng),，由此幫助失眠患者延長(zhǎng)睡眠時(shí)間,。

　　華盛頓大學(xué)遺傳學(xué)教授Barry Ganetsky也參加了研究。他說,，世上大多數(shù)人每天睡眠時(shí)間為七到八個(gè)小時(shí),，如果他們正常的睡眠時(shí)間被剝奪，其認(rèn)知能力就會(huì)受到影響,。然而,，某些人每天僅睡眠三到四個(gè)小時(shí)也能達(dá)到正常人的認(rèn)知水平?？茖W(xué)家們目前研究的重點(diǎn)是弄清楚基因控制人類睡眠的機(jī)制并且改造這些基因使之符合人們的需要,。

　　威斯康辛醫(yī)學(xué)院的研究方向集中在找出調(diào)節(jié)人體生理節(jié)奏的方法。目前科學(xué)家對(duì)控制人體生理節(jié)奏的化學(xué)機(jī)制已經(jīng)清楚,，但是對(duì)于人體調(diào)節(jié)其生理節(jié)奏的適應(yīng)性機(jī)能還不十分了解,。

　　在長(zhǎng)達(dá)四年的時(shí)間里，科學(xué)家總共對(duì)9000只果蠅進(jìn)行了試驗(yàn),。他們發(fā)現(xiàn)其中一些果蠅的睡眠時(shí)間僅為其它果蠅的三分之一,。通過一系列的試驗(yàn)表明，這些果蠅并沒有由于睡眠時(shí)間的減少而在認(rèn)知能力上比其它果蠅差,。但是,，此類果蠅的生命周期卻比一般果蠅要短。

　　科學(xué)家注意到當(dāng)這些睡眠時(shí)間短的果蠅睡醒時(shí)腿會(huì)顫抖,，這個(gè)現(xiàn)象引導(dǎo)科學(xué)家研究使其腿發(fā)生顫抖的基因,。他們還發(fā)現(xiàn)這種顫抖的主要作用是喚醒處于睡眠狀態(tài)的細(xì)胞。人類也有此特點(diǎn),。

　　經(jīng)過對(duì)此類果蠅基因的仔細(xì)分析,，科學(xué)家們發(fā)現(xiàn)其中有一個(gè)胺酸基因發(fā)生了突變。由于此突變,，使得此類果蠅細(xì)胞膜間的化學(xué)物質(zhì)傳輸過程被打亂,，碳酸氫鉀不能像往常那樣自由的在細(xì)胞間傳輸。

　　當(dāng)科學(xué)家對(duì)基因發(fā)生突變的果蠅進(jìn)行研究時(shí)發(fā)現(xiàn),，只有當(dāng)果蠅特定的基因發(fā)生突變時(shí)才會(huì)出現(xiàn)睡眠時(shí)間縮短的現(xiàn)象,。這一結(jié)果或許能夠說明，作一個(gè)正常睡眠時(shí)間短的人也許并不是件好事,。因?yàn)樗麄兊幕蚝芸赡芎驼Ｈ瞬煌?，但是科學(xué)家目前還不能確定此研究結(jié)果,。

　　早期的研究中科學(xué)家已經(jīng)證實(shí)果蠅確實(shí)和哺乳動(dòng)物在睡眠過程中有相似的特點(diǎn)。像人類一樣,，果蠅在睡眠時(shí)很安靜,，通常保持每天睡眠6至12小時(shí)。睡眠過程中果蠅喪失了大部分對(duì)外界刺激作出反應(yīng)的能力,。當(dāng)它們正常的睡眠被打亂時(shí),，他們下一次睡眠所用的時(shí)間也會(huì)相應(yīng)延長(zhǎng)。

　　科學(xué)家還注意到咖啡因?qū)θ祟惡凸壨瑯泳哂袦p少睡眠時(shí)間的作用,。果蠅在睡眠和蘇醒時(shí)細(xì)胞內(nèi)物質(zhì)發(fā)生的化學(xué)變化也和人類十分相似,。

　　睡眠是一個(gè)非常復(fù)雜的生理活動(dòng)，它包含許多基因的相互作用,，只是其中一些基因?qū)λ叩目刂屏Ρ绕渌虼?。此次科學(xué)家發(fā)現(xiàn)的基因?qū)儆诳刂扑叩闹饕颍驗(yàn)樗軌蛲ㄟ^改變神經(jīng)元的興奮性影響生物體的睡眠,。