首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
Transplanting organs brings life to the dying. But most donor organs are harvested from the dead. Shortfalls in the number of vo
Transplanting organs brings life to the dying. But most donor organs are harvested from the dead. Shortfalls in the number of vo
admin
2016-10-21
52
问题
Transplanting organs brings life to the dying. But most donor organs are harvested from the dead. Shortfalls in the number of volunteer donors, the difficulty of gaining the consent of grieving relatives, and a reduction in most countries of the rate of fatal road accidents(the most reliable source of healthy organs), mean that there is a constant lack of them. Thousands die each year while on waiting lists for transplants. Researchers have, therefore, long sought ways to boost supply.
One idea is to harvest animal organs. That is less mad than it sounds. A liver, a kidney or a cornea does the same job, regardless of species. And it works. In 1984 an American child lived for three weeks after receiving a baboon heart intended as a stopgap until a human donor could be found(unfortunately, one was not found in time). Conversely, human organs have been transplanted into animals for the purpose of research. Earlier this year, for example, a paper in the American Journal of Transplantation described moving kidneys from human fetuses into rats.
Until now, though, two technical problems have stood in the way of routinely transplanting animal organs into people. One is that the recipient’s immune system must be persuaded to tolerate a big chunk of foreign tissue. The other is that swapping tissues between species risks swapping diseases, too. This second problem may soon be addressed, if George Church of the Harvard Medical School has his way. For, as he and his colleagues describe this week in Science, genetic engineering can now be used to eliminate one of the most worrying types of pathogen that might be spread via transplants.
The animal most commonly suggested as a donor is the pig. Pigs are roughly the size of human beings. They are reasonably well understood. And millennia of experience mean they are easy to breed. But they are not perfect. In particular, their DNA is full of retroviruses, known specifically as porcine endogenous retroviruses, or PERVs. The genes of these viruses hitch a lift from one pig generation to another as an integral part of the porcine genome, whence they can break out and cause infection. And tests in laboratories suggest that, given the opportunity, they can infect human cells as well. The existence of PERVs, then, has been one of the main obstacles to transplanting pig organs into people.
Dr Church and his colleagues thought PERVs ideal candidates to test the mettle of one of the rising stars of biotechnology, CRISPR/Cas9. This is a gene-editing technique derived from bacteria, which use it as a sort of immune system. In nature, it recognises specific sequences of viral DNA and chops the DNA molecule apart at these points, protecting the bacterium from harm. Tweaked a bit in the laboratory, it can be made to recognise any DNA sequence and do likewise. This permits specific stretches of DNA to be deleted from genomes, and also allows new stretches to be inserted into the gap thus created.
Dr Church and his fellow researchers analysed the genetic sequences of one family of PERVs, with a view to attacking them with CRISPR/Cas9. They found that the sequence of the gene which lets the virus integrate itself into its host’s DNA is the same from one strain of virus to another. That allowed them to program a CRISPR/Cas9 system to look for this particular sequence and chop it out of the genome.
The porcine kidney cells Dr Church used for his experiments had 62 PERVs embedded in their genomes. He and his colleagues tested their molecular scissors on several lines of these cells. In the most responsive, they managed to snip out all 62 copies of the integration gene.
Since PERVs rely on this gene to infect human cells as well as porcine ones, deleting it should stop them jumping into human hosts. Sure enough, tests in Petri dishes showed that the modified pig cells did not infect human cells grown alongside them. And, despite the extensive edits made to their DNA, those pig cells seemed unharmed by the procedure.
A single paper does not make a new medical procedure. In particular, the editing would need to be done to sex cells, or their precursors, if actual lines of "clean" pigs were to be bred for use as organ donors. But this is still a striking result. Not only does it demonstrate that it is possible to cleanse animal cells of unwanted viral passengers, thus helping remove one of the big barriers to cross-species organ transplants: it also shows the power of a genetic-engineering technique that has existed for Only three years. However, the popularity of such techniques waxes and wanes. This year’s favourite can be next year’s also-ran. For now, though, CRISPR/Cas9 is on a roll.
Which of the following factors did NOT partially cause the shortage of donor organs?
选项
A、There is a decreasing number of volunteer donors.
B、It’s hard to gain the consent of grieving relatives of the dead.
C、The rate of fatal road accidents is reducing.
D、The number of healthy organs is decreasing.
答案
D
解析
细节题。文章第一段提到Shortfalls in thenumber of volunteer donors,the difficulty Ofgaining the consent of grieving relatives,anda reduction in most countries of the rate offatal road accidents,说明A、B和C正确。文章没有提及健康器官的数量减少,说明D错误。
转载请注明原文地址:https://kaotiyun.com/show/XV7O777K
0
专业英语八级
相关试题推荐
AccordingtotheAustralianMedicareSystem,______Australianscanenjoyfreecareatpublichospitals.
Manythingsmakepeoplethinkartistsareweirdandtheweirdestmaybethis:artists’onlyjobistoexploreemotions,andyet
"Tworoadsdivergedinayellowwood/AndsorryIcouldnottravelboth/Andbeonetraveler,longIstood/Andlookeddownoneas
Thatexperienceinfluencessubsequentbehaviorisevidenceofanobviousbutneverthelessremarkableactivitycalled"rememberi
Accordingtothetheoryof______,literaturemustbetruetolifeandexactlyreproducesreallife,includingallitsdetailswi
Australiahasalwaysbeenacontinentwithfewpeoplemainlybecause______
BiancaSforzaattractedfewstareswhenintroducedtotheartworldonJanuary30,1998.Shewasjustaprettyfaceinaframet
Aftervaccinesandbednets,couldthehumblecookingstovebethenextbigideatosavemillionsoflivesinpoorcountries?Hi
Aftervaccinesandbednets,couldthehumblecookingstovebethenextbigideatosavemillionsoflivesinpoorcountries?Hi
A、Itissatisfying.B、Itisnotessential.C、Itistoomuch.D、Itisbarelyenough.D本题考查重要细节。根据句(7-1)、句(7—2)和句(7—3)可知,人们每天要摄取75
随机试题
简述目标管理的特点。
当代世界各国的竞争,归根到底是()
牙列拥挤可分为
环境风险评价工作程序的第一步骤是()。
下列关于变动成本法和完全成本法的说法中,正确的有()。
()经承运人或其代理人签章后,既是货物已办妥托运手续的凭证,又是通知船上接收承运货物装船的凭证。
下列不符合定性研究特点的陈述是()。
无线传输分为模拟微波传输和数字微波传输。()
A、 B、 C、 D、 C第一行前一个图形中的阴影依次顺时针移动2格得到后一个图形,第二行前一个图形中的阴影依次顺时针移动4格得到后一个图形,第三行前一个图形中的阴影依次顺时针移动6格得到后一个图形。
某企业发奖金是根据利润提成的。利润低于或等于10万元时可提成10%,低于或等于20万元时,高于10万元的部分按7.5%提成;高于20万元时,高于20万元的部分按5%提成。当利润额为40万元时,应发放奖金多少万元?
最新回复
(
0
)