Of mice and men and grey hair
Greying hair is the most obvious sign of human ageing, yet scientists are only now beginning to understand the cellular mechanism behind this unwelcome transformation. According to researchers at Harvard Medical School, the cause is the gradual disappearance of the particular adult stem cells that spawn hair-colouring melanocyte cells.
David Fisher and colleagues, who investigated the greying process in mice and people, report in Science magazine today that the stem cells not only die off but also make an increasing number of errors; they turn into pigment cells in the wrong place within the hair follicle, where they are useless for colouring hair. Their results contradict the common scientific view that faults in the melanocytes themselves, rather than their precursors, leads to greying.
By studying mice at various ages, the Harvard researchers discovered that the numbers of melanocyte stem cells diminished in proportion to the loss of hair colour. At the same time and the same rate, melanocytes were appearing in places where they could not colour the hair. The investigators then examined human scalp tissue taken at increasing ages and determined that the same pattern occurred.
They also found that a gene called Bcl2 protects melanocyte stem cells in mice. Those lacking Bcl2 lose these cells soon after birth and quickly go grey. The discoveries may eventually help people to stop going grey, but the scientists' main motivation is to tackle the opposite problem: the uncontrolled proliferation of melanocytes that gives rise to the most dangerous skin cancer, melanoma.
“Our goal is to prevent or treat melanoma, and to the extent that this research is revealing the life cycles of melanocytes, we would love to identify a signal that would make a melanoma cell stop growing,” says Dr Fisher.
www.dfci.harvard.eduEurope's challenge for computer powerSome of Europe's most powerful scientific computers are being linked to form a continent-wide supercomputer able to take on “grand research challenges” beyond the capability of individual computing centres, in fields such as environmental research, materials science, biology and astrophysics.
The Distributed European Infrastructure for Supercomputing Applications (Deisa) will start by knitting together two national research centres in Germany with one in France and one in Italy. These all run similar International Business Machines supercomputers so their integration into a “super-cluster” is relatively straightforward. This will be linked to eight other centres, including the European Centre for Medium-range Weather Forecasts in the UK. The complex “grid technologies” will be hidden from end-users, who will be able to use Deisa as a single giant computer. Victor Alessandrini, the project leader, says Deisa will boost Europe's scientific competitiveness against Japan and the US.
www.deisa.org Where did all that dust come from?How much interplanetary dust comes into the earth's atmosphere every year? And where does it end up? A research team from several European universities has come up with new answers. The accumulation of extraterrestrial material is extremely hard to measure. Cosmic dust particles burn up when they enter the atmosphere at high speed, producing meteors or shooting stars. The vaporised materials then react with oxygen in the air to form tiny mineral particles, known as “meteoric smoke”, that are too fine to detect directly. Estimates of the fall-out have ranged from 200 tonnes to 60,000 tonnes a year.
A team from Venice and other universities reports in Nature that the figure is 14,000 tonnes a year, on the basis of ancient ice cores from Greenland. Scientists measured traces of iridium and platinum, which are enriched in cosmic not terrestrial material.
“It has been a mystery up to now where all this material goes,” says John Plane of the University of East Anglia. “Our analysis reveals iridium and platinum consistent with a low but constant fall-out of extraterrestrial matter over the past 10,000 years, and our models suggest most of this material is carried to the polar regions by prevailing winds in the upper atmosphere, before funnelling down to the surface during the polar night.”
www.uea.ac.uk/envDiving is dangerous for whales tooSperm whales sustain the kind of bone damage that is associated in human divers with “the bends”, according to research published in Science, which challenges the traditional notion that marine mammals do not get decompression sickness.
Michael Moore and Greg Early of Woods Hole Oceanographic Institution in Massachusetts found that the ribs, vertebrae and other bones from sperm whale skeletons were pitted and eroded. This condition, called osteonecrosis, is typically associated in humans with divers
who have frequently suffered from the
bends when surfacing too quickly.
人?老鼠?白头发
头发变得灰白是最明显的衰老迹象，但对于这种不愉快的转变背后的细胞机制，科学家们只是刚刚开始了解。据哈佛医学院(Harvard Medical School)的研究员称，这一现象的原因是某种成人干细胞逐渐消失，此种细胞能产生为头发着色的黑色素细胞。
戴维?费歇尔(David Fisher)和同事们研究老鼠和人类毛发变灰白的过程。他们今天在《科学》(Science)杂志上发表一份报告，称那种干细胞不仅会消亡，而且还会造成越来越多的错误。它们在头发毛囊的错误位置转变成色素细胞，而色素细胞在那里根本无法为头发着色。他们的研究结果和普遍的科学观点相矛盾。普遍观点认为，是黑色素细胞自身的缺陷，而不是创造它的干细胞导致头发变灰白。
通过研究不同年龄的老鼠，哈佛的研究人员发现，黑色素干细胞消失的数量与头发颜色变灰白成比例。在同一时间并以相同的速度，黑色素细胞出现在不能为头发着色的位置。研究者随后检查了不同年龄段人群的头皮组织，确定同样的模式也发生在人身上。
他们还发现，一种名为Bc12的基因保护着老鼠体内的黑色素干细胞。Bc12缺乏的老鼠在出生后不久就失去这些细胞，毛发很快变得灰白。这些发现可能最终会帮助让人们的头发停止变白，但科学家们的主要动机是解决相反的问题：黑色素细胞失控性扩散，引发最危险的皮肤癌：黑色素瘤。
“我们的目的是预防或治疗黑色素瘤，而且这项研究将揭示黑色素细胞的生命周期，就此而言，我们希望识别让黑色素瘤细胞停止生长的信号，”费歇尔博士表示。
www.dfci.harvard.edu欧洲向电脑运算能力挑战
欧洲一些最强大的科学电脑正被连接起来，以形成一台泛欧超级电脑，以超越个别电脑运算中心的能力，在环境研究、材料科学、生物学和天体物理学等领域应对“重大的研究挑战”。
德国的两个国家研究中心，以及法国、意大利各一个研究中心将被连接起来，构成一个“欧洲超级计算应用分布式架构”(Deisa)。这些研究中心都运行类似的IBM超级计算机，因此把它们整合为一个“超级联合体”相当容易。这一超级联合体将与其它八个中心联网，其中包括英国的欧洲中期天气预报中心。终端用户看不到这些复杂的“网格科技”，他们能把Deisa当作单个巨型计算机来使用。该项目负责人维克托?亚历山德里尼(Victor Alessandrini)表示，Deisa将提高欧洲相对于日本和美国的科技竞争力。
www.deisa.org星际尘埃都是从哪儿来的？
每年有多少星际尘埃进入地球大气层？它们的归宿又在哪里？一个由几所欧洲大学组成的研究小组提出了新的答案。宇宙物质的累积极难测量。当宇宙灰尘微粒飞速进入地球大气层时，它们会燃烧并产生大气现象或流星。这些汽化的物质随后与空气中的氧气发生反应，形成微小的矿物微粒，被称为“流星雾”，它们太过细密，因此无法直接观察。根据各种估计，这些陨落物质在200吨到6万吨不等。
由威尼斯大学等大学组成的一个研究小组在《自然》（Nature）杂志上发表报告说，根据对格陵兰岛的古老冰核推算，陨落物质的数字为每年1.4万吨，科学家们测算了冰核中铱和铂的含量，这两种成分富含于宇宙而非地球。
“所有这些物质的去向到现在还是个迷，”东英吉利大学(University of East Anglia)的约翰?普莱(John Plane)说。“我们的研究分析表明，过去1万年间，一直有少量但持续不断的宇宙物质坠落下来，铱和铂的含量与这个结论一致，我们的模型显示，大多数此类物质先被高层大气的强风带到极地地区，随后在极夜期间渗向地表。”
www.uea.ac.uk/env潜水对鲸也有危险
《科学》杂志上发表的一份研究报告称，抹香鲸所承受的骨骼损伤，类似人类潜水者的“减压病”。该研究结果对海洋哺乳动物不会得潜水减压病的传统观点提出挑战。
美国马萨诸塞州伍兹霍尔海洋研究院(Woods Hole Oceanographic Institution)的迈克尔?摩尔(Michael Moore)和格雷格?厄尔利(Greg Early)发现，抹香鲸骨架上的肋骨、椎骨和其它骨骼上有凹陷和受侵蚀现象。这种被称为“骨坏死”的症状，在一些人类潜水者中十分典型，这些潜水者常因浮出水面太快而患有减压病。
