生物谷報(bào)道：來(lái)自加州大學(xué)舊金山分校,，霍華德休斯醫(yī)學(xué)院的研究人員通過(guò)遺傳篩選發(fā)現(xiàn)了樹(shù)突和軸突是如何形成截然不同構(gòu)造的，這個(gè)問(wèn)題是神經(jīng)生物學(xué)的基本問(wèn)題,，但是之前科學(xué)家們了解的并不多,。這一研究成果公布在Cell封面上。
神經(jīng)元,，又叫神經(jīng)細(xì)胞,，是構(gòu)成動(dòng)物神經(jīng)系統(tǒng)的基本單位。每個(gè)成熟的神經(jīng)細(xì)胞看起來(lái)都像一棵枝繁葉茂的大樹(shù),。它有很多短而小的突起,，科學(xué)上稱為“樹(shù)突”，還有一個(gè)比樹(shù)突長(zhǎng)幾倍的突起,，科學(xué)上稱為“軸突”,。對(duì)于一個(gè)神經(jīng)細(xì)胞來(lái)講，樹(shù)突就是它的“偵察兵”,，負(fù)責(zé)接受從外界傳來(lái)的信息,，軸突則像個(gè)“傳令兵”，將神經(jīng)細(xì)胞對(duì)外界的反應(yīng)傳遞到其他細(xì)胞中去,。人體的神經(jīng)元們彼此相連,，結(jié)成一張巨大的網(wǎng)絡(luò)，從而調(diào)節(jié)我們的一舉一動(dòng),。
神經(jīng)元細(xì)胞的胞體大部分生活在我們的大腦和脊柱中,。它們感知和控制著人體的各個(gè)部位。通過(guò)“偵察兵”樹(shù)突,，它們能夠感受到我們?cè)诿粋€(gè)嬰兒柔嫩的小臉,，或走路時(shí)腳尖踢到一塊石頭的疼痛；然后“傳令兵”軸突讓我們明白,，可以繼續(xù)撫摸嬰兒,，或者遠(yuǎn)離那塊石頭。
世界上第一次提出神經(jīng)元的樹(shù)突,、軸突概念來(lái)自100多年前的西班牙神經(jīng)解剖學(xué)家拉蒙·卡哈爾,，他通過(guò)一架極粗糙的顯微鏡觀察腦切片，畫了幾百幅畫,，描述看到的神經(jīng)元和神經(jīng)系統(tǒng)的模樣,。出人意料，卡哈爾畫的所有神經(jīng)元都是只有一個(gè)長(zhǎng)的軸突和若干短的樹(shù)突,。他甚至想像出了樹(shù)突與軸突的作用,。在軸突周圍,，他標(biāo)上了從細(xì)胞胞體向外走的箭頭；在樹(shù)突周圍,，他標(biāo)上了相反的方向,。原來(lái)人們認(rèn)為神經(jīng)系統(tǒng)是一張緊密相聯(lián)的網(wǎng)，神經(jīng)元通過(guò)樹(shù)突和軸突手拉著手,，信息就這樣從一個(gè)神經(jīng)元傳遞到另一個(gè)神經(jīng)元,，好比接力賽跑或擊鼓傳花一樣。但卡哈爾設(shè)想神經(jīng)元之間都有微小的空隙,，信息是從一個(gè)神經(jīng)元“蹦”到另一個(gè)神經(jīng)元上去的?，F(xiàn)在通過(guò)普通的光學(xué)顯微鏡能清楚地看到神經(jīng)元的長(zhǎng)相，可以放大1500倍的電子顯微鏡,，幫助人們找到了卡哈爾想像的那個(gè)空隙,。
在這篇文章中，研究人員利用遺傳篩選分離得到了dendritic arbor reduction (dar)突變——果蠅神經(jīng)細(xì)胞這種突變中樹(shù)突棘（dendritic arbors）減少而軸突正常,。并且研究人員識(shí)別出了分泌途徑中Sec23, Sar1和Rab1的同源體dar2, dar3, dar6基因,。
果蠅和嚙齒動(dòng)物神經(jīng)元實(shí)驗(yàn)中，研究人員還發(fā)現(xiàn)Sar1表達(dá)缺陷首先會(huì)影響樹(shù)突生長(zhǎng),，這說(shuō)明樹(shù)突與軸突的發(fā)育在對(duì)分泌途徑限制膜的敏感性上村子進(jìn)化保守差異,。盡管限制ER向Golgi傳遞會(huì)導(dǎo)致體細(xì)胞向樹(shù)突供應(yīng)膜的減少，但是對(duì)軸突的供應(yīng)并不受到影響,。這些研究結(jié)果說(shuō)明樹(shù)突和軸突生長(zhǎng)過(guò)程中對(duì)分泌途徑不同的依賴性幫助建立了樹(shù)突和軸突不同的形態(tài)學(xué)
原始出處：
Cell, Vol 130, 717-729, 24 August 2007
Article
Growing Dendrites and Axons Differ in Their Reliance on the Secretory Pathway
Bing Ye,1,2 Ye Zhang,1,2 Wei Song,1 Susan H. Younger,1 Lily Yeh Jan,1 and Yuh Nung Jan1,
1 Howard Hughes Medical Institute, Departments of Physiology, Biochemistry, and Biophysics, University of California, San Francisco, CA 94143, USA
Corresponding author
Yuh Nung Jan
[email protected]
Summary
Little is known about how the distinct architectures of dendrites and axons are established. From a genetic screen, we isolated dendritic arbor reduction (dar) mutants with reduced dendritic arbors but normal axons of Drosophila neurons. We identified dar2, dar3, and dar6 genes as the homologs of Sec23, Sar1, and Rab1 of the secretory pathway. In both Drosophila and rodent neurons, defects in Sar1 expression preferentially affected dendritic growth, revealing evolutionarily conserved difference between dendritic and axonal development in the sensitivity to limiting membrane supply from the secretory pathway. Whereas limiting ER-to-Golgi transport resulted in decreased membrane supply from soma to dendrites, membrane supply to axons remained sustained. We also show that dendritic growth is contributed by Golgi outposts, which are found predominantly in dendrites. The distinct dependence between dendritic and axonal growth on the secretory pathway helps to establish different morphology of dendrites and axons.
