细胞分裂是父单元格划分并产生两个或更多的子细胞的过程。它是繁殖的单细胞生物方式。在多细胞生物中,细胞分裂有助于生长发育、 修复,、 生殖细胞 (精子和卵子) 的一代。细胞分裂是一个受到严格管制的过程,和异常细胞分裂可以引起的疾病,尤其是癌症。
细胞分裂的朱庇特的简介将涵盖领域具有里程碑意义发现简史。然后,我们讨论几个关键问题和方法,包括细胞周期分析和活细胞成像。最后,我们展示这些技术在细胞分裂研究中一些当前应用的程序。
细胞分裂是由其中一个细胞产生两个或更多的子细胞的过程。单细胞的生物,像酵母,通过细胞分裂繁殖而多细胞生物体,像我们一样,使用相同的过程来发展、 成长,和维持我们的组织。知识的什么控件正常细胞分裂是理解如何中断这一现象可以启动病理过程的关键。
此视频介绍了在细胞分裂领域发现简史、 突出关键提问细胞生物学家、 审查突出使用工具,和展示了一些当今的应用程序。
让我们首先回顾一些意义重大的研究奠定了细胞分裂研究。
细胞的存在,在 17 世纪安东范列文虎克和罗伯特 · 虎克的第一次报告。授权由创新在显微镜,他们拉开面纱上看不见的微观世界。第一次观察到细胞可以分裂 1830 年由两个植物学家,巴泰勒米 Dumortier 和雨果 · 冯 · 莫尔,发现了这一植物细胞可以给两个除以的崛起。之后这一发现,在 1838 年,一位植物学家 — — 马蒂亚斯 · 雅各布曾 — — 和生理学家 — — 西奥多 · 旺 — — 观察植物和动物细胞中的相似之处。这导致雪旺首先假定单元格理论的两个原则:”所有生物都是由一个或多个细胞构成的”;第二:”细胞是一切生命的基本构造块。近二十年后,一名医生,名叫鲁道夫 • 魏尔啸发表细胞理论,指出第三个原则:”所有细胞都产生从预先存在的细胞”。
在 1876 年,瓦尔特 · 弗莱明说查看细胞分裂时观察到的丝状结构的分离。因此,他创造了术语”有丝分裂,”来自希腊字 mitos 意义线程。后来,爱德华 Van Beneden 和西奥多 · 海因里希 · 威利发现这些线程是实际上染色体,分为微管结构,现在称为中心体所引起的帮助。Beneden,以及奥斯卡 Hertwig 和魏斯曼也解释了减数分裂 — — 不同类型的产生像配子细胞的分裂。他们表现出减数分裂与有丝分裂,不同涉及一轮 DNA 复制,但两轮的细胞分裂,从而导致从父到子细胞的染色体数目减半。
在二十世纪下半叶,科学家感兴趣调控细胞周期、 细胞传递通过一系列阶段导致它的分裂过程。在这一领域最重要的发现之一来自于 1972 年利兰 · 哈特韦尔和他的同事。他们用酵母菌株,显示有指导细胞通过细胞周期阶段,重要作用的基因和哈特韦尔博士命名他们作为细胞分裂周期基因或”cdc。”
另一个发现来自于 1983 年由蒂姆 · 亨特,他正在研究海胆。他确定在其丰度与细胞周期阶段同步振荡的蛋白质。由于其振荡的性质,他命名为”细胞周期蛋白,”这些蛋白质,现在我们知道细胞周期蛋白是细胞周期的关键调节。四年后,保罗 · 纳斯爵士和同事表明,cdc 基因,在特定cdc2,高度保守的酵母与人类之间。在一起,这些发现大大增加细胞分裂,我们理解,因而也当之无愧地获得了诺贝尔奖在 2001 年。
既然我们已经回顾了一些历史的亮点,让我们检查细胞分裂领域所面临的几个基本问题。
我们将开始与细胞分裂也许最广泛的问题: 哪些基因和细胞内信号途径调节细胞周期?众所周知的是重复和司由一系列的生化开关,激活或取消激活细胞周期进程控制。研究者们正在更多揭示影响的进展或细胞周期抑制的分子。
生物学家感兴趣确定胞外刺激或抑制细胞分裂的因素。细胞可能会增加在回应外部化学线索称为感受器细胞分裂。科学家们正在试图理解什么外部线索刺激或抑制细胞分裂。
异常细胞分裂可以导致增加或减少细胞增殖。增加的细胞增殖导致癌症等疾病。研究人员已经发现某些基因称为原癌基因突变参与肿瘤形成。此外,科学家也发现在肿瘤进展中发挥着至关重要的作用的几种蛋白质。然而,肿瘤引起的几个因素仍未知,而生物学家正在努力揭示他们。
现在,你有一种感觉的一些悬而未决的问题,让我们看看几个生物学家使用找到答案的研究工具。
在混合的活跃分裂能力的细胞,存在于每个阶段的细胞周期的细胞的比例可以测定细胞周期分析。这是通过特殊的染料,如脱氧或 BrdU 的帮助。胸苷模拟并结合本身在新合成的 DNA 链 DNA 复制过程中。因此,它标签只 S 期细胞。另一方面,荧光的化合物,如 idodide 丙啶 (PI) 染色的 DNA,所有但 PI 绑定的量可以帮助区分不同阶段中的单元格。最后一步是分析使用流式细胞术,被染色的细胞,获得的数据揭示了在不同细胞周期各阶段细胞的分布。
现在成像技术研究进展方便直接观察细胞分裂。科学家们现在可以细胞使用荧光染料染色或执行基因操作来诱导荧光蛋白的表达。在此之后,他们可以直接观察活细胞划分使用延时的显微镜。
最后,科学家们还设计了一种量化的特定单元格进行混合的细胞群内的分段数。这是通过使用”可量化跟踪染料”。这些染料是有用的因为它们生成的信号变得更加扑朔迷离,因为它通过细胞分裂稀释。递减的荧光强度可以用于标识在不同世代的细胞。此外,最高和最低的荧光强度之间的区别可以提供深入了解多少次细胞经历司。
现在,您已经熟悉一些常见的方法研究细胞分裂,让我们看看如何应用这些方法。
如前文所述,基因在细胞周期调控中扮演主要的角色。在这里,科学家们研究上果蝇幼虫细胞分裂的基因突变的影响。他们表演了遗传的十字架要产生苍蝇与特定的基因突变,然后使用观察内翼组织发育突变的细胞周期分析。
使用荧光显微镜,科学家可以还直接观察药物对癌症细胞分裂的影响。在这个实验中,研究人员感兴趣在确定如何潜在的药物,JP-34,影响癌细胞的分裂。结果表明,癌细胞 JP 34 治疗经历了有丝分裂的失败和细胞死亡。
最后,科学家使用跟踪染料来标识在细胞增殖率的差异。在这里,他们雇用标签细胞膜研究各种免疫细胞的细胞分裂的差异可量化跟踪染料。流式数据显示增殖率区别不同类型的免疫细胞。
你刚看了细胞分裂的朱庇特的简介。在这个视频我们审查的一些主要发现在细胞分裂,被要求由细胞生物学家今天,突出工具从事细胞分裂实验室和当前应用程序的关键问题。一如既往,感谢您收看 !
Cell division is a process by which one cell produces two or more daughter cells. Unicellular organisms, like yeast, reproduce by cell division, whereas multicellular organisms, like us, use the same process to develop, grow, and maintain our tissues. Knowledge of what controls normal cell division is critical to understanding how disruption of this phenomenon can initiate pathological processes.
This video presents a brief history of discoveries in the cell division field, highlights key questions asked by cell biologists, reviews prominent tools being used, and showcases some present-day applications.
Let’s start by reviewing some landmark studies that laid the foundation of cell division research.
The existence of cells was first reported in the 1600’s by Anton van Leeuwenhoek and Robert Hooke. Empowered by innovations in microscopy, they pulled back the veil on the invisible microscopic world. The first observation that cells could divide was made in the 1830’s by two botanists, Barthélemy Dumortier and Hugo von Mohl, who discovered that one plant cell can give rise to two by dividing. Following this discovery, in 1838, a botanist—Matthias Jakob Schleiden— and a physiologist—Theodor Schwann—observed similarities in plant and animal cells. This led Schwann to postulate the two tenets of cell theory, first: “all living organisms are composed of one or more cells”; second: “cells are the basic building blocks of all life.” Nearly twenty years later, a physician named Rudolf Virchow published the third tenet of cell theory, which stated: “all cells arise from preexisting cells.”
In 1876, Walther Flemming, while viewing cell division, observed separation of thread-like structures. Therefore, he coined the term “mitosis,” derived from the Greek word mitos meaning thread. Later on, Edouard Van Beneden and Theodor Heinrich Boveri discovered that those threads are actually chromosomes, which are being divided with the help of microtubules arising from structures now known as centrosomes. Beneden, along with Oscar Hertwig and August Weismann, also explained meiosis—a different type of division that produces cells like gametes. They showed that meiosis, unlike mitosis, involves one round of DNA replication but two rounds of cell division, resulting in halving of the chromosome number from the parent to the daughter cells.
In the latter half of the twentieth century, scientists became interested in regulation of the cell cycle, a process in which a cell passes through a series of phases leading to its division. One of the most important discoveries in this field came in 1972 from Leland Hartwell and colleagues. Using yeast strains, they demonstrated that there are genes that play an important role in guiding cells through the cell cycle stages, and Dr. Hartwell named them as the cell division cycle genes or “cdc’s.”
Another discovery came in 1983 by Tim Hunt, who was studying sea urchins. He identified proteins that oscillate in their abundance in synchrony with the cell cycle phases. Due to their oscillatory nature, he named these proteins as “cyclins,” and now we know that cyclins are key regulators of the cell cycle. Four years later, Sir Paul Nurse and colleagues showed that cdc genes, in particular cdc2, was highly conserved between yeasts and humans. Together, these discoveries significantly increased our understanding of cell division, and thus were well deservedly rewarded with a Nobel Prize in 2001.
Now that we’ve reviewed some historical highlights, let’s examine a few fundamental questions facing the field of cell division today.
We’ll begin with perhaps the broadest question in cell division: what genes and intracellular signaling pathways regulate the cell cycle? It is known that duplication and division are controlled by a series of biochemical switches that activate or deactivate the cell cycle processes. Researchers are working to shed more light on the molecules that influence the progression or inhibition of the cell cycle.
Biologists are also interested in identifying the extracellular factors that stimulate or inhibit cell division. Cells may increase cell division in response to external chemical cues called mitogens. Scientists are working to understand what external cues stimulate or inhibit cell division.
Abnormal cell division can lead to increased or decreased cell proliferation. Increased cell proliferation causes diseases like cancer. Researchers have discovered that mutations in certain genes known as oncogenes is involved in initiation of cancer. In addition, scientists have also discovered several proteins that play a critical role in tumor progression. However, several tumor-causing factors still remain unknown, and biologists are striving hard to reveal them.
Now that you have a feel for some of the unanswered questions, let’s look at a few research tools biologists use to find answers.
In a mixture of actively dividing cells, the proportion of cells that exist in each phase of the cell cycle can be determined by cell cycle analysis. This is done with the help of special dyes, like bromodeoxyuridine or BrdU. It is a thymidine analog and incorporates itself in the newly synthesized DNA strand during DNA replication. Hence, it labels S phase cells only. On the other hand, fluorescent compounds like propidium idodide (PI) stain all of the DNA, but the amount of PI bound can help distinguish between cells in different phases. The final step is to analyze the stained cells using flow cytometry, and data obtained reveals distribution of cells amongst different cell cycle stages.
Advances in imaging techniques now facilitate direct observation of cell division. Scientists can now stain cells using fluorescein dyes, or perform genetic manipulation to induce expression of florescent proteins. Following this, they can directly observe live cells dividing using time-lapse microscopy.
Lastly, scientists have also devised a way to quantify the number of divisions that specific cells undergo within a mixed cell population. This is done by using “quantifiable tracking dyes.” These dyes are useful because the signal they generate becomes dimmer as it’s diluted through cell division. The diminishing fluorescence intensity can be used to identify cells in different generations. In addition, the difference between the highest and the lowest fluorescence intensity can provide insight into how many times the cells underwent division.
Now that you’re familiar with some common approaches to studying cell division, let’s look at how these methods are being applied.
As discussed earlier, genes play a major role in cell cycle control. Here, scientists studied the effect of genetic mutation on cell division in Drosophila larvae. They performed genetic crosses to produce flies with specific mutations, and then using cell cycle analysis observed the effects of the mutation within the developing wing tissue.
Using fluorescence microscopy, scientists can also directly observe how drugs affect cell division in cancer. In this experiment, researchers were interested in determining how a potential drug, JP-34, affected cancer cell division. Results showed that cancer cells treated with JP-34 underwent mitotic failure and cell death.
Finally, scientists use tracking dyes to identify differences in cell proliferation rates. Here, they employed a quantifiable tracking dye that labels cell membranes to study differences in cell division of various immune cells. The flow cytometry data analysis revealed that the proliferation rate differs between different types of immune cells.
You’ve just watched JoVE’s introduction to cell division. In this video we reviewed some of the major discoveries in cell division, key questions being asked by cell biologists today, prominent tools employed in cell division labs, and their current applications. As always, thanks for watching!
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