圖1. 源自經誘導多能幹細胞之神經元的螢光顯微照片。
Fluorescence light micrograph of neurons derived from induced pluripotent stem cells.
Hospital nurseries routinely place soft bands around the tiny wrists of newborns that hold important identifying information such as name, sex, mother, and birth date. Researchers at Rockefeller University are taking the same approach with newborn brain cells—but these neonates will keep their ID tags for life, so that scientists can track how they grow and mature, as a means for better understanding the brain’s aging process.
醫院保育室慣例會在新生兒小手腕上繫上，具有諸如姓名、性別、母親及出生日期等，重要識別訊息的軟帶子。美國洛克菲勒大學的研究人員們正以新生兒腦細胞，採取同樣的方式。不過，此些新生兒會終生保有其身份標籤，以便科學家能追蹤其如何生長及成熟，作為更佳瞭解大腦老化過程的一種手段。
As described in a new paper in Cell, the new method developed by Rockefeller geneticist Junyue Cao and his colleagues is called TrackerSci (pronounced “sky”).
如同於《細胞》期刊中，一篇新論文所描述的，該由洛克斐勒大學遺傳學家，Junyue Cao及其同僚們開發的新方法，被稱為TrackerSci(發音為“sky”)。
This low-cost, high-throughput approach has already revealed that while newborn cells continue to be produced through life, the kinds of cells being produced greatly vary in different ages. This groundbreaking work, led by co-first authors Ziyu Lu and Melissa Zhang from Cao’s lab, promises to influence not only the study of the brain but also broader aspects of aging and disease across the human body.
這種低成本、高處理量的方式已經揭露，儘管一生中新生細胞不斷產生，不過於不同年齡產生的細胞種類，極度不同。該由來自Cao實驗室Ziyu Lu 及Melissa Zhang等，首要合撰人領導的開創性研究，有指望不僅影響大腦的研究，而且影響整個人體老化與疾病的更廣泛層面。
“The cell is the basic functional unit of our body, so changes to the cell essentially underlie virtually every disease and the aging process,” says Cao, head of the Laboratory of Single-Cell Genomics and Population Dynamics. “If we can systematically characterize the different cells and their dynamics using this novel technique, we may get a panoramic view of the mechanisms of many diseases and the enigma of aging.”
單一細胞基因體學與群體動態實驗室主任，Cao宣稱：「細胞是咱們身體的基本機能單位，因此細胞的變化本質上，幾乎是每種疾病及老化過程的基礎。倘若我們能使用這種新技術，有系統地顯示出，不同細胞及其動態的特徵，則我們可能獲得諸多疾病的機制及老化，令人費解的全景概觀。」
New cells are continuously produced in the adult mammalian brain, a critical process associated with memory, learning, and stress. They develop from progenitor cells—descendants of adult stem cells that differentiate into specialized cell types.
於成年哺乳動物的大腦中，持續產生新細胞。這是一種與記憶、學習及壓力相關之不可或缺的過程。它們發育自祖細胞，這是分化成特化細胞類型之成熟幹細胞的後代。
How this process unfolds, however, has been largely unknown, both because of technological limitations and cell rarity. Finding progenitor cells in the brain is a needle-in-haystack endeavor; in mammals, they account for a mere .5 percent of all brain cells. That number drops to .1 percent in later stages of life—a downward shift due to cellular instability, a core characteristic of disease and aging.
不過，由於技術上的限制及細胞稀有，此過程如何展開一直大半不詳。於大腦中，尋找祖細胞是一種大海撈針的嘗試。在哺乳動物中，它們僅佔所有腦細胞的0.5%。在生命後期中，那數字下降到0.1%。這是由於細胞不穩定的一種衰微變化(疾病及老化的一種核心特徵)。
Cao studies how tissues and organs maintain stable populations of cells—a hallmark of health—so he and his team wanted to investigate how different cellular populations develop, and whether these varied neuronal cells decline in the same way or forge different paths. Tracking their cellular lifespans from birth to maturity would reveal not just differences, but also when they appeared.
Cao研究組織及器官如何維持穩定的細胞群(健康的一種特徵)，因此他及其團隊想調查研究，不同細胞群如何發育，及此些不同的神經元細胞，是否以相同方式減少，或形成不同的路徑。追蹤其從出生到成熟的細胞壽命，不僅能揭露重大的變化，而且能揭露它們何時出現。
His lab specializes optimizing methods for single-cell sequencing, an increasingly popular approach to analysis that homes in on the genetic expression and molecular dynamics of individual cells.
其實驗室專攻，最佳化單一細胞的排序方法。這是一種日益普遍、專注於個別細胞中，基因表現及分子動態的分析方式。
Cao’s group uses combinatorial indexing, a sophisticated yet cost-effective technique that allows for the simultaneous analysis of millions of cells. This method uniquely tags cellular molecules with distinct barcodes that correlate to each cell’s unique molecular assembly.
Cao的團隊使用一種，考慮到同時分析數百萬個細胞之複雜、不過具成本效益的組合索引技術。此方法以，與每一細胞之獨特分子組合相關的不同條碼，來獨特地標記細胞分子。
With TrackerSci, Cao and his colleagues have fine-tuned this technique even further. This enhancement enables the meticulous labeling and tracking of the dynamics of rare progenitor cells in mammalian organs.“It’s like an ID card and GPS tracker combined,” Cao says.
藉由TrackerSci，Cao及其同僚們已經更進一步，調整了該種技術。此強化使能嚴謹地標記及追蹤，哺乳動物器官中，稀有祖細胞的動態。Cao宣稱：「這如同，身分證與GPS追蹤器的組合。」
For the current study, the researchers analyzed more than 10,000 newborn progenitor cells from across entire mouse brains spanning three ages (young, mature, and elderly) with a synthetic molecule known as 5-ethynyl-2-deoxyuridine (EdU). As these newborn cells differentiated, proliferated, and dispersed, EdU continued to label their DNA, functioning like a GPS tracker.
為了目前的研究，此些研究人員使用一種，被通稱為5-乙炔基-2-脫氧尿苷(EdU)的合成分子，分析了來自跨越三個年齡層(年輕、成熟及老年)之整個小鼠大腦中，1萬多個新生祖細胞。隨著此些新生細胞分化、增殖及分散，EdU繼續標記了其DNA。這起了，如同GPS追蹤器的作用。
This innovative technique allowed the researchers to analyze tens of thousands of gene expressions and the chromatin landscapes of these newborn cells as they grew into families of cell types with different molecular functions.
該創新技術使此些研究人員得以分析，這些新生細胞，當它們生長成具不同分子功能之細胞類型家族時，數萬的基因表現及染色質景觀。
“We were able to quantify cellular proliferation and differentiation rates of many cell types across the entire brain in a single experiment, which wasn’t possible using conventional approaches,” Cao says. “Those only capture static information—the current molecular state of a cell at a single moment. But TrackerSci captures dynamic information over time. It’s like other methods take snapshots, and we shoot a film.”
Cao宣稱：「我們能在一單次實驗中量化，使用傳統方法不可能之整個大腦中，多種細胞類型的細胞增殖及分化率。那些僅捕捉，細胞於單一瞬間進行中的分子狀態。不過，TrackerSci能隨著時間推移，捕捉動態資訊。 這如同拍攝快照及我們拍攝電影的其他方法。」
Some clear—and surprising—characters emerged from these movies. Most strikingly, there were radical shifts in the type of cells generated, depending on the age of the mouse.
從此些影片出現了，一些清晰(且令人驚訝)的特徵。最引人注目的是，依據小鼠的年齡，在產生的細胞類型中，有諸多徹底變化。
For example, the number of progenitors that become neurons, the essential communicative cells of the brain, are higher in young brains. The same is the case for a range of glial cells, which create a stable environment for neurons by ensheathing them, providing nutrients, and defending against pathogens—all important for a young, still-developing organ.
譬如，成為大腦不可或缺之交流細胞(神經元)的祖細胞數量，在年輕的大腦中較多。同樣的是一系列神經膠質細胞，它們藉由包裹神經元、提供營養素及防禦病原體，來為神經元創造一個穩定的環境。這一切，對一個年輕、仍發育中的器官是重要的。
The opposite is true in the elderly brain. Progenitor cells rarely become either neurons or glial cells; in fact, virtually every type of brain cell plummets. Most lost are dentate gyrus neuroblasts, which are essential for creating neurons in the hippocampus, a region linked to memory and diseases like Alzheimer’s. In comparison to the adult brain, the number of these cells drops by 16-fold in the elderly brain.
於老年人的大腦中，確實是相反。祖細胞很少變成神經元，或是神經膠質細胞。實際上，幾乎所有類型的腦細胞，皆會急劇下降。喪失最多的是在，與記憶及阿茲海默症等疾病，被聯繫在一起之海馬迴中，產生神經元不可或缺之鋸齒狀的腦迴神經母細胞。與成人大腦相較下，於老年人大腦中，此些細胞數量下降達16倍。
Instead, immune cells and microglia, a kind of macrophage, proliferate in the aging brain. But rather than protect the brain, they convert into an inflammatory cellular state specific to aging—and these cells are produced at a higher rate. In short, the aging brain creates more of the cells that create more problems for the aging brain.
Cao says TrackerSci could be used to track the regenerative capacity of many organs.
反而，免疫細胞及小膠質細胞(一種巨噬細胞)，在老化的大腦中增殖。不過，並非保護大腦，它們轉變成一種對老化，是特有之發炎細胞的狀態，而且此些細胞以較高的速度被產生。總而言之，老化的大腦產生更多，為老化之大腦產生更多問題的細胞。Cao表示，TrackerSci可能被用來追蹤，諸多器官的再生能力。
“We’re not a brain lab,” he notes. “We also tested the protocol for profiling progenitor cells in the lung, colon, pancreas, and many different organs.”
Other organs have far higher proportions of progenitor cells than brains do; newborn progenitors account for more than 20 percent of the cells in the colon, for instance.
他特別提及：「我們不是一間大腦實驗室。我們也測試了，肺、結腸、胰臟及諸多不同器官中，描繪祖細胞的方案。」其他器官具有，遠高於大腦具有的祖細胞比例。譬如，新生祖細胞佔結腸中細胞的20%以上。
A few years ago, Cao demonstrated the potential for analyzing cell population dynamics in human fetal development by creating a cellular atlas using a similar combinatorial indexing method.
幾年前，藉由使用一種類似的組合索引方法，創造一種細胞圖集。Cao證實了，於人類胎兒發育中，分析細胞群動態的潛力。
TrackerSci is one of several single-sequencing techniques to recently emerge from Cao’s lab. Another, called PerturbSci-Kinetics, developed by graduate student Zihan Xu, decodes the genome-wide regulatory network that underlies RNA temporal dynamics by coupling scalable single-cell genomics with high-throughput genetic perturbations, or manipulations that can influence gene function. The method was recently described in a paper in Nature Biotechnology.
TrackerSci是最近，出現自Cao實驗室的幾種單一細胞排序技術之一。由研究生Zihan Xu所開發，被稱為PerturbSci-Kinetics的另一種技術，藉由結合可擴展之單一細胞基因體學與高處理量遺傳擾動，或能影響基因功能的手法，來解碼引起RNA瞬間動態之全基因體的調節網絡。最近發表於《自然•生物技術》期刊的一篇論文中，記述了此方法。
網址：https://www.rockefeller.edu/news/34647-new-method-tracks-how-brain-cells-age/
翻譯：許東榮
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