Chickens without eggs? De-extinction company creates artificial egg.

没有蛋的鸡？复活灭绝物种公司创造出人造蛋

On Tuesday, biotech startup Colossal announced its newest development on the road to its announced goal: reversing the extinction of species, in this case, avian species. The development itself is essentially an artificial eggshell, one that allows almost the entire developmental process to occur without the shell. The company transferred the contents of eggs to their specially designed container within a day or two of laying and were able to have normal chicks walk away from it.

周二，生物技术初创公司 Colossal 宣布了其在实现既定目标——即复活灭绝物种（此次针对的是鸟类）——道路上的最新进展。这项成果本质上是一个人造蛋壳，它允许几乎整个发育过程在脱离天然蛋壳的情况下进行。该公司在鸡蛋产下后的一两天内，将其内容物转移到特制的容器中，并成功孵化出了能够正常行走的雏鸡。

Beyond its potential utility for Colossal’s intended efforts, the work is personally interesting to me because it may solve a problem I faced in my research days. I’m going to start by describing the research problem that Colossal may have solved, before coming back to what it hopes to use its technology to do—and why the company still has a few key hurdles left to overcome.

除了对 Colossal 的既定目标具有潜在用途外，这项工作对我个人而言也非常有趣，因为它可能解决了我研究生涯中曾面临的一个难题。我将首先描述 Colossal 可能已经解决的研究问题，然后再回到该公司希望利用这项技术实现的目标，以及它为何仍面临几个关键障碍。

Watching development

观察发育过程

For part of my career, I studied the development of vertebrates using chickens. While they’re less closely related to us than something like mice, the basics of their development are largely the same. And, unlike mice, they develop outside of their mother’s body. If you’re careful, you can chip away a hole in the egg, perform manipulations on the developing embryo, and then seal it back up with some tape. The chicken embryo will keep developing, allowing you to see the impact of what you’ve done on normal development.

在我职业生涯的一部分时间里，我曾利用鸡来研究脊椎动物的发育。虽然它们与我们的亲缘关系不如小鼠近，但它们发育的基本原理大体相同。而且，与小鼠不同，它们是在母体外发育的。如果你足够小心，可以在蛋壳上凿一个小孔，对发育中的胚胎进行操作，然后用胶带封好。鸡胚胎会继续发育，让你观察到你的操作对正常发育产生的影响。

Manipulations include everything from surgically removing key tissues to implanting beads soaked with signaling molecules to injecting DNA into cells to instruct them to make a different set of proteins. Any of these can alter the development of the embryo, telling us things about the factors that are normally required. While this has been incredibly powerful, it provides us with a limited view of key events. That’s because you’re only allowed two time points: the moment you perform the manipulations, and when you stop the experiment. You don’t have a complete picture of how things change in between the two.

操作手段包括从手术切除关键组织，到植入浸泡过信号分子的微珠，再到将 DNA 注入细胞以指导其制造不同的蛋白质。任何这些操作都可能改变胚胎的发育，从而告诉我们正常发育所需的因素。虽然这种方法非常强大，但它为我们提供的关键事件视角是有限的。这是因为你只能观察到两个时间点：进行操作的时刻，以及停止实验的时刻。你无法获得两者之间事物如何变化的完整图景。

You can repeat the experiment and stop things at different time points, but you don’t really get a complete picture of what is a dynamic process. This is especially true because development involves a lot of motion: cells move around, tissues rearrange and slide past each other. For example, the spinal cord starts out as a flat plate of neural tissue, but then rolls up into a tube. As the cells mature into neurons, they detach from the inner surface of the tube, move to new locations, and start sending out axons to connect with other neurons.

你可以重复实验并在不同的时间点停止，但你无法真正获得一个动态过程的完整画面。这一点尤为重要，因为发育涉及大量的运动：细胞四处移动，组织重新排列并相互滑动。例如，脊髓最初是一块扁平的神经组织板，随后卷成管状。随着细胞成熟为神经元，它们会从管子的内表面脱离，移动到新的位置，并开始伸出轴突与其他神经元连接。

There was a potential solution to this. A researcher down the hall (Kat Hadjantonakis) developed a microscope system that automated taking repeated exposures of embryos over time, allowing her team to track how cells moved about during key developmental processes. It worked, but only if you could get the embryo to survive in culture. This could work for a day or two with mouse embryos, but chickens were really difficult. There were two big problems. The chicken embryo is embedded in the membrane that encloses the yolk, and the tension on the membrane provided by the yolk is needed for the embryo to develop properly. Let the yolk leak out and the membrane will sag, leaving the embryo a crumpled, disorganized mess. (Colossal told Ars that the curvature of the container it developed had to be tweaked to maintain the proper tensions within the egg’s membranes.) The other issue is that the embryo’s developing circulatory system extends deeply into the yolk. Most embryos I tried to image ended up being disorganized messes with no blood.

对此曾有一个潜在的解决方案。走廊那头的研究员（Kat Hadjantonakis）开发了一种显微镜系统，可以自动对胚胎进行长时间的重复曝光，使她的团队能够追踪细胞在关键发育过程中的移动方式。这很有效，但前提是你必须让胚胎在培养皿中存活下来。对于小鼠胚胎，这可以维持一两天，但鸡胚胎非常困难。这里有两个大问题：鸡胚胎嵌入在包裹卵黄的膜中，而卵黄提供的膜张力对于胚胎的正常发育至关重要。如果卵黄泄漏，膜就会下垂，导致胚胎变成一团皱缩、杂乱无章的物质。（Colossal 告诉 Ars，他们开发的容器曲率必须经过微调，以维持蛋膜内的适当张力。）另一个问题是，胚胎发育中的循环系统深入卵黄内部。我尝试成像的大多数胚胎最终都变成了没有血液、杂乱无章的团块。

Development without the shell

脱离蛋壳的发育

Colossal has basically solved that problem. It made a structural support that supports the entire contents of the egg in a way that keeps everything intact so that the embryo develops normally. No problems with a lack of membrane tension or the loss of blood. In fact, the transfer of the egg contents to Colossal’s new device can take place before the circulatory system even forms. (In the work they’re describing, transfers are done on day one of development, when the embryo is largely a smudge of cells on the surface of the yolk.)

Colossal 基本上解决了这个问题。他们制造了一种结构支撑装置，能够支撑鸡蛋的全部内容物，并保持其完整性，从而使胚胎能够正常发育。不再有膜张力不足或血液流失的问题。事实上，在循环系统形成之前，就可以将蛋内容物转移到 Colossal 的新设备中。（在他们描述的工作中，转移是在发育的第一天进行的，此时胚胎在卵黄表面基本上只是一团细胞。）

The support system is 3D-printed and lined with a special membrane that allows oxygen to be exchanged with the environment. Previous efforts to get this to work had to put the embryo in a high-oxygen environment, which increases the chance of DNA damage from reactive oxygen in the cells. The membrane is efficient enough that the embryo can develop in a normal atmosphere, though humidity has to be controlled. Colossal’s Ben Lamm told Ars that the only thing that needed to be added was calcium, as the embryo normally extracts a bit of that from the interior of the egg shell.

该支撑系统采用 3D 打印技术，内衬一种特殊的膜，允许与环境进行氧气交换。以往的尝试必须将胚胎置于高氧环境中，这增加了细胞内活性氧导致 DNA 损伤的风险。这种膜的效率很高，胚胎可以在正常大气环境下发育，尽管需要控制湿度。Colossal 的 Ben Lamm 告诉 Ars，唯一需要额外添加的是钙，因为胚胎通常会从蛋壳内部提取一部分钙。

Colossal also confirmed that, due to density differences, the yolk naturally floats to the top of the container, with the embryo rotating to the top of that. So, once the egg is placed in this device, all the manipulations that biologists normally do should be possible. And, because it only requires a humidified chamber, it should be possible to film the embryo as it develops afterward and track any changes to cell movements and rearrangements. The company has even designed the container so that light can be diffused in from beneath for microscopy purposes. In other words, Colossal seems to have solved a problem I no longer have (since I’m now a journalist) but is likely still an issue for biologists. However, the company did so purely as a necessary step for one of its de-extinction projects.

Colossal 还证实，由于密度差异，卵黄会自然浮到容器顶部，胚胎则会旋转到卵黄上方。因此，一旦将蛋放入该设备，生物学家通常进行的所有操作都应成为可能。而且，由于它只需要一个加湿室，因此可以在胚胎发育过程中对其进行拍摄，并追踪细胞运动和重排的任何变化。该公司甚至设计了容器，以便光线可以从下方漫射进来，用于显微镜观察。换句话说，Colossal 似乎解决了一个我不再面临的问题（因为我现在是一名记者），但这对于生物学家来说可能仍然是一个难题。然而，该公司这样做纯粹是为了其复活灭绝物种项目所采取的必要步骤。

Not all eggs are created equal

并非所有的蛋都是一样的

Why does it need to externalize the contents of eggs? It comes back to two of its planned de-extinctions, the dodo and the moa. Both of these species are far, far larger than the nearest related species. In the moa’s case, it’s far larger than any existing…

为什么它需要将蛋的内容物外置？这回到了它计划复活的两个物种：渡渡鸟和恐鸟。这两个物种都比其亲缘关系最近的物种大得多。以恐鸟为例，它比现存的任何物种都要大得多……