It would certainly spare mothers the hardships of pregnancy, but mammals do not grow in eggs. In a way, this is also impractical for science. While embryos of fish, amphibians or birds can be easily watched growing, mammalian development evades the gaze of the observer as soon as the embryo implants into the uterus. This is precisely the time when the embryo undergoes profound changes in shape and develops precursors of various organs — a highly complex process that leaves many questions unanswered.

But now a research team at the Max Planck Institute for Molecular Genetics (MPIMG) in Berlin succeeded in replicating a central phase of embryonic development in a cell culture approach by growing the core portion of the trunk from mouse embryonic stem cells for the first time. The method recapitulates the early shape-generating processes of embryonic development in the Petri dish.

The structures are roughly a millimeter in size and possess a neural tube from which the spinal cord would develop. Furthermore, they have somites, which are the precursors of skeleton, cartilage and muscle. Some of the structures even develop the precursors of internal organs such as the intestine. After about five days, the parallels to normal development end.

“This model of embryonic development starts a new era,” says Bernhard G. Herrmann, Director at the MPIMG and head of the Institute of Medical Genetics at Charité — Universitätsmedizin Berlin. “This allows us to observe embryogenesis of the mouse directly, continuously, and with large parallel numbers of samples — which would not be possible in the animal.”

It is considered quite easy to isolate early embryos from the tube or the uterus and grow them in the Petri dish, as long as they are still free to move. But once the embryo has implanted in the endometrium, isolation becomes extremely difficult.

“We can obtain more detailed results more quickly, and without the need for animal research,” says Alexander Meissner, who like Herrmann is Director at the MPIMG and jointly supervised the study that was published in the current issue of the journal Science. “Of the more complex processes such as morphogenesis, we usually only get snapshots — but this changes with our model.”

A gel provides support and spatial orientation

So far, it has only been possible to grow cell clusters from embryonic stem cells, so-called gastruloids. “Cellular assemblies in gastruloids develop to a similar extent like in our trunk-like structures, but they do not assume the typical appearance of an embryo,” says Jesse Veenvliet, one of the two lead authors of the study. “The cell clusters lack the signals that trigger their organization into a meaningful arrangement.”

In the cell culture, the required signal is generated by a special gel that mimics the properties of the extracellular matrix. This jelly-like substance consists of a complex mixture of extended protein molecules that is secreted by cells and is found throughout the body as an elastic filling material, especially in connective tissues. The utilization of this gel is the crucial “trick” of the new method.

“The gel provides support to the cultured cells and orients them in space; they can distinguish inside from outside, for example,” says Veenvliet. It also prevents secreted molecules such as the matrix protein fibronectin from leaking into the cell culture medium. “The cells are able to establish better communication, which leads to better self-organization.”

Cells with similar properties as in the embryo

After four to five-days, the team dissolved the structures into single cells and analyzed them individually. “Even though not all cell types are present in the trunk-like structures, they are strikingly similar to an embryo of the same age,” says Adriano Bolondi, who is also lead author of the paper. Together with bioinformatician Helene Kretzmer, Bolondi and Veenvliet compared the genetic activity of the structures with actual mouse embryos. “We found that all essential marker genes were activated at the right time in the right places in the embryoids, with only a small number of genes being out of line,” says Bolondi.

The researchers introduced a mutation with known developmental effects into their model and could recreate the results from “real” embryos, further validating their model. They also provide examples of manipulating the developmental process with chemical agents.

U of G researchers have discovered honeybees in Vietnam collect and apply spots of animal dung around hive entrances to deter deadly nest raids by an Asian hornet (Vespa soror) whose North American cousins have been dubbed “murder hornets.”

This finding is also the first to document the use of tools by honeybees.

An invasive species in North America that came originally from Asia, giant hornets are almost as long as a golf tee and pack about seven times as much venom in a single sting as an ordinary honeybee.

Murder hornets (V. mandarinia) were discovered in 2019 in British Columbia and Washington. The arrival of the venomous insect to North America has raised concerns about human safety as well as threats to local honeybees and ecosystems.

U of G Prof. Gard Otis, who has studied honeybees in Vietnam for decades, said the hornets could ultimately carry out similar honeybee hive raids in North America.

“Giant hornets are the biggest wasps that threaten honeybees. They are one of their most significant predators,” said the environmental sciences professor.

Otis conducted the study with lead author Heather Mattila, who completed her PhD at the University of Guelph in 2006 and is now a biology professor at Wellesley College in Massachusetts. Other co-authors were former U of G grad students Hanh Pham and Olivia Knight, as well as Ngoc Pham and Lien Nguyen in Vietnam.

Published recently in the journal PLOS ONE, the study was conducted in Vietnam, where U of G researchers studied V. soror.

These two species are the only hornets that recruit nestmates in organized attacks that can lead to nest breaches, said Otis. The hornets raid the nests, killing the bees and carrying away larvae and pupae to feed their own developing brood.

The researchers found that honeybees have developed a pre-emptive defence by collecting animal dung and applying it to hive entrances.

“This study demonstrates a fairly remarkable trait these bees have to defend themselves against a really awful predator,” said Mattila.

She said unlike their Asian counterparts, honeybees in Canada lack similar defences. That means North American beekeepers would have to rely on destroying the hornets’ nests, or hope that climate or other factors will limit the hornets’ spread.

Referring to Apis mellifera, the honeybee species commonly found in Canada, Mattila said, “They haven’t had the opportunity to evolve defences. It’s like going into a war cold.”

Otis began the project after asking beekeepers in Vietnam about dark spots at hive entrances of Asian honeybees. As part of a successful beekeeping development project funded by the Canadian government, he ran fall workshops from 2007 to 2011 in rural villages with high levels of poverty.

During one visit, an experienced beekeeper explained that the substance was buffalo dung. All the beekeepers that Otis worked with linked these hive spots with hornets. “Dung collection is a behaviour never previously reported for honeybees, and no one had studied the phenomenon,” he said.

In 2013, the U of G team received US$25,000 from the National Geographic Society for the study.

The researchers gathered dung from water buffalo, chickens, pigs and cows, and placed it in mounds near an apiary. By the end of the day, some 150 bees had visited the piles, particularly collecting more odoriferous manure of pigs and chickens.

The team marked individual bees to identify them at their hives. Minutes later, they recorded videos of the marked bees applying the material at nest entrances.

The hornets spent less than half as much time at nest entrances with moderate to heavy dung spotting as they did at hives with few spots, and they spent only one-tenth as much time chewing at the hive entrances to get at the bees’ brood. They were also less likely to launch mass attacks on the more heavily spotted hives.

The researchers are unsure just what deters the hornets, although they suspect the insects are repelled by the smell of the dung. Dung may also mask odours emitted by the bees.

To further understand the hornets’ behaviours, the researchers extracted the chemical pheromone applied by hornets when marking their target hive. When the pheromone was applied to the bees’ entrance, it prompted honeybees to apply dung to the hive.

Many scientists disagree over whether certain animals — let alone insects — use tools.

To qualify as tool users, animals must meet several criteria, including using an object from the environment — in this case, dung. The bees clearly use the material to alter the hive with purpose, said Otis. And they shape and mould it with their mouth parts, which he said meets the test of holding or manipulating a tool.

Beekeepers in Vietnam normally control hornets by standing guard and swatting away individuals, preventing them from escalating their attacks.

“If you allow them, a group of hornets assembles, attacks the colony and takes over. The beekeepers control them every day by moving among their hives and whacking hornets.”

Otis said he was terrified at first about working near the giant hornets. The hazmat suits typically worn for protection by researchers in Japan were impracticable in Vietnamese heat, he added. Within a few days, the team learned the hornets were not defensive when they were in the apiary and away from their own nest.

“I got stung by one and it was the most excruciating sting in my life.”

The research shows that existing groundwater wells already penetrate and encroach upon the bases of fresh water that are used to define basin bottoms. In addition, brackish waters exist within current groundwater basins, and fresh water exists outside delineated groundwater basins. Brackish water, which was once deemed unusable, can now be used, thanks to technological advances. Finally, there are concerns about regulating groundwater on the basis of its quality rather than its usage, as is currently the case, since this provides a loophole for potential groundwater users who could drill deeper and skirt existing restrictions on freshwater pumping.

Together, these findings suggest that groundwater may already be poorly safeguarded in some places and that the ‘Base of Fresh Water’ concept may need to be reconsidered as a means to define and sustainably manage groundwater in future.

Need for up-to-date information to manage a critical resource

“It is challenging for groundwater sustainability agencies to manage groundwater because this critical resource is not being sufficiently monitored,” says Mary Kang, an Assistant Professor in McGill University’s Department of Civil Engineering and the lead author on the study. An expert on groundwater issues, she has studied the topic in California since 2014. “The base of fresh water was historically set to protect high quality groundwater from oil and gas development. And we find that there is a mismatch between this base of fresh water and what the water quality data shows.”

“One component to managing groundwater sustainably is evaluating the physical resource within the context of its users,” says Debra Perrone co-author of the study and Assistant Professor in UC Santa Barbara’s Environmental Studies Program. “We evaluate the link between groundwater quality, particularly salinity, and groundwater users. We show that the current approach used to manage deep groundwater in some places may risk overlooking the complex realities pertaining to both groundwater salinity and groundwater users. For example, the data suggest that people are constructing groundwater wells deeper than the base of fresh water in some areas.”

In 2014, in response to repeated droughts, the state passed the Sustainable Groundwater Management Act (SGMA) to regulate groundwater for the first time in California’s history. However, the effectiveness of this legislation is yet to be determined, as it relies upon administrative definitions of groundwater that are based on the extent of fresh water to define a vertical or three-dimensional groundwater basin for managing water.

“The Sustainable Groundwater Management Act currently only applies to fresh groundwater basins since administrative definitions of groundwater originated decades ago when it was economically infeasible to treat and distribute ‘unusable’ brackish or saline groundwater,” says co-author Melissa Rohde, a scientist with The Nature Conservancy of California. Rohde is currently providing scientific support to advance the successful implementation of SGMA. “With technological advances, brackish water is now usable and increasingly desirable with declining access to fresh water. By excluding brackish groundwater from sustainable groundwater management, we run the risk of undermining SGMA and overexploiting this important public resource.”

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According to findings published Dec. 9 in the journal Science Advances, this process could have started 3.75 billion years ago, reshaping Earth’s surface and setting the stage for a planet hospitable to life.

For geochemists like Scripps assistant professor and study lead author Sarah Aarons, the clues to Earth’s earliest habitability lie in the elements that ancient rocks are composed of — specifically titanium. Aarons analyzed samples of Earth’s oldest-known rocks from the Acasta Gneiss Complex in the Canadian tundra — an outcrop of gneisses 4.02 billion years old. These rocks are dated from the Hadean eon, which started at the beginning of Earth’s formation and was defined by hellish conditions on a planet that would look alien to our modern eyes.

Aarons’ research focused on isotopes, which are variations of the same element based on the number of neutrons they have. Taking the samples from Acasta Gneiss provided by Jesse Reimink, an assistant professor at Penn State University, she crushed bits of the rock into a powder that was then heated to form a glass bead, a process that allows dissolution of the titanium she sought to analyze. Once cooled, the bead was dissolved in acid and the titanium was chemically separated from other elements. Aarons was then able to determine the variations of titanium isotopes present in the sample using a mass spectrometer in the Origins lab led by her collaborator Nicolas Dauphas at the University of Chicago.

Aarons compared these samples to newer, modern rocks formed in subduction zones. In samples aged at 3.75 billion years old, she noticed similarities in structure and composition to the modern ones, suggesting that plate subduction began around that time.

“A lot of previous work has been done on these rocks to carefully date them, and provide the geochemical and petrological context,” said Aarons. “We were very lucky to get the opportunity to measure titanium isotope compositions, a burgeoning isotope system in these samples.”

Studying the history and onset of ancient subduction zones is notoriously difficult. Rocks are constantly destroyed as the crust is driven inward into the mantle, leaving behind few samples that date back into Earth’s earliest history. Scientists have long debated when plate tectonics and subduction began, with estimates ranging from 0.85 to 4.2 billion years ago — more than two-thirds of the planet’s history. Discovering when plate subduction began means pinpointing when Earth transitioned from a planet dominated by transient landmasses piercing through the oceans’ surface to one composed of long-lived continents where long-term biogeochemical cycles are controlled by volcanic degassing and recycling into Earth’s interior.

Plate subduction occurs when oceanic crust and continental crust collide. Because continental crust is thicker and less dense, oceanic crust is pushed downward into the Earth’s mantle, at an average rate of a few centimeters each year. This contact with the mantle creates areas that are hot enough for magma to escape to the surface, creating volcanoes such as Mount St. Helens and others found along the Pacific Rim.

Plate tectonics and subduction zones are responsible for the way Earth looks, driving the creation of continental plates and the basins that would fill to become oceans. They are also the primary control on the chemical characteristics of the planet’s surface, and are likely responsible for Earth’s ability to sustain life. These tectonic zones are responsible for the formation of emerged continents and provide an important control on climate by regulating the amounts of the greenhouse carbon dioxide in the atmosphere.

In four-billion-year-old rock samples, Aarons saw similarities to modern rocks that are formed in plume settings, like Hawaii and Iceland, where a landmass is drifting over a hot spot. However, in rocks aged at 3.75 billion years, she noticed a shift in trend to rocks that are formed in modern subduction zones, suggesting that around that time in Earth’s history these areas began forming.

“While the trend in the titanium isotope data does not provide evidence that plate tectonics was happening globally, it does indicate the presence of wet magmatism, which supports subduction at this time,” said Aarons.

The technique used in this study could be applied to other ancient rock formations around the world to gain more information about the composition and evolution of Earth’s emerged lands through time.

Other institutions involved in the study were Pennsylvania State University (USA) and the University of Bern (Switzerland). The study was funded by the National Science Foundation, NASA, the Ford Foundation Postdoctoral Fellowship, and the Swiss National Science Foundation.