Researchers charted how developmental processes unfold across the human brain from the ages of 8 to 23 years old through magnetic resonance imaging (MRI). The findings indicate a new approach to understanding the order in which individual brain regions show reductions in plasticity during development.

Brain plasticity refers to the capacity for neural circuits — connections and pathways in the brain for thought, emotion, and movement — to change or reorganize in response to internal biological signals or the external environment. While it is generally understood that children have higher brain plasticity than adults, this study provides new insights into where and when reductions in plasticity occur in the brain throughout childhood and adolescence.

The findings reveal that reductions in brain plasticity occur earliest in “sensory-motor” regions, such as visual and auditory regions, and occur later in “associative” regions, such as those involved in higher-order thinking (problem solving and social learning). As a result, brain regions that support executive, social, and emotional functions appear to be particularly malleable and responsive to the environment during early adolescence, as plasticity occurs later in development.

“Studying brain development in the living human brain is challenging. A lot of neuroscientists’ understanding about brain plasticity during development actually comes from studies conducted with rodents. But rodent brains do not have many of what we refer to as the association regions of the human brain, so we know less about how these important areas develop,” said corresponding author Theodore D. Satterthwaite, MD, the McLure Associate Professor of Psychiatry in the Perelman School of Medicine at the University of Pennsylvania, and director of the Penn Lifespan Informatics and Neuroimaging Center (PennLINC).

To address this challenge, the researchers focused on comparing insights from previous rodent studies to youth MRI imaging insights. Prior research examining how neural circuits behave when they are plastic uncovered that brain plasticity is linked to a unique pattern of “intrinsic” brain activity. Intrinsic activity is the neural activity occurring in a part of the brain when it is at rest, or not being engaged by external stimuli or a mental task. When a brain region is less developed and more plastic, there tends to be more intrinsic activity within the region, and that activity also tends to be more synchronized. This is because more neurons in the region are active, and they tend to be active at the same time. As a result, measurements of brain activity waves show an increase in amplitude(or height).

“Imagine that individual neurons within a region of the brain are like instruments in an orchestra. As more instruments begin to play together in synchrony, the sound level of the orchestra increases, and the amplitude of the sound wave gets higher,” said first author Valerie Sydnor,a Neuroscience PhD student. “Just like decibel meters can measure the amplitude of a sound wave, the amplitude of intrinsic brain activity can be measured with functional MRI while kids are simply resting in the scanner. This allowed our team to study a functional marker of brain plasticity safely and non-invasively in youth.”

Analyzing MRI scans from more than 1,000 individuals, the authors found that the functional marker of brain plasticity declined in earlier childhood in sensory-motor regions but did not decline until mid-adolescence in associative regions.

“These slow-developing associative regions are also those that are vital for children’s cognitive attainment, social interactions, and emotional well-being,” Satterthwaite added. “We are really starting to understand the uniqueness of human’s prolonged developmental program.”

“If a brain region remains malleable for longer, it may also remain sensitive to environmental influences for a longer window of development,” Sydnor said. “This study found evidence for just that.”

The authors studied relationships between youths’ socioeconomic environments and the same functional marker of plasticity. They found that the effects of the environment on the brain were not uniform across regions nor static across development. Rather, the effects of the environment on the brain changed as the identified developmental sequence progressed.

Critically, youths’ socioeconomic environments generally had a larger impact on brain development in the late-maturing associative brain regions, and the impact was found to be largest in adolescence.

“This work lays the foundation for understanding how the environment shapes neurodevelopmental trajectories even through the teenage years,” said Bart Larsen, PhD, a PennLINC postdoctoral researcher and co-author.

Sydnor elaborated, “The hope is that studying developmental plasticity will help us to understand when environmental enrichment programs will have a beneficial impact on each child’s neurodevelopmental trajectory. Our findings support that programs designed to alleviate disparities in youths’ socioeconomic environments remain important for brain development throughout the adolescent period.”

This study was supported by the National Institute of Health (R01MH113550, R01MH120482, R01MH112847, R01MH119219, R01MH123563, R01MH119185, R01MH120174, R01NS060910, R01EB022573, RF1MH116920., RF1MH121867, R37MH125829, R34DA050297, K08MH120564, K99MH127293, T32MH014654). The study was also supported by the National Science Foundation Graduate Research Fellowship (DGE-1845298).

Additional support was provided by the Penn-CHOP Lifespan Brain Institute and the Penn Center for Biomedical Image Computing and Analytics.

But did humans also favor certain wild plants for domestication because they were more easily “tamed”? Research from Washington University in St. Louis calls for a reappraisal of the process of plant domestication, based on almost a decade of observations and experiments. The behavior of erect knotweed, a buckwheat relative, has WashU paleoethnobotanists completely reassessing our understanding of plant domestication.

“We have no equivalent term for tameness in plants,” said Natalie Mueller, assistant professor of archaeology in Arts & Sciences at Washington University. “But plants are capable of responding to people. They have a developmental capacity to be tamed.”

Her work with early indigenous North American crops shows that some wild plants respond quickly to clearing, fertilizing, weeding or thinning. Plants that respond in ways that make cultivation easier or more productive could be considered more easily tamed than those that cannot.

“If plants responded rapidly in ways that were beneficial to early cultivators — for example by producing higher yields, larger seeds, seeds that were easier to sprout, or a second crop in a single growing season — this would have encouraged humans to continue investing in the co-evolutionary relationship,” she said.

This capacity to express different traits and characteristics in response to the environment is called plasticity, and not all species are equally plastic.

“Some plants respond quickly and obviously to cultivation and care,” Mueller said. “I think ancient people would have noticed that they could double their yields just by thinning out dense stands of plants. This is one of the simplest and most common gardening techniques, but it has many important effects on the development of plants.”

What would an early farmer do?

Mueller’s study, published April 7 in PLOS ONE, focuses on work with a plant called erect knotweed, a member of the buckwheat family that was domesticated by indigenous farmers in eastern North America. The domesticated sub-species is now extinct; humans don’t eat it anymore. But Mueller and others have previously uncovered caches of seeds stored in caves, charred plant remnants in ancient hearths, and even the seeds of erect knotweed in human feces, clear evidence that this species was once consumed as a staple food.

Mueller, who studies lost crops, has spent years growing erect knotweed and other crop progenitors in experimental gardens, including at Washington University’s environmental field station, Tyson Research Center. She hasn’t always been successful with growing the plants she collects in the wild. In that way, Mueller can relate to the early farmers who similarly experimented with plants to discover their potential.

Her efforts have often been stymied by seed dormancy, a common feature among wild plants.

Unlike seeds you buy at the garden store, the seeds of most wild plants will not germinate if you simply sprinkle some water on them. Their requirements for germination are diverse and shaped by their evolutionary history. For example, if a plant has evolved in a place with a winter, like the Midwest, its seeds may not germinate unless they experience a long cold period. This prevents them from germinating too soon in the wild — they are waiting for spring. Domesticated plants have lost their diverse germination requirements.

The loss of germination inhibitors has presented a paradox to theorists of domestication. Many of the selective pressures that could have favored the evolution of this trait derive from planting seeds. But why would ancient people have started planting seeds if none of them germinated?

With erect knotweed, Mueller experienced a breakthrough of sorts. Based on four seasons of observations, Mueller determined that growing wild plants in the low-density conditions typical of a cultivated garden (i.e. spaced out and weeded) triggers plants to produce seeds that germinate more easily. This makes the harvests easier to plant successfully the next time around, eliminating a key barrier to further selection.

“Our results show that erect knotweed grown in low-density agroecosystems spontaneously ‘act domesticated’ in a single growing season, before any selection has occurred,” Mueller said.

Think of it as the plant equivalent to that first wolf who, though still a wild animal, sat down with its human friend around the fire. This is a behavioral shift, rather than an evolutionary one, but it allows new evolutionary pathways to open up.

A role for plant behavior

Mueller believes there is a bias in domestication studies toward viewing this changeability, or plasticity, as noise that is getting in the way of attempts to explain evolutionary change. Instead, this paper argues that we need to understand the development and behavior of wild crop relatives in order to explain the evolutionary process of domestication.

“Because we lack the practical experience with crop progenitors that ancient people had, these effects of the environment on plant development have gone mostly unnoticed and understudied,” Mueller said.

Her findings could have applications for developing new food crops: there is no reason why we have to be limited to the plants that our ancestors domesticated thousands of years ago.

Some researchers have been calling for de novo domestication — selecting wild plants with desirable characteristics and intentionally domesticating them. It may make sense to start looking to wild plants that are easily tamed as potential crops that could be developed for the future, Mueller said.

This paper also contributes to a growing awareness that plants are responsive and communicative beings. Though this idea is cutting-edge and hotly debated in biology and ecology, it is widespread in indigenous North American philosophies and probably would have been held by the people who domesticated erect knotweed and other plants thousands of years ago.

Recent research has shown how plants warn relatives about herbivores using chemical signaling, share resources through mycorrhizal networks and even emit noises when they are injured or stressed.

“You can’t explain plant domestication if you only consider the behaviors of humans, because domestication is the result of reciprocal relationships between multiple species that are all capable of responding to each other,” Mueller said.

In a clinical trial, 32 men with high-risk or very high-risk prostate cancers who were scheduled for prostate cancer surgery were treated with six weekly infusions of enoblituzumab prior to surgery, and were followed for an average of 30 months thereafter. Twenty-one patients, or 66%, had an undetectable prostate-specific antigen (PSA) level 12 months following surgery, suggesting that there was no sign of residual disease. Additionally, the drug was well-tolerated overall; no patients had any surgical delays or medical complications during or after the operation.

A description of the work was published April 3 in the journal Nature Medicine.

If enoblituzumab continues to perform well in further larger randomized studies, it could represent a new pathway for immunotherapy against multiple cancers, and the first one that may have a role for prostate cancer, says lead study author and cancer immunology researcher Eugene Shenderov, M.D., Ph.D., assistant professor of oncology at the Johns Hopkins University School of Medicine. Other existing antibody-based immunotherapy drugs have targeted immune checkpoints, natural on/off switches mediating immune responses, such as CTLA-4, PD-1 and LAG-3. Cancer cells hijack these checkpoints, turning off the immune response to cancer. “Drugs that block these checkpoints have had success in other types of cancers, including lung cancer and melanoma, but not in prostate cancer,” says Shenderov.

Enoblituzumab works by binding to a protein called B7-H3 that is overexpressed on prostate cancer cells and believed to impede the immune system’s ability to attack cancer cells. The new therapy could pack a one-two punch against cancer, Shenderov says, by blocking B7-H3’s inhibition of the immune system’s recognition and elimination of cancer cells, and also triggering a process called antibody-dependent cellular cytoxicity (ADCC), which leads to tumor cell destruction by activating additional immune cells such as macrophages and natural killer cells.

“Enoblituzumab appears safe and seems to activate the immune system in a way that involves both T-cells and myeloid cells,” Shenderov says. “What this means is if these results can be replicated in a larger, randomized study, it opens the possibility that combining this therapy with local, curative-intent therapies like surgical prostate removal or radiation therapy, would allow this drug to potentially kill micrometastatic disease hiding elsewhere in the body, and therefore prevent a significant number of men from experiencing recurring disease. That could be a paradigm shift in prostate cancer.”

The median age of study participants was 64 (age range 48-74). About half (47%) had a PSA greater than 10 ng/mL at diagnosis, which is abnormally high, and 50% had Gleason grade group 5 at biopsy, meaning they had highly aggressive disease. Patients were enrolled from February 2017 through June 2019. Enoblituzumab was confirmed to penetrate into prostate tumors and to bind to B7-H3 in the vast majority of participants, according to prostate samples studied after surgery.

Side effects of enoblituzumab were generally mild and included fatigue, neurological symptoms such as headache or dizziness, and flu-like or cold symptoms. One patient developed inflammation of the heart (myocarditis), which fully resolved with steroid treatment, and is a known side effect of other immune checkpoint drugs.

Beyond safety and anti-tumor activity based on PSA dropping to undetectable levels, investigators also looked for changes in the tumor microenvironment before and after enoblituzumab treatment. They found increased markers of cytotoxicity after treatment, consistent with the concept that the immune system was activated against tumor cells. The tumors showed increased infiltration with granulocytes, leukocytes and effector T-cells, and there was roughly a doubling of the density of cytotoxic T cells after treatment.

“The findings are exciting but exploratory, and need to be confirmed in larger study cohorts,” cautions senior study author Emmanuel S. Antonarakis, M.D., the Clark Endowed Professor of Medicine and director of GU Oncology for the University of Minnesota Masonic Cancer Center. Antonarakis was the senior investigator of the study while he was at the Johns Hopkins Kimmel Cancer Center.

“However, these results in high-risk prostate cancer patients, and the broader need for immunotherapeutic strategies with efficacy in prostate cancers, provide justification to further develop multipronged approaches that include targeting B7-H3 to optimize antitumor activity in prostate cancers and other solid malignancies,” he says.

Investigators are now planning a larger, randomized trial of enoblituzumab in newly diagnosed prostate cancer patients to assess clinical activity of the drug compared to current standards of care.

Coauthors of the current study were Angelo M. De Marzo, Tamara L. Lotan, Hao Wang, Sin Chan, Su Jin Lim, Hogkai Ji, Mohamad El Allaf, Carolyn Chapman, Samuel R. Denmeade, Kenneth J. Pienta, Christian P. Pavlovich, and Drew M. Pardoll of Johns Hopkins. Other study authors contributing to the paper were from MacroGenics Inc. of Rockville, Maryland (the maker of enoblituzumab); NanoString Technologies Inc. of Seattle; Adaptive Biotechnologies of Seattle; CDI Labs of Baltimore; the Northwestern University Feinberg School of Medicine in Chicago; and Charles G. Drake formerly at Johns Hopkins, who currently leads Immuno-Oncology at Janssen Research and Development.

The work was supported by the National Institutes of Health (Cancer Center Support Grant P30 CA006973), an NCI SPORE in Prostate Cancer (P50CA58236), a Prostate Cancer Foundation Young Investigator Award, the Department of Defense (grants W81XWH-16-PCRP-CCRSA and W81XWH-18-2-0015), and the Bloomberg~Kimmel Institute for Cancer Immunotherapy and by Macrogenics Inc, of Rockville, Maryland.

E. Shenderov is a paid consultant to GT Biopharma, Guidepoint Global, FirstThought, GLG, and receives institutional research funding from MacroGenics Inc., manufacturer of enoblituzumab. These relationships are managed by The Johns Hopkins University in accordance with its conflict of interest policies. E. Antonarakis has served as a paid consultant for Janssen, Astellas, Sanofi, Bayer, Bristol Myers Squibb, Amgen, Constellation, Blue Earth, Exact Sciences, Invitae, Curium, Pfizer, Merck, AstraZeneca, Clovis and Eli Lilly; and has received research support from MacroGenics, Janssen, Johnson & Johnson, Sanofi, Bristol Myers Squibb, Pfizer, AstraZeneca, Novartis, Curium, Constellation, Celgene, Merck, Bayer, Clovis and Orion. These relationships are managed by the University of Minnesota (Antonarakis’ current institution) in accordance with their conflict of interest policies.

Critically, they’ve shown how the production of these molecules can be efficiently managed so as not to hamper normal plant growth.

Pheromones are complex chemicals produced and released by an organism as a means of communication. They allow members of the same species to send signals, which includes letting others know they’re looking for love.

Farmers can hang pheromone dispersers among their crops to mimic the signals of female insects, trapping or distracting the males from finding a mate. Some of these molecules can be produced by chemical processes but chemical synthesis is often expensive and creates toxic byproducts.

Dr Nicola Patron, who led this new research and heads the Synthetic Biology Group at the Earlham Institute, uses cutting-edge science to get plants to produce these valuable natural products.

Synthetic biology applies engineering principles to the building blocks of life, DNA. By creating genetic modules with the instructions to build new molecules, Dr Patron and her group can turn a plant such as tobacco into a factory that only needs sunlight and water.

“Synthetic biology can allow us to engineer plants to make a lot more of something they already produced, or we can provide the genetic instructions that allow them to build new biological molecules, such as medicines or these pheromones,” said Dr Patron.

In this latest work, the team worked with scientists at the Plant Molecular and Cell Biology Institute in Valencia to engineer a species of tobacco, Nicotiana benthamiana, to produce moth sex pheromones. The same plant has previously been engineered to produce ebola antibodies and even coronavirus-like particles for use in Covid vaccines.

The Group built new sequences of DNA in the lab to mimic the moth genes and introduced a few molecular switches to precisely regulate their expression, which effectively turns the manufacturing process on and off.

An important component of the new research was the ability to fine tune the production of the pheromones, as coercing plants to continuously build these molecules has its drawbacks.

“As we increase the efficiency, too much energy is diverted away from normal growth and development,” explained Dr Patron.

“The plants are producing a lot of pheromone but they’re not able to grow very large, which essentially reduces the capacity of our production line. Our new research provides a way to regulate gene expression with much more subtlety.”

In the lab, the team set about testing and refining the control of genes responsible for producing the mix of specific molecules that mimic the sex pheromones of moth species, including navel orangeworm and cotton bollworm moths.

They showed that copper sulphate could be used to finely tune the activity of the genes, allowing them to control both the timing and level of gene expression. This is particularly important as copper sulphate is a cheap and readily-available compound already approved for use in agriculture.

They were even able to carefully control the production of different pheromone components, allowing them to tweak the cocktail to better suit specific moth species.

“We’ve shown we can control the levels of expression of each gene relative to the others,” said Dr Patron. “This allows us to control the ratio of products that are made.

“Getting that recipe right is particularly important for moth pheromones as they’re often a blend of two or three molecules in specific ratios. Our collaborators in Spain are now extracting the plant-made pheromones and testing them in dispensers to see how well they compare to female moths.”

The team hope their work will pave the way to routinely using plants to produce a wide range of valuable natural products.

“A major advantage of using plants is that it can be far more expensive to build complex molecules using chemical processes,” said Dr Patron. “Plants produce an array of useful molecules already so we’re able to use the latest techniques to adapt and refine the existing machinery.

“In the future, we may see greenhouses full of plant factories — providing a greener, cheaper and more sustainable way to manufacture complex molecules.”

The research is part of the SUSPHIRE project, which received support from ERACoBiotech funded by the Horizon 2020 research and innovation program and the UKRI Biotechnology and Biological Sciences Research Council (BBSRC).