How stem cells know the right way to make a heart . And what goes wrong when they don’t

Gladstone scientists Deepak Srivastava (left), Yvanka De Soysa (center), and Casey Gifford (right) publish a complete catalog of the cells involved in heart development.

The invention of GPS navigation systems has made finding your way around so much easier, providing simple instructions on how to get from point A to point B. Now, a new study shows that our bodies have their own internal navigation system that helps stem cells know where to go, and when, in order to build a human heart. And the study also shows what can go wrong when even a few cells fail to follow directions.

In this CIRM-supported study, a team of researchers at the Gladstone Institutes in San Francisco, used a new technique called single cell RNA sequencing to study what happens in a developing heart. Single cell RNA sequencing basically takes a snapshot photo of all the gene activity in a single cell at one precise moment. Using this the researchers were able to follow the activity of tens of thousands of cells as a human heart was being formed.

In a story in Science and Research Technology News, Casey Gifford, a senior author on the study, said this approach helps pinpoint genetic variants that might be causing problems.

“This sequencing technique allowed us to see all the different types of cells present at various stages of heart development and helped us identify which genes are activated and suppressed along the way. We were not only able to uncover the existence of unknown cell types, but we also gained a better understanding of the function and behavior of individual cells—information we could never access before.”

Then they partnered with a team at Luxembourg Centre for Systems Biomedicine (LCSB) of the University of Luxembourg which ran a computational analysis to identify which genes were involved in creating different cell types. This highlighted one specific gene, called Hand2, that controls the activity of thousands of other genes. They found that a lack of Hand2 in mice led to an inability to form one of the heart’s chambers, which in turn led to impaired blood flow to the lungs. The embryo was creating the cells needed to form the chamber, but not a critical pathway that would allow those cells to get where they were needed when they were needed.

Gifford says this has given us a deeper insight into how cells are formed, knowledge we didn’t have before.

“Single-cell technologies can inform us about how organs form in ways we couldn’t understand before and can provide the underlying cause of disease associated with genetic variations. We revealed subtle differences in very, very small subsets of cells that actually have catastrophic consequences and could easily have been overlooked in the past. This is the first step toward devising new therapies.”

These therapies are needed to help treat congenital heart defects, which are the most common and deadly birth defects. There are more than 2.5 million Americans with these defects. Deepak Srivastava, President of Gladstone and the leader of the study, said the knowledge gained in this study could help developed strategies to help address that.

“We’re beginning to see the long-term consequences in adults, and right now, we don’t really have any way to treat them. My hope is that if we can understand the genetic causes and the cell types affected, we could potentially intervene soon after birth to prevent the worsening of their state over time.

The study is published in the journal Nature.

Genetic defect leads to slower production of brain cells linked to one form of autism

Child with Fragile X syndrome

Fragile X syndrome (FXS) is a genetic disorder that is the most common form of inherited intellectual disability in children, and has also been linked to a form of autism. Uncovering the cause of FXS could help lead to a deeper understanding of autism, what causes it and ultimately, it’s hoped, to treating or even preventing it.

Researchers at Children’s Hospital in Chicago looked at FXS at the stem cell level and found how a genetic defect has an impact on the development of neurons (nerve cells in the brain) and how that in turn has an impact on the developing brain in the fetus.

In a news release on Eurekalert, Dr. Yongchao Ma, the senior author of the study, says this identified a problem at a critical point in the development of the brain:

“During embryonic brain development, the right neurons have to be produced at the right time and in the right numbers. We focused on what happens in the stem cells that leads to slower production of neurons that are responsible for brain functions including learning and memory. Our discoveries shed light on the earliest stages of disease development and offer novel targets for potential treatments.”

The team looked at neural stem cells and found that a lack of one protein, called FMRP, created a kind of cascade that impacted the ability of the cells to turn into neurons. Fewer neurons meant impaired brain development. 

The findings, published in the journal Cell Reports, help explain how genetic information flows in cells in developing babies and, according to Dr. Ma, could lead to new ideas on how to treat problems.

“Currently we are exploring how to stimulate FMRP protein activity in the stem cell, in order to correct the timing of neuron production and ensure that the correct amount and types of neurons are available to the developing brain. There may be potential for gene therapy for fragile X syndrome.”

Stem cell study shows how smoking attacks the developing liver in unborn babies

smoking mom

It’s no secret that smoking kills. According to the Centers for Disease Control and Prevention (CDC) smoking is responsible for around 480,000 deaths a year in the US, including more than 41,000 due to second hand smoke. Now a new study says that damage can begin in utero long before the child is born.

Previous studies had suggested that smoking could pose a serious risk to a fetus but those studies were done in petri dishes in the lab or using animals so the results were difficult to extrapolate to humans.

Researchers at the University of Edinburgh in Scotland got around that problem by using embryonic stem cells to explore how the chemicals in tobacco can affect the developing fetus. They used the embryonic stem cells to develop fetal liver tissue cells and then exposed those cells to a cocktail of chemicals known to be found in the developing fetus of mothers who smoke.

Dangerous cocktail

They found that this chemical cocktail proved far more potent, and damaged the liver far more, than individual chemicals. They also found it damaged the liver of males and females in different ways.  In males the chemicals caused scarring, in females it was more likely to negatively affect cell metabolism.

There are some 7,000 chemicals found in cigarette smoke including tar, carbon monoxide, hydrogen cyanide, ammonia, and radioactive compounds. Many of these are known to be harmful by themselves. This study highlights the even greater impact they have when combined.

Long term damage

The consequences of exposing a developing fetus to this toxic cocktail can be profound, including impaired growth, premature birth, hormonal imbalances, increased predisposition to metabolic syndrome, liver disease and even death.

The study is published in the Archives of Toxicology.

In a news release Dr. David Hay, one of the lead authors, said this result highlights yet again the dangers posed to the fetus by women smoking while pregnant or being exposed to secondhand smoke :

“Cigarette smoke is known to have damaging effects on the foetus, yet we lack appropriate tools to study this in a very detailed way. This new approach means that we now have sources of renewable tissue that will enable us to understand the cellular effect of cigarettes on the unborn foetus.”

Discovering stem cells and science at Discovery Day

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The CIRM booth at Discovery Day at AT&T Park

Someone stole my thigh bone. One minute it was there. The next, gone. I have narrowed down the list of suspects to the more than 25,000 people attending Discovery Day at San Francisco’s AT&T Park.

To be honest, the bone was just a laminated image of a bone, stuck to the image of a person drawn on a white board. We were using it, along with laminated images of a brain, liver, stomach and other organs and tissues, to show that there are many different kinds of stem cells in the body, and they all have different potential uses.

The white board and its body parts were gimmicks that we used to get kids to come up to the CIRM booth and ask what we were doing. Then, as they played with the images, and tried to guess which stem cells went where, we talked to their parents about stem cell research, and CIRM and the progress being made.

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Dr. Karen Ring explaining embryonic development to kids

We also used Play Doh so that the kids could model cell division and specialization during embryonic development. But mostly it was so the kids could play with the Play Doh while we talked to their parents.

It is shameless I know but when you are competing against more than 130 other booths for people’s attention – and some of these booths had live snakes, virtual reality devices, or they just let kids throw and hit things – you have to be creative.

And creativity was certainly the key word, because Discovery Day – part of the annual week-long Bay Area Science Fair – was filled with booths from companies and academic institutions promoting every imaginable aspect of science.

So why were we there? Well, first, education has been an important part of CIRM’s mission ever since we were created. Second, we’re a state agency that gets public funding so we feel we owe it to the public to explain how their money is being used. And third, it’s just a lot of fun.

NASA was there, talking about exploring deep space. And there were booths focused on exploring the oceans, and saving them from pollution and over-fishing. You could learn about mathematics and engineering by building wacky-looking paper airplanes that flew long distances, or you could just sit in the cockpit of a fighter jet.

discoveryday-victor

And everywhere you looked were families, with kids running up to the different booths to see what was there. All they needed was a little draw to get them to stick around for a few minutes, so you could talk to them and explain to them what stem cells are and why they are so amazing. Some of the kids were fascinated and wanted to know more: some just wanted to use the Play Doh;  at least one just wanted to eat the Play Doh, but fortunately we were able to stop that happening.

It was an amazing sight to see a baseball stadium filled with tens of thousands of people, all there to learn about science. At a time when we are told that kids don’t care about science, that they don’t like math, this was the perfect response. All you had to do was look around and see that kids were fascinated by science. They were hungry to learn how pouring carbon dioxide on a candle puts out the flame. They delighted in touching an otter pelt and feeling how silky smooth it is, and then looking at the pelt under a microscope to see just how extraordinarily dense the hairs are and how that helps waterproof the otter.

And so yes, we used Play Doh and a white board person to lure the kids to us. But it worked.

There was another booth where they had a couple of the San Francisco 49er’s cheerleaders in full uniform. I don’t actually know what that had to do with teaching science but it was very popular with some of the men. Maybe next year I could try dressing up like that. It would certainly draw a crowd.


Check us out on Instagram to learn more about CIRM’s educational outreach efforts.

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We had a lot of fun this weekend teaching young minds about what stem cells are and where they are located in the human body at the @bayareascience #DiscoveryDay festival. We had one activity where kids learned about embryonic stem cells and development using playdoh and another white board activity about adult stem cells. Students learned that each organ has its own set of adult stem cells that can regenerate lost or damaged cells in that specific organ. It was really fun to explain to kids and their parents why stem cells and regenerative medicine research are important. • • • #BASF2016 #stemcells #stemcellresearch #stemeducation #STEM #teaching #education #research #attpark #CIRM #development #embryonicstemcells

A post shared by CALIFORNIA'S STEM CELL AGENCY (@cirm_stemcells) on

Embryos with abnormal chromosomes can repair themselves

CVS

In a chorionic villus sampling (CVS) test, cells from the fetal side of the placenta are collected and tests for genetic defects.
Image credit: ADAM Health Solutions

Like an increasing number of women, Magdalena Zernicka-Goetz waited later in life to have kids and was pregnant at 44 with her second child. Because older moms have an increased risk of giving birth to children with genetic disorders, Zernicka-Goetz opted to have an early genetic screening test about 12 weeks into her pregnancy. The test, which looks for irregular amounts of chromosomes in the cells taken from the placenta, showed that a quarter of the cells in the developing fetus had genetic abnormalities.

Expectant mothers and tough choices

If she carried the child to term, would the baby have a birth defect? Zernicka-Goetz learned from geneticists that this question was difficult to answer due to a lack of data about what happens to abnormal cells in the developing fetus. Fortunately, her baby was born happy and healthy. But the experience motivated her to seek out a better understanding for the sake of other women who would be faced with similar difficult decisions based on screening tests.

As a professor of developmental biology at Cambridge University, Zernicka-Geotz had the expertise to follow through on this challenge. And in a Nature Communications journal article published yesterday, she and her team report a fascinating result: the very early embryo has the ability to essentially repair itself by getting rid of abnormal cells.

Aneuploidy: You Have the Wrong Number

aneuploidy

Aneuploidy in the developing fetus can lead to genetic disorders. Image credit: Deluca Lab Colorado State University

To reach this finding, the team first had to recreate chromosomal abnormalities in mouse embryos. If you remember your high school or college biology, you’ll recall that before a cell divides, it duplicates each chromosome and then each resulting “daughter” cell grabs one chromosome copy using a retracting spindle fiber structure. The scientists took advantage of the fact that treating dividing cells with the drug reversine destabilizes the spindle fibers and in turn causes an unequal divvying up of the chromosomes between the daughter cells. In scientific jargon the condition is called aneuploidy.

Rescuing the embryo by cellular suicide

Blog embryo repair fig 3

Generating early mouse embryos with an equal mix of normal cells and cells with abnormal chromosome numbers (induced via reversine treatment). Image credit: Bolton et al. Nat Commun. 2016 Mar 29;7:11165

The researchers created mosaic embryos at the eight cell stage in which half the cells had a normal set of chromosomes while the other half we’re the reversine-treated cells with abnormal numbers of chromosomes. With these genetically mosaic embryos, the team tagged the cells with fluorescent dye and used time-lapsed imaging to track the fate of each cell for 48 hours. They found a decrease specifically in the portion of cells that stemmed from the abnormal cells.

A follow up experiment examined cell death as a way to help explain the reduced number of abnormal cells. The researchers found that compared to the normal set of cells in the embryo, the abnormal cells had a significantly higher evidence of apoptosis, or programmed cell death, a natural process that occurs to eliminate harmful or damaged cells. According to Zernicka-Geota and the team, this is the first study to directly show the elimination of abnormal cells in the growing embryo.

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Time lapse images showing an abnormal cell (green cell indicated by arrow) being eliminated by apoptosis (programmed cell death) and then engulfed by normal (red) cells (engulfment indicated by star).
Image credit: Bolton et al. Nat Commun. 2016 Mar 29;7:11165

To look at their fate beyond the very early stages of development, the mosaic mouse embryos were implanted into foster mothers and allowed to develop to full term. Thirteen of the twenty-six embryos transferred to foster mothers gave rise to live pups which were all healthy after four months of age.

As Zermicka-Geota stated in a university press release picked up by Medical Express, if these findings reflect what goes on in human development, then decisions based on genetic screening results may not be clear cut:

“We found that even when half of the cells in the early stage embryo are abnormal, the embryo can fully repair itself. It will mean that even when early indications suggest a child might have a birth defect because there are some, but importantly not all abnormal cells in its embryonic body, this isn’t necessarily the case.”

Implications for genetic testing on days-old IVF embryos

These new results don’t suggest that current genetic testing is obsolete. For instance, the amniocentesis test, which collects fetal tissue from the mother’s amniotic fluid between 14 and 20 weeks of pregnancy, can detect genetic disorders with 98-99% accuracy. But this study may have important implications for testing done much earlier. When couples conceive via in vitro fertilization, a so-called pre-implantation genetic diagnosis (PGD) test can be performed on embryos that are only a few days old. In the test, a single cell is removed – without damaging the embryo – and the cell is tested for chromosomal defects. Based on this study, a positive PGD test may be misleading if that abnormal cell was destined to be eliminated from the embryo.

CIRM Scientists Discover Key to Blood Cells’ Building Blocks

Our bodies generate new blood cells—both red and white blood cells—each and every day. But reproducing that feat in a petri dish has proven far more difficult.

Pictured: sections from zebrafish embryos. Blood vessels are labeled in red, the protein complex that regulates inflammation green and cell nuclei in blue. The arrowhead indicates a potential HSC. The image at bottom right combines all channels. [Credit: UC San Diego School of Medicine]

Pictured: sections from zebrafish embryos. Blood vessels are labeled in red, the protein complex that regulates inflammation green and cell nuclei in blue. The arrowhead indicates a potential HSC. The image at bottom right combines all channels.
[Credit: UC San Diego School of Medicine]

But now, scientists have identified the missing ingredient to producing hematopoietic stem cells, or HSC’s—the type of stem cell that gives rise to all blood and immune cells in the body. The results, published last week in the journal Cell, describe how a newly discovered protein plays a key role in generating HSC’s in the developing embryo—giving scientists a more complete recipe to reproduce these cells in the lab.

The research, which was led by University of California, San Diego (UCSD) professor David Traver and supported by a grant from CIRM, offers renewed hope for the possibility of generating patient-specific blood or immune cells using induced pluripotent stem cell (iPS cell) technology.

As Traver explained in last week’s news release:

“The development of some mature cell lineages from iPS cells, such as cardiac or neural, has been reasonably straightforward, but not with HSCs. This is likely due, at least in part, to not fully understanding all the factors used by the embryo to generate HSCs.”

Indeed, the ability to generate HSCs has long challenged scientists, as outlined in a CIRM workshop from last year. But now, says Traver, they have found a crucial piece to the puzzle.

Specifically, the researchers investigated a signaling protein called tumor necrosis factor alpha—or TNFα for short— a protein known to be important for regulating inflammation and immunity. Previous research by this study’s first author, Raquel Espin-Palazon, and others also discovered it was related to the healthy function of blood vessels during embryonic development.

In this study, Traver, Espin-Palazon and the UCSD drilled down even further—and found that TNFα was required for the normal development of HSCs in the embryo. This surprised the research team, as the young embryo is generally considered to be sterile—with no need for a protein normally charged with regulating immune response to be switched on. Explained Traver:

“There was no expectation that pro-inflammatory signaling would be active at this time or in the blood-forming regions.”

While preliminary, establishing this relationship between TNFα and HSC formation will be a boon to researchers looking for new ways to generate large quantities of healthy, patient-specific red and white blood cells for those patients who so desperately need them.

Learn more about how stem cell technology could help treat blood diseases in our Thalassemia Fact Sheet.