teeth

Stem cell stories that caught our eye: lab-grown blood stem cells and puffer fish have the same teeth stem cells as humans

/ Karen Ring / Leave a comment

Here are some stem cell stories that caught our eye this past week. Some are groundbreaking science, others are of personal interest to us, and still others are just fun.

Scientists finally grow blood stem cells in the lab!

Two exciting stem cell studies broke through the politics-dominated headlines this week. Both studies, published in the journal Nature, demonstrated that human hematopoietic or blood stem cells can be grown in the lab.

This news is a big deal because scientists have yet to make bonafide blood stem cells from pluripotent stem cells or other human cells. These stem cells not only create all the cells in our blood and immune systems, but also can be used to develop therapies for patients with blood cancers and genetic blood disorders.

But to do these experiments, you need a substantial source of blood stem cells – something that has eluded scientists for decades. That’s where these two studies come to the rescue. One study was spearheaded by George Daley at the Boston Children’s Hospital in Massachusetts and the other was led by Shahin Rafii at the Weill Cornell Medical College in New York City.

Researchers have made blood stem cells and progenitor cells from pluripotent stem cells. Credit: Steve Gschmeissner Getty Images

George Daley and his team developed a strategy that matured human induced pluripotent stem cells (iPS cells) into blood-forming stem and progenitor cells. It’s a two-step process that first uses a cocktail of chemicals to make hemogenic endothelium, the embryonic tissue that generates blood stem cells. The second step involved treating these intermediate cells with a combination of seven transcription factors that directed them towards a blood stem cell fate.

These modified human blood stem cells were then transplanted into mice where they developed into blood stem cells that produced blood and immune cells. First author on the study, Ryohichi Sugimura, explained the applications that their technology could be used for in a Boston Children’s Hospital news release,

“This step opens up an opportunity to take cells from patients with genetic blood disorders, use gene editing to correct their genetic defect and make functional blood cells. This also gives us the potential to have a limitless supply of blood stem cells and blood by taking cells from universal donors. This could potentially augment the blood supply for patients who need transfusions.”

The second study by Shahin Rafii and his team at Cornell used a different strategy to generate blood-forming stem cells. Instead of genetically manipulating iPS cells, they selected a more mature cell type to directly reprogram into blood stem cells. Using four transcription factors, they successfully reprogrammed mouse endothelial cells, which line the insides of blood vessels, into blood-forming stem cells that repopulated the blood and immune systems of irradiated mice.

Raffii believe his method is simpler and more efficient than Daley’s. In coverage by Nature News, he commented,

“Using the most efficient method to generate stem cells matters because every time a gene is added to a batch of cells, a large portion of the batch fails to incorporate it and must be thrown out. There is also a risk that some cells will mutate after they are modified in the lab, and could form tumors if they are implanted into people.”

To play devil’s advocate, Daley’s technique might appeal more to some because the starting source of iPS cells is much easier to obtain and culture in the lab than endothelial cells that have to be extracted from the blood vessels of animals or people. Furthermore, Daley argued that his team’s method could “be made more efficient, and [is] less likely to spur tumor growth and other abnormalities in modified cells.”

The Nature News article compares the achievements of both studies and concluded,

“Time will determine which approach succeeds. But the latest advances have buoyed the spirits of researchers who have been frustrated by their inability to generate blood stem cells from iPS cells.”

 

Humans and puffer fish have the same tooth-making stem cells.

Here’s a fun fact for your next blind date: humans and puffer fish share the same genes that are responsible for making teeth. Scientists from the University of Sheffield in England discovered that the stem cells that make teeth in puffer fish are the same stem cells that make the pearly whites in humans. Their work was published in the journal PNAS earlier this week.

Puffer fish. Photo by pingpogz on Flickr.

But if you look at this puffer fish, you’ll see a dramatic difference between its smile and ours – their teeth look more like a beak. Research has shown that the tooth-forming stem cells in puffer fish produce tooth plates that form a beak-like structure, which helps them crush and consume their prey.

So why is this shared evolution between humans and puffer fish important when our teeth look and function so differently? The scientists behind this research believe that studying the pufferfish could unearth answers about tooth loss in humans. The lead author on the study, Dr. Gareth Fraser, concluded in coverage by Phys.org,

“Our study questioned how pufferfish make a beak and now we’ve discovered the stem cells responsible and the genes that govern this process of continuous regeneration. These are also involved in general vertebrate tooth regeneration, including in humans. The fact that all vertebrates regenerate their teeth in the same way with a set of conserved stem cells means that we can use these studies in more obscure fishes to provide clues to how we can address questions of tooth loss in humans.”

Scientists Sink their Teeth into Stem Cell Evolution

/ cirmweb / Leave a comment

Sometimes, answers to biology’s most important questions can be found in the most unexpected of places.

As reported in the most recent issue of the journal Cell Reports, researchers at the University of California, San Francisco (UCSF) and the University of Helsinki describe how studying fossilized rodent teeth has helped them inch closer to grasping the origins of a particular type of stem cell.

Rodents' ever-growing teeth hold clues to the evolution of stem cells, according to a new study.

Rodents’ ever-growing teeth hold clues to the evolution of stem cells, according to a new study.

Understanding the microenvironment that surrounds each stem cell, known as a stem cell niche, is key to grasping the key mechanisms that drive stem cell growth. But as UCSF scientist Ophir Klein explained, many aspects remain a mystery.

“Despite significant recent strides in the field of stem cell biology, the evolutionary mechanisms that give rise to novel stem cell niches remain essentially unexplored,” said Klein, who served as the study’s senior author. “In this study, we have addressed this central question in the fields of evolutionary and developmental biology.”

In this study, Klein and his team focused on the teeth of extinct rodent species. Why? Because many species of rodent—both extinct species and those alive today—have what’s called ‘ever-growing teeth.’

Unlike most mammals, including we humans, the teeth of some rodent species continue to grow as adults—with the help of stem cell ‘reservoir’ hidden inside the root.

And by analyzing the fossilized teeth of extinct rodent species, the researchers could gain some initial insight into how these reservoirs—which were essentially a type of stem cell niche—evolved.

Most stem cell niche studies take cell samples from hair, blood or other live tissue. Teeth, as it turns out, are the only stem cell niches that can be found in fossil form.

In fact, teeth are “the only proxy…for stem cell behavior in the fossil record,” says Klein.

After analyzing more than 3,000 North American rodent fossils that varied in age between 2 and 50 million years ago, the researchers began to notice a trend. The earlier fossils showed short molar teeth. But over the next few million years, the molars began to increase in length. Interestingly, this coincided with the cooling of the climate during the Cenozoic Period. The types of food available in this cooler, drier climate likely became tougher and more abrasive—leading to evolutionary pressures that selected for longer teeth. By 5 million years ago, three-quarters of all species studied had developed the capability for ever-growing teeth.

The team’s models suggest that this trend has little chance of slowing down, and predicts that more than 80% of rodents will adopt the trait of ever-growing teeth.

The next step, says Klein, is to understand the genetic mechanism that is behind the evolutionary change. He and his team, including the study’s first author Vagan Tapaltsyan, will study mice to test the link between the genetics of tooth height and the appearance of stem cell reservoirs.

Stem Cell Stories that Caught our Eye: Lasers Regenerate Dental Tissue, European Commission Rejects Stem Cell Ban

/ cirmweb / Leave a comment

Here are a couple of stem cell stories that caught our eye this past week. Some are groundbreaking science, others are of personal interest to us, and still others are just for fun.

Laser therapy spurs stem cells to repair teeth. Harvard University scientists have, for the first time, used a type of laser trigger to coax stem cells to regenerate dental tissue. As reported this week in the journal Science Translational Medicine, the research team—led by Harvard Bioengineer Dr. David J. Mooney—sets the stage for one day harnessing this therapy to regenerate many types of tissue.

Specifically, Mooney and his team used a low-power laser to trigger dental stem cells to grow into dentin—the layer of tissue encased inside the tooth enamel that makes up the majority of the tooth. Scientists have used a variety of methods to get these stem cells to grow dentin, with limited success. But as Mooney explained in this week’s news release, the team took a different approach:

“Our treatment modality does not introduce anything new to the body, and lasers are routinely used in medicine and dentistry, so the barriers to clinical translation are low.”

These studies were performed first in animal models and then in human dental tissue in a dish. Next, the team plans to start human clinical trials. If their principle proves successful, Mooney is optimistic that this technique could be applied to a variety of cell types.

European Commission Votes No on Stem Cell Ban. In a move hailed by scientists in Europe and around the world, the European Commission has rejected a request by the organization One of Us to ban funding for human embryonic stem cell research.

One of Us filed their petition, which had garnered 1.7 million signatures, with the Commission’s new European Citizens’ Initiative scheme. This scheme was launched to boost participatory democracy throughout the European Union. As a rule, any petition with at least 1 million signatures automatically triggers a parliamentary hearing and formal response from the Commission.

As reported in Nature News, the Commission’s reasoning for rejecting the petition was as follows:

“It said that the EU Council of Member States and the European Parliament had last year debated the issue thoroughly, and no new information was available to warrant a return to the debate so soon. At the time, member states and parliament both agreed that stem-cell research held great promise for currently incurable diseases such as Parkinson’s disease, and it was thus in the public interest to support it. They also agreed that human embryonic stem cells are still sometimes required in such research.”

In fact, support for human embryonic stem cell (hESC) research has been steadily increasing around the world, including back here at home. A Gallup poll published today showed that 65% of Americans support hESC research—a record high.