Since the late 1970s, biologists have known that blood develops in a specific body location. But they’ve wondered why different creatures house their blood stem cells in different places. In humans and other mammals, they’re in the bone. In fish, they’re in the kidney. Why?
Stem cell researchers at Boston Children’s Hospital have, for the first time, profiled a highly elusive kind of stem cell in the early embryo – a cell so fleeting that it makes its entrance and exit within a 12-hour span. They describe this “poised pluripotent” cell in the journal Cell Stem Cell.
In mice, poised cells appear 4.75 to 5.25 days after egg and sperm join to form the embryo, right at the time when the embryo stops floating around and implants itself in the uterine wall.
“People have had a hard time capturing the peri-implantation period because it’s really hard to define,” says Richard Gregory, PhD, who led the research. “It’s a very dynamic stage. Everything happens within a few hours, which is quite remarkable considering the extent of the changes occurring in the properties of the cells.” …
The small intestine is much more than a digestive organ. It’s a major home to our microbiome, it’s a key site where mucosal immunity develops and it provides a protective barrier against a variety of infections. Animal models don’t do justice to the human intestine in all its complexity.
Attempts to better model human intestinal function began with intestinal “organoids,” created from intestinal stem cells. The cells, from human biopsy samples, form hollowed balls or “mini-intestines” bearing all the cell types of the intestinal lining, or epithelium. Recently, intestinal organoids helped reveal how Clostridium difficile causes such devastating gastrointestinal infections.
But while organoids have all the right cells, they don’t fully replicate the environment of a real small intestine. Real intestines are awash in bacteria and nutrients, are fed by blood vessels and are stretched and compressed by peristalsis, the intestines’ cyclical muscular contractions that push nutrients forward.
Hematopoietic stem cells (HSCs) have long been regarded as the granddaddy of all blood cells. After we’re born, these multipotent cells give rise to all our cell lineages: lymphoid, myeloid and erythroid cells. Hematologists have long focused on capturing HSCs’ emergence in the embryo, hoping to recreate the process in the lab to provide a source of therapeutic blood cells.
But in the embryo, oddly enough, blood development unfolds differently. The first blood cells to show up are already partly differentiated. These so-called “committed progenitors” give rise only to erythroid and myeloid cells — not lymphoid cells like the immune system’s B and T lymphocytes.
Researchers in the lab of George Q. Daley, MD, PhD, part of Boston Children’s Hospital’s Stem Cell Research program, wanted to know why. Does nature deliberately suppress blood cell multipotency in early embryonic development? And could this offer clues about how to reinstate multipotency and more readily generate different blood cell types? …
Surgeons at Boston Children’s Hospital have long sought a better solution for long-gap esophageal atresia, a rare birth defect in which part of the esophagus is missing. The current state-of-the art operation, called the Foker process, uses sutures anchored to children’s backs to gradually pull the unjoined ends of esophagus until they’re long enough to be stitched together. To keep the esophagus from tearing, children must be paralyzed in a medically induced coma, on mechanical ventilation, for one to four weeks. The lengthy ICU care means high costs, and the long period of immobilization can cause complications like bone fractures and blood clots.
Now, a Boston Children’s Hospital team has created an implantable robot that could lengthen the esophagus — and potentially other tubular organs like the intestine — while the child remains awake and mobile. As described today in Science Robotics, the device is attached only to the tissue being lengthened, so wouldn’t impede a child’s movement. …
Genetic labels, or “barcodes,” are shedding new light on the natural process of blood development and immune-cell production, finds a study published in Nature this week. It was led by Fernando Camargo, PhD, and first author Alejo Rodriguez Fraticelli, PhD, at Boston Children’s Hospital’s Stem Cell Research Program, the Harvard Department of Stem Cell and Regenerative Biology and the Harvard Stem Cell Institute.
Most of what we know about blood production is through observing what happens when blood stem and progenitor cells are transplanted into an animal. To observe what happens “in the wild,” researchers went in and tagged the blood stem and progenitor cells of mice, using genetic elements called transposons. This allowed them to track how the cells differentiated into five kinds of blood cells (above: megakaryocytes, erythroid cells, granulocytes, monocytes and B-cell progenitors). …
The amniotic fluid surrounding babies in the womb contains fetal mesenchymal stem cells (MSCs) that can differentiate into many cell types and tissues. More than a decade ago, Dario Fauza, MD, PhD, a surgeon and researcher at Boston Children’s Hospital, proposed using these cells therapeutically. His lab has been exploring these cells’ healing properties ever since.
Replicated in great quantity in the lab and then reinfused into the amniotic fluid in animal models — a reverse amniocentesis if you will — MSCs derived from amniotic fluid have been shown to repair or mitigate congenital defects before birth. In spina bifida, they have induced skin to grow over the exposed spinal cord; in gastroschisis, they have reduced damage to the exposed bowel. Fauza calls this approach Trans-Amniotic Stem Cell Therapy, or TRASCET.
To stay healthy, our lungs have to maintain two key populations of cells: the alveolar epithelial cells, which make up the little sacs where gas exchange takes place, and bronchiolar epithelial cells (also known as airway cells) that are lined with smooth muscle.
Neuron cells have long finger-like structures, called axons, that extend outward to conduct impulses and transmit information to other neurons and muscle fibers. After spinal cord injury or stroke, axons originating in the brain’s cortex and along the spinal cord become damaged, disrupting motor skills. Now, reported today in Neuron, a team of scientists at Boston Children’s Hospital has developed a method to promote axon regrowth after injury. …
Getting a damaged optic nerve to regenerate is vital to restoring vision in people blinded through nerve trauma or disease. A variety of growth-promoting factors have been shown to help the optic nerve’s retinal ganglion cells regenerate their axons, but we are still far from restoring vision. A new study published yesterday in Neuron underscores the complexity of the problem.
A research team led by Fengfeng Bei, PhD, of Brigham and Women’s Hospital, Zhigang He, PhD, and Michael Norsworthy, PhD, of Boston Children’s Hospital, and Giovanni Coppola, MD, of UCLA conducted a screen for transcription factors that regulate the early differentiation of RGCs, when axon growth is initiated. While one factor, SOX11, appeared to be critical in helping certain kinds of RGCs regenerate their axons, it simultaneously killed another type — alpha-RGCS (above)— when tested in a mouse model.
At least 30 types of retinal ganglion cell message the brain via the optic nerve. “The goal will be to regenerate as many subtypes of neurons as possible,” says Bei. “Our results here suggest that different subtypes of neurons may respond differently to the same factors.”