To the eye, nervous systems look like a tangled mess of neurons and their tree-like branches known as dendrites, but it’s really organized chaos. How the system finds order has intrigued but eluded scientists. In the worm C. elegans, Max Heiman, PhD and graduate student Candice Yip found an elegant system to help explain how neurons each maintain their own space.
Normally, worms have just one neuron of a certain type on either side of their bodies. Yip did a “forward genetic screen” — mutating genes at random to find factors important for neuron wiring. One mutation caused the worm to grow not one set of neurons but five. By engineering the neurons to make a color-changing signal — as shown above — Yip showed that these extra neurons didn’t overlap with each other, but instead carved out discrete territories — a phenomenon known as tiling. How?
Acting on a hunch, Yip and Heiman, of Harvard Medical School and Boston Children’s Hospital’s Division of Genetics and Genomics, showed that C. elegans, faced with an increase in neurons, pressed a molecule called netrin into service to enforce boundaries between them. Netrin is better known for helping nerve fibers navigate to their destinations. When Yip took netrin out of action, the dendrites from the five neurons crossed the invisible borders and grew entangled.
The findings, published today in Cell Reports, could provide insight into neuropsychiatric diseases, believes Heiman, also part of Boston Children’s F.M. Kirby Neurobiology Center. “It’s fundamental to neuropsychiatric disease to make sure brain wiring goes right,” he says. “This is also story about how new features evolve, and how you can form something as complicated as a nervous system. There are pathways that bring everything into order.”
Nine-year-old Haley Hilt has had intractable seizures all her life. Though she cannot speak, she communicates volumes with her eyes. Using a tablet she controls with her gaze, she can tell her parents when her head hurts and has shown that she knows her letters, numbers and shapes.
Haley is one of a growing group of children who are advancing the science around CDKL5 epilepsy, Haley’s newly recognized genetic disorder. When Boston Children’s Hospital geneticist Joan Stoler, MD, diagnosed Haley in 2009, there were perhaps 100 cases known in the world; today, there are estimated to be a few thousand. Haley’s neurologist, Heather Olson, MD, leads a CDKL5 Center of Excellence at the hospital that is bringing the condition into better view. …
A deep genetic analysis, involving nearly 65,000 people, finds a surprising risk factor for schizophrenia: variation in an immune molecule best known for its role in containing infection, known as complement component 4 or C4.
The findings, published this week in Nature, also support the emerging idea that schizophrenia is a disease of synaptic pruning, and could lead to much-needed new approaches to this elusive, devastating illness. …
When Zhigang He, PhD, started a lab at Boston Children’s Hospital 15 years ago, he hoped to find a way to regenerate nerve fibers in people with spinal cord injury. As a proxy, he studied optic nerve injury, which causes blindness in glaucoma — a condition affecting more than four million Americans — and sometimes in head trauma.
By experimenting with different growth-promoting genes and blocking natural growth inhibitors, he was able to get optic nerve fibers, or axons, to grow to greater and greater lengths in mice. But what about vision? Could the animals see? …
As far back as she can remember, neuroscientist Beth Stevens, PhD, of the Boston Children’s Hospital Department of Neurology and the F.M. Kirby Neurobiology Center, has loved science. The concept of a career in the field began to take root in high school, nurtured in part by her biology teacher — a scientist on the side — who was both encouraging and inspiring.
Today, Stevens, winner of the 2015 MacArthur “genius” grant for her groundbreaking research on microglia cells, is doing her part to inspire a new generation of scientists and show them, as she says, “Scientists aren’t just nerdy guys in white coats.”
Hover over the objects in Stevens’s office to learn more about her work, life and innovations, and read more about her science.
When 2015 MacArthur “genius” grant winner Beth Stevens, PhD, began studying the role of glia in the brain in the 1990s, these cells—“glue” from the Greek—weren’t given much thought. Traditionally, glia were thought to merely protect and support neurons, the brain’s real players.
But Stevens, from the Department of Neurology and the F.M. Kirby Neurobiology Center at Boston Children’s Hospital, has made the case that glia are key actors in the brain, not just caretakers. Her work—at the interface between the nervous and immune systems—is helping transform how neurologic disorders like autism, amyotrophic lateral sclerosis (ALS), Alzheimer’s disease and schizophrenia are viewed. …
Nerve regeneration. From Santiago Ramón y Cajal’s “Estudios sobre la degeneración y regeneración del sistema nervioso” (1913-14). Via Scholarpedia.
First in a two-part series on nerve regeneration. Read part 2.
Researchers have tried for a century to get injured nerves in the brain and spinal cord to regenerate. Various combinations of growth-promoting and growth-inhibiting molecules have been found helpful, but results have often been hard to replicate. There have been some notable glimmers of hope in recent years, but the goal of regenerating a nerve fiber enough to wire up properly in the brain and actually function again has been largely elusive.
“The majority of axons still cannot regenerate,” says Zhigang He, PhD, a member of the F.M. Kirby Neurobiology Center at Boston Children’s Hospital. “This suggests we need to find additional molecules, additional mechanisms.”
Microarray analyses—which show what genes are transcribed (turned on) in injured nerves—have helped to some extent, but the plentiful leads they turn up are hard to analyze and often don’t pan out. The problem, says Judith Steen, PhD, who runs a proteomics lab at the Kirby Center, is that even when the genes are transcribed, the cell may not actually build the proteins they encode.
That’s where proteomics comes in. “By measuring proteins, you get a more direct, downstream readout of the system,” Steen says. …
Ending a 30-year search by scientists, researchers have identified two proteins in the inner ear that are critical for hearing, which, when damaged by genetic mutations, cause a form of delayed, progressive hearing loss.
The proteins are essentially transducers: They form channels that convert mechanical sound waves entering the inner ear into electrical signals that talk to the brain. Corresponding channels for each of the other senses were identified years ago, but the sensory transduction channel for both hearing and the sense of balance had been unknown.
The channels are the product of two related genes known as TMC1 and TMC2. TMC1 mutations were first reported in people with a prominent form of hereditary deafness back in 2002 by Andrew Griffith, MD, PhD, of the National Institute on Deafness and Other Communication Disorders (NIDCD) and collaborators. Children with recessive mutations in TMC1 are completely deaf at birth. …