Scientists Find Single Molecule that Controls Fate of Mature Sensory Neurons

In the neocortex, neighboring cells are shown making connections to the visual cortex (red) and the somatosensory cortex (green). Image: Salk Institute for Biological Studies

Molecular Neuroscience May 12, 2015

La Jolla, CA (Scicasts) — Scientists at the Salk Institute have discovered that the role of neurons—which are responsible for specific tasks in the brain—is much more flexible than previously believed.

By studying sensory neurons in mice, the Salk team found that the malfunction of a single molecule can prompt the neuron to make an “early-career” switch, changing a neuron originally destined to process sound or touch, for example, to instead process vision.

The finding, reported May 11, 2015 in PNAS, will help neuroscientists better understand how brain architecture is molecularly encoded and how it can become miswired. It may also point to ways to prevent or treat human disorders (such as autism) that feature substantial brain structure abnormalities.

“We found an unexpected mechanism that provides surprising brain plasticity in maturing sensory neurons,” says the study’s first author, Andreas Zembrzycki, a senior research associate at the Salk Institute.

The mechanism, a transcription factor called Lhx2 that was inactivated in neurons, can be used to switch genes on or off to change the function of a sensory neuron in mice. It has been known that Lhx2 is present in many cell types other than in the brain and is needed by a developing foetus to build body parts. Without Lhx2, animals typically die in utero. However, it was not well known that Lhx2 also affects cells after birth.

“This process happens while the neuron matures and no longer divides. We did not understand before this study that relatively mature neurons could be reprogrammed in this way,” says senior author Dennis O’Leary, Salk professor and holder of the Vincent J. Coates Chair in Molecular Neurobiology. “This finding opens up a new understanding about how brain architecture is established and a potential therapeutic approach to altering that blueprint.”

Scientists had believed that programming neurons was a one-step process. They thought that the stem cells that generate the neurons also programmed their functions once they matured. While this is true, the Salk team found that another step is needed: the Lhx2 transcription factor in mature neurons then ultimately controls the fate of the neuron.

In the mouse study, the scientists manipulated Lhx2 to make the switch in neuronal fate shortly after birth (when the mouse neurons are fully formed and considered mature). The team observed that controlling Lhx2 let them instruct neurons situated in one sensory area to process a different sense, thus enlarging one region at the expense of the other. The scientists don’t know yet if targeting Lhx2 would allow neurons to change their function throughout an organism’s life.

“This study provides proof that the brain is very plastic and that it responds to both genetic and epigenetic influences well after birth,” says O’Leary. “Clinical applications for brain disorders are a long way away, but we now have a new way to think about them.”

“Since this study was conducted in mice, we don’t know the time frame in which Lhx2 would be operating in humans, but we know that post-birth, neurons in a baby’s brain still have not settled into their final position—they are still being wired up. That could take years,” Zembrzycki says.

However, the findings may be an ingredient that contributes to the success of early intervention in some very young children diagnosed with autism, adds Zembrzycki. “The brain’s wiring is determined genetically as well as influenced epigenetically by environmental influences and early intervention preventing brain miswiring may be an example of converging genetic and epigenetic mechanisms that are controlled by Lhx2.”

Article adapted from a Salk Institute for Biological Studies news release.

Publication: Postmitotic regulation of sensory area patterning in the mammalian neocortex by Lhx2. Andreas Zembrzycki, Carlos G. Perez-Garcia, Chia-Fang Wang, Shen-Ju Chou, Dennis D.M. O’Leary. PNAS (2015):
http://www.pnas.org/content/early/2015/05/12/1424440112

ORIGINAL: SciCasts

New mitochondrial DNA editing technique prevents genetic diseases in mice

Image: Wire_man/Shutterstock

And it could prevent the transmission of incurable diseases from mother to child.

A new technique to edit mitochondrial DNA has been tested on mice, and if replicable in humans, could help prevent mothers living with certain incurable disease from passing them onto their children, researchers say.

Mitochondria are tiny powerhouses found inside nearly all human cells, and are responsible for generating the chemical energy that allows our cells to perform many essential functions. For example, this energy enables communication between brain cells, and it allows our muscle cells to keep us moving around.

However, defects in these cellular components, which have their own DNA, can lead to a range of incurable conditions, known collectively as mitochondrial diseases. 

While the diseases present differently in each individual, they can generally be characterised by symptoms such as poor muscle development and weakness; hearing, vision and other neurological impairments; learning disabilities; and heart, liver, gastrointestinal and respiratory diseases.

For thousands of women around the world living with one of these incurable diseases, having children is a gamble, as it's likely their defective mitochondrial DNA will be passed on.

Now, researchers at the Salk Institute for Biological Studies in the US have developed a technique to eliminate mitochondrial mutations from eggs or early embryos, while leaving the healthy mitochondria intact.

The proof-of-concept demonstration, which has been described in the journal Cell, could help prevent children from inheriting these chronic diseases.

The researchers used to two different enzymes - or nucleases - inside cells, which can be engineered to cut specific strands of nucleic acid, functioning kind of like 'molecular scissors'. 

As Smitha Mundasad from the BBC reports, the team tested the "molecular scissors on mice with two different types of mitochondrial DNA (mtDNA). They were able to recognise and cut out disease-causing mtDNA in mouse embryos."

The mice offspring were born healthy and developed naturally into adulthood without any diseases, the researchers say.

"We might not be able to eliminate 100 percent of the mutated copies of mitochondrial DNA," said lead author Pradeep Reddy in a press release. "But you don't need to eliminate all of the mutated copies: just reducing the percentage significantly enough can prevent the disease in the next generation."

The team also successfully demonstrated their technique on defective human mitochondrial DNA, which had been inserted into mouse eggs.

Stem cell scientist Duscko Ilic from King's College London in the UK, who was not involved in the research, told the BBC that the group's method for correcting mitochondrial defects was a "technical masterpiece" but said it was unlikely to make it to clinical trials in near future.

"Replacing faulty genes in human pre-implantation embryos, germ cells or gametes poses serious risks," Ilic said.

Another independent expert, geneticist Frances Flinter from Guy's and St Thomas' Hospital in the UK, told the BBC: "The biggest question to address will be the possibility that DNA cutting enzymes may disrupt adjacent genes that are important, leading to unintended adverse consequences." 

While the results seen in mice are promising, there's obviously a long way to go before this technology can be used to help humans. And the route to clinical trials might become increasingly murky given the concerns over gene editing, which have resurfaced in a big way after Chinese scientists admitted to tweaking the genes of human embryos. 

Source: BBC

Via: Science Alert

By MYLES GOUGH

27 APR 2015

Physicists, biologists unite to expose how cancer spreads

ORIGINAL: Princeton
by Catherine Zandonella

April 26, 2013; 01:00 p.m.

Cancer cells that can break out of a tumor and invade other organs are more aggressive and nimble than nonmalignant cells, according to a new multi-institutional nationwide study. These cells exert greater force on their environment and can more easily maneuver small spaces.

The researchers report in the journal Scientific Reports that a systematic comparison of metastatic breast-cancer cells to healthy breast cells revealed dramatic differences between the two cell lines in their mechanics, migration, oxygen response, protein production and ability to stick to surfaces. The researchers discovered new insights into how cells make the transition from nonmalignant to metastatic, a process that is not well understood.

The resulting catalogue of differences could someday help researchers detect cancerous cells earlier and someday prevent or treat metastatic cancer, which is responsible for 90 percent of all cancer deaths, according to the study. It was conducted by a network of 12 federally funded Physical Sciences-Oncology Centers (PS-OC) sponsored by the National Cancer Institute. PS-OC is a collaboration of researchers in the physical and biological sciences seeking a better understanding of the physical and chemical forces that shape the emergence and behavior of cancer.

(Image by Guillaume Lambert)

A multi-institutional study including researchers from Princeton University's Physical Sciences-Oncology Center found that metastatic cancer cells are more aggressive and nimble than nonmalignant cells. The Princeton group used silicon-etched microchannels (above) to study the behavior and physical properties of cancer cells. In this device, metastatic cancer cells enter the narrow channels at one end and accelerate as they rapidly move down the channel. Such high motility is a hallmark of metastasis and also indicative of high glucose metabolism, another hallmark of cancer.

"By bringing together different types of experimental expertise to systematically compare metastatic and nonmetastatic cells, we have advanced our knowledge of how metastasis occurs," said Robert Austin, professor of physics and leader of the Princeton PS-OC, along with senior co-investigator Thea Tlsty of the University of California-San Francisco.

Researchers with the Princeton PS-OC, for instance, determined that metastatic cells, in spite of moving more slowly than nonmalignant cells, move farther and in a straighter line, Austin said. The investigators studied the cells' behavior in tiny cell-sized chambers and channels etched out of silicon and designed to mimic the natural environment of the body's interior.

"The mobility of these metastatic cells is an essential feature of their ability to break through the tough membrane [the extracellular matrix] that the body uses to wall off the tumor from the rest of the body," Austin said. "These cells are essentially jail-breakers."

The tiny silicon chambers were built using Princeton's expertise in microfabrication technology — typically used to create small technologies such as integrated circuits and solar cells — and are an example of the type of expertise that physicists and engineers can bring to cancer research, Austin said. For the current study, the Princeton team included physics graduate students David Liao and Guillaume Lambert, and postdoctoral researchers Liyu Liu and Saurabh Vyawahare. They worked closely with a research group led by James Sturm, Princeton's William and Edna Macaleer Professor of Engineering and Applied Science and director of the Princeton Institute for the Science and Technology of Materials (PRISM) where the microfabrication was done.

The Princeton PS-OC also includes collaborators at the Johns Hopkins University School of Medicine, the Salk Institute for Biological Studies and the University of California-Santa Cruz.

The nationwide PS-OC program aims to crack the difficulty of understanding and treating cancer by bringing in researchers from physics, engineering, computer science and chemistry, said Nastaran Zahir Kuhn, program manager for the PS-OC at the National Cancer Institute.

Other notable findings from the paper include that metastatic cells recover more rapidly from the stress of a low-oxygen environment than nonmetastatic cells, which is consistent with previous studies. Although the low-oxygen environment did kill many of the metastatic cells, the survivors rebounded vigorously, underscoring the likely role of individual cells in the spread of cancer. The study also looked at total protein production and detected proteins in the metastatic cells that are consistent with the physical properties such as mobility that malignant cells need to invade the extracellular matrix.

"The PS-OC program aims to bring physical sciences tools and perspectives into cancer research," Kuhn said. "The results of this study demonstrate the utility of such an approach, particularly when studies are conducted in a standardized manner from the beginning."

For the nationwide project, nearly 100 investigators from 20 institutions and laboratories conducted their experiments using the same two cell lines, reagents and protocols to assure that results could be compared. The experimental methods ranged from physical measurements of how the cells push on surrounding cells to measurements of gene and protein expression.

"Roughly 20 techniques were used to study the cell lines, enabling identification of a number of unique relationships between observations," Kuhn said.

For example, a technique known as atomic force microscopy indicated that metastatic cells are softer than nonmalignant cells whereas a different technique, traction force microscopy, suggested that metastatic cells exert more force on their surroundings, Kuhn said. Together these two findings may indicate that metastatic cells can exert force to stick to, migrate on and remodel the tough extracellular matrix that surrounds the tumor, while remaining flexible enough to squeeze through small spaces in that membrane.