Scientists at the Stowers Institute for Medical Research have reported a detailed description of how function-impairing mutations in polr1c and polr1d genes cause Treacher Collins syndrome (TCS), a rare congenital craniofacial development disorder that affects an estimated 1 in 50,000 live births.
Collectively the results of the study reveal that a unifying cellular and biochemical mechanism underlies the etiology and pathogenesis of TCS and its possible prevention, irrespective of the causative gene mutation.

Loss-of-function mutations in three human genes, TCOF1, POLR1C and POLR1D, have been implicated in TCS and are thought to be responsible for about 90 percent of the diagnoses of this congenital craniofacial condition.
The clinical manifestations of TCS include facial anomalies such as small jaws and cleft palate, hearing loss, and respiratory problems. Patients with TCS typically undergo multiple surgeries, but rarely are they fully corrective. By uncovering a mechanism of action common to all three genes, Stowers scientists have advanced scientific understanding of TCS etiology and pathogenesis and identified possible new avenues for preventing or treating the birth defect. This latest study from the laboratory of Stowers Investigator Paul Trainor, Ph.D., focused on Polr1c and Polr1d, whose roles as a genetic cause of TCS were revealed in a 2011 study of a small group of patients who had been diagnosed with TCS but who did not have the TCOF1 mutation. Unlike POLR1C and POLR1D, TCOF1 has been long recognized as a causative gene in TCS and as a result has been more extensively investigated.
“Before we began the study, nothing was known about the role of Polr1c and Polr1d in craniofacial development,” said Kristin Watt, Ph.D., lead author of the PLoS Genetics paper and postdoctoral scientist in the Trainor Lab. “Using zebrafish as our animal model, we set out to explore the functional roles of polr1c and polr1d during embryogenesis and more specifically in craniofacial development.”
Trainor, Watt and their collaborators compared the results of their findings on polr1c and polr1d with their and other labs’ previous research results on Tcof1. In all three loss-of-function models, the researchers found that the chain of cellular events that led to the TCS phenotype of abnormal craniofacial development originated in ribosomes, the cellular components that translate messenger RNA into proteins. Like the Tcof1 gene, polr1c and polr1d mutations were found to perturb ribosome biogenesis, or production of ribosomes, which affects the generation and survival of progenitor neural crest cells, the precursors of craniofacial bone, cartilage and connective tissue.
In animal models of all three causative genes, the scientists determined that deficient ribosome biogenesis triggered a p53-dependent cell death mechanism in progenitor neural crest cells. As a result of the activation of the p53 gene, developing embryos no longer made the quantity of neural crest cells needed to properly form the craniofacial skeleton.
However, in the polr1c and polr1d models as in the Tcof1 models, Stowers scientists found that by experimentally blocking p53 activation, they could restore the neural crest cell population and thereby rescue the animal models’ cranioskeletal cartilage.
Despite the rescue effect, Trainor said that he does not view the “guardian of the genome,” as the p53 gene is often called due to its ability to suppress cancer, as the basis of a potential therapy to prevent or reduce TCS during embryonic development. The p53 gene’s association with cancer makes inhibiting its function too risky, he said.
A less risky and perhaps more effective target for the prevention or treatment of TCS could be enhancing ribosomes, Trainor said, because the loss-of-function mutations in all three causative genes involve ribosome RNA (rRNA) transcription. Polr1c and Polr1d, for example, are subunits of RNA polymerases I and III that are essential for ribosome biogenesis.
“Rather than blocking p53, a better approach may be to try to prevent TCS by treating the problem in ribosome biogenesis that triggers the activation of p53 and the loss of neural crest cells,” said Trainor.
In their research with zebrafish embryos, Trainor and collaborators also determined that polr1c and polr1d are spatiotemporally and dynamically expressed, particularly during craniofacial development. Furthermore, zebrafish embryos with the polr1c and polr1d loss-of-function mutations develop abnormalities in craniofacial cartilage development that mimic the clinical manifestations of TCS in patients. Trainor said that he and his fellow researchers were surprised that mutations in polr1c and polr1d as well as Tcof1 specifically affected craniofacial development, because ribosome biogenesis occurs in every cell of the body. The mutation of a gene that is part of the ribosome complex would be expected to be detrimental to each of these cells, he said. However, in the zebrafish models, the mutation appears to primarily affect progenitor neural crest cells. Trainor said that he and his team theorize that progenitor neural crest cells may be particularly sensitive to deficiencies in ribosome biogenesis during embryogenesis.
Thus, the study revealed new animal models for TCS: zebrafish with polr1c and polr1d loss-of-function mutations. Moreover, the existence of a common mechanism of action may simplify the research, particularly the search for a therapy to prevent or treat TCS. Because of the similarities among the three causative genes, “we may be able to develop creative ways of preventing TCS that will prove effective in at-risk individuals who have one of the gene mutations,” said Trainor, who has investigated the molecular origins and development of TCS and related craniofacial developmental disorders for 10 years.

Stowers Institute for Medical Research www.stowers.org/media/news/jul-22-2016

A strong association between a genetic mutation and a rare kind of heart muscle disease has been discovered by researchers at the University of Colorado Anschutz Medical Campus.

“There are many kinds of cardiomyopathies that can lead to heart failure so this is a serious problem,” said Teisha J. Rowland, PhD, a post-doctoral fellow in the lab of Luisa Mestroni, MD, and Matthew R. G. Taylor, MD, PhD, at the University of Colorado School of Medicine and first author of the study.

The Mestroni and Taylor lab sequenced nearly 5,000 genes in 335 patients with a family history of heart muscle disease, looking for mutations that could cause a variety of cardiomyopathies.

“Many kinds of heart disease are caused by genetics. When that happens, the disease is often more severe and happens at an earlier age,” said Rowland, who studies genetics and cardiology. “So we look at the DNA in entire families to see what sort of genetic variants those with the illness have in common.”

They found that several people with left ventricular noncompaction (LVNC) had a mutation in a gene called Obscurin. Obscurin is part of the sarcomere, the basic unit of striated muscles that pull and glide past each other when muscles contract.  That includes the heart muscle. If there is a mutation in Obscurin that process may not function properly.

 “We found a strong association between this gene, which has not been studied much, and this rare form of genetic heart disease,” Rowland said. “Left ventricular noncompaction is thought to happen during early human development. It would be interesting to see if mutated Obscurin affects heart formation during development.”

Rowland said the findings point to areas warranting further attention.

“We expect this will ultimately improve our understanding of the disease,” she said.

University of Colorado www.cuanschutztoday.org/researchers-find-association-gene-mutation-rare-heart-disease/

A small stretch of ribonucleic acid called microRNA could make the difference between a healthy adult brain and one that’s prone to disorders including schizophrenia.

Scientists at the Salk Institute discovered that miR-19 guides the placement of new neurons in the adult brain, and the molecule is disrupted in cells from patients with schizophrenia. The findings pave the way toward a better understanding of how the adult brain controls the growth of new neurons and how it can go wrong.

“This is one of the first links between an individual microRNA and a specific process in the brain or a brain disorder,” says senior author Rusty Gage, professor in Salk’s Laboratory of Genetics and holder of the Vi and John Adler Chair for Research on Age-Related Neurodegenerative Disease.

While most RNA molecules contain the instructions for making proteins—the physical workhorses of cells—microRNAs don’t encode proteins. Instead, they’re active themselves, binding to other strands of RNA to block them from creating proteins. Previously, scientists have shown that levels of microRNA molecules are altered in brain disorders but not which microRNAs are responsible.

“People have broadly studied microRNAs in the brain quite a bit,” says Jinju Han, a senior research associate at Salk and first author of the new paper. “But there are more than 2,000 microRNAs and only a few have been looked at in any depth.”

In a few discrete areas of the human brain, new cells can emerge during adulthood. Gage, Han and their colleagues found that levels of miR-19 changed more than levels of any other microRNA when precursors to new brain cells in these areas (called neural progenitor cells) were coaxed to become neurons in the adult brain.

“The microRNA miR-19 has been implicated in cancer and people never thought it was related to the brain,” says Han. “But we saw that its levels changed quite dramatically when stem cells differentiated into neurons.”

The researchers went on to show that when miR-19 was blocked in neural progenitor cells, levels of RNA corresponding to a gene called Rapgef2 were altered. Moreover, new neurons did not migrate to the correct areas of the brain.

Because the incorrect migration of new brain cells has been implicated in neuropsychiatric disorders like schizophrenia, Gage’s group next analysed the levels of miR-19 and Rapgef2 in neural progenitor cells that had been created by reprogramming skin cells from schizophrenic patients. Although the patients had no mutations in the gene for Rapgef2, they had high levels of miR-19 that corresponded with low levels of both the RNA and protein for Rapgef2. The team is now studying the role of miR-19 in mouse models of schizophrenia, as well as looking at cells from broader cohorts of human patients.

Because miR-19 has been linked to cancers—including breast cancer, prostate cancer and B cell lymphoma—researchers have already been working to develop drugs that block the molecule. But the new results, Han says, suggest that such drugs could have an effect on the brain. “This means that if miR-19 is being targeted in cancer, effects on the brain need to be carefully considered,” she says. “But it also means that people might use these therapies to treat neuropsychiatric disorders.” More work is needed, though, to see whether the results hold true in humans.

Salk Institute www.salk.edu/news-release/small-molecule-keeps-new-adult-neurons-from-straying-may-be-tied-to-schizophrenia/

A research team at the Krembil Research Institute has discovered a pair of tissue biomarkers that directly contribute to the harmful joint degeneration associated with spine osteoarthritis.

The study is the first to show that elevated levels of both of these biomarkers cause inflammation, cartilage destruction and collagen depletion.

‘These biomarkers are actively involved in increasing inflammation and destructive activities in spine cartilage and assist in its destruction,’ says principal investigator Dr. Mohit Kapoor, Senior Scientist at the Krembil Research Institute and Associate Professor in the Department of Surgery and the Department of Laboratory Medicine and Pathobiology at the University of Toronto. Dr. Kapoor specializes in arthritis research.

Osteoarthritis affects about three million Canadians and is characterized by a breakdown of the protective cartilage found in the body’s spine, hand, knee and hip joints. There is no known cure.

The study involved tissue biopsies from 55 patients undergoing decompression or discectomy at the Krembil Neuroscience Centre at Toronto Western Hospital. As part of the study, the research team – led by Dr. Kapoor and comprising Dr. Akihiro Nakamura, a post-doctoral fellow, and Dr. Y. Raja Rampersaud, a clinical expert and spine surgeon – explored the role, function and signaling mechanisms of two tissue biomarkers: microRNA-181a-5p and microRNA-4454.

The study screened 2,100 microRNAs and found that measuring the levels of these two specific biomarkers can help clinicians determine the stage to which the disease has progressed, and provide a tool for determining the degree of cartilage destruction.

‘These are biologically active molecules. By detecting them in the tissue biopsies, we have a tool for determining the stage of spine osteoarthritis,’ says Dr. Kapoor. ‘What is really significant, however, is we have discovered that these biomarkers are actively involved in destroying cartilage and increasing inflammation. Furthermore, they promote cartilage cells to die and deplete the most important component of your cartilage, which is your collagen.’

The discovery represents the end of the first stage of research. The team is now investigating whether these biomarkers can be detected in the blood – which would help clinicians more simply determine the stage of spine osteoarthritis – and whether further studying the biomarkers will allow researchers to halt and reverse spine degeneration.

‘The most critical aspect of this discovery is that we have found that they are active. Now that we know what they are, we are currently looking at blocking them and restoring the joint,’ says Dr. Kapoor.

Krembil Research Institute www.uhn.ca/corporate/News/PressReleases/Pages/research_team_discovers_two_biomarkers_that_contribute_to_spine_osteoarthritis.aspx