Neurobiology > Laboratory Projects
Northcott Neuroscience Laboratory Projects
Gene Discovery and Animal Models of Inherited Peripheral Neuropathies
M Kennerson, M Brewer, A Cutrupi, G Perez-Siles, M Ellis, C Ly, G Nicholson
Inherited peripheral neuropathies (IPN) are one of the most common hereditary disorders affecting 1 in 3000 people. There are many types of IPN and the disorder is classified based on the involvement of the motor and/or sensory nerves. The neuropathies can include hereditary sensory neuropathy (HSN), hereditary motor neuropathy (HMN) and hereditary motor and sensory neuropathy (HMSN) also known at Charcot-Marie-Tooth (CMT) neuropathy.
Charcot-Marie-Tooth (CMT) neuropathy is the most common group of the IPNs. The syndrome affects both the motor and sensory neurons. CMT is a disabling disorder that afflicts 8800 Australians for their lifetime. It, therefore, has major economic impacts in terms of productive years lost and the requirement for medical, paramedical and pension support. Motor and sensory neurons represent a unique cell type with long axons (up to 1 metre) that require continuous maintenance from the cell body to the nerve endings. The breakdown of this maintenance leads to the dying back of nerve ends going to the extremities of the body and patients suffer gradual muscle weakness in the arms and legs as well as some loss of sensory nerve function.
Animation by Michael Chu.
Identifying CMT Genes Using Family Studies
Our CMT research team at the Northcott Neuroscience Laboratory, ANZAC Research Institute has been recruiting CMT, HSN and HMN families over 20 years. Through our association with the Neurogenetics Clinic at Concord Hospital and as the primary Australian centre for DNA testing of inherited peripheral neuropathies we have over 700 families documented in one of the largest IPN databases in the world.
Our research group has expertise in genetic linkage studies and using state of the art genome technologies for gene discovery. The overall aim of our research is to discover new genes causing CMT and to understand the underlying pathogenic biology causing the demise of the motor and sensory nerves in CMT families that do not have mutations in the known genes. By understanding the disease mechanisms this may lead to the development of treatments and therapeutic intervention for CMT. Many of our gene discoveries have been developed and implemented for diagnostic testing.
Our team is actively recruiting new families and individuals to participate in our family studies. For further information in participating in our research, please contact Khim Perkins on (02) 9767 6796 or email mailto:email@example.com
The projects below showcase our current research to identify new genes and develop cell and animal models for CMT.
Discovering CMT Genes Using Next Generation Sequencing
M Kennerson, M Brewer, A Cutrupi, A Drew, G Perez-Siles, M Ellis, C Ly, G Nicholson
Whole-exome sequencing (WES) is a new approach which utilises the power of next generation sequencing to identify very rare variants in approximately 1% of our DNA that codes for proteins. This strategy of gene mutation identification is very useful for families with CMT as many of the mutations identified in genes causing CMT have occurred in the protein coding portion of the DNA. With this technology we have the ability to sequence over 20,000 genes in a single sequencing experiment. By sequencing key individuals in small nuclear families we can identify all the possible DNA changes in genes for these individuals and then determine which variant is the disease-causing mutation. With NHMRC funding we used this technology to identify and validate the PDK3 gene (Kennerson …. Nicholson 2013) and MORC2 genes (Albulym, Kennerson …. Nicholson 2016) respectively. In collaboration with colleagues at the University of Malaya (Dr Azlina Ahmad Annuar and Dr Nortina Shahrizaila) we are using a combination of gene mapping and WES to identify a new recessive CMT gene.
Structural variation and gene dysregulation is a new disease mechanism for inherited peripheral neuropathies
M Brewer, A Cutrupi, A Drew, G Nicholson, M Kennerson
Although over 80 genes with coding mutations causing IPNs have been found, up to 50% of families remain unsolved after whole exome sequencing. As no mutations can be found in the coding DNA of these unsolved families, they are likely due to point mutations in non-coding DNA or structural variation (SV). SVs can include copy number variation (CNV), insertions, inversions and translocations. Gene dosage alteration of the PMP22 gene through CNV causes the most common IPN, Charcot-Marie-Tooth type 1A (CMT1A). Drug compounds are now becoming available for trials to downregulate PMP22 expression. Other SVs such as insertions, inversions, and translocations can also alter gene expression by disrupting gene regulation. However, this mechanism as a cause of undiagnosed IPNs is unexplored as the proof of pathogenic genomic re-arrangements requires large families with statistical power to establish a disease SV linkage locus.
We have recently identified large DNA insertions leading to gene dysregulation as a cause of two different IPNs: X-linked Charcot-Marie-Tooth neuropathy (CMTX3) caused by 78 kb insertion (Brewer ….. Kennerson 2016) and distal hereditary motor neuropathy (DHMN1) (Drew ….. Kennerson 2016) caused by a 1.35 Mb insertion. In contrast to single base changes and small insertion and deletions (indels) which account for the majority of known IPN mutations our discoveries involve thousands to millions of base pairs and was considered ground breaking by suggesting a new pathogenic DNA mechanism for IPNs. If SVs causing gene dysregulation proves to be a relatively common cause of undiagnosed neuropathies, this will represent a potentially treatable group of IPNs. We are now implementing a cell biology program to include re-programming patient skin cells to motor neuron using induced pluripotent stem cell (iPSC) technologies for these families. This will allow us to understand the gene dysregulation in patient nerves using the natural mutation and genetic background derived from their own tissues.
Worm models for inherited peripheral neuropathies
M Brewer, M Ellis, C Ly, G Nicholson, M Kennerson
This year we have introduced worm technology into the laboratory as a possible fast track screen for drug therapies for degenerative disorders of nerve. Caenorhabditis elegans (C. elegans) is a small (about 1 mm in length), transparent nematode with a short life cycle and a well characterised nervous system – making them ideal for studying axonal degeneration caused by genetic mutations found in patients with inherited peripheral neuropathy.
Candidate gene mutations will be overexpressed in the worm’s GABA-motor neurons – which innervate the muscles that control worm locomotion. Gene variants that are pathogenic are expected to cause axonal degeneration as evidenced by abnormal locomotive behaviour and disrupted axon structure (observed visually by the endogenous expression of green fluorescent protein in the GABAergic neurons). This project complements our current gene discovery program by providing additional in vivo evidence as to whether a candidate gene mutation is the cause of inherited peripheral neuropathy in our patients. In collaboration with Dr Brett Neumann (Monash University) we will continue develop a comprehensive C. elegans program for ongoing IPN gene mutations discovered. The models established in this project will be used for downstream functional studies and therapeutic drug screens.
Cell and animals models of inherited peripheral neuropathies
G Perez-Siles, M Ellis, C Ly, G Nicholson, M Kennerson
Our group has a cell biology program for the study of mutations causing inherited peripheral neuropathies. Understanding the normal function and the consequences of the mutations in neuronal cell lines, will further our understanding of the mechanisms causing degenerative nerve disease.
Two of the main projects currently developed in our lab involve the study of PDK3 and ATP7A mutations, previously identified by our group as causative disease mutations of two forms of X-linked forms of inherited peripheral neuropathy.
Using patient skin cells with the PDK3 gene mutation we have recently identified a highly potential ‘druggable’ target for therapeutic intervention (Perez-Siles …. Kennerson 2016a). We have also successfully developed a knock-in mouse model that expresses a human mutation in the copper transporter ATP7A (Perez-Siles …. Kennerson 2016b). This model faithfully recapitulates the defective molecular events observed in the human patient fibroblasts. We believe this model represents an ‘early stage’ of motor neuropathy prior to the dying back of the nerves and will facilitate identification and testing of therapeutic targets to develop effective copper based therapies that could ameliorate or prevent progression of the disease.
Motor Neuron Disease (MND) and Disorders
The motor neurons are nerves that extend from the brain to the muscles and provide the stimulus through which we move, breathe, eat and drink. The motor neuron diseases (MND) are a group of related neurodegenerative diseases that cause the progressive death of motor neurons. These diseases range from slowly progressive, non-fatal forms to the rapidly progressive fatal disorder amyotrophic lateral sclerosis (ALS). ALS typically leads to death within 3 to 5 years of first symptoms. ALS causes progressive paralysis and the cause of death is usually respiratory failure.
There are no specific diagnostic tests for MND and treatment is extremely limited. The only known causes of MND are mutations in particular genes that lead to death of motor neurons. The known MND genes only account for about 2% of all cases. We are working to understand the biological basis of MND through identification and analysis of defective genes that cause the death of motor neurons. This understanding is a prerequisite to effective diagnosis, treatment and prevention of MND.
The laboratory has been at the forefront of MND discoveries for many years. After demonstrating that MND can be caused by any of a number of genes with mutations we showed that TDP43 mutation variants cause MND. Protein expressed by this gene is found in all dying nerves in MND. This has led to world attention to find ways to correct this. Our work is continuing as a research collaboration with Macquarie University’s motor neurone research group, where Professor Nicholson has mentored both the Genetics group and the Zebra fish group. At the ANZAC Northcott laboratory we are continuing to find new gene variants causing non-fatal forms of motor neurone disorders in families attending our neurogenetic clinic by using next generation DNA sequencing. Genes causing motor neurone disorders can sometimes be severe and life threatening and may play a role in the fatal forms of MND.