How do the spatiotemporal dynamics of insulin signalling control neuron size and function?
Lead Research Organisation:
King's College London
Department Name: Developmental Neurobiology
Abstract
The brain is staggeringly complex. It is made of billions of neurons that extend tree-like branches and connect with 1000s of partners. These complex networks of connections are essential for the correct functioning of the nervous system, they need to be stable enough to process and store information (memories) but also dynamic to respond and change from experience (learning). How brains are built is still one of the biggest questions in biology.
How neuron growth is controlled and how a particular neuron 'knows' what size to reach is intriguing. The growth of a neurons branches determines the potential partners it can make connections with and also sets in place some electrical properties which dictate how it fires. Some neurons have small trees with branches that don't spread very far and process local information within brain circuits whereas others send information long distances, like the neurons that run from your spine down to the muscles that control your big toe. We would like to understand what allows the small neurons to be small and big neurons to be big.
To gain new insights into neuron size control we are using the powerful genetics and complex nervous system of fruit flies (Drosophila). Our preliminary data show a pathway called the Insulin/Insulin-like Growth factor signalling and Target of Rapamycin is required to generate appropriately sized trees. We have tested many different neurons in flies and these experiments point toward insulin signalling being a global player in the nervous system. Each neuron appears to have a distinct tuning that sets what size it should be. How this is controlled and what part it plays shaping neurons will be investigated.
We are able to watch neurons growing live during metamorphosis using fluorescent proteins from jellyfish and high-magnification microscopes. We are now able to do many new experiments with specially engineered flies where the gene have peen precisely edited. This will allow us to get fine measurements of the components in the pathways we are interested in.
Our hope is that we will find something important and universal about nervous system design principles. Alongside this we know that developmental wiring defects can have very serious consequences and manifest as disorders such as autism, schizophrenia and epilepsy. All of which have a massive impact on society. The genes in the pathways above have been found in patients with autism and epilepsy. For both fundamental and medical science we need to know more about how neurons grow and set their size.
How neuron growth is controlled and how a particular neuron 'knows' what size to reach is intriguing. The growth of a neurons branches determines the potential partners it can make connections with and also sets in place some electrical properties which dictate how it fires. Some neurons have small trees with branches that don't spread very far and process local information within brain circuits whereas others send information long distances, like the neurons that run from your spine down to the muscles that control your big toe. We would like to understand what allows the small neurons to be small and big neurons to be big.
To gain new insights into neuron size control we are using the powerful genetics and complex nervous system of fruit flies (Drosophila). Our preliminary data show a pathway called the Insulin/Insulin-like Growth factor signalling and Target of Rapamycin is required to generate appropriately sized trees. We have tested many different neurons in flies and these experiments point toward insulin signalling being a global player in the nervous system. Each neuron appears to have a distinct tuning that sets what size it should be. How this is controlled and what part it plays shaping neurons will be investigated.
We are able to watch neurons growing live during metamorphosis using fluorescent proteins from jellyfish and high-magnification microscopes. We are now able to do many new experiments with specially engineered flies where the gene have peen precisely edited. This will allow us to get fine measurements of the components in the pathways we are interested in.
Our hope is that we will find something important and universal about nervous system design principles. Alongside this we know that developmental wiring defects can have very serious consequences and manifest as disorders such as autism, schizophrenia and epilepsy. All of which have a massive impact on society. The genes in the pathways above have been found in patients with autism and epilepsy. For both fundamental and medical science we need to know more about how neurons grow and set their size.
Technical Summary
Neurons are the largest and most structurally diverse cell type we know of. Their complex tree-like arborizations play a critical role in collecting, integrating and disseminating information between different synaptic partners. Growing appropriate arborizations is key to the proper functioning of mature neurons. How growth is controlled and how particular neurons consistently reach their stereotypical size is a fundamental question.
To gain novel insights into neuronal size control we are using the powerful genetics of Drosophila. In a screen of cell size regulators we found the most significant changes occurred with the Insulin/Insulin-like Growth factor signalling and Target of Rapamycin IIS/TOR pathway. Importantly, our preliminary data show they are required in pupal motoneurons, interneurons and sensory neurons for generating appropriate sized arborizations. This suggest the pathway plays a global role in the nervous system.
We will first characterise insulin receptor expression in the pupal nervous system, using clonal techniques and a battery of CRISPR knockin InR reporters and then establish the developmental mechanisms that underlie that pattern. Secondly, we will establish the differential effects of InR levels on the size of pre- and postsynaptic arborisations and then disrupt the IIS/TOR pathway in identified interneurons during their development. With this we will establish whether there is a 'critical period'. We we will then investigate local, dynamic InR signalling in synaptic terminal arbors. Using state of the art tools to look at InR localization in single cells. Finally we will ascertain where and when insulin like peptides are expressed in relation to growing arborizations. For both fundamental biology and translational biomedical science we need to know more about mechanisms neurons use to grow and set their size within a network.
To gain novel insights into neuronal size control we are using the powerful genetics of Drosophila. In a screen of cell size regulators we found the most significant changes occurred with the Insulin/Insulin-like Growth factor signalling and Target of Rapamycin IIS/TOR pathway. Importantly, our preliminary data show they are required in pupal motoneurons, interneurons and sensory neurons for generating appropriate sized arborizations. This suggest the pathway plays a global role in the nervous system.
We will first characterise insulin receptor expression in the pupal nervous system, using clonal techniques and a battery of CRISPR knockin InR reporters and then establish the developmental mechanisms that underlie that pattern. Secondly, we will establish the differential effects of InR levels on the size of pre- and postsynaptic arborisations and then disrupt the IIS/TOR pathway in identified interneurons during their development. With this we will establish whether there is a 'critical period'. We we will then investigate local, dynamic InR signalling in synaptic terminal arbors. Using state of the art tools to look at InR localization in single cells. Finally we will ascertain where and when insulin like peptides are expressed in relation to growing arborizations. For both fundamental biology and translational biomedical science we need to know more about mechanisms neurons use to grow and set their size within a network.
Planned Impact
The general public is eager to learn about the latest discoveries in neuroscience, with brain development being among the main topics of interest (Suzana Herculano-Houzel, Nature Neuroscience, volume 6, page 325, 2003). This is demonstrated today by a large attendance to talks on neuroscience within public outreach events such as Pint of Science (with a 95% attendance in 175 venues in the UK, personal communication from Praveen Paul, director and co-founder of Pint of Science), or by the frequent publication of articles on how the brain works and develops in magazines such as 'New Scientist'.
Feeding off the general public's enthusiasm for neuroscience, we plan to use findings and resources from this proposal with the following impact goals in mind:
1. To inspire the next generation of researchers through workshops with primary school children and sixth form students.
2. To encourage and support students from non-selective state schools, who are underrepresented in highly selective universities, to apply to these universities.
3. To increase public understanding of how the brain develops, particularly how neurons acquire their shape and wire together.
4. To change attitudes towards Drosophila research. We will demonstrate to the lay public that the fruit fly is a powerful research model and explain that, by using it as an engine for discovery, we can decrease the use of more sentient animal models.
5. To increase creative output by collaborating with the artist Suki Chan, who will use our images of developing neurons.
The beneficiaries will be:
1. Primary school children in Sidmouth.
2. Sixth form students from schools in South London that have low progression to higher education (http://tinyurl.com/jsmvsep)
3. General public attending Sidmouth Science Festival.
4. General public attending Suki Chan's exhibitions, purchasing her art and visiting her website (http://www.sukichan.co.uk/).
Feeding off the general public's enthusiasm for neuroscience, we plan to use findings and resources from this proposal with the following impact goals in mind:
1. To inspire the next generation of researchers through workshops with primary school children and sixth form students.
2. To encourage and support students from non-selective state schools, who are underrepresented in highly selective universities, to apply to these universities.
3. To increase public understanding of how the brain develops, particularly how neurons acquire their shape and wire together.
4. To change attitudes towards Drosophila research. We will demonstrate to the lay public that the fruit fly is a powerful research model and explain that, by using it as an engine for discovery, we can decrease the use of more sentient animal models.
5. To increase creative output by collaborating with the artist Suki Chan, who will use our images of developing neurons.
The beneficiaries will be:
1. Primary school children in Sidmouth.
2. Sixth form students from schools in South London that have low progression to higher education (http://tinyurl.com/jsmvsep)
3. General public attending Sidmouth Science Festival.
4. General public attending Suki Chan's exhibitions, purchasing her art and visiting her website (http://www.sukichan.co.uk/).
Organisations
People |
ORCID iD |
| Darren Williams (Principal Investigator) |