Genetic background mutations drive neural circuit hyperconnectivity in a fragile X syndrome model
Abstract Background Neural circuits are initially assembled during development when neurons synapse with potential partners and later refined as appropriate connections stabilize into mature synapses while inappropriate contacts are eliminated. Disruptions to this synaptogenic process impair connect...
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| Format: | Article |
| Language: | English |
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BMC
2020-07-01
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| Series: | BMC Biology |
| Subjects: | |
| Online Access: | http://link.springer.com/article/10.1186/s12915-020-00817-0 |
| _version_ | 1811331582286364672 |
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| author | Tyler Kennedy David Rinker Kendal Broadie |
| author_facet | Tyler Kennedy David Rinker Kendal Broadie |
| author_sort | Tyler Kennedy |
| collection | DOAJ |
| description | Abstract Background Neural circuits are initially assembled during development when neurons synapse with potential partners and later refined as appropriate connections stabilize into mature synapses while inappropriate contacts are eliminated. Disruptions to this synaptogenic process impair connectivity optimization and can cause neurodevelopmental disorders. Intellectual disability (ID) and autism spectrum disorder (ASD) are often characterized by synaptic overgrowth, with the maintenance of immature or inappropriate synapses. Such synaptogenic defects can occur through mutation of a single gene, such as fragile X mental retardation protein (FMRP) loss causing the neurodevelopmental disorder fragile X syndrome (FXS). FXS represents the leading heritable cause of ID and ASD, but many other genes that play roles in ID and ASD have yet to be identified. Results In a Drosophila FXS disease model, one dfmr1 50M null mutant stock exhibits previously unreported axonal overgrowths at developmental and mature stages in the giant fiber (GF) escape circuit. These excess axon projections contain both chemical and electrical synapse markers, indicating mixed synaptic connections. Extensive analyses show these supernumerary synapses connect known GF circuit neurons, rather than new, inappropriate partners, indicating hyperconnectivity within the circuit. Despite the striking similarities to well-characterized FXS synaptic defects, this new GF circuit hyperconnectivity phenotype is driven by genetic background mutations in this dfmr1 50M stock. Similar GF circuit synaptic overgrowth is not observed in independent dfmr1 null alleles. Bulked segregant analysis (BSA) was combined with whole genome sequencing (WGS) to identify the quantitative trait loci (QTL) linked to neural circuit hyperconnectivity. The results reveal 8 QTL associated with inappropriate synapse formation and maintenance in the dfmr1 50M mutant background. Conclusions Synaptogenesis is a complex, precisely orchestrated neurodevelopmental process with a large cohort of gene products coordinating the connectivity, synaptic strength, and excitatory/inhibitory balance between neuronal partners. This work identifies a number of genetic regions that contain mutations disrupting proper synaptogenesis within a particularly well-mapped neural circuit. These QTL regions contain potential new genes involved in synapse formation and refinement. Given the similarity of the synaptic overgrowth phenotype to known ID and ASD inherited conditions, identifying these genes should increase our understanding of these devastating neurodevelopmental disease states. |
| first_indexed | 2024-04-13T16:22:53Z |
| format | Article |
| id | doaj.art-57b49953f5e44045ad32a91ddbd172af |
| institution | Directory Open Access Journal |
| issn | 1741-7007 |
| language | English |
| last_indexed | 2024-04-13T16:22:53Z |
| publishDate | 2020-07-01 |
| publisher | BMC |
| record_format | Article |
| series | BMC Biology |
| spelling | doaj.art-57b49953f5e44045ad32a91ddbd172af2022-12-22T02:39:51ZengBMCBMC Biology1741-70072020-07-0118112110.1186/s12915-020-00817-0Genetic background mutations drive neural circuit hyperconnectivity in a fragile X syndrome modelTyler Kennedy0David Rinker1Kendal Broadie2Department of Biological Sciences, Vanderbilt University and Medical CenterDepartment of Biological Sciences, Vanderbilt University and Medical CenterDepartment of Biological Sciences, Vanderbilt University and Medical CenterAbstract Background Neural circuits are initially assembled during development when neurons synapse with potential partners and later refined as appropriate connections stabilize into mature synapses while inappropriate contacts are eliminated. Disruptions to this synaptogenic process impair connectivity optimization and can cause neurodevelopmental disorders. Intellectual disability (ID) and autism spectrum disorder (ASD) are often characterized by synaptic overgrowth, with the maintenance of immature or inappropriate synapses. Such synaptogenic defects can occur through mutation of a single gene, such as fragile X mental retardation protein (FMRP) loss causing the neurodevelopmental disorder fragile X syndrome (FXS). FXS represents the leading heritable cause of ID and ASD, but many other genes that play roles in ID and ASD have yet to be identified. Results In a Drosophila FXS disease model, one dfmr1 50M null mutant stock exhibits previously unreported axonal overgrowths at developmental and mature stages in the giant fiber (GF) escape circuit. These excess axon projections contain both chemical and electrical synapse markers, indicating mixed synaptic connections. Extensive analyses show these supernumerary synapses connect known GF circuit neurons, rather than new, inappropriate partners, indicating hyperconnectivity within the circuit. Despite the striking similarities to well-characterized FXS synaptic defects, this new GF circuit hyperconnectivity phenotype is driven by genetic background mutations in this dfmr1 50M stock. Similar GF circuit synaptic overgrowth is not observed in independent dfmr1 null alleles. Bulked segregant analysis (BSA) was combined with whole genome sequencing (WGS) to identify the quantitative trait loci (QTL) linked to neural circuit hyperconnectivity. The results reveal 8 QTL associated with inappropriate synapse formation and maintenance in the dfmr1 50M mutant background. Conclusions Synaptogenesis is a complex, precisely orchestrated neurodevelopmental process with a large cohort of gene products coordinating the connectivity, synaptic strength, and excitatory/inhibitory balance between neuronal partners. This work identifies a number of genetic regions that contain mutations disrupting proper synaptogenesis within a particularly well-mapped neural circuit. These QTL regions contain potential new genes involved in synapse formation and refinement. Given the similarity of the synaptic overgrowth phenotype to known ID and ASD inherited conditions, identifying these genes should increase our understanding of these devastating neurodevelopmental disease states.http://link.springer.com/article/10.1186/s12915-020-00817-0Giant fiberFragile X syndromeGenetic backgroundBulk Segregant analysisDrosophilaNeuron |
| spellingShingle | Tyler Kennedy David Rinker Kendal Broadie Genetic background mutations drive neural circuit hyperconnectivity in a fragile X syndrome model BMC Biology Giant fiber Fragile X syndrome Genetic background Bulk Segregant analysis Drosophila Neuron |
| title | Genetic background mutations drive neural circuit hyperconnectivity in a fragile X syndrome model |
| title_full | Genetic background mutations drive neural circuit hyperconnectivity in a fragile X syndrome model |
| title_fullStr | Genetic background mutations drive neural circuit hyperconnectivity in a fragile X syndrome model |
| title_full_unstemmed | Genetic background mutations drive neural circuit hyperconnectivity in a fragile X syndrome model |
| title_short | Genetic background mutations drive neural circuit hyperconnectivity in a fragile X syndrome model |
| title_sort | genetic background mutations drive neural circuit hyperconnectivity in a fragile x syndrome model |
| topic | Giant fiber Fragile X syndrome Genetic background Bulk Segregant analysis Drosophila Neuron |
| url | http://link.springer.com/article/10.1186/s12915-020-00817-0 |
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