The Effect of Mecp2 Mutation on Cortical Projections Revealed by Correlated Single-Cell Transcriptomics and Projectomics
Abstract
The brain is composed of myriad types of neurons, each sending different long-range projections to contact neurons in other brain areas. These projections are extremely diverse even within the same type of neurons, which allow the neurons to send different information to the correct downstream brain areas for processing. These long-range projections thus underlie neuronal circuits responsible for functions such as cognition and behavior. Disruption of these projections may contribute to neurological symptoms associated with many neuropsychiatric diseases, including autism spectrum disorders, bipolar disorder, and schizophrenia. Therefore, determining the defects of long-range projections in neuropsychiatric diseases is important to understanding and potentially correcting neurological problems associated with these diseases. Here we focus on Rett syndrome, a type of autism spectrum disorder caused by mutations in the gene Mecp2. Mecp2 is expressed in neurons when neurons first establish long-range projections and connections with other neurons, suggesting that Mecp2 may affect the establishment and further refinement of long-range projections. Such a role of Mecp2 in refining long-range projections is supported by previous studies. Even though a lot has been learned about functions of Mecp2 at a molecular and cellular level, it is still unclear what effects mutations in Mecp2 have on the long-range projections of diverse types of neurons at a circuit level. In this study, we focus on the roles of Mecp2 in the cerebral cortex and hypothesize that mutations in Mecp2 disrupt long-range projections in the cortex, possibly by affecting the refinement of cortical projections. Because individual neurons have different projection patterns from one another, we need a method to determine the projections of many neurons simultaneously, but still be able to distinguish one neuron from another. Furthermore, because neurons can be classified into different ?types,? and each type may be affected differently by Mecp2, we need to associate the projection patterns with the types of neurons. Both of these two goals are difficult to achieve using conventional neuroanatomical techniques due to the complexity in both the projection patterns and neuronal types in the cortex. We propose to overcome this technical difficulty by leveraging recent advancements in Next-Gen Sequencing technology. To map neuronal projections, we will employ MAPseq, a novel technique that allows projection mapping of thousands of neurons simultaneously without mixing up the neurons. MAPseq achieves this high-throughput by labeling each neuron with a unique RNA sequence, or a ?barcode.? The barcode will replicate within a neuron and fill up both the projections and the neuronal cell body, so the projection patterns of a neuron can be read out by finding the same barcode in the projection target areas using sequencing. Given the parallel nature of Next-Gen Sequencing technology, MAPseq allows us to map the projections of many neurons in a single experiment. Because MAPseq relies on sequencing, we will further combine MAPseq with single-cell RNA sequencing, which reads out the genes expressed in each neuron. The combination of these two techniques thus allows us to associate changes in projection patterns with neuronal type as read out by gene expression. Using these tools, we will examine how Mecp2 affects the projection patterns in diverse types of neurons over the developmental period when long-range projections are refined. We expect to see a gradual increase in projection defects caused by Mecp2 mutations as the animals age, which would be consistent with a role of Mecp2 in projection refinement. Our proposed study will provide a systematic view of aberrant long-range projections caused by Mecp2 mutations, allowing identification of projections and/or types of neurons for further studies. Furthermore, the technique we propose can be used to st
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Mar 05, 2019
- Source ID
- W81XWH1910083
Entities
People
- Xiaoyin Chen
Organizations
- Cold Spring Harbor Laboratory
- United States Army