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Thomas, Mark P.

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Two of the most challenging problems in neuroscience may be the characterization of different neuron types and determining the various decision points over the course of development that defines those different cell types. Part of the problem is that for the clear majority of neuron types, no single gene so far has been shown to act as a type marker. Instead it seems that signatures involving multiple genes are necessary to define each type. The identity of the genes in these signatures remains an important gap in our knowledge. However, recent developments in bioinformatics have produced population level transcript sequencing of single cell types. These datasets provide a rich resource for identifying marker genes for neuronal type and for decoding their developmental timeline as well. Here I present a method for analyzing cortical neuron datasets and verifying the expression profiles of the identified marker-gene protein products. Type I and Type II pyramidal neurons within layer V of the neocortex are important output neurons of the neocortical circuit and are associated with several brain disorders such as Schizophrenia, Alzheimer’s and some types of Autism. They are found in all regions of the neocortex and are defined by their axonal targets; Type I neurons project subcortically while Type II neurons project contralaterally. In the mouse, the primary somatosensory cortex is probably the most studied region. The less studied medial prefrontal cortex is associated with executive functions such as working memory and decision making processes. Fourteen putative genetic type markers for layer V pyramidal neurons of the mouse medial prefrontal and primary somatosensory cortices (seven Type I, seven Type II) were identified and eight were assessed for protein expression via fluorescence immunohistochemistry at ages P1 and P7. This is the first study assessing the protein expression of PCP4 and TCERG1L in Layer V pyramidal neurons in comparison between the two brain regions. This is also the first time that PCP4 has been shown to be present in Type I neurons of the mouse medial prefrontal cortex or at postnatal ages. Ultimately, PCP4 was determined to be a viable Type I marker at both ages and in both cortical locations. Finding new marker genes for these neurons is important for understanding not only their function and development but also for that of the whole neocortex. Once identified, their role in function and development can be determined for each neuron type which may help shed light on some of the disorders associated with them.


112 pages

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