Authors: Alveena Jacks, Karina Leung, and Anner Harris
In neurons, the BLOC-1 complex is necessary for trafficking membrane proteins from the cell body to the axonal terminal. Many of the membrane proteins necessary for proper neuronal differentiation are trafficked in an endosomal dependent manner. Because the BLOC-1 complex regulates endosomal trafficking, we hypothesized that BLOC-1 may regulate neuronal differentiation. To test this, we utilized a neuronal cell line, N2A cells in both the undifferentiated and in the differentiated state, to compare protein levels via western blot of the BLOC-1 complex as well as trafficking. This model allows us to investigate the role of BLOC-1 vesicle trafficking in neuronal differentiation.
Authors: Hannah Rudolph, Miranda Arnold1, Kaela S. Singleton, Rebecca Cross, Martha V. Bruegge, Andrea Sweetman, Cecilia Garza, Eli Whisnant and Jennifer Larimore
Dysbindin, a subunit of the octomeric BLOC-1 complex, is necessary for proper synaptic function and GABAerigic interneuron development. In post-mortem tissue of patients with schizophrenia, there is a significant reduction of dysbindin in the hippocampus. Dysbindin null mice and mouse models of neurodevelopmental disorders are characterized with defective GABAerigic transmission, potentially due to an observable loss of parvalbumin-positive interneurons. This could describe a common molecular pathway is several diverse neurodevelopmental disorders. For this study, we define the transcriptome of the wild type and dysbindin null mouse. We report changes in parvalbumin in agreement with previously reported data. We further examined the number of paravlbumin-positive neurons within the subregions of the hippocampus. We also demonstrate changes in chloride co-transporters NKCC1, KCC2, and NCKX2. Additionally we observed changes in potassium channel subunits Kcne2 and Kcnj13. This study suggests that loss of dysbindin results in altered expression of molecules that regulate the excitatory/inhibitory balance in the hippocampus.
Author: Miranda Arnold
Arf1 GTPase activating protein (AGAP1) interacts with the vesicle associated Biogenesis of Lysosome Related Organelles Complex-1 (BLOC-1) and adaptor protein 3 (AP-3). In non-neuronal cells, overexpression of AGAP1 results in a build up of endosomal content suggesting it regulates endosome-dependent trafficking. In GWAS studies, AGAP1 has been implicated two neurodevelopmental disorders, Schizophrenia (SZ) and Autism Spectrum Disorder (ASD). However, AGAP1’s localization or function within neurons has yet to be reported. In this study, we demonstrate AGAP1 localizes in axons, dendrites, dendritic spines and synapses, and also colocalizes preferentially with markers of early and recycled endosomes. Through both down regulation and overexpression of AGAP1, neuronal endosomal trafficking and spine morphology are affected. Additionally, AGAP1 mRNA and protein exhibited a decrease in the hippocampus of mice lacking dysbindin, which is associated with risk of SZ. We propose that endosomal trafficking regulated by BLOC-1 and AGAP1 contributes to the synapse morphology of neurodevelopmental disorders.
Author: Kaela Singleton and Jasmine Spraggins
Endsomes: Their potential role in Rett Syndrome
The neurodevelopment disorder, Rett Syndrome (RTT), affects an estimated one in every 10,000 to 15,000 female live births each year. Nearly all cases of RTT are caused by a mutation in the methyl CpG binding protein 2 (MECP2) gene.Categorized as an autism spectrum disorder, RTT propagates distinct decrease in the development of grey matter in the central nervous system affecting learning and motor control specifically through disregulation of BDNF and TrkB receptors. Recent work has focused on understanding the role of endosomal trafficking, specifically focusing on upstream targets of BDNF, a prominent neurotrophic factor essential for proper neuronal growth and function. By examining protein levels of endosomal markers, we will better understand endosomal trafficking in RTT. The present study will further define the role of these known endosomal regulators including, Rab11, EEA1, and Trf using immunoblotting of MeCP2 deficient mouse brain sections.
Author: Rebecca Cross
Advisor: Jennifer Larimore
The Role of Signaling Cascades in Rett Syndrome
Rett Syndrome (RTT) is a neurodegenerative disorder that primarily affects females and is classified under the Autism Spectrum. Children affected by this disease have difficulties with motor control and learning. This disease is caused by mutations on the MECP2 gene, which codes for the transcriptional regulator methyl-CpG-binding protein 2 (MeCP2). One protein regulated by MeCP2 is brain-derived neurotrophic factor (BDNF) which is key for normal neuronal functioning. BDNF activates MAPK cell signaling cascades to aid in normal neuronal formation and growth. In RTT, BDNF expression is reduced. MAPK and PhophoMAPK are involved in signaling cascades that are vital for cell differentiation, cell growth, and neuronal function. So we hypothesize that they may be impaired in RTT. The present study utilizes Western blotting to measure protein levels for MAPK and PhosphoMAPK to investigate the role of signaling cascades in RTT in MeCP2 deficient brain sections from mice.
Authors: Olivia Bello and Pamela Guinn
Alteriations of Receptor Levels in Rett Syndrome
Rett Syndrome (RTT) is a postnatal neurological disorder affecting one in every 10,000-15,000 female births. RTT is caused by a mutation on the X-linked gene, MECP2. MECP2 encodes for the methyl-CpG-binding protein 2, MeCP2, which is expressed throughout the body. In RTT patients there is an observed decrease in brain-derived neurotrophic factor (BDNF) and Nerve Growth Factor (NGF). BDNF influences synaptic plasticity in rats, β-amyloid-induced apoptotic death and neuroinflammation in the hippocampus. BDNF binds and activates the TrkB receptor. NGF is important for growth and survival of neurons and binds to receptor p75. We are interested in determining the protein levels of both TrkB and p75 receptors in the hippocampus, by monitoring the presence of these receptors, it allows us to better understand their role in RTT.
Authors: Karima Johnson and Leila Ibrahim
Endosomal Trafficking in Rett Syndrome
Rett Syndrome is an X-linked neurodevelopmental disorder affecting approximately 1 in 10,000 female children in the US. This disorder is known to be caused by mutation in the MeCP2 gene, which is a transcriptional regulator within cells and is also implicated in mental retardation as well as autism. The main characteristics associated with Rett Syndrome are immature spines, often seen within the CA3, CA1 and dentate gyrus of the hippocampus. The endosome is the primary organelle associated with spine formation, and as such, transports important proteins throughout the cell and to the cell membrane. We seek to further understand the cellular mechanisms underlying Ret Syndrome by studying endosomal trafficking and the role that it plays in spine development within the hippocampus in patients with Rett Syndrome.
Author: Laurel Alex Ambrose
A common molecular pathway in Rett Syndrome and Schizophrenia
Rett syndrome is a disorder within the autism spectrum disorder (ASD) that primarily affects females. Our lab is exploring a potential common molecular pathway shared in schizophrenia and Rett syndrome. To do this we utilized the Mecp2 null mouse, a mouse model for Rett Syndrome. We also used the Pallid and Sandy mice. These mice lack subunits of the BLOC-1 (Biogensis for Lysosme related Organlle Complex-1) complex, which is strongly implicated schizophrenia. BDNF was found to be down-regulated in the hippocampus in both Mecp2 null mice and BLOC-1 null mice. Our lab is further exploring this finding by examining the BDNF receptor (TrkB) in hippocampal subregions, immunohistochemistry, confocal fluorescence microscopy, and image analysis software were utilized to examine the protein receptor levels. Our novel findings indicate the TrkB receptor levels in the Mecp2, Pallid, and Sandy mice were altered compared to the control mouse in the sub-regions of the hippocampus. These results provide more evidence that Rett syndrome and schizophrenia share a common molecular pathway.