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Description
Environmental and genetic factors contribute to schizophrenia etiology, yet few studies have demonstrated how environmental stimuli impact genes associated with the disorder. Immediate early genes (IEGs) are of great interest to schizophrenia research because they are activated in response to physiological stress from the environment, and subsequently regulate the expression of downstream genes that are essential to neuropsychiatric function. An IEG, early growth response 3 (EGR3) has been identified as a main gene involved in a network of transcription factors implicated in schizophrenia susceptibility. The serotonin 2A receptor (5-HT2AR) seems to play an important role in schizophrenia and the dysfunction of the 5-HT2AR encoding gene, HTR2A, within the prefrontal cortex (PFC) contributes to multiple psychiatric illnesses including schizophrenia. EGR3's role as a transcription factor that is activated by environmental stimuli suggests it may regulate Htr2a transcription in response to physiological stress, thus affecting 5-HT2AR function in the prefrontal cortex (PFC). The aim of this study was to examine the relationship between Egr3 activation and Htr2a expression after an environmental stimulus. Sleep deprivation is an acute physiological stressor that activates Egr3. Therefore to examine the relationship between Egr3 and Htr2a expression after an acute stress, wild type and Egr3 knockout mice that express EGFP under the control of the Htr2a promoter were sleep deprived for 8 hours. We used immunohistochemistry to determine the location and density of Htr2a-EGFP expression after sleep deprivation and found that Htr2a-EGFP expression was not affected by sex or subregions of the PFC. Additionally, Htr2a-EGFP expression was not affected by the loss of Egr3 or sleep deprivation within the PFC. The LPFC subregions, layers V and VI showed significantly more Htr2a-EGFP expression than layers I-III in all animals for both sleep deprivation and control conditions. Possible explanations for the lack of significant effects in this study may be the limited sample size or possible biological abnormalities in the Htr2a-EGFP mice. Nonetheless, we did successfully visualize the anatomical distribution of Htr2a in the prefrontal cortex via immunohistochemical staining. This study and future studies will provide insight into how Egr3 activation affects Htr2a expression in the PFC and how physiological stress from the environment can alter candidate schizophrenia gene function.
ContributorsSabatino, Alissa Marie (Author) / Gallitano, Amelia (Thesis director) / Hruschka, Daniel (Thesis director) / Maple, Amanda (Committee member) / Barrett, The Honors College (Contributor)
Created2014-05
Description
About 1% of the United States adult population currently suffers from schizophrenia. The symptoms of schizophrenia can be broken down into three main categories including: positive symptoms such as psychoses, negative symptoms such as anhedonia, and cognitive symptoms such as memory difficulties. The early growth response 3 (Egr3) is part of a family of genes known as the immediate early genes (IEGs), which are zinc-finger transcription factors. IEGs are not protein synthesis dependent, which means that they can be activated quickly, within 30-45 minutes, in response to certain environmental stimuli such as sleep deprivation. Egr3, an activity dependent gene, may be up-regulated by both genetic and environmental cues. Egr3 is thought to play an integral role in a biochemical pathway that may explain the onset of schizophrenia. However, the exact causes of schizophrenia remain unknown. Egr3 is not only activated in response to environmental factors, but has also been linked to many genes that are associated with schizophrenia in humans (Huentelman et al., 2015). Post-mortem brain tissue studies of patients with schizophrenia have decreased levels of EGR3 in their prefrontal cortex (PFC) and mice lacking Egr3 (Egr3 -/-) exhibit schizophrenia-like phenotypes such as locomotor hyperactivity. Egr 3 -/- mice also exhibit a diminished head twitch response to 2,5-Dimethoxy-4-iodoamphetamine (DOI), a 5-HT2A agonist (Yamada, et al., 2007; Gallitano-Mendel, et al., 2008). A link was established between schizophrenia patients and the serotonin 2A receptor (5-HT2AR) upon recognizing that 5-HT2AR agonists like lysergic acid diethylamide (LSD) create hallucinations similar to those in schizophrenic patients and 5-HT2AR antagonists such as the second-generation antipsychotic clozapine can reverse those hallucinations (Sommer, 2012). Paradoxically, however, post-mortem studies of schizophrenia patients have actually shown a decrease in PFC 5-HT2ARs as well as a 70% decrease found in the PFC of Egr3 -/- mice (Rasmussen, et al., 2010; Williams, et al., 2012). Therefore, we hypothesize that EGR3 directly regulates expression of 5-HT2ARs. To test this we will use virus-mediated overexpression of 5-HT2ARs in the PFCs of mice to see if we can rescue the schizophrenia-like phenotypes of the Egr3 -/- mice. After bilateral PFC stereotaxic injection of herpes simplex virus (HSV) with enhanced green fluorescent protein (EGFP) or HSV-Htr2a-EGFP in both wild type (WT) and Egr3 -/- mice, the mice were behaviorally tested using locomotor activity and DOI-induced head twitch response. We found that Egr3-/- mice, compared to WT mice, demonstrated locomotor hyperactivity and a decreased DOI-induced head twitch response, confirming prior findings, but no significant main effect of virus. A significant effect of the HSV-Htr2a-EGFP was seen when comparing DOI-induced head twitch response in WT mice to Egr3 -/- mice. WT mice showed a higher number of head twitches in comparison to the knockout mice. These findings suggest further research must be conducted in order to investigate whether a functional 5-HT2AR is being translated and correctly transported to the membrane. These findings may also point to an unknown factor mediating the regulation between Egr3 and 5-HT2ARs.
ContributorsHoebee, Shelby Marie (Author) / Van Horn, Wade (Thesis director) / Gallitano, Amelia (Committee member) / Department of Psychology (Contributor) / School of Molecular Sciences (Contributor) / School of Criminology and Criminal Justice (Contributor) / School of Life Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2016-05