Biology Department Theses and Dissertations

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Characterizing Changes in the Brain During Hydrocephalic Development and Exploring Potential Treatment Strategies
(2024-05) Reed, Makenna M.; Blazer-Yost, Bonnie; Belecky-Adams, Teri; Cummins, Theodore; Baucum, A. J.; Jantzie, Lauren
A neurological disorder, hydrocephalus, has an estimated global pediatric prevalence of 380,000 new cases each year [1]. It is a family of diseases that can occur at any age when cerebrospinal fluid builds up within the ventricles of the brain. Thus, the only available treatments are surgical, invasive, and prone to complications. There is a global need for successful treatment strategies without brain surgery. Choroid plexus epithelial cells (CPEC) are responsible for production of cerebrospinal fluid (CSF). Ependymal cells line the ventricles and play roles in CSF maintenance and waste clearance. Astrocytes perform various functions, one being blood-brain barrier (BBB) maintenance. Collectively these cells contribute to brain fluid/electrolyte regulation and barrier integrity. Increased glial fibrillary acidic protein (GFAP) fluorescence, a marker of activated astrocytes, appeared in hydrocephalic (Tmem67-/-) animals by immunohistochemistry as early as postnatal day (P)10. The tight junction proteins expressed in choroid plexus (CP); claudin-1 (Cl-1) and zona occludin 1 (ZO-1) fluorescent intensity increased in P15 hydrocephalic animals compared to wildtype (Tmem67+/+). These cells also contain aquaporins (AQP), aquaporin-1 (AQP1) and aquaporin-4 (AQP4), important in regulating CSF and interstitial fluid (ISF). Increased fluorescent intensity of AQP4 in the subventricular zone and increased AQP1 apical localization and protein amount in the CP was observed in hydrocephalic animals at postnatal day (P)15. Many of these may be targeted for the treatment of hydrocephalus. However, there is no consensus in pathological findings between models of hydrocephalus and these finding may not translate to common pharmacological targets. A transient receptor potential cation channel, subfamily vanilloid, member 4 (TRPV4) antagonist (RN1734) ameliorates hydrocephalus in a rat model of congenital hydrocephalus (Tmem67 model). It was hypothesized that targeting this mechanosensitive ion channel may slow production of CSF by targeting the CP. However, hydrocephalus pathology can have various effects on the brain. Astrocytes were visualized using fluorescent immunohistochemistry of glial fibrillary acidic protein (GFAP) and RN1734 did not seem to change immunoreactivity to wildtype untreated levels. Increased immunoreactivity of TRPV4 and AQP1 was observed in CP of untreated and RN1734 treated Tmem67-/- rats. AQP4 and TRPV4 immunoreactivity increased in the subventricular zone and periventricular white matter (WM) of hydrocephalic rats. With RN1734, TRPV4 immunoreactivity, but not AQP4, had similar immunoreactivity to wildtype untreated. Increased GFAP and AQP immunoreactivity may indicate residual inflammation in the Tmem67-/- rats. More experiments must be done to further elucidate TRPV4’s role in hydrocephalus pathology. Serum and glucocorticoid-regulated kinase 1 (SGK1) is a kinase implicated in cell volume regulation and CSF production. SI113, an SGK1 inhibitor, ameliorates hydrocephalus in the Tmem67 rodent model. The goal of this study was to determine if SI113 could be used with a new solvent other than dimethyl sulfoxide (DMSO), which can have possible toxic effects. 1-methyl-2-pyrrolidinone (NMP) has high solubility and ability to cross the BBB. These studies showed that NMP as a solvent did not have adverse effects on body weight, however thus far, it has not ameliorated hydrocephalus significantly at the concentration used in this study. There is a possibility that the concentration in NMP that we used was not efficacious enough. CSF and blood plasma samples from animals treated with SI113 24 hours and 30 minutes before euthanasia will be used to investigate the concentration of SI113 that remains in the circulation and the amount that crosses the BBB and blood-cerebrospinal fluid (BCSFB) barriers. We hope that the results will inform dosage for our future studies. Future studies may also examine SI113 mechanism of action in hydrocephalus. This thesis addresses hydrocephalus cell and molecular pathology in the Tmem67 model and examines potential treatment strategies. Future directions include comparing models of hydrocephalus to find common treatment strategies in the hope to find pharmaceutical strategies to better manage human hydrocephalus.
Dyrk1a Dynamics: The Influence of Gene Copy Number on Neurodevelopment in the Ts65dn Mouse Model of Down Syndrome
(2024-05) Hawley, Laura E.; Roper, Randall; Belecky-Adams, Teri; Cummins, Theodore; Goodlett, Charles; Hardy, Tabitha; Marrs, Kathleen
Down syndrome (DS) arises from the triplication of human chromosome 21 (Hsa21), leading to a spectrum of phenotypes characterized by neurodevelopmental and cognitive abnormalities. The Ts65Dn mouse model emulates DS by harboring three copies of genes found on Hsa21 resulting in trisomy 21 (Ts21)- like traits, including disruptions in neuronal pathways, delays in sensorimotor and behavior milestones, and deficits in learning and memory tasks. There is no cure for DS and available therapies primarily address symptoms stemming from Ts21-associated phenotypes. DYRK1A, a gene triplicated in Ts21, has a pivotal role in pathways of neurodevelopment and has been a focus of inhibition treatment research aimed at preempting abnormal brain phenotypes. This study aimed to find a point of substantial Dyrk1a expression dysregulation during a period of critical neonatal neurodevelopment and employ targeted pharmacological and genetic knockdown methods to alleviate the presence or severity of characteristically abnormal brain and behavior phenotypes. The hypothesis of this study was that administering a targeted intervention prior to a point of known overexpression in trisomic pups would ameliorate molecular, sensorimotor, and neurobehavioral deficits, redirecting growth trajectories of Ts65Dn neonatal pups towards more neurotypical outcomes. To test this hypothesis, the spatiotemporal pattern of DYRK1A expression was quantified during the first three weeks of neonatal development across the hippocampus, cerebral cortex, and cerebellum of the Ts65Dn mouse model and found to fluctuate according to the genotype, age, sex, and brain region of the subject. Dyrk1a protein and mRNA expression levels were delineated in trisomic animals by age, exploring the correlation between expression and age, sex, genotype, and brain region. Next a constitutive Dyrk1a knockdown model was integrated with the Ts65Dn model to investigate the impact of gene copy number reduction on protein and mRNA expression levels during phases of known DYRK1A dysregulation. On postnatal day 6, protein expression was rescued in all three brain regions of male animals but was rescued only in the cerebellum of females. There were no significant differences in mRNA transcript levels in either sex at this age. Finally, genetic elements were introduced into the Ts65Dn model to facilitate a spatiotemporally controlled functional reduction of Dyrk1a and discern how the timing of gene copy number reduction affects molecular and neurobehavioral development in a trisomic system. Results from these studies suggest that only functionally reducing Dyrk1a gene copy number on the day of birth is not sufficient to rescue the majority of deficits and delays present in the Ts65Dn mouse model of DS. These findings significantly enhance the understanding of trisomic Dyrk1a expression dynamics during neonatal development and shed light on tailored therapeutic approaches to modulate intrinsic DS characteristics based on age, sex, and phenotypic considerations.
Dynamic Ciliary Localization in the Mouse Brain
(2024-05) Brewer, Katlyn; Berbari, Nicolas F.; Mastracci, Teresa; Balakrishnan, Lata
Primary cilia are hair-like structures found on nearly all mammalian cell types, including cells in the developing and adult brain. Cilia establish a unique signaling compartment for cells. For example, a diverse set of receptors and signaling proteins localize within cilia to regulate many physiological and developmental pathways including the Hh pathway. Defects in cilia structure, protein localization, or cilia function lead to genetic disorders called ciliopathies, which present with various clinical features including several neurodevelopmental phenotypes and hyperphagia associated obesity. Despite their dysfunction being implicated in several disease states, understanding their roles in CNS development and signaling has proven challenging. I hypothesize that dynamic changes to ciliary protein composition contributes to this challenge and may reflect unrecognized diversity of CNS cilia. The proteins ARL13B and ADCY3 are established ciliary proteins in the brain and assessing their localization is often used in the field to visualize cilia. ARL13B is a regulatory GTPase important for regulating cilia structure, protein trafficking, and Hh signaling, while ADCY3 is a ciliary adenylyl cyclase thought to be involved in ciliary GPCR singaling. Here, I examine the ciliary localization of ARL13B and ADCY3 in the perinatal and adult mouse brain by defining changes in the proportion of cilia enriched for ARL13B and ADCY3 depending on brain region and age. Furthermore, I identify distinct lengths of cilia within specific brain regions of male and female mice. As mice age, ARL13B cilia become relatively rare in many brain regions, including the hypothalamic feeding centers, while ADCY3 becomes a prominent cilia marker. It is important to understand the endogenous localization patterns of these proteins throughout development and under different physiological conditions as these common cilia markers may be more dynamic than initially expected. Understanding regional and development associated cilia signatures and physiological condition cilia dynamic changes in the CNS may reveal molecular mechanisms associated with ciliopathy clinical features such as obesity.
Meningeal Fibrosis in the Axolotl Spinal Cord: Extracellular Matrix and Cellular Responses
(2024-05) Sarria, Deborah A.; Chernoff, Ellen; Belecky-Adams, Teri; Blazer-Yost, Bonnie; Cummins, Theodore; Dai, Guoli
Though mammalian spinal cord injury (SCI) has long been a topic of study, effective therapies that promote functional recovery are not yet available. The axolotl, Ambystoma mexicanum, is a valuable animal model in the investigation of spinal cord regeneration, as this urodele is able to achieve functional recovery even after complete spinal cord transection. Understanding the similarities and differences between the mammalian SCI response and that of the axolotl provides insight into the process of successful regeneration, and bolsters the fundamental knowledge used in the development of future mammalian SCI treatments. This thesis provides a detailed analysis of the ultrastructure of the axolotl meninges, as this has not yet been presented in existing literature, and reveals that the axolotl meninges consist of 3 distinct layers as does mammalian meninges; the dura mater, arachnoid mater, and pia mater. The role of reactive meningeal and ependymal cells is also investigated in regard to the deposition and remodeling of the fibrotic ECM, which is found to be similar in composition to hydrogel scaffolds being studied in mammalian SCI. It is shown that meningeal fibroblasts are the primary source of the extensive fibrillar collagen deposition that fills the entire spinal canal, peaking at approximately 3 weeks post transection and remaining until approximately 5 weeks post transection, and that there is no deposition of type IV collagen within the lesion site. Mesenchymal ependymal cells are shown to contribute to the ECM deposition through the production of glycosaminoglycans that are used in sidechains of both unsulfated and sulfated proteoglycans, while simultaneously remodeling the ECM through the production of MMPs and phagocytosis of cellular debris. Further, this study shows that mesenchymal ependymal cells and a population of foamy macrophages contribute to the degradation of the fibrin clot that forms in the acute phase of injury, and that this fibrin clot provides a necessary and permissive substrate for early mesenchymal outgrowth.
Spinophilin Signaling: Impacts on Body Weight, Obesity, and Beta-Cell Function
(2023-12) Stickel, Kaitlyn Christine; Cummins, Theodore; Baucum, Anthony, II; Belecky-Adams, Teri; Mastracci, Teresa; Linneman, Amelia
Obesity is a worldwide epidemic that is partially linked to changing lifestyles within the modern world, including increased access to calorically dense foods and decreased energy output due to more sedentary jobs. Obesity can lead to many different health complications, such as cardiovascular diseases or Type 2 Diabetes (T2D). Obesity-induced T2D is caused by dysfunction of the insulin-producing beta cells of the pancreas. However, mechanisms that promote obesity and the mechanisms by which obesity leads to beta cell dysfunction are not fully known. Spinophilin is a filamentous (F)-actin binding, protein scaffolding, and protein phosphatase 1 (PP1)-targeting protein that can regulate protein. Spinophilin has multiple actions. Spinophilin can bundle filamentous actin to modulate the cellular cytoskeleton. Spinophilin also mediates substrate phosphorylation by targeting and modulating PP1 activity. In addition, spinophilin interacts with multiple proteins, including certain G-protein coupled receptors and can scaffold them with F-actin and/or PP1. Previous studies established that spinophilin KO mice have decreased fat mass, increased lean mass, and improved glucose tolerance. Yet, how spinophilin modulates the above metabolic parameters is unclear. We found that spinophilin is expressed in hypothalamic tissue and appears to also be expressed in the feeding center of the hypothalamus, as well as in other glucose-sensing cells known as tanycytes that neighbor the arcuate nucleus and the third ventricle. We found that loss of spinophilin limited weight gain observed in both a leptin receptor db/db mouse line (Leprdb/db) and mice fed a high-fat diet. Moreover, we found that the decreased fat mass seen in global spinophilin KO mice, at least in the Leprdb/db mice, was not due to major differences in feeding behaviors, consistent with what was observed by other groups using high-fat diet-fed mice. As spinophilin was not associated with alterations in feeding, we posited that its ability to modulate glucose homeostasis may be linked to non-neuronal actions of the protein. Previous studies have found that spinophilin may regulate adipose tissue function and in vitro pancreatic beta cell function; however, its role in the pancreas and beta cells in vivo is not well characterized. We found that spinophilin is expressed in mouse pancreas. Using proteomics-based approaches we identified multiple putative spinophilin interacting proteins isolated from intact pancreas, including: PP1, the spinophilin homolog neurabin, and myosin-9. KEGG pathway analysis of proteomic proteins identified multiple pathways regulating ER stress, such as the unfolded protein response, and cytoskeletal arrangement. We observed decreased associations of spinophilin with PP1 and neurabin and increased association with myosin-9 in obese, Leprdb/db mice as early as 6 weeks, as well as significant decreases in body weight when spinophilin was knocked out in Leprdb/db mice. Moreover, we confirmed a robust and specific increased interaction of spinophilin with myosin-9, and other cytoskeletal proteins. Additionally, we found specific spinophilin interactions with ribosomal proteins, and exocrine and digestion proteins in high-fat diet-fed mice. Using our recently generated pancreatic beta cell-specific spinophilin KO mice, we found that loss of spinophilin in mice on a high-fat diet significantly reduces weight gain and improves whole- body glucose tolerance, and loss of spinophilin specifically within the beta cells also improves whole-body glucose tolerance, with no effect on body weight, further suggesting cell type-specific and independent roles for spinophilin on body weight and glucose homeostasis.
The Effects of Hydrocephalus on the Retina and the Optic Nerve
(2023-12) Loftin, Michelle; Belecky-Adams, Teri; Blazer-Yost, Bonnie; Jantzie, Lauren
Papilledema is the swelling of the optic disc resulting from increased cranial pressure (ICP). A diagnosis of papilledema is important to not only treat pathologies of the eye, but it also can be an important indicator of underlying brain pathology since the subarachnoid space surrounding the optic nerve is contiguous with the brain. Therefore, the increased cranial pressure from brain pathology can be transmitted to the eye. Thus, it is important to have further understanding of the mechanism of papilledema and the anatomical and cellular changes that occur with sustained ICP. To study papilledema, a reproducible post hemorrhagic hydrocephalic (PHH) rat model was used to study the changes of the retina, optic disc, and optic nerve when exposed to high levels of ICP. Multiple retinal changes were noted in the PHH rats including decreased retinal thickness in the peripheral retina in female rats and increased retinal thickness close to the optic disc in male rats. PHH caused a decrease in ganglion cell layer thickness in the peripheral retina. In addition, vascular changes were noted with the PHH rats having an increased occurrence of enlarged retinal vasculature. In addition, the PHH rats had an increased optic disc width from analyzed retinal sections and increased optic disc diameter on optical coherence tomography (OCT). Also, PHH caused a decrease in retinal ganglion cells (RGC). These experiments confirm that PHH model in rats can produce retinal and optic disc phenotypes that are similar to those found in human pathology. Therefore, future studies are indicated utilizing the PHH rat model to provide further understanding of the mechanism of papilledema progression and to allow for the study of possible therapeutics.
Investigating the Modulation of Voltage-Gated Sodium Channel Nav1.1 Neuronal Excitability by Fibroblast Growth Factor Homologous Factor 2 and Il-6
(2023-12) Frazee, Ashley; Cummins, Theodore; Berbari, Nicolas; Baucum, A.J.; Boehm, Stephen
Migraine is a condition that has affected many for generations and yet remains poorly understood. Mutations to the Nav1.1 voltage gated sodium channels have been implicated in various diseases such as Familial Hemiplegic Migraine 3 (FHM3), epilepsy, and autism spectrum disorder (ASD). Various proteins have been found to modify the function of these channels. Fibroblast growth factor homologous factors (FHFs) have been found to regulate the activity of some voltage-gated sodium channels (Navs). More work is needed to determine which FHFs affect which Navs. Here I looked at FHF2A and FHF2B in Nav1.1 as well as an FHM3-causing mutation to this channel, F1774S. I found that FHF2A, but not 2B, induced long-term inactivation (LTI) in the wild-type (WT) Nav1.1 and that FHF2A induced LTI in the F1774S mutant channel to a greater extent. Several changes in channel function caused by the mutation were attenuated with the addition of FHF2A, including persistent currents, leading to a possible rescue in the mutant phenotype. By contrast, the P1894L mutation, which has been found to cause ASD, greatly attenuated LTI and other impacts of FHF2A on Nav1.1. The inflammatory cytokine IL-6 was also investigated as a possible modulator of the Nav1.1 channel. There does not appear to be any direct interaction between this cytokine and the channel. Overall, my data shows for the first time that FHF2A, but FHF2B or IL-6, might be a significant modulator of Nav1.1 and can differentially modulate disease mutations.
Exploring the Effects of Ancestry on Inference and Identity Using Bioinformatics
(2023-08) Herrick, Noah; Walsh, Susan; Picard, Christine; Wilson, Jeremy; Balakrishnan, Lata; Roper, Randall
Ancestry is a complex and layered concept, but it must be operationalized for its objective use in genetic studies. Critical decisions in research analyses, clinical practice, and forensic investigations are based on genetic ancestry inference. For example, in genetic association studies for clinical and applied research, investigators may need to isolate one population of interest from a worldwide dataset to avoid false positive results, or in human identification, ancestry inferences can help reveal the identity of unknown DNA evidence by narrowing down a suspect list. Many studies seek to improve ancestry inference for these reasons. The research presented here offers valuable resources for exploring and improving genetic ancestry inference and intelligence toward identity. First, analyses with ‘big data’ in genomics is a resource-intensive task that requires optimization. Therefore, this research introduces a suite of automated Snakemake workflows, Iliad, that was developed to give the research community an easy-to-learn, hands-off computational tool for genomic data processing of multiple data formats. Iliad can be installed and run on a Google Cloud Platform remote server instance in less than 20 minutes when using the provided installation code in the ReadTheDocs documentation. The workflows support raw data processing from various genetic data types including microarray, sequence, and compressed alignment data, as well as performing micro-workflows on variant call format (VCF) files to merge data or lift over variant positions. When compared to a similar workflow, Iliad completed processing one sample’s raw paired-end sequence reads to a human-legible VCF file in 7.6 hours which was three-times faster than the other workflow. This suite of workflows is paramount towards building reference population panels from human whole-genome sequence (WGS) data which is useful in many research studies including imputation, ancestry estimation, and ancestry informative marker (AIM) discovery. Second, there are persistent challenges in ancestry inference for individuals of the Middle East, especially with the use of AIMs. This research demonstrates a population genomics study pertaining to the Middle East, novel population data from Lebanon (n=190), and an unsupervised genetic clustering approach with WGS data from the 1000 Genomes Project and Human Genome Diversity Project. These efforts for AIM discovery identified two single nucleotide polymorphisms (SNPs) based on their high allelic frequency differences between the Middle East and populations in Eurasia, namely Europe and South/Central Asia. These candidate AIMs were evaluated with the most current and comprehensive AIM panel to date, the VISAGE Enhanced Tool (ET), using an external validation set of Middle Eastern WGS data (n=137). Instead of relying on pre-defined biogeographic ancestry labels to confirm the accuracy of validation sample ancestry inference, this research produced a deep, unsupervised ADMIXTURE analysis on 3,469 worldwide WGS samples with nearly 2 million independent SNPs (r2 < 0.1) which provided a genetic “ground truth”. This resulted in 136/137 validation samples as Middle East and provided valuable insights toward reference samples with varying co-ancestries that ultimately affects the classification of admixed individuals. Novel deep learning methods, specifically variational autoencoders, were introduced for visualizing one hundred percent of the genetic variance found using these AIMS in an alternative method to PCA and presents distinct population clusters in a robust ancestry space that remains static for the projection of unknown samples to aid in ancestry inference and human identification. Third, this research delves into a craniofacial study that makes improvements toward key intelligence information about physical identity by exploring the relationship between dentition and facial morphology with an advanced phenotyping approach paired with robust dental parameters used in clinical practice. Cone-beam computed tomography (CBCT) imagery was used to analyze the hard and soft tissue of the face at the same time. Low-to-moderate partial correlations were observed in several comparisons of dentition and soft tissue segments. These results included partial correlations of: i) inter-molar width and soft tissue segments nearest the nasal aperture, the lower maxillary sinuses, and a portion of the upper cheek, and ii) of lower incisor inclination and soft tissue segments overlapping the mentolabial fold. These results indicate that helpful intelligence information, potentially leading towards identity in forensic investigations, may be present where hard tissue structures are manifested in an observable way as a soft tissue phenotype. This research was a valuable preliminary study that paves the way towards the addition of facial hard tissue structures in combination with external soft tissue phenotypes to advance fundamental facial genetic research. Thus, CBCT scans greatly add to the current facial imagery landscape available for craniofacial research and provide hard and soft tissue data, each with measurable morphological variation among individuals. When paired with genetic association studies and functional biological experiments, this will ultimately lead to a greater understanding of the intricate coordination that takes place in facial morphogenesis, and in turn, guide clinical orthodontists to better treatment modalities with an emphasis on personalized medicine. Lastly, it aids intelligence methodologies when applied within the field of forensic anthropology.
Characterizing Femoral Structure of the Ts66Yah Mouse Model of Down Syndrome
(2023-08) Sloan, Kourtney; Roper, Randall J.; Li, Jiliang; McNulty, Margaret A.; Picard, Christine J.
Down syndrome (DS) is caused by the partial or complete trisomy of human chromosome 21 (Hsa21) and can result in skeletal deficits, including lower bone mineral density (BMD) and increased risk of fracture and osteoporosis or osteopenia earlier than the general population. Mouse models of DS have been developed to understand the genetic mechanisms resulting in these phenotypes, but models differ due to the complex genetic nature of DS and differing genome structures between humans and mice. Ts65Dn mice have been a popular model of DS as they contain ~50% of Hsa21 orthologous genes on a freely segregating minichromosome, but there is speculation that the phenotypes are exaggerated by non-Hsa21 orthologous trisomic genes also present. To address this issue, the Ts66Yah mouse model was developed to remove the non-Hsa21 orthologous trisomic genes. In this study, male and female Ts66Yah mouse femurs were evaluated during bone accrual and peak bone mass to investigate structural differences using micro-computed tomography. Additionally, the role of trisomic Dyrk1a, a Hsa21 gene previously linked to bone deficits in Ts65Dn mice, was evaluated through genetic and pharmacological means in Ts66Yah femurs at postnatal day 36. Ts66Yah mice were found to have little or no trabecular deficits at any age evaluated, but sex-dependent cortical deficits were present at all ages investigated. Reducing Dyrk1a copy number in Ts66Yah mice significantly improved cortical deficits but did not return cortical bone to euploid levels. Pharmacological treatment with DYRK1A inhibitor L21 was confounded by multiple variables, making it difficult to draw conclusions about DYRK1A inhibition in this manner. Overall, these results indicate trabecular deficits associated with Ts65Dn mice may be due to the non-Hsa21 orthologous trisomic genes, and more Hsa21 orthologous trisomic genes are necessary to produce trabecular deficits in DS model mice. As more mouse models of DS are developed, multiple models need to be assessed to accurately define DS-associated phenotypes and test potential treatments.
Examining Postnatal Retinal Thickness and Retinal Ganglion Cell Count in the Ts65Dn Mouse Model of Down Syndrome
(2023-05) Folz, Andrew; Roper, Randall; Goodlett, Charles; Belecky-Adams, Teri
Down syndrome (DS) is a genetic condition caused by the triplication of human chromosome 21 and presents with many phenotypes including decreased brain size, hypocellularity in the brain, and assorted ocular phenotypes. Some of the ocular phenotypes seen are increased risk of cataracts, accommodation difficulties, increased risk of refractive errors, and increased retinal thickness. The Ts65Dn mouse model of DS is a classically used mouse model as it presents a number of phenotypes also seen in those with DS. Some of these phenotypes include decreased brain volume, abnormal synaptic plasticity, and ocular phenotypes. These ocular phenotypes include decreased visual acuity, cataracts, and increased retinal thickness. The Ts65Dn mouse model is trisomic for Dyrk1a, a gene of interest in DS research. We hypothesize that there will be a genotypic and sex effect of retinal thickness and retinal ganglion cell (RGC) count at postnatal day 15 in the Ts65Dn mouse model of DS. Retinal slices were taken from male and female trisomic and euploid Ts65Dn mice at P15 and fluorescently labeled for RGCs and bipolar cells via immunohistochemistry. The retinas were measured for total retinal thickness and RNA-binding protein (RBPMS) positive cells in the RGC layer were counted. There was no genotypic or sex effect when comparing retinal thickness in trisomic mice as compared to euploid mice. There was a genotypic effect of RBPMS positive cell count in which the trisomic mice had a higher number of RBPMS positive cells than euploid mice. Increased retinal thickness along with increased RGC number have both been implicated with decreased apoptosis in the retina. In the Ts65Dn mouse model along with in individuals with DS, this could be due to an increase in DYRK1A protein levels reducing apoptosis. In future studies, determining DYRK1A’s influence in retinal thickness and RGC number could result in a treatment for overactive DYRK1A that could normalize retinal thickness and RGC number in those with DS.

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