Olfactory Granule cells (GCs) are a population of inhibitory interneurons responsible for maintaining normal olfactory bulb (OB) function and circuitry. Through dendrodendritic synapses with the OBs projection neurons, the GCs regulate information sent to the olfactory cortices. Throughout adulthood, GCs continue to integrate into the OB and contribute to olfactory circuitry. However, only ~50% will integrate and survive longterm. Factors aiding in the survival and morphological development of these neurons are still being explored. The neurotrophin brain-derived neurotrophic factor (BDNF) aids in the survival and dendritic spine maturation/maintenance in several populations of CNS neurons. Investigators show that increasing BDNF in the adult-rodent SVZ stimulates proliferation and increases numbers of new OB GCs. However, attempts to replicate these experiments failed to find that BDNF affects proliferation or survival of adult-born granule cells (abGCs). BDNFs regulation of dendritic spines in the CNS is well characterized. In the OB, absence of BDNF’s receptor on abGCs hinders normal spine development and demonstrates a role for BDNF /TrkB signaling in abGCs development. In this study, we use transgenic mice over-expressing endogenous BDNF in the OB (TgBDNF) to determine how sustained increased in BDNF affect the morphology of olfactory GCs and the survival and development of abGCs. Using protein assays, we discovered that TgBDNF mice have higher BDNF protein levels in their OB. We employed a Golgi-cox staining technique to show that increased BDNF expression leads to an increase in dendritic spines, mainly the mature, headed-type spine on OB GCs. With cell birth-dating using 5-bromo-2’- deoxyuridine (BrdU), immunofluorescent cell markers, TUNEL staining and confocal microscopy, we demonstrate that over-expression of BDNF in the OB does not increase survival of abGCs or reduce cell death in the GC population. Using virally labeled abGCs, we concluded that abGCs in TgBDNF mice had similar integration patterns compared to wild-type (WT) mice, but maintained increases in apical headed-type spine density from 12 to 60 days PI. The evidence combined demonstrates that although increased BDNF does not promote cell survival, BDNF modifies GC morphology and abGC development through its regulation of dendritic spine development, maturation and maintenance in vivo. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2018. / FAU Electronic Theses and Dissertations Collection

Tsim Ting Yuk. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references (leaves 119-135). / Abstracts in English and Chinese. / ABSTRACT --- p.i / 摘要 --- p.iii / 英漢譯名對照 --- p.v / ABBREVIATIONS --- p.vi / ACKNOWLEDGMENTS --- p.viii / Chapter 1. --- Introduction / Chapter 1.1. --- Olfactory system --- p.1 / Chapter 1.1.1. --- Olfactory bulb (OB) --- p.1 / Chapter 1.1.2. --- Accessory olfactory bulb (AOB) --- p.3 / Chapter 1.2. --- Stem cells --- p.5 / Chapter 1.3. --- Sexual differentiation --- p.8 / Chapter 1.3.1. --- Sexual dimorphic olfactory system --- p.8 / Chapter 1.3.2. --- Androgen receptor (AR) & estrogen receptor beta (ERβ) --- p.13 / Chapter 1.3.3. --- Aromatase --- p.15 / Chapter 1.3.4. --- Oligomycin sensitivity-conferringrotein (OSCP) --- p.18 / Chapter 1.4. --- rogrammed cell death (PCD) --- p.18 / Chapter 1.4.1. --- CD in the olfactory development --- p.18 / Chapter 1.4.2. --- Caspase 3 --- p.22 / Chapter 1.4.3. --- B cell leukemia/ Lymphoma 2 (Bcl-2) --- p.23 / Chapter 1.5. --- Axon guidance molecules --- p.25 / Chapter 1.5.1. --- Growth cone --- p.25 / Chapter 1.5.2. --- Mechanisms of growth cone advance --- p.26 / Chapter 1.5.3. --- Semaphorins --- p.28 / Chapter 1.5.4. --- Neuropilin --- p.31 / Chapter 1.5.5. --- lexin --- p.32 / Chapter 1.5.6. --- Collapsin response mediatorroteins (CRMPs) --- p.32 / Chapter 1.6. --- Olfactory markerroteins --- p.33 / Chapter 1.6.1. --- Markerroteins in ORNs --- p.33 / Chapter 1.6.2. --- Growth associatedrotein (GAP-43) --- p.34 / Chapter 1.6.3. --- Is the expression of GAP-43 in rat OB sexually dimorphic? --- p.36 / Chapter 1.6.4. --- Olfactory markerrotein (OMP) --- p.38 / Chapter 1.6.5. --- Golf --- p.39 / Chapter 1.7. --- Miscellaneous genes --- p.40 / Chapter 1.7.1. --- Substance (SP) --- p.40 / Chapter 1.7.2. --- Gonadotropin releasing hormone (GnRH) --- p.41 / Chapter 1.7.3. --- Metabotropic glutamate receptor 2 (mGluR2) --- p.42 / Chapter 1.7.4. --- Insulin-like growth factor binding protein-2 (IGFBP2) --- p.43 / Chapter 2. --- Materials and methods / Chapter 2.1. --- Animal study --- p.46 / Chapter 2.2. --- RNA extraction --- p.46 / Chapter 2.3. --- Quantitation of total RNA --- p.49 / Chapter 2.4. --- Reverse Transcription (RT) --- p.50 / Chapter 2.5. --- olymerase Chain Reaction (PCR) --- p.51 / Chapter 2.6. --- urification ofCRroducts --- p.55 / Chapter 2.7. --- Confirmation ofCRroducts --- p.56 / Chapter 2.8. --- Quantitation of cDNA --- p.57 / Chapter 2.9. --- Radioactive labeledCR --- p.58 / Chapter 2.10. --- Electrophoresis ofCRroducts --- p.59 / Chapter 2.11. --- Statistical analysis --- p.60 / Chapter 3. --- Results / Chapter 3.1. --- Standard curve construction --- p.61 / Chapter 3.2. --- β-actin --- p.62 / Chapter 3.3. --- Sexual differentiation related genes --- p.64 / Chapter 3.3.1. --- AR --- p.64 / Chapter 3.3.2. --- ERβ --- p.65 / Chapter 3.3.3. --- Aromatase --- p.65 / Chapter 3.3.4. --- OSCP --- p.66 / Chapter 3.4. --- CD related genes --- p.66 / Chapter 3.4.1. --- Bcl-2α --- p.66 / Chapter 3.4.2. --- Caspase 3 --- p.67 / Chapter 3.5. --- Axon guidance molecules and related genes --- p.67 / Chapter 3.5.1. --- SemaIII --- p.67 / Chapter 3.5.2. --- Neuropilin-1 --- p.68 / Chapter 3.5.3. --- lexin-1 --- p.68 / Chapter 3.5.4. --- CRMP-1 --- p.69 / Chapter 3.5.5. --- CRMP-2 --- p.70 / Chapter 3.5.6. --- CRMP-3 --- p.70 / Chapter 3.5.7. --- CRMP-4 --- p.71 / Chapter 3.6. --- Olfactory markerrotein genes --- p.71 / Chapter 3.6.1. --- GAP-43 --- p.71 / Chapter 3.6.2. --- OMP --- p.72 / Chapter 3.6.3. --- Golf --- p.72 / Chapter 3.7. --- Miscellaneous genes --- p.73 / Chapter 3.7.1. --- SubstanceP --- p.73 / Chapter 3.7.2. --- GnRH --- p.73 / Chapter 3.7.3. --- mGluR2 --- p.74 / Chapter 3.7.4. --- IGFBP-2 --- p.74 / Chapter 3.8. --- Graphs and tables --- p.75 / Chapter 4. --- Discussion / Chapter 4.1. --- Quantitation of cDNA and normalization of CR results --- p.97 / Chapter 4.2. --- Sexual differentiation related genes --- p.98 / Chapter 4.3. --- CD related genes --- p.100 / Chapter 4.4. --- Axon guidance molecule and related genes --- p.103 / Chapter 4.5. --- Olfactory markerrotein genes --- p.109 / Chapter 4.6. --- Miscellaneous genes --- p.112 / Chapter 5. --- References --- p.119

As células provenientes do epitélio olfatório apresentam capacidade regenerativa durante toda a vida, embora este mecanismo ainda não esteja completamente elucidado. O potencial de diferenciação de células-tronco provenientes do epitélio olfatório de cães sem raça definida (Canis familiaris Linnaeus, 1758) foi avaliado utilizando-se 12 cães adultos e 12 cães com 60 dias de vida intra-uterina, oriundos do Hospital Veterinário da FMVZ-USP. Após coletado, o epitélio olfatório foi submetido a protocolo histológico padrão para hematoxilina-eosina, azul de toluidina e PAS. O material fixado em glutaraldeído 2,5% foi processado para observação sob microscopia eletrônica de transmissão. O índice de proliferação nuclear foi medido para detecção de PCNA e Ki67 nuclear. Células foram expandidas em cultura em meio D-MEM/F-12 acrescido de Soro Fetal Bovino hyclone (CO2-95% à 37ºC) para caracterização e diferenciação celular (osteogênica, adipogência e neurogênica). O cultivo das células provenientes do epitélio olfatório de cães com 60 dias de vida intra-uterina mostrou maior evolução em cultura quando comparados aos animais adultos, sendo as primeiras utilizadas para execução dos protocolos de caracterização e diferenciação. As células em cultivo apresentaram expressão CD29 positiva e marcação positiva para OCT-4, citoqueratina 18 (Ck18) e vimentina. A diferenciação osteogênica demonstrou, ao final de 21 dias, células com morfologia típica, caracterizadas pela coloração de Alizarin Red e Von Kossa. A diferenciação adipogênica mostrou pouco número de células, apresentando grânulos adipogênicos, corados por Oil Red, contudo sem morfologia típica. A diferenciação neurogênica demonstrou células que expressaram marcação para GFAP, Neurofilamentos, Oligodendrócitos e βtubulina III. As células isoladas a partir do epitélio olfatório de cães com 60 dias de vida intra-uterina evidenciaram populações de células-tronco, determinadas pela expressão de marcadores específicos e diferenciação em outros tipos de tecido, devendo-se considerar este epitélio como uma fonte potencial para aquisição de células, particularmente progenitores neuronais, que possam somar aos estudos e seu uso em terapia celular. / Olfactory cells demonstrate regenerative capacity along life, although, its mechanism is still obscure. We evaluated the differentiation capacity of olfactory stem cell of mongrel dogs (Canis familiaris Linnaeus, 1758) in 12 adult dogs and 12 fetuses at term (60 days of pregnancy) from the Veterinary Hospital of FMVZ-USP. Following the sampling, the epithelia were submitted to standard histological process and stained with HE, toluidine blue and PAS. Samples fixed with 2.5% glutaraldehyde solution were processed for transmission electron microscopy. Proliferative index were obtained with the detection of PCNA and Ki67. Cells were kept in culture in D-MEM/F-12 medium supplemented with hyclone bovine fetal serum (CO2-95% at 37ºC) for characterization and cell differentiation (osteogenesis, adipogenesis, and neurogenesis). Cell culture of fetuses at term demonstrated higher evolution in comparison to adult animals, being submitted to the protocols of characterization and differentiation. Cell culture demonstrated positive reaction for CD29, OCT-4, Ck18 (citokeratin) and vimentin. Osteogenic differentiation demonstrated, 21 days, typical morphological cells characterized by Alizarin Red and Von Kossa staining. Adipogenic differentiation demonstrated less number of cells containing granules, stained with Oil Red, although being not typical shape. Neurogenic differentiation demonstrated positive staining for GFAP, Neurofilament, Oligodendrocyte and III β-tubulin. Cells isolated from epithelia of fetuses at term demonstrated population of stem cells determined by the expression of specific-staining and differentiation into other type of cells, which lead us to consider the olfactory epithelia as a source of potential stem cells particularly for neurogenic differentiation to be applied for further studies in cell therapy.

Transplants of olfactory ensheathing cells (OECs) from olfactory bulbs have recently been shown to support regrowth and reinnervation of damaged spinal cord, which has led to improved functional recovery. Using complete transection in adult rat, the studies presented in this thesis examine the role of peripherally derived olfactory tissue in promoting axonal regeneration and functional recovery. Chapter One and Two provide the background to the area of spinal cord regeneration and the methods used in this thesis. Chapter Three shows that transplants of OECs from rat olfactory lamina propria (OLP) are able to support axon regrowth in the lesioned spinal cord. The BBB score was significantly higher in experimental rats (5.4???0.84) compared with control animals (1.9???0.33) (P&lt0.001). These dissociated OECs from OLP can promote axonal regrowth through the lesion. Histological assessment showed that: 1) axons labelled with Fluororuby grew into the injury site in OECs-transplanted rats, with occasional fibres extending into the rostral cord; 2) brainstem neurons in the raphe nucleus were retrogradely labeled with Fluororuby; and 3) serotonergic axons were detectable distal to the lesion in OECs-transplanted rats. No fibres grew into the injured region and no retrograde labeling or serotonergic fibres were seen in control animals. The role of regenerated serotonergic fibres in OECs-transplanted rats is discussed. Chapter Four demonstrates that solid pieces of OLP dissected from the nose can re-establish the continuity of the transected cord and supply the OECs that can migrate to the cord stumps to support the axon regeneration. Experimental rats which received OLP from olfactory mucosa showed significantly greater locomotive recovery (BBB scores: OLP, 5.0???1.9; control, 1.5???0.5, p&lt0.0001). In animals with OLP transplants, histological analysis indicated that nerve fibres, expressing neurofilament and serotonin were present at the transection site. Locomotive recovery of the hindlimbs occurred, similar to that seen after OECs transplantation. Retrograde labeling of medullary raphe neurons and gigantocellular reticular nucleus occurred following Fluororuby injection in the cord distal to the lesion, further supporting the supraspinal origin of the 5-HT innervation in the present studies. These results indicate that OLP is effective in promoting partial spinal cord repair. Chapter Five examines functional recovery of spinal reflex circuitry, ie., H-reflex excitability using paired stimuli, in OLP-transplanted rats compared with normal and respiratory lamina propria (RLP) transplanted animals. H-reflex amplitude of the conditioned response was significantly reduced in OLP transplanted rats compared to RLP transplanted animals (p&lt 0.05). Therefore, hindlimb reflex excitability can be modulated by OLP transplants after transection of the spinal cord in adult rats. Chapter Six examines whether functional recovery can occur if transplantation of OLP tissue is delayed by 1 month after the spinal cord transection. The BBB score was significantly higher in experimental rats (4.3???0.8 for OLP) compared with control animals (1.0???0.3, P&lt 0.001), but recovery was less than after acute transplantation. Asx before, histological assessment of OLP animals showed: a) serotonergic axons were present in the cord below the transection site; b) brainstem raphe nuclei was retrogradely labeled; c) bisbenzimide pre-labeled cells from OLP transplants migrated in host spinal cord. These changes were not seen in control animals. These results indicate that OLP has the ability to promote axonal regeneration in chronically injured cord of adult rats. Chapter Seven compares the results from these three types of intervention. In conclusion, these studies show that peripherally derived OECs or solid pieces of OLP can promote partial spinal cord repair in acute or chronic transection injuries. Such tissue might provide a potential source for autologous grafting in human paraplegia.

Behavioral evidence suggests that Asian elephants strongly rely on their sense of smell in a variety of contexts including foraging and social communication. Using a food-rewarded two-alternative operant conditioning procedure, three female Asian elephants were tested on their olfactory discrimination ability with 1-aliphatic alcohols, n-aldehydes, 2-ketones, n-carboxylic acids and with a set of twelve enantiomeric odor pairs. When presented with pairs of structurally related aliphatic odorants, the discrimination performance of the elephants increased with decreasing structural similarity of the odorants. Nevertheless, the animals successfully discriminated between all aliphatic odorants even when these only differed by one carbon atom. The elephants were also able to discriminate between all twelve enantiomeric odor pairs tested. Additionally, the elephants showed an excellent long-term odor memory and remembered the reward value of previously learned odor pairs after three weeks and one year of recess. Compared to other species tested previously on the same sets of odorants, the Asian elephants performed at least as good as mice and clearly better than human subjects, South African fur seals, squirrel monkeys, pigtail macaques, and honeybees. Taken together, these results support the notion that the sense of smell may play an important role in regulating the behavior of Asian elephants.

Transplants of olfactory ensheathing cells (OECs) from olfactory bulbs have recently been shown to support regrowth and reinnervation of damaged spinal cord, which has led to improved functional recovery. Using complete transection in adult rat, the studies presented in this thesis examine the role of peripherally derived olfactory tissue in promoting axonal regeneration and functional recovery. Chapter One and Two provide the background to the area of spinal cord regeneration and the methods used in this thesis. Chapter Three shows that transplants of OECs from rat olfactory lamina propria (OLP) are able to support axon regrowth in the lesioned spinal cord. The BBB score was significantly higher in experimental rats (5.4???0.84) compared with control animals (1.9???0.33) (P&lt0.001). These dissociated OECs from OLP can promote axonal regrowth through the lesion. Histological assessment showed that: 1) axons labelled with Fluororuby grew into the injury site in OECs-transplanted rats, with occasional fibres extending into the rostral cord; 2) brainstem neurons in the raphe nucleus were retrogradely labeled with Fluororuby; and 3) serotonergic axons were detectable distal to the lesion in OECs-transplanted rats. No fibres grew into the injured region and no retrograde labeling or serotonergic fibres were seen in control animals. The role of regenerated serotonergic fibres in OECs-transplanted rats is discussed. Chapter Four demonstrates that solid pieces of OLP dissected from the nose can re-establish the continuity of the transected cord and supply the OECs that can migrate to the cord stumps to support the axon regeneration. Experimental rats which received OLP from olfactory mucosa showed significantly greater locomotive recovery (BBB scores: OLP, 5.0???1.9; control, 1.5???0.5, p&lt0.0001). In animals with OLP transplants, histological analysis indicated that nerve fibres, expressing neurofilament and serotonin were present at the transection site. Locomotive recovery of the hindlimbs occurred, similar to that seen after OECs transplantation. Retrograde labeling of medullary raphe neurons and gigantocellular reticular nucleus occurred following Fluororuby injection in the cord distal to the lesion, further supporting the supraspinal origin of the 5-HT innervation in the present studies. These results indicate that OLP is effective in promoting partial spinal cord repair. Chapter Five examines functional recovery of spinal reflex circuitry, ie., H-reflex excitability using paired stimuli, in OLP-transplanted rats compared with normal and respiratory lamina propria (RLP) transplanted animals. H-reflex amplitude of the conditioned response was significantly reduced in OLP transplanted rats compared to RLP transplanted animals (p&lt 0.05). Therefore, hindlimb reflex excitability can be modulated by OLP transplants after transection of the spinal cord in adult rats. Chapter Six examines whether functional recovery can occur if transplantation of OLP tissue is delayed by 1 month after the spinal cord transection. The BBB score was significantly higher in experimental rats (4.3???0.8 for OLP) compared with control animals (1.0???0.3, P&lt 0.001), but recovery was less than after acute transplantation. Asx before, histological assessment of OLP animals showed: a) serotonergic axons were present in the cord below the transection site; b) brainstem raphe nuclei was retrogradely labeled; c) bisbenzimide pre-labeled cells from OLP transplants migrated in host spinal cord. These changes were not seen in control animals. These results indicate that OLP has the ability to promote axonal regeneration in chronically injured cord of adult rats. Chapter Seven compares the results from these three types of intervention. In conclusion, these studies show that peripherally derived OECs or solid pieces of OLP can promote partial spinal cord repair in acute or chronic transection injuries. Such tissue might provide a potential source for autologous grafting in human paraplegia.

Thesis (Ph. D.)--University of Washington, 1997. / Vita. Includes bibliographical references (leaves [90]-110).

Thesis (Ph.D. in Neuroscience) -- University of Colorado Denver, 2008. / Typescript. Includes bibliographical references (leaves 140-153). Free to UCD Anschutz Medical Campus. Online version available via ProQuest Digital Dissertations;

As células provenientes do epitélio olfatório apresentam capacidade regenerativa durante toda a vida, embora este mecanismo ainda não esteja completamente elucidado. O potencial de diferenciação de células-tronco provenientes do epitélio olfatório de cães sem raça definida (Canis familiaris Linnaeus, 1758) foi avaliado utilizando-se 12 cães adultos e 12 cães com 60 dias de vida intra-uterina, oriundos do Hospital Veterinário da FMVZ-USP. Após coletado, o epitélio olfatório foi submetido a protocolo histológico padrão para hematoxilina-eosina, azul de toluidina e PAS. O material fixado em glutaraldeído 2,5% foi processado para observação sob microscopia eletrônica de transmissão. O índice de proliferação nuclear foi medido para detecção de PCNA e Ki67 nuclear. Células foram expandidas em cultura em meio D-MEM/F-12 acrescido de Soro Fetal Bovino hyclone (CO2-95% à 37ºC) para caracterização e diferenciação celular (osteogênica, adipogência e neurogênica). O cultivo das células provenientes do epitélio olfatório de cães com 60 dias de vida intra-uterina mostrou maior evolução em cultura quando comparados aos animais adultos, sendo as primeiras utilizadas para execução dos protocolos de caracterização e diferenciação. As células em cultivo apresentaram expressão CD29 positiva e marcação positiva para OCT-4, citoqueratina 18 (Ck18) e vimentina. A diferenciação osteogênica demonstrou, ao final de 21 dias, células com morfologia típica, caracterizadas pela coloração de Alizarin Red e Von Kossa. A diferenciação adipogênica mostrou pouco número de células, apresentando grânulos adipogênicos, corados por Oil Red, contudo sem morfologia típica. A diferenciação neurogênica demonstrou células que expressaram marcação para GFAP, Neurofilamentos, Oligodendrócitos e βtubulina III. As células isoladas a partir do epitélio olfatório de cães com 60 dias de vida intra-uterina evidenciaram populações de células-tronco, determinadas pela expressão de marcadores específicos e diferenciação em outros tipos de tecido, devendo-se considerar este epitélio como uma fonte potencial para aquisição de células, particularmente progenitores neuronais, que possam somar aos estudos e seu uso em terapia celular. / Olfactory cells demonstrate regenerative capacity along life, although, its mechanism is still obscure. We evaluated the differentiation capacity of olfactory stem cell of mongrel dogs (Canis familiaris Linnaeus, 1758) in 12 adult dogs and 12 fetuses at term (60 days of pregnancy) from the Veterinary Hospital of FMVZ-USP. Following the sampling, the epithelia were submitted to standard histological process and stained with HE, toluidine blue and PAS. Samples fixed with 2.5% glutaraldehyde solution were processed for transmission electron microscopy. Proliferative index were obtained with the detection of PCNA and Ki67. Cells were kept in culture in D-MEM/F-12 medium supplemented with hyclone bovine fetal serum (CO2-95% at 37ºC) for characterization and cell differentiation (osteogenesis, adipogenesis, and neurogenesis). Cell culture of fetuses at term demonstrated higher evolution in comparison to adult animals, being submitted to the protocols of characterization and differentiation. Cell culture demonstrated positive reaction for CD29, OCT-4, Ck18 (citokeratin) and vimentin. Osteogenic differentiation demonstrated, 21 days, typical morphological cells characterized by Alizarin Red and Von Kossa staining. Adipogenic differentiation demonstrated less number of cells containing granules, stained with Oil Red, although being not typical shape. Neurogenic differentiation demonstrated positive staining for GFAP, Neurofilament, Oligodendrocyte and III β-tubulin. Cells isolated from epithelia of fetuses at term demonstrated population of stem cells determined by the expression of specific-staining and differentiation into other type of cells, which lead us to consider the olfactory epithelia as a source of potential stem cells particularly for neurogenic differentiation to be applied for further studies in cell therapy.

Pattern formation during development is guided by tightly controlled gene regulatory networks that lead to reproducible cell fate outcomes. However, stochastic choices are often employed to further diversify cell fates. These two mechanisms are closely interlinked in the mouse olfactory system, where stochastic expression of one of one out of >1,000 olfactory receptor (OR) genes is restricted to anatomical segments, or “zones”, organized along the dorsoventral axis of the olfactory epithelium (OE). Despite recent progress in understanding the processes underlying OR choice, the mechanism by which the dorsoventral position of an olfactory sensory neuron (OSN) dictates its OR repertoire has remained elusive and is the focus of this thesis. To gain insight into a possible mechanism I compared the transcriptomes, chromatin landscape, and nuclear architecture of cells isolated from ventral and dorsal zonal segments of the OE. I determined the developmental window in which cells become restricted in their zonal OR repertoire and found this coincided with both the deposition of heterochromatic histone marks H3K9me3 and H3K79me3 on OR genes and their coalescence into a multi-chromosomal compartment. Comparing heterochromatin levels and OR compartment composition in OSNs from different zones, I determined in each case OR genes with more dorsal indexes have higher levels of H3K9me3/H3K79me3 and thus become silenced, while OR genes with more ventral indexes have no heterochromatin and consequently are excluded from OR compartments. Thus, ORs that are “competent” for activation are relatively more accessible, while still being recruited into the OR compartment where they can interact with the proximally positioned enhancer hub. I found that this mechanism is regulated by Nfi family transcription factors that are expressed in a ventral (high) to dorsal (low) gradient in the OE. Deletion of Nfi A, B and X transforms the heterochromatin and OR compartmentalization in ventral OSNs to a more dorsal state, and shifts their preferred OR repertoire towards more dorsal ORs. This result implicates Nfi proteins as key regulators of zonal OR expression. Finally, I probed the nuclear architecture in single cells to look for the source of stochastic choice within zonal segments. I found high variability in inter-chromosomal OR compartment and enhancer hub composition between individual OSNs that stemmed from the unpredictable and variable positioning of chromosomes in the interphase nucleus. Overall, this thesis provides evidence for a mechanism of zonal OR choice that combines deterministic restrictions imposed by a gradient of Nfi with random inter-chromosomal contacts.