Date of Award

1-1-2022

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

College/School/Department

Department of Biological Sciences

Content Description

1 online resource (x, 119 pages) : illustrations (some color)

Dissertation/Thesis Chair

Paolo E Forni

Committee Members

Melinda Larsen, Morgan Sammons, Jean-Francois Cloutier

Keywords

basal vomeronasal neurons, cell fate determination, Dll4 ligand, Notch signaling, Notch1 receptor, Vomeronasal organ, Jacobson's organ, Olfactory receptors, RNA, Neurons, Cellular signal transduction, Mice

Subject Categories

Biology | Developmental Biology | Neuroscience and Neurobiology

Abstract

The Vomeronasal organ (VNO) is a specialized olfactory sensory organ located in the ventral region of the nasal cavity in rodents. The vomeronasal epithelium (VNE) of rodents is composed of 2 major types of vomeronasal sensory neurons (VSNs): 1) VSNs distributed in the apical VNE regions that express vomeronasal type-1 receptors (V1Rs) and the G protein subunit Gi2, and 2) VSNs in the basal territories of the VNE that express vomeronasal type-2 receptors (V2Rs) and the G subunit Go. Besides these two neuronal types, VNE also accommodate a third non-neuronal cell type called Sustentacular cells that lie anatomically above apical and basal VSNs. Close to the lumen. Both V1R+ apical VSNs and V2R+ basal VSNs send their axons to distinct regions of the accessory olfactory bulb (AOB). Together, VNO and AOB form the accessory olfactory system (AOS), an olfactory subsystem that coordinates the social and sexual behaviors of many vertebrate species. In mice, both V1R and V2R+ VSNs form from a common pool of progenitors but have distinct differentiation programs. Interestingly VNO is one of the very few neuronal systems that can show adult neurogenesis throughout the life that is responsible for homeostasis in normal physiological conditions and regeneration in post injury conditions. During development, VNO is formed from the olfactory placode during the secondary invagination of olfactory pit. The vomeronasal epithelium (VNE) is believed to share multiple features with the epithelium of the main olfactory epithelium (MOE), however it has been less characterized compared to MOE.My doctoral research focused on two different aspects of the VNO development in mice - 1) identifying the mechanisms underlying the cell-fate determination of V1R+ apical and V2R+ basal VSNs, and 2) identifying horizontal basal cells, a second multipotent stem cell population in the VNO (vHBCs) and study their role in the development and adult neurogenesis in the VNO. We used single cell RNA sequencing of the adult VNO, Cre recombinase induced constitutive and conditional lineage tracing, gain of function and loss of function methods to study these developmental questions of the VNO. In the first part of my dissertation, we identified the differential expression of Notch1 receptor and Dll4 ligand among the neuronal precursors at the VSN dichotomy. We further demonstrated using loss of function studies that Notch signaling is required for the effective differentiation of V2R+ basal VSNs. Interestingly, gain of function studies gave two different phenotypes depending upon the cell stage where we artificially induced Notch signaling. Ectopic Notch signaling at the immediate neuronal precursors stage diverted them towards an expected basal VSN cell fate, however ectopic Notch expression at much earlier neuronal progenitor’s stage redirected them to a non-neuronal sustentacular cell fate. Together, these results demonstrate that Dll4-Notch1 signaling plays a crucial role in triggering the binary dichotomy between the two main types of VSNs in mice. Nonetheless, further research is needed to understand the formation of non-neuronal sustentacular cells. The second part of my dissertation showed the presence of vHBCs in the adult VNO similar to the MOE but show much delayed development. Constitutive and conditional lineage tracing techniques in normal physiological conditions reported that vHBCs are multipotent stem cells giving to rise to both neuronal and non-neuronal cells during both early postnatal development and in adult stages of the VNO. Overall, both the studies explored two long standing developmental questions in the VNO that further opened new areas of research.

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