The mouse olfactory bulb (OB) has highly populated and molecularly varied interneurons. In particular, more than half of the interneurons in the mouse OB are developed during the first week after birth, and dominantly connect to neural circuits with excitatory tufted cells near the superficial granule cell layer, unlike late-born interneurons. However, the molecular mechanism underlying the temporal specification and physiological functions of superficial granule cells are yet to be identified. In this study, I marked only postnatal early-born OB interneurons by incorporating 5-bromo-2’-deoxyuridine (BrdU) at postnatal day 0 (P0) aged-mice and found that early-born interneu-rons are dominantly integrated into superficial granule cell layer, differentially with late-born interneu-rons. To determine the molecular-driving force for arriving into superficial granule cell layer of early-born OB interneurons, I investigated the migratory machineries in early-born OB interneurons. I dis-closed the temporal developmental role of Abelson Tyrosine-Protein Kinase 1 (Abl1) in the early-born OB interneurons. Lentiviral knock-down of Abl1 disrupts superficial granule cell layer-specific circuits of the early-born OB interneuron by integratory and functional defects, resulting in enhanced olfactory sensitivity. From a proteomics approach, I identified that Doublecortin (Dcx) as a timely substrate of Abl1 in OB during postnatal early stage and further found that the phosphorylation of Dcx by Abl1 con-tributes to the stabilization of Dcx, thereby regulating microtubule dynamics. Finally, restoration of Dcx rescues anatomical deficits as well as dysregulated olfactory detection by knock-down of Abl1 in vivo. In summary, I disclosed that postnatal early-born OB interneurons are predominantly inte-grated into superficial granule cell layer, migrating farther distances than late-born interneurons. Espe-cially, the Abl1-Dcx signaling in the early-born OB interneurons facilitates their long migration into su-perficial granule cell layer by regulating microtubule dynamics. In addition, the temporal development of superficial granule cell-circuit is critical for formation of primary olfactory behaviors, such as detec-tion and sensitivity. This my study will provide new insights for an advanced understanding of the neu-rodevelopmental disorder patients having enhanced sensory sensitivity.
Table Of Contents
Ⅰ. Introduction 1.1 Fundamental architecture of brain: lamination. 1 1.2 Assemblies in the brain: neurons. 1 1.3 Minority, but amazing cell type: interneuron. 3 1.3.1 Interneuron diversity. 3 1.3.2 Birth-timing of interneurons as a good predictor of their positioning. 3 1.4 Interneurons in the olfactory bulb (OB). 6 1.4.1 Distinct features of OB interneurons. 6 1.4.2 OB interneuron diversity. 9 18.104.22.168 A great number of granule cells. 9 22.214.171.124 Other interneurons. 12 1.4.3 Segregation of OB interneurons based on their birth-time. 12 126.96.36.199 Distributed positioning of granule cells by their birth-time. 14 188.8.131.52 Distinct circuits between early- and late-born interneurons. 14 1.5 Migratory machineries for correct neuronal positioning during development. 16 1.5.1 Tyrosine phosphorylation as a migratory machinery. 16 1.5.2 Abl1 (Abelson Tyrosine-Protein Kinase 1). 16
Ⅲ. Characterization of Postnatal Early-born OB Interneurons. 3.1 Background. 26 3.2 Results. 27 3.2.1 Distribution of interneurons in OB Layers based on their birth-time. 27 3.2.2 Integration of P0-generated OB Interneurons into superficial GCL. 27 3.3 Discussion. 30
Ⅳ. Driving Force for Arriving into Final Destination of Postnatal Early-born Interneurons. 4.1 Background. 31 4.2 Results. 32 4.2.1 Active wave of Abl1 expression during postnatal early OB development. 32 4.2.2 Requirement of Abl1 for proper localization of postnatal early-born interneu-rons into MCL and sGCL of OB. 36 4.2.3 Necessity of Abl1 for maturation and functionality of postnatal early-born OB interneurons. 41 4.2.4 Abl1 activity-dependent maturation of postnatal early-born OB interneu-rons.46 4.2.5 Dcx is a timely substrate of Abl1 in OB during postnatal early stage. 50 4.2.6 Phosphorylation at tyrosine 125 of Dcx by Abl1 regulate Dcx stability. 54 4.2.7 Abl1-Dcx signaling is involved in neuritogenesis via regulation of microtu-bule dynamics. 57 4.2.8 Restoration of Dcx rescues integratory deficits Abl1 KD in vivo. 60 4.2.9 Restoration of Dcx rescues anatomical deficits Abl1 KD in vivo. 64 4.3 Discussion. 68
Ⅴ. Innate Olfactory Behavior Development of Postnatal Early-born Interneu-rons. 5.1 Background. 72 5.2 Results. 72 5.2.1 Postnatal early stage-Abl1 deficient mice having the deficit in spontaneous odor-behaviors. 72 5.2.2 Pharmacological inhibition of Abl1 activity having the deficit in odor detec-tion. 77 5.2.3 Recovery of defective odor detection behavior in Dcx-restored Abl1 KD mice or Abl1 KA mice. 79 5.3 Discussion. 81
Ⅵ. Conclusion. 6.1 Summary and conclusion. 82 6.2 Limitations and further studies. 84