Research Topics

We conduct a variety of research in our laboratory. Its features are a combination of morphological analysis and molecular biological methods. Especially we perform morphological observation by using various types of electron microscopes. This section introduces the three main research themes of our laboratory: "Analysis of neural circuits focused on the olfactory system", "Intercellular interactions that control the development of neural circuits", and "Reconstruction of spermatogonial niche and seminiferous tubules. The Urothelial cell biology in bladder".

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Analysis of neurological circuits centering on the olfactory system
(Professor Toida, Assistnat Professor Notsu, AssistantProfessor Horie, Assistnat Professor Sato, Professor Kiyokage)

Figure 1. Neural Circuit of the Olfactory Bulb, the Primary Center of Olfactory System

　Olfactory Nerve (ON), the primary neuron of the olfactory system, enter the olfactory bulb (OB) and terminate in the glomerulus (sky bule circle) at the superficial layer of the OB. In the glomerulus, the ON then synapse to projection neurons, Mitral/Tufted cells (M/T cells; the secondary neurons), which send olfactory information to higher center in the brain. On the way of projection, M/T cells made synaptic contacts with juxtaglomerular (JG) cells in the glomerular layer (GL) and with granule cells in the granule cell layer (GCL), where olfactory information processing are performed. JG cells have subpopulations depending of chemical substances in them. Tyrosine Hydroxy (TH) neurons received direct synaptic input from ON. TH neuron also received asymmetrical synapse from M/T cells and made symmetrical synapse to the different M/T cells. TH neuron do not make reciprocal synapse with the same M/T cells but formed serial synapse between different M/T cells. In contrast, Calbindin (CB)-neurons do not receive synapse from ON but form reciprocal synapse with M/T cells. These findings indicate that TH-neurons and CB-neurons might be concerned to odor-discrimination and olfactory sensitivity, respectively.

　(Toida Anat. Sci. I. Int. 2008, Kiyokage et al J. Neurosci. 2010, Kiyokage et al J. Comp. Neurol. 2017, Matsuno et al J. Comp. Neurol. 2017, Notsu et al Microscopy 2019)

Figure 2. Regulation of Olfactory Bulb Neural Circuit by Centrifugal Input

　Olfactory bulb neural circuit is regulated by centrifugal projection from other brain regions. As representative inputs, Serotonergic neurons from Raphe nucleus (RN), Cholinergic neurons from Horizontal limb of Diagonal band of Broca (HDB), and Noradrenergic neurons from Locus Coeruleus (LC) have been well known. Fig. 2 indicates input patters to the OB by Acetylcholine (Ach) neurons and Fig.3 indicates by Noradrenergic (NA) neurons. Fiber of Ach-neurons are dense in the glomerular layer (including intraglomerular region) and internal plexiform layer but those of NA-neurons are dense in the glomerular layer (excluding intraglomerular region) and external plexiform layer, thus indicating complementally innervating pattern. The both types paly roles in regulation of olfactory circuit.

　 (Suzuki et al J. Comp. Neurol. 2015, Hamamoto et al J. Comp. Neurol. 2017, Horie et al J. Comp. Neurol. 2021)

Cell-cell interactions underlying neuronal wiring in brain development.（Associate Professor Syuich Hayashi）

Fig.3. Model for Protocadherin-17 (Pcdh17)-dependent regulation of collective axon growth in brain development. Non-clustered protocadherins, a group of cell-cell adhesion molecules, are expressed in the developing brain of vertebrates. Although previous studies have suggested that non-clustered protocadherins are involved in the maintenance of neural progenitors, axon extension and synapse formation, the underlying mechanisms are largely unknown. We found that Pcdh17 is localised at axon-axon contacts of neurons in the medial amygdala and recruits actin polymerisation regulators including WAVE-complex proteins and Ena/VASP to the contact sites. Axons lacking Pcdh17 stop their migration when they contact with each other, suggesting that Pcdh17 is required for axons to extend together. We propose that Pcdh17 counteracts with ‘contact inhibition of locomotion’ by recruiting actin polymerisation regulators to axon-axon contact sites and thereby sustains collective axon extension.

Fig.4. 3D-electron microscopy imaging of axon terminals in the posterior thalamic nucleus (Po). First-order thalamic nuclei, such as the ventrobasal complex (VB), relay sensory information from the periphery to the cerebral cortex, whereas higher-order nuclei such as Po receive main inputs from cortical layer 5. Recent studies have suggested that higher-order nuclei are essential for information transfer between different cortical areas. To understand the synaptic development of higher-order thalamic nuclei, we use a transgenic mouse line, in which layer 5 neurons in the cerebral cortex are labelled with Cre-driven fluorescence. We have shown that activity of cortical layer 5 is required for the maturation of complex synaptic structures in Po (B, control; C, Snap25-cKO). We are currently focusing on the molecular mechanisms for synaptic maturation in higher-order thalamic nuclei and their function in sensorimotor coordination.

Reconstruction of spermatogonial niche and seminiferous tubules. The Urothelial cell biology in bladder.（Assistant Professor Tetsuhiro Yokonishi）

Fig5． Reconstruction of spermatogonial niche and seminiferous tubules. We found the drug to ablate Sertoli cells and replace spermatogonial stem cells and spermatogonial niche components such as Sertoli cells, PTM and Leydig cells with combination of seminiferous transplantation. This technique allows us to invest the application of xenogeneic transplantation for preserving endangered species and fertility of young cancer patients. Now we’re focusing on 1. Establishing more efficient method to rebuilt seminiferous tubules, 2. Xenogeneic transplantation between mice and Rats, cats and pigs, and 3. Sertoli cell regeneration after drug treatment especially contribution of Sertoli cells in transitional zone.

Fig6．The Urothelial cell biology in bladder. Urothelial cells play important role for prevent urine from invading human body by producing uroplakin and constitution of tight junction at surface, but whose biology is not fully appreciated. We’re trying to reveal their function and regeneration by using urothelial cell depletion model.