Molecular composition and expression pattern of the extracellular matrix in a mossy fiber-generating precerebellar nucleus of rat, the prepositus hypoglossi

Analysis of the expression and distribution of protein O-linked mannose β1,2-N-acetylglucosaminyltransferase 1 in the normal adult mouse brain

Introduction

Protein O-linked mannose β1,2-N-acetylglucosaminyltransferase 1 (POMGNT1) is crucial for the elongation of O-mannosyl glycans. Mutations in POMGNT1 cause muscle-eye-brain (MEB) disease, one of the main features of which is anatomical aberrations in the brain. A growing number of studies have shown that defects in POMGNT1 affect neuronal migration and distribution, disrupt basement membranes, and misalign Cajal-Retzius cells. Several studies have examined the distribution and expression of POMGNT1 in the fetal or neonatal brain for neurodevelopmental studies in the mouse or human brain. However, little is known about the neuroanatomical distribution and expression of POMGNT1 in the normal adult mouse brain.

Methods

We analyzed the expression of POMGNT1 mRNA and protein in the brains of various neuroanatomical regions and spinal cords by western blotting and RT-qPCR. We also detected the distribution profile of POMGnT1 in normal adult mouse brains by immunohistochemistry and double-immunofluorescence.

Results

In the present study, we found that POMGNT1-positive cells were widely distributed in various regions of the brain, with high levels of expression in the cerebral cortex and hippocampus. In terms of cell type, POMGNT1 was predominantly expressed in neurons and was mainly enriched in glutamatergic neurons; to a lesser extent, it was expressed in glial cells. At the subcellular level, POMGNT1 was mainly co-localized with the Golgi apparatus, but expression in the endoplasmic reticulum and mitochondria could not be excluded.

Discussion

The present study suggests that POMGNT1, although widely expressed in various brain regions, may has some regional and cellular specificity, and the outcomes of this study provide a new laboratory basis for revealing the possible involvement of POMGNT1 in normal physiological functions of the brain from a morphological perspective.

Development of the human perihypoglossal nuclei from mid-gestation to the perinatal period: A morphological study

INTRODUCTION

Morphological data on the development of the human perihypoglossal nuclei (PHN) are scarce. This study describes the morphology of the human PHN from mid-gestation to the perinatal period.

MATERIALS AND METHODS

Ten brains were collected from infants aged 21-43 postmenstrual weeks (PW). Serial sections were cut and stained using the Klüver-Barrera method. Morphometric parameters [volume, neuronal numerical density (Nv) and total number (Nt), and neuronal profile area (PA)] were analyzed from microscopic observations.

RESULTS

Four PHN [nucleus of Roller (RO), interfascicular nucleus (IF), intercalated nucleus (IC), and prepositus nucleus (PR)] were identified at 21 PW. Medium-sized to large, oval, or polygonal neurons were concentrated in the ventral nuclei (RO and IF) and localized regions near the IC-PR transition of the dorsal nuclei (IC and PR). Small to large neurons of various shapes were scattered across the dorsal nuclei. The PR showed rostrocaudal differences in the neuronal cytoarchitecture. The volume of each nucleus increased between 21 and 43 PW, with a typical exponential increase for the dorsal nuclei. The Nv in each nucleus exponentially decreased, whereas the Nt was almost stable. The median PA linearly increased for every nucleus, and the increasing rates were greater for the ventral nuclei than those for the dorsal nuclei.

CONCLUSIONS

The dorsal and ventral PHN are identifiable at mid-gestation. The topographic relationships of the four nuclei are conserved until the perinatal period. The characteristic neuronal cytoarchitecture of each group is rapidly formed by 28-30 PW.

Hapln1b, a central organizer of the extracellular matrix, modulates kit signalling to control developmental haematopoiesis

During early vertebrate development, hematopoietic stem and progenitor cells (HSPCs) are produced from hemogenic endothelium located in the dorsal aorta, before they migrate to a transient niche where they expand, the fetal liver and the caudal hematopoietic tissue (CHT), in mammals and zebrafish, respectively. In zebrafish, previous studies have shown that the extracellular matrix (ECM) around the aorta needs to be degraded to allow HSPCs to leave the aortic floor and reach blood circulation. However, the role of the ECM components in HSPC specification has never been addressed. We show here that hapln1b, a key component of the ECM is specifically expressed in hematopoietic sites in the zebrafish embryo. Gain- and loss-of-function experiments all resulted in the absence of HSPCs in the early embryo, showing that hapln1b is required, at the correct level, to specify HSPCs in the hemogenic endothelium. Furthermore, we show that the expression of hapln1b is necessary to maintain the integrity of the ECM through its link domain. By combining functional analyses and computer modelling, we show that kitlgb interacts with the ECM to specify HSPCs. We demonstrate that the ECM is an integral component of the microenvironment and mediates cytokine signalling that is required for HSPC specification.

Distinct proportions of cholinergic neurons in the rat prepositus hypoglossi nucleus according to their cerebellar projection targets

Cerebellar functions are modulated by cholinergic inputs, the density of which varies among cerebellar regions. Although the prepositus hypoglossi nucleus (PHN), a brainstem structure involved in controlling gaze holding, is known as one of the major sources of these cholinergic inputs, the proportions of cholinergic neurons in PHN projections to distinct cerebellar regions have not been quantitatively analyzed. In this study, we identified PHN neurons projecting to the cerebellum by applying retrograde labeling with dextran-conjugated Alexa 488 in choline acetyltransferase (ChAT)-tdTomato transgenic rats and compared the proportion of cholinergic PHN neurons in the PHN projections to four different regions of the cerebellum, namely the flocculus (FL), the uvula and nodulus (UN), lobules III-V in the vermis (VM), and the hemispheric paramedian lobule and crus 2 (PC). In the PHN, the percentage of cholinergic PHN neurons was lower in the projection to the FL than in the projection to the UN, VM or PC. Preposito-cerebellar neurons, except for preposito-FL neurons, included different proportions of cholinergic neurons at different rostrocaudal positions in the PHN. These results suggest that cholinergic PHN neurons project to not only the vestibulocerebellum but also the anterior vermis and posterior hemisphere and that the proportion of cholinergic neurons among projection neurons from the PHN differs depending on cerebellar target areas and the rostro-caudal regions of the PHN. This study provides insights regarding the involvement of cerebellar cholinergic networks in gaze holding.

Distribution of the Extracellular Matrix in the Pararubral Area of the Rat

Previously we described similarities and differences in the organization and molecular composition of an aggrecan based extracellular matrix (ECM) in three precerebellar nuclei, the inferior olive, the prepositus hypoglossi nucleus and the red nucleus of the rat associated with their specific cytoarchitecture, connection and function in the vestibular system. The aim of present study is to map the ECM pattern in a mesencephalic precerebellar nucleus, the pararubral area, which has a unique function among the precerebellar nuclei with its retinal connection and involvement in the circadian rhythm regulation. Using histochemistry and immunohistochemistry we have described for the first time the presence of major ECM components, the hyaluronan, aggrecan, versican, neurocan, brevican, tenascin-R (TN-R), and the HAPLN1 link protein in the pararubral area. The most common form of the aggrecan based ECM was the diffuse network in the neuropil, but each type of the condensed forms was also recognizable. Characteristic perineuronal nets (PNNs) were only recognizable with Wisteria floribunda agglutinin (WFA) and aggrecan staining around some of the medium-sized neurons, whereas the small cells were rarely surrounded by a weakly stained PNNs. The moderate expression of key molecules of PNN, the hyaluronan (HA) and HAPLN1 suggests that the lesser stability of ECM assembly around the pararubral neurons may allow quicker response to the modified neuronal activity and contributes to the high level of plasticity in the vestibular system.

Heterogeneous expression of extracellular matrix molecules in the red nucleus of the rat

Previous studies in our laboratory showed that the organization and heterogeneous molecular composition of extracellular matrix is associated with the variable cytoarchitecture, connections and specific functions of the vestibular nuclei and two related areas of the vestibular neural circuits, the inferior olive and prepositus hypoglossi nucleus. The aim of the present study is to reveal the organization and distribution of various molecular components of extracellular matrix in the red nucleus, a midbrain premotor center. Morphologically and functionally the red nucleus is comprised of the magno- and parvocellular parts, with overlapping neuronal population. By using histochemical and immunohistochemical methods, the extracellular matrix appeared as perineuronal net, axonal coat, perisynaptic matrix or diffuse network in the neuropil. In both parts of the red nucleus we have observed positive hyaluronan, tenascin-R, link protein, and lectican (aggrecan, brevican, versican, neurocan) reactions. Perineuronal nets were detected with each of the reactions and the aggrecan showed the most intense staining in the pericellular area. The two parts were clearly distinguished on the basis of neurocan and HAPLN1 expression as they have lower intensity in the perineuronal nets of large cells and in the neuropil of the magnocellular part. Additionally, in contrast to this pattern, the aggrecan was heavily labeled in the magnocellular region sharply delineating from the faintly stained parvocellular area. The most characteristic finding was that the appearance of perineuronal nets was related with the neuronal size independently from its position within the two subdivisions of red nucleus. In line with these statements none of the extracellular matrix molecules were restricted exclusively to the magno- or parvocellular division. The chemical heterogeneity of the perineuronal nets may support the recently accepted view that the red nucleus comprises more different populations of neurons than previously reported.

In Sickness and in Health: Perineuronal Nets and Synaptic Plasticity in Psychiatric Disorders

Rapidly emerging evidence implicates perineuronal nets (PNNs) and extracellular matrix (ECM) molecules that compose or interact with PNNs, in the pathophysiology of several psychiatric disorders. Studies on schizophrenia, autism spectrum disorders, mood disorders, Alzheimer's disease, and epilepsy point to the involvement of ECM molecules such as chondroitin sulfate proteoglycans, Reelin, and matrix metalloproteases, as well as their cell surface receptors. In many of these disorders, PNN abnormalities have also been reported. In the context of the “quadripartite” synapse concept, that is, the functional unit composed of the pre- and postsynaptic terminals, glial processes, and ECM, and of the role that PNNs and ECM molecules play in regulating synaptic functions and plasticity, these findings resonate with one of the most well-replicated aspects of the pathology of psychiatric disorders, that is, synaptic abnormalities. Here we review the evidence for PNN/ECM-related pathology in these disorders, with particular emphasis on schizophrenia, and discuss the hypothesis that such pathology may significantly contribute to synaptic dysfunction.