Biology subjects

Hirai, K.

Publications and source records attributed to Hirai, K..

3 recordsLinked to original sources

bioRxiv2023

Spatial transcriptome of developmental mouse brain reveals temporal dynamics of gene expressions and heterogeneity of the claustrum

During the development of the mammalian cerebral cortex, numerous neurons are arranged in a six-layer structure with an inside-out fashion to form the neocortex and wire neural circuits. This process includes cell proliferation, differentiation, migration, and maturation, supported by precise genetic regulation. To understand this sequence of processes at the cellular and molecular levels, it is necessary to characterize the fundamental anatomical structures by gene expression. However, markers established in the adult brain sometimes behave differently in the fetal brain, actively changing during development. Spatial transcriptomes yield genome-wide gene expression profiles from each spot patterned on tissue sections, capturing RNA molecules from fresh-frozen sections and enabling sequencing analysis while preserving spatial information. However, a deeper understanding of this data requires computational estimation, including integration with single-cell transcriptome data and aggregation of spots on the single-cell cluster level. The application of such analysis to biomarker discovery has only begun recently, and its application to the developing fetal brain is largely unexplored. In this study, we performed a spatial transcriptome analysis of the developing mouse brain to investigate the spatiotemporal regulation of gene expression during development. Using these data, we conducted an integrated study with publicly available mouse data sets, the adult brains spatial transcriptome, and the fetal brains single-cell transcriptome. Our data-driven analysis identified novel molecular markers of the choroid plexus, piriform cortex, thalamus, and claustrum. In addition, we revealed that the internal structure of the embryonic claustrum is composed of heterogeneous cell populations.

developmental biology↗

bioRxiv2022

ADAMTS2 regulates radial neuronal migration by activating TGF-β signaling at the subplate layer of the developing neocortex

During the development of the mammalian brain, neocortical structures are formed by the sequential radial migration of newborn excitatory neurons. The early migrating neurons exhibit a multipolar shape, but they undergo a multipolar-to-bipolar transition at the subplate (SP) layer, where extracellular matrix (ECM) components are abundantly expressed. In this study, we revealed that the TGF-{beta} signaling-related ECM proteins, such as latent TGF-{beta}-binding protein 1 (LTBP1) and fibrillin 2, and TGF-{beta} receptor II (TGF-{beta}RII) and its downstream effector, p-smad2/3, are selectively expressed at the SP layer, suggesting that TGF-{beta} is sequestered in a latent form by forming complexes with these ECM components and then its signaling is activated by ECM remodeling. We found that the migrating multipolar neurons transiently express a disintegrin and metalloproteinase with thrombospondin motif 2 (ADAMTS2), an ECM metalloproteinase, just below the SP layer. Knockdown and knockout of Adamts2 suppressed the multipolar-to-bipolar transition of migrating neurons, and therefore, disturbed radial migration. Similar phenotypes were observed by the perturbation of TGF-{beta} signaling in the migrating neurons. Time-lapse luminescence imaging of TGF-{beta} signaling indicated that ADAMTS2 activates this signaling pathway in the migrating neurons during the multipolar-to-bipolar transition at the SP layer. These results suggest that the ADAMTS2 secreted by the migrating multipolar neurons activates TGF-{beta} signaling by ECM remodeling of the SP layer, leading to the multipolar-to-bipolar transition. We propose that the SP layer plays an essential role in the radial neuronal migration as a signaling center of the developing neocortex. SIGNIFICANCEThe neocortex is formed by the sequential radial migration of newborn neurons, which undergo a multipolar-to-bipolar transition at the subplate (SP) layer. The extracellular matrix (ECM) is abundantly expressed in the SP layer. However, the roles of the ECM in the SP layer have been unclear. We found that migrating neurons transiently express a disintegrin and a metalloproteinase with thrombospondin motif 2 (ADAMTS2), an ECM metalloproteinase, just below the SP layer. We show that ADAMTS2 secreted by multipolar migrating neurons activates TGF-{beta} signaling through remodeling of the ECM in the SP layer, leading to the multipolar-to-bipolar transition. Thus, the SP layer plays an essential role in radial migration as a signaling center of the developing neocortex

neuroscience↗

bioRxiv2021

Transcriptome features of trained immunity in Drosophila

Immune memory is an ability of organisms to potentiate immune responses at secondary infection. Current studies have revealed that innate immunity, as well as adaptive immunity, exhibits the memory character called "trained immunity". Although it is suggested that epigenetic reprogramming plays important roles in trained immunity, its underlying mechanism is not fully understood, especially on the individual level. Here we established experimental systems for detecting trained immunity in Drosophila melanogaster. Namely, training infection with low-pathogenic bacteria enhanced the survival rate of the flies at subsequent challenge infection with high-pathogenic bacteria. We found that among low-pathogenic bacteria, Micrococcus luteus (Ml) and Salmonella typhimurium (St) mediated apparent training effects in fly, but seemed to act through different ways. Ml left training effects even after its removal from flies, while living St persisted inside flies for a long time. Our RNA-Seq analysis revealed that Ml-training enhanced the expression of immune-related genes during the challenge infection, but did not do so without challenge infection. In contrast, St-training maintained high expression of the immune-related genes with or without challenge. These results suggest that training effects with Ml and St were due to memory and persistence of immune responses, respectively. Furthermore, we searched the factor involved in Ml-training and identified a candidate, Ada2b, which is a component of the histone modification complex. We found that the Ada2b RNAi and mutant flies showed dampened enhancement of survival rates after Ml-training. These results suggest that Ada2b is involved in the Drosophila trained immunity.

immunology↗