大脳皮質形成
Development of Cerebral Cortex
O3-6-4-1
大脳新皮質構築を担う哺乳類特異的分子機序の解析
Molecular logic underlying the origins of the neocortex

○隈元拓馬1, 花嶋かりな1
○Takuma Kumamoto1, Carina Hanashima1
理化学研究所 発生・再生科学総合研究センター1
Laboratory for Neocortical Development, RIKEN Center for Developmental Biology, Kobe, Japan1

The mammalian neocortex arises from the dorsal pallium and has characteristic six-layered structure that mediate higher-order information processing. Although homologous domains exist in sauropsids, neither avian or reptilian dorsal pallium exhibits identical layer structure despite their common gene expressions. Therefore, an interesting question remains how the six-layered neocortex is derived from a common ancestral pallium during evolution.We recently demonstrated that Foxg1, a conserved forkhead transcription factor expressed in the telencephalon, is a key regulatory gene in initiating projection neuron production in mouse neocortex. Using temporal transcriptome and ChIP-sequencing, we further show that Foxg1 binds to highly mammalian-conserved non-coding sequences to repress a global gene program during this early event, whereas these sequences were under-represented in the non-mammalian vertebrates. A large portion of these Foxg1 suppressed genes were expressed in earliest-born neuron class, namely the Cajal-Retzius (CR) cells. CR cells play crucial roles in radial neuron migration through its secretion of the glycoprotein Reelin, and recent studies have implied that CR cells expand both in number and molecular diversity in mammalian vertebrates, where direct comparison to the closest ancestral chimpanzees have identified an evolutionally accelerated gene expressed in human CR cells. Here, we report seven novel genes that are expressed in mouse CR cells. Consistent with our ChIP-seq data, comparative expression analysis in birds and primates implies that these genes are differentially regulated amongst the mammalian and non-mammalian vertebrates. Our studies indicate that the molecular diversity of CR cells and its mammalian-specific regulatory system may be a primary step in transforming a dorsal pallium into a six-layered neocortical structure.
O3-6-4-2
発生期終脳におけるグリア細胞に蓄積するグリコーゲン顆粒の解析
The role of glial glycogen in the developing telencephalon

○後藤仁志1, 野村真1, 小野勝彦1
○Hitoshi Gotoh1, Tadashi Nomura1, Katsuhiko Ono1
京都府立医大 神経発生生物1
Dept of Biol, Kyoto Pref Univ of Medicine, Kyoto1

It is known that metabolic activity affects cellular events such as cell cycle progression. In the central nervous system, glial cells are known to support energy status. Glycogen, which is a branched polysaccharide and serves as energy stores, is reported to be present in astrocytes and serves as a resource of lactate in the adult. However, the localization of glycogen during development remains to be elucidated.We examined the glycogen localization by classical Periodate Acid Schiff (PAS) staining. In the developing telencephalon, we found that PAS-positive granule is observed after E16 and highly accumulated in the cells along the rostral migratory stream. Double immunohistochemical staining shows that accumulated glycogen particles are present in GLAST-positive immature glial cells but not in the DCX or Tuj1-positive neuronal lineage cells in the subventricular zone and the rostral migratory stream. We also found that the content of glycogen is decreased upon birth concomitant with activation of glycogen phosphorylase, a rate-limiting enzyme of glycogenolysis. Furthermore, inhibition of early postnatal (P0-P2) glycogen phosphorylase by injecting its inhibitor, 1, 4-dideoxy-1,4-imino-d-arabinitol (DAB), lead to decreased cell proliferation in immature glial cells near the ventricular zone. Moreover, decreased cell proliferation was not rescued by co-injecting lactate with DAB. These results suggest that embryonic glycogen might act as energy stores for metabolic changes upon early postnatal period only in restricted area. Moreover, the function of embryonic glycogen might not be mediated by intercellular lactate-shuttling, thus mediated thorough different mechanisms from mature astrocytes.
O3-6-4-3
Phosphatidylinositol 4-phosphate 5 kinaseγは 大脳皮質層形成において神経細胞の移動を制御する
Phosphatidylinositol 4-phosphate 5 kinaseγ is required for the neuronal migration in the mouse developing cerebral cortex

○原芳伸1, 深谷昌弘1, 阪上洋行1
○Yoshinobu Hara1, Masahiro Fukaya1, Hiroyuki Sakagami1
北里大学医学部 解剖学教室1
Dept Anatomy, Kitasato Univ, Kanagawa1

The mammalian cerebral cortex is composed of distinct six layers and undergoes dynamic processes during the development. Neurons were generated from neuroepithelal cells and migrate to their appropriate positions with an inside-out manner. Recent accumulating evidences revealed the functional importance of cytoskeleton and membrane trafficking in cortical migration, while it remains unclear the role of plasma membrane-derived signaling factors, such as phosphatidylinositol (4,5)-bisphosphate (PIP2) and phosphatidylinositol (3,4,5)-bisphosphate (PIP3). Phosphatidylinositol 4-phosphate 5-kinase (PIP5K)γ is one of phosphoinositide kinases that produce PIP2. Despite the evidences for the importance of PIP5Kγ-mediated PIP2 in mature neuronal functions, the roles of PIP5Kγ in the neural development remain elusive. To address this issue, we examined the functional roles of PIP5Kγ in the cortical formation. RT-PCR analysis revealed that among three splicing variants, PIP5Kγ661 and PIP5Kγ687 were expressed throughout the cortical development with distinct expression patterns. In situ hybridization analysis showed that PIP5Kγ mRNA started to express at the ventricular zone and was expressed throughout cortical layers. Immunohistochemical analysis revealed that PIP5Kγ was localized with a punctate manner in the radial glia and migrating neuroblasts. Knockdown of PIP5Kγ by in utero electroporation resulted in the decrease in the cell population invading to layer II-IV at P0 and the redistribution of talin and FAK from the plasma membrane to the cytoplasm. Moreover, overexpression of kinase-dead mutant of PIP5Kγ661, but not PIP5Kγ635 or PIP5Kγ687 inhibited neuronal migration. Taken together with the previous findings the implication of FAK and talin in the cortical formation, it is suggested that PIP5Kγ, especially PIP5Kγ661, may regulate the neuronal migration possibly through the assembly of focal adhesion in migrating neuroblasts.
O3-6-4-4
脳室下帯分裂細胞の産生調節に関わる分子の探索
Screening of the genes involving in the production of progenitor cells in the subventricular zone

○田畑秀典1,2, 榊原康文3, 永田浩一1, 仲嶋一範2
○Hidenori Tabata1,2, Yasubumi Sakakibara3, Koh-ichi Nagata1, Kazunori Nakajima2
愛知県心身障害者コロニー発達障害研究所 神経制御学部1, 慶應大・医・解剖2, 慶應大・理工・生命情報3
Dept Mol Neurobiol, Inst for Dev Res, Aichi Human Service Center1, Dep. Anat., Sch. Med., Keio Univ., Tokyo, Japan2, Dep. Biosciences and Informatics, Keio Univ., Kanagawa, Japan3

During the neocortical development, excitatory neurons are produced from the apical progenitors in the ventricular zone (VZ) or from the nonsurface progenitors in the SVZ. We previously reported the migratory difference between the direct progenies of the VZ and the further dividing cells in the SVZ. Former population finishes the cell division in the VZ, stays there for more than 10 hours, and then accumulates just above the VZ as multipolar cells. The other exits the VZ earlier than the former using a somal translocation mode, in which cells having long ascending process toward the pail surface shorten the process to translocate the cell body, distributes widely in the SVZ, and further divides. These populations are differ each other in the timing of VZ exit, we, therefore, called them slowly exiting population (SEP) and rapidly exiting population (REP), respectively. The histological locations, morphologies, and the mitotic activities of SEP and REP in mice well correlate with the inner SVZ (ISVZ) and outer SVZ (OSVZ) in primates, respectively. During the development of the human embryos, the OSVZ is expanded and becomes the main source of the cortical neurons. Hence, understanding the molecular mechanisms for REP production in mice is thought to be important to understand the cortical expansion during the human evolution. In the previous study we observed in mice that the REP production in the lateral region is higher than in the dorsomedial region. Taking advantage of this difference, we conducted a screening for genes involved in the regulation of REP production by DNA microarray analyses of these two regions. We identified 29 and 9 genes expressed in lateral-higher to medial-low gradient and the opposite gradient in the cortical VZ cells, respectively. We examined the function of candidates using in utero electroporation system, and identified several genes that can affect the REP production rate.
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