Takami Naoya, Kato Kagayaki, Yoshihi Koya, Kawamura Akihito, Iida Hideaki, Kondoh Hisato
Faculty of Life Sciences, Kyoto Sangyo University, Kyoto, Japan.
Optics and Imaging Facility, Trans-Scale Biology Center, National Institute for Basic Biology, Okazaki, Japan.
Front Cell Dev Biol. 2025 May 21;13:1599287. doi: 10.3389/fcell.2025.1599287. eCollection 2025.
Although Otx2 has been a topic of research for over 3 decades, the role of Otx2 expressed in the brain-forming anterior epiblast during gastrulation has not been clarified. We focused on epiblast regions where Otx2 expression is absent or downregulated, namely, the posterior epiblast and tissue belts along the bending of the neural plate. The developmental events that occurred after filling these gaps with exogenous Otx2 provided information about the roles of Otx2 during gastrulation. The following pleiotropic effects were observed: (1) development of an open and flat midbrain and hindbrain, which occurred by unzippering the previously closed neural tube; (2) precocious neural tube development at the cervical level, which resulted in thick and unclosed neural tissue; (3) absence of the sinus rhomboidalis, where neuromesodermal progenitor (NMP) stem cells multiply to provide a cell source for the trunk posterior extension; and (4) inhibition of somite development. To elucidate the principles underlying these developmental abnormalities, the cellular events were analyzed using live imaging of epiblast cells, the cell states were characterized via transcriptome analysis, and the spatial organization of transcription factor expression was determined by immunohistology. Common Otx2 activities that accounted for these pleiotropic effects were identified: (1) significant promotion of neuroepithelium development, which overrides the bipotential nature of NMPs, resulting in the loss of paraxial mesoderm precursors and multiplying NMP stem cell populations, and (2) the development of bending-refractory neural tissues. Owing to these Otx2 functions, Otx2-expressing anterior epiblast cells develop into vast amounts of brain tissue in advance of trunk neurogenesis, which occurs on a much smaller scale. We did not observe that exogenous Otx2 expression affected CNS regional specification during gastrulation.
尽管Otx2已经成为30多年来的研究课题，但原肠胚形成过程中在形成大脑的前外胚层中表达的Otx2的作用尚未阐明。我们聚焦于Otx2表达缺失或下调的外胚层区域，即后外胚层和沿神经板弯曲处的组织带。用外源性Otx2填补这些间隙后发生的发育事件提供了有关原肠胚形成过程中Otx2作用的信息。观察到以下多效性效应：（1）开放且扁平的中脑和后脑的发育，这是通过拉开先前闭合的神经管实现的；（2）颈部水平神经管的早熟发育，导致神经组织增厚且未闭合；（3）菱形窦缺失，神经中胚层祖细胞（NMP）在那里增殖以为躯干后延伸提供细胞来源；（4）体节发育受到抑制。为了阐明这些发育异常背后的原理，通过外胚层细胞的实时成像分析细胞事件，通过转录组分析表征细胞状态，并通过免疫组织学确定转录因子表达的空间组织。确定了导致这些多效性效应的常见Otx2活性：（1）显著促进神经上皮发育，这超越了NMP的双能性质，导致近轴中胚层前体的丧失和NMP干细胞群体的增殖，以及（2）抗弯曲神经组织的发育。由于这些Otx2功能，表达Otx2的前外胚层细胞在躯干神经发生之前就发育成大量脑组织，而躯干神经发生的规模要小得多。我们没有观察到外源性Otx2表达在原肠胚形成过程中影响中枢神经系统区域特化。
