哺乳類の大脳皮質は6層構造を形成するが,特に胎生期および新生直後に層形成が盛んに進むことが知られている.胎生期の脳室に面する脳室帯において,神経幹細胞は神経前駆細胞を経て神経細胞へ分化し,さらに神経細胞が脳表層方向に移動することで6層構造が形成される(insideout).このことから,胎生期の脳室帯は脳の形成に重要な役割を果たしていると考えられる.本研究は,大脳皮質の形成メカニズムの解析を目的とし,脳室帯の組織構造に変化を与えた場合に,どのように脳形成システムに異常を来たすのか,検討を行った.脳室帯は上皮組織のため,細胞間結合が強固である.そこで,上皮細胞間のカルシウム(Ca^)依存性接着分子であるカドヘリンに着目し,脳室面の細胞間結合の阻害が脳形成に与える影響を観察した.実験手法として,マウス胎生14.5日目の脳室内へ,Ca^を特異的にキレートするEGTA(Ethylene glycol tetraacetic acid)を注入したのち,胎生期および生後の脳組織構造について詳細な解析を行った.解析の結果,高濃度のEGTAの作用により,一部のマウスは脳浮腫をきたした.また脳室の拡大および大脳皮質の菲薄化も認めた.さらに,大脳皮質各層のマーカーであるSATB2(2/3層),Ctip2(5層)を用いた解析から,脳室帯の細胞間接着構造の破壊により,それ以降の神経細胞の新生は減少するが,層構造のinside-outの法則は維持されていることが分かった.これらのことより,脳室帯構造および脳室帯での神経新生が,inside-outの原理に関与している可能性は低いことがわかった.The cerebral cortex of mammals is a structure consisting of six layers. The progression of layer formation is known to be particularly active during the embryonic and immediate postnatal periods. In the ventricular zones, which adjoin the embryonic cerebral ventricles, neural stem cells differentiate first into neuronal precursor cells and then into neurons. The neurons then migrate toward the surface layer of the brain, forming the 6-layered structure (inside-out). The ventricular zones are thus thought to play an important role in the formation of the brain during the embryonic period. We therefore examined how altering the tissue structure of the cerebral ventricular zones results in abnormalities of the brain formation system. Because the ventricular zones consist of epithelial tissue, the cell junctions are rigid. Consequently, we observed the effect on brain formation of disrupting cell junctions on the ventricular surface, focusing on cadherins, which are calcium (Ca^)-dependent adhesion molecules between epithelial cells. The experimental method involved injecting ethylene glycol tetraacetic acid (EGTA), which specifically chelates Ca^, into the cerebral ventricles of 14.5-day-old mouse embryos, then analyzing the tissue structure of the brain in the embryonic and postnatal periods in detail. The results showed that EGTA at high concentration resulted in cerebral edema in some mice. Enlargement of the cerebral ventricles and thinning of the cerebral cortex were also observed. In addition, analysis using SATB2 as a marker of layers 2 and 3 and Ctip2 as a marker of layer 5 showed that although subsequent neurogenesis decreased with the breakdown of the adhesive structure of the ventricular zones, the inside-out rule was maintained for the layer structure. These findings show that the ventricular zone structure and neurogenesis in the ventricular zones are unlikely to play a role in the mechanism underlying the inside-out principle
