Toxic effects of in utero exposure to dioxins on cerebral histogenesis: quantitative analysis using mathematical model of cerebral histogenesis.

2，3，7，8-四氯二苯并-对二恶英(TCDD)是一种普遍存在的环境污染物，可扰乱激素的动态平衡和更基本的细胞增殖行为。已知的在子宫内暴露于TCDD对组织发生的特定影响包括损害小鼠的免疫和泌尿生殖系统的发育以及甲状腺功能的损害。在细胞增殖行为方面，TCDD通过诱导肝癌细胞株和啮齿动物胎儿胸腺细胞中p27Kip1的表达来抑制G1期进展，宫内暴露TCDD可能与空间学习和记忆受损有关。这种损伤的细胞生物学基础及其对中枢神经系统组织发生的影响尚不清楚。由于细胞周期动力学受到p27Kip1作用在G1限制点的严格控制，我们认为TCDD暴露可能至少部分地作用于这一调节机制，从而扰乱脑组织发生。我们研究了由此产生的…通过观察出生后第21天脑组织细胞构筑和胎龄12天胎鼠脑室壁发育及细胞周期动力学，观察胎龄7天宫内暴露TCDD的可能性。方法在胎龄7天经口灌胃(20μg/kg体重)染毒C57BL/6N小鼠。我们分析了胚胎12天神经前体细胞(NPC)中细胞周期调控基因的表达水平和亚细胞定位模式、细胞周期各时相的长度、分化概率(Q)。此外，我们还测量了P21小鼠端脑的大小、皮质的厚度、GABA阳性神经元、阴性神经元和神经胶质细胞的数量和密度。结果子宫内暴露于TCDD后，E12时鼻咽癌细胞核内p27Kip1蛋白水平增加，细胞周期G1期长度增加，Q增加。暴露于TCDD的P21端脑显示出长度、宽度和皮质厚度的减少。这种皮质变薄主要是由于V-VIDD层非GABA能投射神经元数量减少所致。我们推测，TCDD暴露增加了鼻咽癌细胞核中p27Kip1蛋白的表达，导致了G1期和Q期的增加，从而过早地增加了Q，从而降低了神经发生过程中NPC的最大数目，从而减少了新皮质投射神经元的总量。我们推测，TCDD染毒小鼠V-VI层投射神经元数量的减少可能是由于TCDD染毒后Q分数异常增加，导致神经元命运从深层提前转变为浅层神经元表型所致。较少

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is a ubiquitous environmental pollutant known to disturb hormonal homeostasis as well as more fundamental cell proliferative behavior. Among the recognized specific effects upon histogenesis due to exposure to TCDD in utero are impairment of development of immune and urogenital systems in mice and impairment of thyroid function. With respect to cellular proliferative behavior, TCDD inhibits G1 phase progression by inducing p27Kip1 expression in a hepatoma cell line and in fetal thymocytesis In rodents exposure to TCDD in utero may be associated with impaired spatial learning and memory. The cell biological basis for this impairment and its consequences for CNS histogenesis are unknown. Because cell cycle kinetics is critically controlled at the G1 restriction point by the action of p27Kip1, we consider that TCDD exposure may act upon this regulatory mechanism, at least in part, to disturb cerebral histogenesis.We have investigated the conseque … More nce of TCDD exposure in utero on embryonic day (E) 7 upon cerebral histogenesis, by examining the cytoarchitecture of the postnatal day 21 brain and developing cerebral wall and cell cycle kinetics of the PVE at E12.MethodWe exposed C57BL/6N mice fetus with TCDD by oral gavage (20 μg/kg body weight) at E7. We analyzed 1.mRNA expression level and subcellular localization pattern of cell cycle regulatory genes, 2.length of each phase of cell cycle, 3.probability of differentiation (Q) in neuronal progenitor cells (NPC) at E12. Additionally, we measured 1.size of telencephalon, 2.thickness of cortices, 3.numbers and densities of GABA-positive, negative neurons and glial cells, respectively, in layer specific manner at P21 mice.ResultIn utero exposure to TCDD resulted in 1.increase in p27Kip1 protein level in nuclei, 2.increase in length of G1 phase of cell cycle, 3.increase in Q in NPC at E12. TCDD-exposed P21 telencephalon showed decrease in length, width, and cortical thickness. This cortical thinning was mainly due to decrease in number of non-GABAergic projection neurons in layer V-VIDiscussionTCDD exposure in utero resulted in abnormal cortical histogenesis (decreased thickness of neocortex). We speculate that TCDD exposure increased p27Kip1 protein in nuclei of NPC that lead to increase in both G1 phase and Q. Thus premature increase in Q decrease the total output of projection neurons in the neocotex by decreasing the maximum number of NPC in the course of neuronogenesis. We speculate that decrease in number of projection neurons in layer V-VI in TCDD exposed mice might be resulted from premature switch of neuronal fate from deep layer to superficial neuronal phenotype by abnormal increase in Q fraction by TCDD exposure. Less