The role of neuronal migration disorder in microcephaly induced by Ara-C in mice

原发性小头畸形是各种遗传和染色体缺陷以及环境侮辱的结果。小头畸形可伴有许多移行异常，包括灰质异位。核苷类似物阿糖胞苷(Ara-C)能抑制增殖细胞的DNA合成。怀孕期间给小鼠服用Ara-C会导致小头畸形，并导致其后代细胞结构异常和灰质异位。本实验旨在研究神经元异常迁移在给予阿糖胞苷小鼠小头畸形形成过程中的作用。分别于妊娠13.5天和14.5天，按30 mg/kg体重给妊娠小鼠腹腔注射阿糖胞苷。为研究细胞增殖，于孕15.5d(50μg/g体重)腹腔注射S时相标志物5-溴脱氧尿苷(BrdU)。胚胎15.5d，扣带回脑室带神经上皮细胞缺乏BrdU免疫反应。Nestin免疫反应阳性的放射状胶质纤维和Calretinin阳性的亚板纤维断裂。末端脱氧核苷酸转移酶(TdT)介导的dUTP缺口末端标记(TUNEL)反应在整个大脑半球均显着。扣带回皮质下异位和侧脑室背外侧部室管膜下结节异位分别在出生后第1天和第13天出现。出生后32天，小头畸形明显；皮质下异位增大，但仍位于额叶和扣带回皮质。本实验证明Ara-C可诱导整个大脑半球的神经细胞凋亡。这提示小头畸形伴发的灰质异位症是由于Ara-C对发育未成熟的大脑的毒性而引起的径向和切向神经元迁移障碍所致。

Primary microcephaly is the result of a variety of genetic and chromosomal defects, as well as environmental insults. Microcephaly can be accompanied by numerous migration anomalies including gray matter heterotopia. The nucleoside analog, cytosine arabinoside (Ara-C), can inhibit DNA synthesis in proliferating cells. The administration of Ara-C to mice during pregnancy gives rise to microcephaly with dysgenetic cytoarchitecture and gray matter heterotopia in their offspring. This experiment was undertaken to examine the role of abnormal neuronal migration in the development of microcephaly that is produced by giving Ara-C to mice. Pregnant mice were injected intraperitoneally with Ara-C at 30 mg/kg body weight on days 13.5 and 14.5 of gestation. For the study of cell proliferation, 5-bromodeoxyuridine (BrdU), an S-phase marker, was injected intraperitoneally on day 15.5 of gestation (50 μg/g body weight). On embryonic day 15.5, in the ventricular zone of the cingulate cortex, the neuroepithelial cells lacked BrdU immunoreactivity. Nestin-immunoreactive radial glial fibers and calretinin-positive subplate fibers were disrupted. The terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end-labeling (TUNEL) reaction was remarkable throughout the cerebral hemisphere. Subcortical heterotopia in the cingulate cortex and subependymal nodular heterotopia in the dorsolateral part of the lateral ventricles became detectable by the first and the thirteenth day after birth, respectively. Thirty-two days after birth, microcephaly was apparent ; subcortical heterotopia was increased in size and still located in the frontal and cingulate cortices. This experiment demonstrated that Ara-C induces neuronal apoptosis throughout the cerebral hemisphere. This suggests that the gray matter heterotopia that accompanies the microcephaly was produced by a disturbance of radial and tangential neuronal migrations due to the toxicity of Ara-C in the immature developing brain.