Cheema Zulfiqar F, Santillano Daniel R, Wade Stephen B, Newman Joseph M, Miranda Rajesh C
Department of Human Anatomy & Medical Neurobiology, & Center for Environmental and Rural Health, 228 Reynolds Medical Bldg, Texas A&M University System Health Science Center, College Station, TX 77843-1114, USA.
BMC Neurosci. 2004 Mar 23;5:11. doi: 10.1186/1471-2202-5-11.
Apoptosis is important for normal cerebral cortical development. We previously showed that the Fas suicide receptor was expressed within the developing cerebral cortex, and that in vitro Fas activation resulted in caspase-dependent death. Alterations in cell-surface Fas expression may significantly influence cortical development. Therefore, in the following studies, we sought to identify developmentally relevant cell biological processes that regulate cell-surface Fas expression and reciprocal consequences of Fas receptor activation.
Flow-cytometric analyses identified two distinct neural sub-populations that expressed Fas on their cell surface at high (FasHi) or moderate (FasMod) levels. The anti-apoptotic protein FLIP further delineated a subset of Fas-expressing cells with potential apoptosis-resistance. FasMod precursors were mainly in G0, while FasHi precursors were largely apoptotic. However, birth-date analysis indicated that neuroblasts express the highest levels of cell-surface Fas at the end of S-phase, or after their final round of mitosis, suggesting that Fas expression is induced at cell cycle checkpoints or during interkinetic nuclear movements. FasHi expression was associated with loss of cell-matrix adhesion and anoikis. Activation of the transcription factor p53 was associated with induction of Fas expression, while the gonadal hormone estrogen antagonistically suppressed cell-surface Fas expression. Estrogen also induced entry into S-phase and decreased the number of Fas-expressing neuroblasts that were apoptotic. Concurrent exposure to estrogen and to soluble Fas-ligand (sFasL) suppressed p21/waf-1 and PCNA. In contrast, estrogen and sFasL, individually and together, induced cyclin-A expression, suggesting activation of compensatory survival mechanisms.
Embryonic cortical neuronal precursors are intrinsically heterogeneous with respect to Fas suicide-sensitivity. Competing intrinsic (p53, cell cycle, FLIP expression), proximal (extra-cellular matrix) and extrinsic factors (gonadal hormones) collectively regulate Fas suicide-sensitivity either during neurogenesis, or possibly during neuronal migration, and may ultimately determine which neuroblasts successfully contribute neurons to the differentiating cortical plate.
细胞凋亡对正常大脑皮质发育至关重要。我们之前发现，Fas自杀受体在发育中的大脑皮质中表达，且体外Fas激活会导致半胱天冬酶依赖性死亡。细胞表面Fas表达的改变可能会显著影响皮质发育。因此，在接下来的研究中，我们试图确定与发育相关的细胞生物学过程，这些过程调节细胞表面Fas表达以及Fas受体激活的相互影响。
流式细胞术分析确定了两个不同的神经亚群，它们在细胞表面以高（FasHi）或中等（FasMod）水平表达Fas。抗凋亡蛋白FLIP进一步划分出了具有潜在抗凋亡能力的Fas表达细胞亚群。FasMod前体细胞主要处于G0期，而FasHi前体细胞大多处于凋亡状态。然而，出生日期分析表明，神经母细胞在S期结束时或最后一轮有丝分裂后表达最高水平的细胞表面Fas，这表明Fas表达是在细胞周期检查点或核内运动期间被诱导的。FasHi表达与细胞-基质黏附丧失和失巢凋亡有关。转录因子p53的激活与Fas表达的诱导有关，而性腺激素雌激素则拮抗抑制细胞表面Fas表达。雌激素还诱导细胞进入S期，并减少凋亡的Fas表达神经母细胞数量。同时暴露于雌激素和可溶性Fas配体（sFasL）会抑制p21/waf-1和增殖细胞核抗原（PCNA）。相反，雌激素和sFasL单独或共同诱导细胞周期蛋白A表达，提示激活了代偿性生存机制。
胚胎皮质神经元前体细胞在Fas自杀敏感性方面本质上是异质性的。相互竞争的内在因素（p53、细胞周期、FLIP表达）、近端因素（细胞外基质）和外在因素（性腺激素）在神经发生期间或可能在神经元迁移期间共同调节Fas自杀敏感性，并可能最终决定哪些神经母细胞成功地为分化中的皮质板贡献神经元。
