Muscarella D E, Rachlinski M K, Bloom S E
Department of Microbiology and Immunology, College of Veterinary Medicine, Cornell University, Ithaca, New York 14853, USA.
Mol Reprod Dev. 1998 Oct;51(2):130-42. doi: 10.1002/(SICI)1098-2795(199810)51:2<130::AID-MRD2>3.0.CO;2-R.
Apoptosis is a well-established cellular mechanism for selective cell deletion during development. However, little is known about the expression of an apoptotic pathway and its role in determining the relative sensitivity of the early, pre-gastrula, avian embryo to stress-induced cell death. We examined the sensitivity of avian blastodermal cells to engage in apoptosis upon exposure to etoposide, a topoisomerase II-inhibitor that rapidly and efficiently induces apoptosis in many cell types. We found that while the blastodermal cells are capable of engaging in apoptosis, they are highly resistant to such induction with respect to both concentration of drug required and length of exposure, even when compared to a tumor cell line with a known multi-drug resistant phenotype. Additionally, we assessed the expression of several candidate regulatory genes in blastodiscs from infertile eggs (i.e., maternal RNA transcripts), blastodermal cells immediately following oviposition, and various stages of early development up to gastrulation. This analysis revealed that several genes whose products have anti-apoptotic activity, including bcl-2, bcl-xL, hsp70, grp78 and the glutathione S-transferases, are expressed as early as the stage 1 embryo in the newly oviposited egg. These transcripts are also found in the infertile blastodisc, suggesting a role for maternally derived transcripts in the protection of the oocyte and zygote. Significantly, constitutive levels of hsp70 mRNA exceeded those of the other anti-apoptotic genes in the blastodermal cells. These results contribute to an emerging picture of stress resistance at the earliest stages of avian embryo development which involves multiple anti-apoptotic genes that act at different regulatory points in the apoptotic cascade.
细胞凋亡是发育过程中一种成熟的选择性细胞清除的细胞机制。然而，关于凋亡途径的表达及其在决定早期原肠胚形成前的禽类胚胎对应激诱导的细胞死亡的相对敏感性方面的作用，我们所知甚少。我们检测了禽类胚盘细胞在暴露于依托泊苷（一种拓扑异构酶II抑制剂，能在许多细胞类型中快速有效地诱导细胞凋亡）时发生凋亡的敏感性。我们发现，虽然胚盘细胞能够发生凋亡，但就所需药物浓度和暴露时间而言，它们对这种诱导具有高度抗性，即使与具有已知多药耐药表型的肿瘤细胞系相比也是如此。此外，我们评估了来自未受精卵（即母源RNA转录本）的胚盘、产卵后立即获取的胚盘细胞以及直至原肠胚形成的早期发育各个阶段中几个候选调控基因的表达。该分析表明，几种其产物具有抗凋亡活性的基因，包括bcl-2、bcl-xL、hsp70、grp78和谷胱甘肽S-转移酶，早在新产卵中处于1期胚胎阶段时就已表达。这些转录本在未受精的胚盘中也有发现，表明母源转录本在保护卵母细胞和受精卵方面发挥作用。值得注意的是，胚盘细胞中hsp70 mRNA的组成型水平超过了其他抗凋亡基因。这些结果有助于描绘出禽类胚胎发育最早阶段的应激抗性新图景，其中涉及多个在凋亡级联反应的不同调控点起作用的抗凋亡基因。
