The significance of fertilization.

C R Austin
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Abstract

The fertilization of a human egg, often thought of as initiating the life of a person, is in reality but the beginning of a beginning for one or more individuals. While pronuclear fusion establishes a diploid genome, this is at first a structural entity without function. No significant RNA synthesis occurs between germinal vesicle breakdown and early cleavage, and in fact embryonic genes do not begin to find expression until about the 4- to 8- cell stage. Gene expression then progressively spreads throughout the genome, during prenatal development and beyond. The progressive nature is well shown in the early mouse embryo by the widening range of energy sources utilizable, by the rising levels of glycogen storage and by the increasing uptake of nucleic acids and protein precursors. While HCG-B RNA is transcribed in human embryos about 2 days after fertilization, it is not expressed until 16-cell stage is not linked to physical or functional integration, each cell being inherently capable of giving rise to an entire person (together with a complex of placental structures); alternatively, cells from separate embryos on being brought together can jointly lead to the establishment of a chimeric individual. Multiplicity can also originate later, the primitive streak stage being the normal time for monozygotic twinning. Only when that stage has passed does true individuality exist, for (excluding anomalies) just one person can now eventuate. The gene-transfer function of fertilization can be replaced or augmented by intranuclear or intra-blastocyst gene injection, or by the use of teratocarcinoma or embryo-stem cells.

施肥的重要性。
人类卵子的受精,通常被认为是一个人生命的开始,实际上只是一个或多个个体开始的开始。虽然原核融合建立了二倍体基因组,但它最初是一个没有功能的结构实体。在生发囊泡破裂和早期卵裂之间没有显著的RNA合成,事实上,胚胎基因直到大约4到8个细胞阶段才开始表达。基因表达随后在整个基因组中逐渐扩散,在产前发育期间和之后。在早期小鼠胚胎中,可利用的能量来源范围不断扩大,糖原储存水平不断提高,核酸和蛋白质前体的摄取不断增加,这充分显示了这种进行性。虽然HCG-B RNA在受精后约2天在人类胚胎中转录,但直到16个细胞阶段才表达,这与物理或功能整合无关,每个细胞本身都有能力产生一个完整的人(连同胎盘结构的复合体);或者,来自不同胚胎的细胞在结合在一起时可以共同导致嵌合个体的建立。多重性也可以晚一些产生,原始条纹期是同卵双胞胎的正常时期。只有当那个阶段过去了,真正的个性才会存在,因为(不包括异常)现在只有一个人可能最终出现。受精的基因转移功能可以通过核内或囊胚内基因注射,或使用畸胎瘤细胞或胚胎干细胞来替代或增强。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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