Translational control in early sea urchin embryogenesis: initiation factor eIF4F stimulates protein synthesis in lysates from unfertilized eggs of Strongylocentrotus purpuratus.
Translational control in early sea urchin embryogenesis: initiation factor eIF4F stimulates protein synthesis in lysates from unfertilized eggs of Strongylocentrotus purpuratus.
复制标题
早期海胆胚胎发生的翻译控制：起始因子 eIF4F 刺激紫海胆未受精卵裂解物中的蛋白质合成。
DOI：
10.1021/bi00401a053
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发表时间：
1988
期刊：
影响因子：
2.9
通讯作者：
Hershey,JW
中科院分区：
文献类型：
--
作者：
Lopo,AC;MacMillan,S;Hershey,JW
Department of Biological Chemistry, University of California School of Medicine, Davis, California 95616 Received February 11, 1987; Revised Manuscript Received September 1, 1987 abstract: We have used cell-free translation systems from unfertilized eggs and embryos of the sea urchin Strongylocentrotus purpuratus to analyze themechanisms limiting protein synthesis in early embryogenesis. Unfertilized egg lysatessupplemented with nuclease-treated reticulocyte lysate were stimulated 2-4-fold in incorporation of radioactive amino acid into protein. Thirty-minute zygotelysates supplemented in this way were not stimulated. These results suggested that a component limiting translation in the unfertilized egg lysate was provided by the nuclease-treated lysate and that thiscomponent was no longer limiting protein synthesis following fertilization. In view of these results, partially fractionated lysates and individual purified translational components from mammalian cells were tested for stimulation of the unfertilized egg lysate. A lOOOOOg supernatant devoid of ribosomal subunits also stimulated the unfertilized egg lysate. Thus, the stimulation was not due to the addition of active ribosomal subunits but to soluble elements in the reticulocyte lysate. Of the soluble components tested, only the cap-binding protein complex eIF4F caused a dramatic stimulation of the unfertilized egg lysate (2-3.5-fold). The 30-minzygote lysate was not stimulated by eIF4F or by any of the other components tested, supporting the hypothesis that a block in the translational machinery is removedat fertilization. A rabbit reticulocyte shift assay was used to analyze whether mRNA is limiting in early development. When unfertilized egg lysate was added to the shift assay, there was no shift in radioactivity from 43S to 80S complexes, indicating the unfertilized egg mRNA is not available for translation. These results suggest that there are at least two mechanisms of translational control in early embryogenesis: one operating at the level of the translational machinery, via initiation factor 4F, and the other regulating mRNA availability.Following fertilization in sea urchins, there is a rapid increase in the rate of protein synthesis that is maintained throughout early development (Epel, 1967; Goustin & Wilt, 1981). Since this translational activation was first described 35 years ago (Hultin, 1952), it has been extensively documented in the eggs and embryos of vertebrates and invertebrates alike (Davidson, 1982, 1986). In sea urchins, the increase in protein synthesis at fertilization begins several minutesafter sperm-egg fusion (Epel, 1967). Within 1 h after fertilization, protein synthesis has increased to 10-15 times the rate in the unfertilized egg, and within several hours, this figure has increased to100-fold. This increase in protein synthesis is reflected both in mea-surements of incorporation of radiolabeled amino acids into protein and in the recruitment of ribosomes into polysomes (Humphreys, 1969, 1971). Prior to fertilization, less than 1% of the large number of free ribosomes in the egg are in poly-
