A major substrate of maturation promoting factor identified as elongation factor 1 beta gamma delta in Xenopus laevis

Protein synthesis is believed to be under control of the cell cycle during meiosis and mitosis. Any relationship between substrates for cdc2 kinase and components of the protein synthetic apparatus would therefore be of prime importance. During meiosis of Xenopus laevis oocytes one of the substrates for this kinase is a p47 protein, which is complexed to two other proteins, P36 and P30. Judged from partial amino acid sequence data on P47 and P30, the P30 and P47 proteins were reported to resemble the protein synthetic elongation factors (EF) 1 beta and 1 gamma from Artemia salina (Bellé, R., Derancourt, J., Poulhe, R., Capony, J.P., Ozon, R., and Mulner-Lorillon, O. (1989) FEBS Lett. 255, 101-104). This paper shows that the complex composed of P30, P47, and P36 from Xenopus is identical to the complex of EF-1 beta, EF-1 gamma, and EF-1 delta from Artemia according to two criteria. 1) Both stimulate elongation factor 1 alpha-mediated transfer RNA binding to ribosomes and exchange of guanine nucleotides on elongation factor 1 alpha to a comparable degree. 2) Each of the three subunits of the protein complex P30.P47.P36 from Xenopus shows a structural homology with one of the corresponding subunits of EF-1 beta gamma delta from Artemia. Presumably the phosphorylation of EF-1 gamma, which associates with tubulin at least in vitro, is important in processes following the onset of meiosis which is accompanied by a rise of protein synthesis.     

Three genes under different developmental control encode elongation factor 1-alpha in Xenopus laevis.

We have cloned cDNAs encoding two variants of the elongation factor for protein synthesis in Xenopus laevis, called EF-1 alpha. One of these (42Sp50) is expressed exclusively in immature oocytes. It is one of two protein components of a 42S RNP particle that is very abundant in previtellogenic oocytes. The 42S RNP particle consists of various tRNAs, 5S RNA, 42Sp50 and a 5S RNA binding protein (42Sp43). A major function served by 42Sp50 appears to be the storage of tRNAs for later use in oogenesis and early embryogenesis. The second EF-1 alpha variant (EF-1 alpha O) is expressed mainly in oocytes but transiently in early embryogenesis as well. Its mRNA cannot be detected after neurulation in somatic cells. EF-1 alpha O is closely related to a third EF-1 alpha (EF-1 alpha S), discovered originally by Krieg et al. (1). EF-1 alpha S is expressed at low levels in oocytes but actively in somatic cells. The latter two proteins are very similar to known eukaryotic EF-1 alpha from other organisms and presumably function in their respective cell types to support protein synthesis.     

Xenopus laevis Stromal cell-derived factor 1: conservation of structure and function during vertebrate development

Transmembrane signaling of the CXC chemokine stromal cell-derived factor-1 (SDF-1) is mediated by CXCR4, a G protein-coupled receptor initially identified in leukocytes and shown to serve as a coreceptor for the entry of HIV into lymphocytes. Characterization of SDF-1- and CXCR4-deficient mice has revealed that SDF-1 and CXCR4 are of vital developmental importance. To study the role of the SDF-1/CXCR4-chemokine/receptor system as a regulator of vertebrate development, we isolated and characterized a cDNA encoding SDF-1 of the lower vertebrate Xenopus laevis (xSDF-1). Recombinant xSDF-1 was produced in insect cells, purified, and functionally characterized. Although xSDF-1 is only 64-66% identical with its mammalian counterparts, it is indistinguishable from human (h)SDF-1alpha in terms of activating both X. laevis CXCR4 and hCXCR4. Thus, both xSDF-1 and hSDF-1alpha promoted CXCR4-mediated activation of heterotrimeric G(i2) in a cell-free system and induced release of intracellular calcium ions in and chemotaxis of intact lymphoblastic cells. Analysis of the time course of xSDF-1 mRNA expression during Xenopus embryogenesis revealed a tightly coordinated regulation of xSDF-1 and X. laevis CXCR4. xSDF-1 mRNA was specifically detected in the developing CNS, incipient sensory organs, and the embryonic heart. In Xenopus, CXCR4 mRNA appears to be absent from the heart anlage, but present in neural crest cells. This observation suggests that xSDF-1 expressed in the heart anlage may attract cardiac neural crest cells expressing CXCR4 to migrate to the primordial heart to regulate both septation of the cardiac outflow tract and differentiation of the myocardium during early heart development.     

A role for Xlim-1 in pronephros development in Xenopus laevis

Xlim-1, a LIM class homeobox gene expressed in Xenopus laevis, is one of the earliest known marker genes of pronephros development and is expressed in pronephros rudiment. In this study, we examined the role of Xlim-1 in pronephros development. Temporal expression of Xlim-1 in explants was analyzed in a series of induction assays using RT-PCR analysis. Xlim-1 was expressed 9 to 15 h after activin/retinoic acid treatment, corresponding to pronephros differentiation in explants. We further examined the role of Xlim-1 using a series of microinjection experiments. Presumptive pronephric anlagen of embryos were injected with various Xlim-1 mutants, and effects of these Xlim-1 mutants on pronephrogenesis in embryos and in explants were analyzed by RT-PCR and immunohistochemistry. Dominant-negative Xlim-1 inhibited differentiation of pronephros in activin/retinoic acid-treated animal caps. In embryos injected with a dominant-negative form of Xlim-1, development of pronephric tubules was inhibited at the late tail-bud stage. Our results suggest that Xlim-1 may not initiate differentiation of the pronephros, but that it is necessary for growth and elongation in the development of pronephric tubules.     

Purification and characterization of a germ cell-specific form of elongation factor 1 alpha (EF-1 alpha) from Xenopus laevis.

Elongation factor 1 alpha (EF-1 alpha) was purified to homogeneity from full-grown oocytes of Xenopus laevis. This protein is encoded by a gene previously shown to be expressed in male and female germ cells, and repressed in somatic cells. The purified protein was identified with EF-1 alpha on criteria of molecular mass, cross-reaction with antibodies raised against Artemia salina EF-1 alpha, affinity for guanine nucleotides, and ability to promote the mRNA-dependent binding of aminoacyl tRNA to 80S ribosomes.     

非洲爪蟾GATA-1转录因子与爪蟾发育

GATA－1是GATA结合蛋白（GATA－binding protein）家族的成员之一,正向调节红细胞特异性基因的表达,是红系终末分化所必需的因子。与其他物种不同的是,非洲爪蟾GATA－1转录因子具有两业型,两者结构极为相似,但存在功能上的差异,非洲爪蟾GATA－1转录因子在爪蟾发育过程中起着重要的调节作用。     

Downregulation of the translation elongation factor 2 kinase in Xenopus laevis oocytes at the final stages of oogenesis

Phosphorylation of translation elongation factor 2(eEF-2) by a specific Ca2+/calmodulin-dependent eEF-2 kinase plays an important role in the regulation of protein synthesis in mammalian cells. We show here that an eEF-2 kinase similar to the mammalian enzyme is present in tissues of the amphibian Xenopus laevis. We investigated changes in the activity of eEF-2 kinase in extracts of Xenopus oocytes at different stages of oogenesis. The eEF-2 kinase activity was constant from stage I to stage IV of oogenesis, but dramatically decreased after stage IV. Extracts of fully grown stage-VI oocytes showed no eEF-2 kinase activity. However, when extracts were analyzed by two-dimensional gel electrophoresis, eEF-2 was found to be present mostly, if not exclusively, in the dephosphorylated form throughout oogenesis. It is suggested that eEF-2 kinase disappears late in oogenesis to make protein synthesis insensitive to changes in intracellular Ca2+ concentration. This may be important for the induction of meiotic maturation.