共查询到20条相似文献，搜索用时 31 毫秒
1.
The ras oncoprotein and M-phase activity. 总被引：12，自引：0，他引：12
I Daar A R Nebreda N Yew P Sass R Paules E Santos M Wigler G F Vande Woude 《Science (New York, N.Y.)》1991,253(5015):74-76
The endogenous mos proto-oncogene product (Mos) is required for meiotic maturation. In Xenopus oocytes, the ras oncogene product (Ras) can induce meiotic maturation and high levels of M-phase--promoting factor (MPF) independent of endogenous Mos, indicating that a parallel pathway to metaphase exists. In addition, Ras, like Mos and cytostatic factor, can arrest Xenopus embryonic cell cleavage in mitosis and maintain high levels of MPF. Thus, in the Xenopus oocyte and embryo systems Ras functions in the M phase of the cell cycle. The embryonic cleavage arrest assay is a rapid and sensitive test for Ras function. 相似文献
2.
Xotch, the Xenopus homolog of Drosophila notch 总被引：16，自引：0，他引：16
During the development of a vertebrate embryo, cell fate is determined by inductive signals passing between neighboring tissues. Such determinative interactions have been difficult to characterize fully without knowledge of the molecular mechanisms involved. Mutations of Drosophila and the nematode Caenorhabditis elegans have been isolated that define a family of related gene products involved in similar types of cellular inductions. One of these genes, the Notch gene from Drosophila, is involved with cell fate choices in the neurogenic region of the blastoderm, in the developing nervous system, and in the eye-antennal imaginal disc. Complementary DNA clones were isolated from Xenopus embryos with Notch DNA in order to investigate whether cell-cell interactions in vertebrate embryos also depend on Notch-like molecules. This approach identified a Xenopus molecule, Xotch, which is remarkably similar to Drosophila Notch in both structure and developmental expression. 相似文献
3.
The presence of fibroblast growth factor in the frog egg: its role as a natural mesoderm inducer 总被引：30，自引：0，他引：30
D Kimelman J A Abraham T Haaparanta T M Palisi M W Kirschner 《Science (New York, N.Y.)》1988,242(4881):1053-1056
4.
5.
Cloning and expression of a Xenopus embryonic gap junction protein 总被引：26，自引：0，他引：26
L Ebihara E C Beyer K I Swenson D L Paul D A Goodenough 《Science (New York, N.Y.)》1989,243(4895):1194-1195
Gap junctions in the early amphibian embryo may play a fundamental role in the regulation of differentiation by mediating the cell-to-cell transfer of chemical signals. A complementary DNA encoding a gap junction present in Xenopus oocytes and early embryos has now been cloned and sequenced. This protein sequence is homologous to the well-characterized gap junction structural proteins rat connexin32 and connexin43. RNA blot analysis of total Xenopus oocyte RNA showed hybridization to a single 1.6-kilobase band. This messenger RNA is abundant in oocytes, decreases to levels below the sensitivity of our assay by stage 15 (18 hours), and is not detectable in RNA from a number of adult organs. To confirm that the oocyte cDNA encodes a gap junction channel, the protein was over expressed in Xenopus oocytes by injection of RNA synthesized in vitro. Pairs of RNA-injected oocytes formed many more time- and voltage-sensitive cell-cell channels than water-injected pairs. 相似文献
6.
Positive feedback is a ubiquitous signal transduction motif that allows systems to convert graded inputs into decisive, all-or-none outputs. Here we investigate why the positive feedback switches that regulate polarization of budding yeast, calcium signaling, Xenopus oocyte maturation, and various other processes use multiple interlinked loops rather than single positive feedback loops. Mathematical simulations revealed that linking fast and slow positive feedback loops creates a "dual-time" switch that is both rapidly inducible and resistant to noise in the upstream signaling system. 相似文献
7.
The guanosine triphosphatase Ran stimulates assembly of microtubule asters and spindles in mitotic Xenopus egg extracts. A carboxyl-terminal region of the nuclear-mitotic apparatus protein (NuMA), a nuclear protein required for organizing mitotic spindle poles, mimics Ran's ability to induce asters. This NuMA fragment also specifically interacted with the nuclear transport factor, importin-beta. We show that importin-beta is an inhibitor of microtubule aster assembly in Xenopus egg extracts and that Ran regulates the interaction between importin-beta and NuMA. Importin-beta therefore links NuMA to regulation by Ran. This suggests that similar mechanisms regulate nuclear import during interphase and spindle assembly during mitosis. 相似文献
8.
Requirement of ets-2 expression for Xenopus oocyte maturation 总被引：6，自引：0，他引：6
Z Q Chen L A Burdett A K Seth J A Lautenberger T S Papas 《Science (New York, N.Y.)》1990,250(4986):1416-1418
9.
Direct demonstration of impaired functionality of a purified desensitized beta-adrenergic receptor in a reconstituted system 总被引：4，自引：0，他引：4
B Strulovici R A Cerione B F Kilpatrick M G Caron R J Lefkowitz 《Science (New York, N.Y.)》1984,225(4664):837-840
Long-term exposure of various cell types to beta-adrenergic agonists such as isoproterenol leads to an attenuated responsiveness ("desensitization") of the adenylate cyclase system to further challenge with these agonists. The turkey erythrocyte model system was used earlier to show that a covalent modification of the receptor (phosphorylation) is associated with this process. The functionality of the "desensitized" beta-adrenergic receptor was assessed by implanting purified beta-adrenergic receptor preparations from control and desensitized turkey erythrocytes into phospholipid mixtures and then fusing them with receptor-deficient cells (Xenopus laevis erythrocytes). Desensitized beta-adrenergic receptors showed a 40 to 50 percent reduction in their ability to couple to the heterologous adenylate cyclase system, comparable to the reduction in their functionality observed in their original membrane environment. These results demonstrate the utility of recently developed receptor reconstitution techniques for assessing the functionality of purified receptors and show a direct link between a covalent modification of a membrane-bound receptor and its impaired functionality in a reconstituted system. 相似文献
10.
Verma R Peters NR D'Onofrio M Tochtrop GP Sakamoto KM Varadan R Zhang M Coffino P Fushman D Deshaies RJ King RW 《Science (New York, N.Y.)》2004,306(5693):117-120
To identify previously unknown small molecules that inhibit cell cycle machinery, we performed a chemical genetic screen in Xenopus extracts. One class of inhibitors, termed ubistatins, blocked cell cycle progression by inhibiting cyclin B proteolysis and inhibited degradation of ubiquitinated Sic1 by purified proteasomes. Ubistatins blocked the binding of ubiquitinated substrates to the proteasome by targeting the ubiquitin-ubiquitin interface of Lys(48)-linked chains. The same interface is recognized by ubiquitin-chain receptors of the proteasome, indicating that ubistatins act by disrupting a critical protein-protein interaction in the ubiquitin-proteasome system. 相似文献
11.
Persistent synaptic modifications are essential for experience-dependent refinement of developing circuits. However, in the developing Xenopus retinotectal system, activity-induced synaptic modifications were quickly reversed either by subsequent spontaneous activity in the tectum or by exposure to random visual inputs. This reversal depended on the burst spiking and activation of the N-methyl-D-aspartate subtype of glutamate receptors. Stabilization of synaptic modifications can be achieved by an appropriately spaced pattern of induction stimuli. These findings underscore the vulnerable nature of activity-induced synaptic modifications in vivo and suggest a temporal constraint on the pattern of visual inputs for effective induction of stable synaptic modifications. 相似文献
12.
The nuclear envelope (NE) forms a controlled boundary between the cytoplasm and the nucleus of eukaryotic cells. To facilitate investigation of mechanisms controlling NE assembly, we developed a cell-free system made from Xenopus laevis eggs to study the process in the absence of chromatin. NEs incorporating nuclear pores were assembled around beads coated with the guanosine triphosphatase Ran, forming pseudo-nuclei that actively imported nuclear proteins. NE assembly required the cycling of guanine nucleotides on Ran and was promoted by RCC1, a nucleotide exchange factor recruited to beads by Ran-guanosine diphosphate (Ran-GDP). Thus, concentration of Ran-GDP followed by generation of Ran-GTP is sufficient to induce NE assembly. 相似文献
13.
Axons from eyes transplanted to the tail in Xenopus larvae enter the caudal spinal cord and follow two adjacent tracts rostrally to the level of the cerebellum. When eyes are transplanted to the ear area, optic axons enter the hindbrain and follow the same tracts rostrally and caudally. These sensory pathways normally contain the embryonic sensory system of the Rohon-Beard axons and the descending and ascending tracts of nerve V. We propose that the transplanted optic axons have followed a continuous substrate sensory pathway normally shared by a number of different sensory tracts. 相似文献
14.
Ras p21 as a potential mediator of insulin action in Xenopus oocytes 总被引：36，自引：0，他引：36
The oncogene protein product (p21) of the ras gene has been implicated in mediating the effects of a variety of growth factors and hormones. Microinjection of monoclonal antibody 6B7, which is directed against a synthetic peptide corresponding to a highly conserved region of p21 (amino acids 29 to 44) required for p21 function, specifically inhibited Xenopus oocyte maturation induced by incubation with insulin. The inhibition was dose-dependent and specific since (i) the same antibody had no effect on progesterone-induced maturation, (ii) immunoprecipitation and Western blotting indicated that the antibody recognized a single protein of molecular weight 21,000 in oocyte extracts, and (iii) inhibition was not observed with identical concentrations of normal immunoglobulin. Thus, p21 appears to be involved in mediating insulin-induced maturation of Xenopus oocytes. Furthermore, the mechanism may involve phosphorylation of p21, as p21 was found to be a substrate of the insulin receptor kinase. 相似文献
15.
Electrical activity plays a critical role in shaping the structure and function of synaptic connections in the nervous system. In Xenopus nerve-muscle cultures, a brief burst of action potentials in the presynaptic neuron induced a persistent potentiation of neuromuscular synapses that exhibit immature synaptic functions. Induction of potentiation required an elevation of postsynaptic Ca2+ and expression of potentiation appeared to involve an increased probability of transmitter secretion from the presynaptic nerve terminal. Thus, activity-dependent persistent synaptic enhancement may reflect properties characteristic of immature synaptic connections, and bursting activity in developing spinal neurons may promote functional maturation of the neuromuscular synapse. 相似文献
16.
Microinjection of a conserved peptide sequence of p34cdc2 induces a Ca2+ transient in oocytes 总被引：3，自引：0，他引：3
A Picard J C Cavadore P Lory J C Bernengo C Ojeda M Dorée 《Science (New York, N.Y.)》1990,247(4940):327-329
The product of the yeast cell cycle control gene cdc2, and its homologs in higher eukaryotes (p34cdc2), all contain a perfectly conserved sequence of 16 amino acids that has not been found in any other protein sequence. Microinjection of this peptide triggers a specific increase in the concentration of intracellular free Ca2+ that originates from intracellular stores in both starfish and Xenopus oocytes. Thus, p34cdc2 might interact through its conserved peptide domain with some component of the Ca2(+)-regulatory system. 相似文献
17.
Heterogeneity of glycine receptors and their messenger RNAs in rat brain and spinal cord 总被引：18，自引：0，他引：18
Messenger RNAs isolated from adult or newborn rat spinal cord were fractionated in a sucrose gradient. The fractions were injected into Xenopus oocytes to determine their potencies for expression of glycine receptors (GlyRs), which were then examined electrophysiologically. The sedimentation profiles disclosed two classes of GlyR mRNAs, one heavy and the other light. The adult spinal cord was rich in heavy GlyR mRNA, whereas the light GlyR mRNA was more abundant in neonatal spinal cord and in adult cerebral cortex. Glycine receptors encoded by heavy and light mRNAs of adult spinal cord showed some electrophysiological differences. Thus there are two types of GlyRs encoded by mRNAs of different sizes, and the expression of these mRNAs is developmentally regulated. A tissue- and age-dependent distribution of heterogeneous GlyR mRNAs may imply diverse roles of the GlyRs in neuronal function in the central nervous system. 相似文献
18.
Visual input during a critical period of development plays a major role in the establishment of orderly connections in the developing visual system. In Xenopus laevis, the matching of visual maps from the two eyes to the optic tectum depends on binocular visual input during the critical period, which extends from late tadpole to early juvenile stages. Alterations in eye position, which produce a mismatch of the tectal maps, normally evoke a compensatory adjustment in the map of the ipsilateral eye only during the critical period. However, continuous application of the glutamate receptor agonist N-methyl-D-aspartate (NMDA) after the normal end of the critical period restores this ability to realign the visual map. 相似文献
19.
过氧化物酶体增殖剂激活受体(Peroxisome proliferator activated receptor,PPAR)是核激素受体家族中的配体激活受体,在不同的物种中已经发现了它的3种亚型,即PPARα、PPARβ(也有称δ)和PPARγ。它们在多细胞动物进化的过程中获得配体结合能力,通过结合到相应的激活剂上,在一些重要的代谢途径中刺激靶基因的表达。其中PPARα和β在爪蟾的胚胎发育早期表达的组织范围较广,在后期表现出较大的组织特异性;在啮齿动物中PPARα、β和γ在胎儿发育和成年动物体内表现出特定的时间和组织上的依赖性的表达模式;PPARα和γ在人体内的表达范围较窄,而PPARβ则较广。 相似文献