Characterization of a Caenorhabditis elegans recA-like gene Ce-rdh-1 involved in meiotic recombination.
A recA-like gene was identified in the Caenorhabditis elegans genome project database. The putative product of the gene, termed Ce-rdh-1 (C. elegans RAD51 and DMC1/LIM15 homolog 1), consists of 357 amino acid residues. The predicted amino acid sequence of Ce-rdh-1 showed 46-60% identity to both RAD51 type and DMC1/LIM15 type genes in several eukaryote species. The results of RNAi (RNA-mediated interference) indicated that repression of Ce-rdh-1 blocked chromosome condensation of six bivalents and dissociation of chiasmata in oocytes of F1 progeny. Oogenesis did not proceed to the diakinesis stage. Accordingly, all the eggs produced (F2) died in early stages. These results suggest that Ce-rdh-1 participates in meiotic recombination. (+info)
Formation of mature egg envelope subunit proteins from their precursors (choriogenins) in the fish, Oryzias latipes: loss of partial C-terminal sequences of the choriogenins.
The inner layer of egg envelope of the medaka, Oryzias latipes, comprises two major groups of glycoprotein subunits, ZI-1,2 and ZI-3. Their precursor proteins, choriogenin H (Chg H) and choriogenin L (Chg L), respectively, are synthesized in spawning female liver. In the present study, the primary structures of the precursors and the corresponding mature subunits were compared by peptide mapping and amino acid sequencing to find what difference in their molecular structures is relevant to the assembly of the soluble precursors into the insoluble inner layer. The primary structures of the solubilized subunits were mostly identical to those of the respective precursors, but they lacked C-terminal partial sequences that their precursors possessed, namely, ZI-1,2 subunit was shorter than Chg H by 34 amino acid residues and ZI-3 was shorter than Chg L by 27 residues. In addition, a consensus amino acid sequence, Arg-Lys-X-Arg, was found at the putative cleavage sites in the C-terminal region of the precursors. It is conjectured that the truncation of the precursor proteins is prerequisite for formation of mature chorion subunit proteins and their assembly into chorion. (+info)
Fertilization, embryonic development, and offspring from mouse eggs injected with round spermatids combined with Ca2+ oscillation-inducing sperm factor.
Round spermatids, precursor male gametes, are known to possess the potential to achieve fertilization and embryonic development when injected into eggs. However, injection of spermatids alone seldom activates eggs in the mouse, as spermatids by themselves cannot induce an increase in intracellular Ca2+, a prerequisite for egg activation. We injected a mouse round spermatid into an egg simultaneously with partially purified sperm factor from differentiated hamster spermatozoa. The combined injection produced repetitive Ca2+ increases (Ca2+ oscillations) lasting for at least 4 h as observed at fertilization, and induced activation in 92% of eggs. This method provided 75% fertilization success associated with male and female pronucleus formation and development to 2-cell embryos, while only 7% of eggs were fertilized by injection of a spermatid alone. Of the 2-cell embryos, approximately 50% developed to blastocysts during 5 days of culture in vitro, while no blastocysts were obtained following injection of sperm factor alone. Furthermore, the 2-cell embryos, that were created by spermatids and sperm factor and transplanted into foster mothers, developed into normal offspring, although the percentage was only 22%. All infants grew into healthy adults carrying normal chromosomes. The sperm factor served as a complementary factor for successful fertilization by round spermatid injection. (+info)
Experimental murine schistosomiasis in the absence of B7 costimulatory molecules: reversal of elicited T cell cytokine profile and partial inhibition of egg granuloma formation.
The granulomatous inflammation in infection with the helminth Schistosoma mansoni represents a cellular hypersensitivity reaction mediated by, and dependent upon, MHC class II-restricted CD4+ Th cells sensitized to parasite egg Ags. The current work examines the role and significance of the B7:CD28/CTLA-4 pathway in providing the costimulation necessary for the activation of these pathogenic T cells. In vitro T cell responses in B7-1-/- mice, 7-8 wk postinfection, were no different from wild-type controls, but the absence of B7-2 molecules resulted in a decrease in egg Ag-induced proliferation with increased IFN-gamma production. Both B7-1-/- and B7-2-/- mice exhibited intact granuloma formation. In contrast, CD4+ Th cells from B7-1/2 double-deficient mice displayed a dramatic loss of proliferative capacity upon stimulation with egg Ag. Most strikingly, these T cells secreted only IFN-gamma, but not IL-4 and IL-10, a pattern entirely opposite to that displayed by wild-type controls. Despite these major differences in T cell reactivity, B7-1/2-/- mice had only a limited reduction of granuloma size and fibrosis, without appreciable difference in cellular composition. These results show that substantial granuloma formation can occur under conditions of limited T cell expansion and restricted Th1-type cytokine production. They also support the notion that the combined effect of B7 signaling is not as critical for Th1 cell activation as it is for the development of the Th2 dominant environment characteristic of the evolving schistosome infection in H-2b mice. (+info)
The RLF-B component of the replication licensing system is distinct from Cdc6 and functions after Cdc6 binds to chromatin.
Replication licensing factor (RLF) is an essential initiation factor that can prevent re-replication of DNA in a single cell cycle  . It is required for the initiation of DNA replication, binds to chromatin early in the cell cycle, is removed from chromatin as DNA replicates and is unable to re-bind replicated chromatin until the following mitosis. Chromatography of RLF from Xenopus extracts has shown that it consists of two components termed RLF-B and RLF-M . The RLF-M component consists of complexes of all six Xenopus minichromosome maintenance (MCM/P1) proteins (XMcm2-7), which bind to chromatin in late mitosis and are removed as replication occurs     . The identity of RLF-B is currently unknown. At least two factors must be present on chromatin before licensing can occur: the Xenopus origin recognition complex (XORC)   and Xenopus Cdc6 (XCdc6) . XORC saturates Xenopus sperm chromatin at approximately one copy per replication origin whereas XCdc6 binds to chromatin only if XORC is bound first   . Although XORC has been shown to be a distinct activity from RLF-B , the relationship between XCdc6 and RLF-B is currently unclear. Here, we show that active XCdc6 is loaded onto chromatin in extracts with defective RLF, and that both RLF-M and RLF-B are still required for the licensing of XCdc6-containing chromatin. Furthermore, RLF-B can be separated from XCdc6 by immunoprecipitation and standard chromatography. These experiments demonstrate that RLF-B is both functionally and physically distinct from XCdc6, and that XCdc6 is loaded onto chromatin before RLF-B function is executed. (+info)
Ku-dependent nonhomologous DNA end joining in Xenopus egg extracts.
An extract from activated Xenopus eggs joins both matching and nonmatching ends of exogenous linear DNA substrates with high efficiency and fidelity (P. Pfeiffer and W. Vielmetter, Nucleic Acids Res. 16:907-924, 1988). In mammalian cells, such nonhomologous end joining (NHEJ) is known to require the Ku heterodimer, a component of DNA-dependent protein kinase. Here I investigated whether Ku is also required for the in vitro reaction in the egg extract. Immunological assays indicate that Ku is very abundant in the extract. I found that all NHEJ was inhibited by autoantibodies against Ku and that NHEJ between certain combinations of DNA ends was also decreased after immunodepletion of Ku from the extract. The formation of a joint between a DNA end with a 5'-protruding single strand (PSS) and an end with a 3'-PSS, between two ends with 3'-PSS, and between two blunt ends was most Ku dependent. On the other hand, NHEJ between two DNA ends bearing 5'-PSS was Ku independent. These results show that the Xenopus cell-free system will be useful to biochemically dissect the role of Ku in eukaryotic NHEJ. (+info)
Purification and characterization of a serine protease with fibrinolytic activity from Tenodera sinensis (praying mantis).
Mantis egg fibrolase (MEF) was purified from the egg cases of Tenodera sinensis using ammonium sulfate fractionation, gel filtration on Bio-Gel P-60 and affinity chromatography on DEAE Affi-Gel blue gel. The protease was assessed homogeneous by SDS-polyacrylamide gel electrophoresis and has a molecular mass of 31500 Da. An isoelectric point of 6.1 was determined by isoelectric focusing. Amino acid sequencing of the N-terminal region established a primary structure composed of Ala-Asp-Val-Val-Gln-Gly-Asp-Ala-Pro-Ser. MEF readily digested the Aalpha- and Bbeta-chains of fibrinogen and more slowly the gamma-chain. The nonspecific action of the enzyme results in extensive hydrolysis of fibrinogen and fibrin releasing a variety of fibrinopeptide. The enzyme is inactivated by Cu2+ and Zn2+ and inhibited by PMSF and chymostatin, yet elastinal, aprotinin, TLCK, TPCK, EDTA, EGTA, cysteine, beta-mercaptoethanol, iodoacetate, E64, benzamidine and soybean trypsin inhibitor do not affect activity. Antiplasmin was not sensitive to MEF but antithrombin III inhibited the enzymatic activity of MEF. Among chromogenic protease substrates, the most sensitive to MEF hydrolysis was benzoyl-Phe-Val-Arg-p-nitroanilide with maximal activity at pH 7.0 and 30 degrees C. MEF preferentially cleaved the oxidized B-chain of insulin between Leu15 and Tyr16. D-Dimer concentrations increased on incubation of cross-linked fibrin with MEF, indicating the enzyme has a strong fibrinolytic activity. (+info)
A novel 62-kilodalton egg antigen from Schistosoma mansoni induces a potent CD4(+) T helper cell response in the C57BL/6 mouse.
In infection with Schistosoma mansoni, hepatic granuloma formation is mediated by CD4(+) T helper (Th) cells sensitized to schistosomal egg antigens. There is considerable variation among infected individuals with respect to both severity of disease and the T-cell response to egg antigens. In the BL/6 mouse, the egg granulomas are relatively small and the relevant sensitizing egg antigens are largely unknown. We investigated the CD4(+) Th cell response of infected BL/6 mice to egg antigens fractionated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and found a prominent lymphoproliferative response to be directed against a 62-kDa component. With the aid of a specific T-cell hybridoma, 4E6, the 62-kDa antigen was isolated; following partial digestion with endoproteinase Glu-C, an internal amino acid sequence was found to be identical with one present in the enzyme phosphoenolpyruvate carboxykinase (PEPCK) of the organisms Caenorhabditis elegans and Treponema pallidum and to differ by one residue from PEPCK of various other species. In CD4(+) Th cells from 7.5- 8.5-week-infected BL/6 mice, the purified 62-kDa molecule elicited a potent proliferative response which, based on cytokine analysis, was of a mixed Th-1 and Th-2 type. Our results reveal a novel egg antigen of particular prominence in the BL/6 mouse and suggest that the immune response in schistosomiasis is a product of sensitization to egg antigens that may vary considerably in immunogenicity from strain to strain. (+info)