Xenopus system

The Xenopus system has proven instrumental in determining the mechanism controlling exit from mitosis at the metaphase/anaphase transition. Studies in this area have relied heavily on extracts prepared from fully mature oocytes/ unfertilized eggs that are arrested at metaphase of the second meiotic division. Upon Ca2+ addition, anaphase is initiated and the extract enters the first embryonic cell cycle to replicate DNA. The activity responsible for metaphase arrest was discovered by Masui at the same time as MPF (Masui Markert 1971), and given the name cytostatic factor (CSF). CSF has never been purified... 

Ca waves in systems [ike Xenopus laevis oocytes and pancreatic (3 cells fall into this category Electrochemical waves in cardiac and nerve tissue have this origin and the appearance and/or breakup of spiral wave patterns in excitable media are believed to be responsible for various types of arrhythmias in the heart [39, 40]. Figure C3.6.9 shows an excitable spiral wave in dog epicardial muscle [41]. 

Heterologous expression systems comprise prokaryotic organisms (e.g., E. coli) and eukaryotic cells (e.g., yeast, HEK293, Xenopus oocytes), which are used to functionally express foreign genes or cDNAs. 

The first clue to a role for Wnt/(3-catenin-dependent signaling in vertebrate development came from overexpression studies in the classical embryonic system, the frog Xenopus loevis. When Wntl is ectopically expressed in cells that would normally contribute to the ventral embryo (i.e. the future belly), they instead adopt... 

The molecular analysis of the Sh K channel transcription unit indicated that at least ten different channel subunits may be expressed in Drosophila cells. This observation raised a number of important questions only some of them can be addressed here. Each subunit has been expressed in the Xenopus oocyte expression system [11,12,29,39]. These experiments indicate that each subunit expresses distinct... 

Petti M.A., Matheson S.F. and Burd G.D. (1999). Differential antigen expression during metamorphosis in the tripartite olfactory system of the African clawed frog, Xenopus laevis. Cell Tiss Res 297, 383-396. 

Observations from various systems, including yeast, suggest that phosphorylation and dephosphorylation of proteins play important roles in the mitotic and meiotic cell cycles and the differentiation of germ cells. Extracts from mitotic HeLa cells contained phosphoproteins also present in other mitotic and meiotic cell types, but not in interphase cells (Davis et al., 1983). Exposure of Xenopus oocytes to progesterone results in a burst of protein phosphorylation shortly before GVBD (Mailer et al.,... 

Other phosphatases have also been identified and may be implicated in mitotic and meiotic germ cell functions. For example, INH was originally isolated from a Xenopus oocyte cell free system as an inhibitor of pre-MPF activity (Cyert and Kirschner, 1988). INH encodes a protein phosphatase 2Athat negatively regulates MPF activity by dephosphory-lating Cdc2 on thr-161 (Lee et al., 1991 Solomon et al., 1990). 

Xenopus oocytes and embryos present a model system for understanding the interface between cell cycle controls and developmental decisions. Maturation of... 

Chong JP, Thommes P, Rowles A, Mahbubani HM, Blow JJ 1997 Characterization of the Xenopus replication licensing system. Methods Enzymol 283 549-564 Dasso M, Newport JW 1990 Completion of DNA replication is monitored by a feedback system that controls the initiation of mitosis in vitro-, studies in Xenopus. Cell 61 811-823... 

Bertran, J., et al. Stimulation of system y(+)-like amino acid transport by the heavy chain of human 4F2 surface antigen in Xenopus laevis oocytes. Proc. Natl. Acad. Sci. U. S. A. 1992, 89, 5606-5610. 

This chapter describes some of the modified mammalian cell-based systems that have been developed to express intestinal cytochrome P450 enzymes and intestinal transporters. The reader should be aware that other experimental systems, such as transporter expression and drug uptake studies in Xenopus laevis oocytes, have also shown considerable promise [1],... 

Fort, D.J., B.L. James, and J.A. Bantle. 1989. Evaluation of the developmental toxicity of five compounds with the frog embryo teratogenesis assay Xenopus (FETAX) and a metabolic activation system. Jour. Appl. Toxicol. 9 377-388. 

Turpen, J.B., Induction and early development of the hematopoietic and immune systems in Xenopus. Dev. Comp. Immunol., 22, 265, 1998. 

Christin, M.S., et al., Effects of agricultural pesticides on the immune system of Xenopus laevis and Rana pipiens, Aquat. Toxicol., SI, 33, 2004. 

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