Linkage of cadherins to the cytoskeleton is crucial for their adhesive function. Since alpha- and beta-catenin play a key role in this linkage, these proteins are possible targets for processes that control cell-cell adhesion. To achieve a better understanding of the regulation of cell-cell adhesion in embryonic morphogenesis, we used immunohistology to investigate how in Xenopus blastomeres catenins respond to disturbances in the expression of maternal cadherins. Overexpression of myc-tagged maternal cadherin leads to a proportionate increase of the level of beta-catenin. The two proteins colocalize in the endoplasmic reticulum, in cytoplasmic vesicles, and along the cell membrane, indicating that the beta-catenin binds to overexpressed cadherin early in its passage to the plasma membrane. Expression of cadherin is essential for the stable presence of beta-catenin, as depletion from maternal cadherin mRNA leads to a complete loss of beta-catenin from the blastomeres. alpha-Catenin behaves differently. Overexpression of cadherin leaves the amount and localization of alpha-catenin largely unaffected, and additional cadherin inserts itself into the membrane without a proportionate rise in the level of membrane-bound alpha-catenin. However, cadherin mRNA depletion leads to a redistribution of alpha-catenin from the membrane to the cytoplasm. Thus, cadherin is required to localize alpha-catenin to the membrane, but the amount of alpha-catenin along the membrane seems to be restricted to a certain level which cannot be exceeded. The relevance of these observations for the regulation of cadherin-mediated cell adhesion in the Xenopus embryo is discussed. Additionally, we demonstrate that plakoglobin, like beta-catenin an armadillo repeat protein, shows neither accumulation after overexpression nor colocalization with the overexpressed cadherin.
The chromosomal translocation t(8;21) is one of the most frequent aberrations associated with acute myeloid leukaemia. It joins the 5 H section of the AML1 gene with the almost complete open reading frame of MTG8 (ETO). The resulting fusion RNA represents a leukaemia-specific target for antisense/ribozyme inhibition. We tested several asymmetric hammerhead ribozymes targeted against the fusion site for their ability to cleave the AML1/MTG8 RNA at low magnesium concentrations. One ribozyme cleaves AML1/ MTG8 RNA with high catalytic efficiency without binding or cleaving the wild-type AML1 transcript. The presence of cellular RNA does not affect the cleavage. Injection of AML1/MTG8 RNA and ribozyme RNA into Xenopus eggs or oocytes causes a specific reduction of AML1/MTG8 protein expression. Asymmetric anti-AML1/MTG8 ribozymes may be valuable modulators of AML1/MTG8 expression in leukaemic cells.Keywords: catalytic RNA; RNA cleavage; acute myeloid leukaemia.The translocation t(8;21) is one of the most frequent chromosomal aberrations in acute myeloid leukaemia (AML) fusing the AML1 gene on chromosome 21 to the MTG8 gene on chromosome 8 [1,2]. This translocation replaces the C-terminal transactivation domain of AML1 by MTG8, the latter lacking only a few N-terminal amino acids. The resulting fusion protein, AML1/MTG8, can still bind to DNA via the runt homology domain of AML1 [3]. AML1/MTG8 leads to the repression of gene expression by recruiting a histone deacetylase complex to the promotor/ enhancer [4±6]. Because AML1 regulates the expression of many genes important for normal haematopoiesis, their repression by AML1/MTG8 may be essential for the malignant transformation of normal progenitors [7]. Both the homozygous disruption of AML1 [8] and the heterozygous insertion of AML1/MTG8 [9,10] by homologous recombination abolish definitive haematopoiesis in the liver of mouse embryos. These results emphasize the central role of AML1 and AML1/MTG8 in haematopoiesis. Moreover, they demonstrate a gain of function for the fusion protein, as the AML1/MTG8 knock-in cells still contain one intact AML1 allele. Therefore, inhibition of AML1/MTG8 expression by an antisense or ribozyme strategy may revert the malignant phenotype.Ribozymes, in particular, have been applied to modulate the expression of leukaemic fusion proteins such as bcr-abl [11,12]. The chromosomal rearrangement creates a fusion RNA, which is specific to the leukaemic cell, and therefore represents a unique target for an antisense molecule or a ribozyme. Recently, Matsushita et al. [13,14] reported that preformed anti-AML1/MTG8 ribozymes delivered with cationic lipids led to a reduced proliferation of a t(8;21) positive cell line, Kasumi-1. Similar results were obtained with anti-AML1/MTG8 oligodeoxynucleotides [15]. However, it remained unclear whether the observed inhibition of cell proliferation was indeed due to a reduction of AML1/ MTG8 or other antisense-or ribozyme-independent effects.Recently, the groups of Sczakiel and Tabler described asymmetric rib...
The homophilic nature of cadherin-mediated cell-cell adhesion provides an organism with the opportunity of altering the adhesive capabilities of its cells by selectively modulating the expression of different cadherin types. Differential cadherin expression is of major importance in regulating the cell rearrangements involved in the processes which shape tissues and organs during embryogenesis. The pregastrula embryo of Xenopus laevis expresses two maternally supplied cadherins: XB/U-cadherin and EP-cadherin. Since these two proteins are almost 92% identical at the amino acid level, it was unclear whether heterophilic interactions between them were possible. Different functional roles can only be ascribed to the two cadherins if the possibility of heterophilic binding between them can be excluded. We describe a simple and straightforward assay which can be used to assess interactions between adhesion molecules. A combination of antisense oligonucleotide and enzyme treatments eliminates endogenous cadherins in Xenopus oocytes and subsequent injection of a specific mRNA yields oocytes carrying only one or the other cadherin. After removal of the vitelline membranes, two oocytes expressing the appropriate cadherins will adhere to one another when they are placed in close contact. By scoring for adhesion in homotypic and heterotypic pairings, we demonstrate that XB/U-cadherin and EP-cadherin do not interact with one another.
We report the cloning of Xenopus laevis Xsap-1 cDNA, encoding a member of the ternary complex factor subfamily of ETS transcription factors. The expression pattern of Xsap-1 was examined during Xenopus embryogenesis using whole-mount in situ hybridization. Spatial expression of Xsap-1 mRNA is first detected at the animal pole at the mid-blastula stage. During neurulation Xsap-1 is expressed in cells participating in neural tube formation, in the sensorial layer of the epidermal ectoderm, and in an anterior region of the ventral mesoderm. Later, Xsap-1 expression is observed in the eye, ear vesicle, branchial arches, heart, pronephros, in the somites, and the developing nervous system, such as fore-, mid-, and hindbrain as well as in the cranial ganglion X.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.