A developmental biological study of aldolase gene expression in Xenopus laevis

We cloned cDNAs for Xenopus aldolases A, B and C. These three aldolase genes are localized on different chromosomes as a single copy gene. In the adult, the aldolase A gene is expressed extensively in muscle tissues, whereas the aldolase B gene is expressed strongly in kidney, liver, stomach and intestine, while the aldolase C gene is expressed in brain, heart and ovary. In oocytes aldolase A and C mRNAs, but not aldolase B mRNA, are extensively transcribed. Thus, aldolase A and C mRNAs, but not B mRNA, occur abundantly in eggs as maternal mRNAs, and strong expression of aldolase B mRNA is seen only after the late neurula stage. We conclude that aldolase A and C mRNAs are major aldolase mRNAs in early stages of Xenopus embryogenesis which proceeds utilizing yolk as the only energy source, aldolase B mRNA, on the other hand, is expressed only later in development in tissues which are required for dietary fructose metabolism. We also isolated the Xenopus aldolase C genomic gene (ca. 12 kb) and found that i     

Cloning and developmental expression of Baf57 in Xenopus laevis

Mammalian and Drosophila homologues of Baf57 have been previously isolated as being a subunit of SWI/SNF-like chromatin remodeling complexes. Here, we report the cloning and developmental expression of Xenopus Baf57. We isolated XBaf57 by using an expression cloning approach to identify novel modulators of Xenopus Smad7. XBaf57 co-operates with XSmad7 by increasing the expression of neural markers in ectodermal explants. XBaf57 is expressed in the ectoderm and pre-involuting mesoderm during gastrula stages and in the central nervous system during neurula and tailbud stages. These results raise the possibility that XBaf57 (or XBaf57-containing chromatin remodelling complexes) may be involved in the process of neural induction during Xenopus embryonic development.     

Tetracycline-regulated gene expression switch in Xenopus laevis

Xenopus is a well-characterized model system for the investigation of biological processes at the molecular, cellular, and developmental level. The successful application of a rapid and reliable method for transgenic approaches in Xenopus has led to renewed interest in this system. We have explored the applicability of tetracycline-regulated gene expression, first described by Gossen and Bujard in 1992, to the Xenopus system. By optimizing conditions, tetracycline repressor induced expression of a luciferase reporter gene was readily and reproducibly achieved in both the Xenopus oocyte and developing embryo. This high level of expression was effectively abrogated by addition of low levels of tetracycline. The significance of this newly defined system for studies of chromatin dynamics and developmental processes is discussed.     

Identification and developmental expression of Xenopus paraxis

During vertebrate embryogenesis, the paraxial mesoderm becomes segmented in a rostro-caudal progression and gives rise to the somites. In this paper we report the isolation of a Xenopus orthologue of paraxis, a member of a family of basic helix-loop-helix proteins, which has been suggested to play a role in paraxial mesoderm development. Xenopus paraxis is initially expressed in the presomitic paraxial mesoderm and later in the dorsal portion of the developing somites. Finally, paraxis expression becomes restricted to the most dorso-lateral region of mature somites.     

Isolation and developmental expression of tyrosinase family genes in Xenopus laevis

The tyrosinase family of genes in vertebrates consists of three related members encoding melanogenic enzymes, tyrosinase (Tyr), tyrosinase-related protein-1 (TRP-1, Tyrp1) and tyrosinase-related protein-2 (Dct, TRP-2, Tyrp2). These proteins catalyze melanin production in pigment cells and play important roles in determining vertebrate coloration. This is the first report examining melanogenic gene expression in pigment cells during embryonic development of amphibians. Xenopus provides a useful experimental system for analyzing molecular mechanisms of pigment cells. However, in this animal little information is available not only about the developmental expression but also about the isolation of pigmentation genes. In this study, we isolated homologues of Tyr, Tyrp1 and Dct in Xenopus laevis (XlTyr, XlTyrp1, and XlDct). We studied their expression during development using in situ hybridization and found that all of them are expressed in neural crest-derived melanophores, most of which migrate through the medial pathway, and in the developing diencephalon-derived retinal pigment epithelium (RPE). Further, XlDct was expressed earlier than XlTyr and XlTyrp1, which suggests that XlDct is the most suitable marker gene for melanin-producing cells among them. XlDct expression was detected in migratory melanoblasts and in the unpigmented RPE. In addition, the expression of XlDct was detected in the pineal organ. The sum of these studies suggests that expression of the tyrosinase family of genes is conserved in pigment cells of amphibians and that using XlDct as a marker gene for pigment cells will allow further study of the developmental mechanisms of pigment cell differentiation using Xenopus.     

Abdominal B-type Hox gene expression in Xenopus laevis

Previously, we reported a zebrafish iroquois gene, ziro3, and its expression during early embryogenesis (Mech. Dev. 87 (1999) 165). In the present study, we have isolated two novel zebrafish iroquois genes, ziro1 and ziro5, homologs of mouse Irx1 and mouse Irx5, respectively. The expression of both genes is initiated in dorsal neuroectoderm and mesoderm during gastrulation. Later, their expression appears in the central nervous system (CNS), excluding the telencephalon and most of the diencephalon. ziro1 expression is complementary to that of ziro3 in the notochord and later in the gut. In contrast, ziro5 expression mostly overlaps with that of ziro3. Interestingly, all three iroquois zebrafish genes are expressed in the notochord while only Irx3 is active in the mouse notochord. Their expression in later stages of embryogenesis was also compared.     

Histone gene expression in early development of Xenopus laevis

Abstract. This study comprises the hybridization analysis of electrophoretically separated histone mRNAs from oocytes and embryos of Xenopus laevis , and analysis of in vitro translation products of these mRNAs on polyacrylamide gels containing sodium dodecyl sulfate (SDS) or Triton X-100. In oocytes and embryos up to the tailbud stage, four types of mRNAs complementary to histone H2B DNA and two complementary to histone H4 DNA can be discriminated by their different electrophoretic mobilities on polyacrylamide gels. Electrophoretic heterogeneity was not detected for messengers for histones H2A and H3.
Histone mRNA, purified by hybridization under stringent conditions with a cloned histone gene cluster, was used to direct histone protein synthesis in a wheat-germ cell free system. The proteins synthesized comigrate with purified marker histones when electrophoresed on SDS-gels or acid-urea gels containing Triton X-100. When hybrid-selected histone mRNAs from oocytes and embryos in different developmental stages are translated, the proteins made by the mRNA from one stage can not be discriminated from those made by the mRNA from another stage after electrophoresis on SDS-gels or acid urea Triton X-100 gels.     

Global gene expression profiling and cluster analysis in Xenopus laevis

We have undertaken a large-scale microarray gene expression analysis using cDNAs corresponding to 21,000 Xenopus laevis ESTs. mRNAs from 37 samples, including embryos and adult organs, were profiled. Cluster analysis of embryos of different stages was carried out and revealed expected affinities between gastrulae and neurulae, as well as between advanced neurulae and tadpoles, while egg and feeding larvae were clearly separated. Cluster analysis of adult organs showed some unexpected tissue-relatedness, e.g. kidney is more related to endodermal than to mesodermal tissues and the brain is separated from other neuroectodermal derivatives. Cluster analysis of genes revealed major phases of co-ordinate gene expression between egg and adult stages. During the maternal-early embryonic phase, genes maintaining a rapidly dividing cell state are predominantly expressed (cell cycle regulators, chromatin proteins). Genes involved in protein biosynthesis are progressively induced from mid-embryogenesis onwards. The larval-adult phase is characterised by expression of genes involved in metabolism and terminal differentiation. Thirteen potential synexpression groups were identified, which encompass components of diverse molecular processes or supra-molecular structures, including chromatin, RNA processing and nucleolar function, cell cycle, respiratory chain/Krebs cycle, protein biosynthesis, endoplasmic reticulum, vesicle transport, synaptic vesicle, microtubule, intermediate filament, epithelial proteins and collagen. Data filtering identified genes with potential stage-, region- and organ-specific expression. The dataset was assembled in the iChip microarray database, , which allows user-defined queries. The study provides insights into the higher order of vertebrate gene expression, identifies synexpression groups and marker genes, and makes predictions for the biological role of numerous uncharacterized genes.     

Identification and preliminary function study of Xenopus laevis DRR1 gene

Xenopus laevis has recently been determined as a novel study platform of gene function. In this study, we cloned Xenopus DRR1 (xDRR1), which is homologous to human down-regulated in renal carcinoma (DRR1) gene. Bioinformatics analysis for DRR1 indicated that xDRR1 shared 74% identity with human DRR1 and 66% with mouse DRR1, and the phlogenetic tree of DRR1 protein was summarized. The xDRR1 gene locates in nuclei determined by transfecting A549 cells with the recombinant plasmid pEGFP-N1/xDRR1. RT-PCR analysis revealed that xDRR1 gene was expressed in all stages of early embryo development and all kinds of detected tissues, and whole-mount in situ hybridization showed xDRR1 was mainly present along ectoderm and mesoderm. Furthermore, xDRR1 expression could suppress A549 cell growth by transfecting with plasmid pcDNA3.1(+)/xDRR1. xDRR1 probably plays important roles involving in cell growth regulation and Xenopus embryo development.