The olig family: phylogenetic analysis and early gene expression in Xenopus tropicalis.

The olig genes form a small subfamily of basic helix-loop-helix transcription factors. They were discovered in 2000 as genes required for oligodendrocyte lineage specification. Since then, olig genes have been identified in various vertebrate species and corresponding sequences accumulated within genomic databases.

Exploring nervous system transcriptomes during embryogenesis and metamorphosis in Xenopus tropicalis using EST analysis.

Background: The western African clawed frog Xenopus tropicalis is an anuran amphibian species now used as model in vertebrate comparative genomics. It provides the same advantages as Xenopus laevis but is diploid and has a smaller genome of 1.7 Gbp.

XSEB4R, a novel RNA-binding protein involved in retinal cell differentiation downstream of bHLH proneural genes.

RNA-binding proteins play key roles in the post-transcriptional regulation of gene expression but so far they have not been studied extensively in the context of developmental processes. We report on the molecular cloning and spatio-temporal expression of a novel RNA-binding protein, XSEB4R, which is strongly expressed in the nervous system. This study is focused on the analysis of Xseb4R in the context of primary neurogenesis and retinogenesis.

In vitro effect of metal ions on the activity of two amphibian glyceraldehyde-3-phosphate dehydrogenases: potential metal binding sites.

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH, EC 1.2.1.

Identification of metaflothionein in Pleurodeles waltl.

The characterization of metallothionein in the Urodele amphibian species Pleurodeles waltl was achieved. A simple and rapid method for identification of metallothionein, based on its strong affinity for cadmium (109Cd), was used. We were able to show that metallothionein is constitutively synthesized in liver, ovary and brain.

Glyceraldehyde-3-phosphate dehydrogenase from the newt Pleurodeles waltl. Protein purification and characterization of a GapC gene.

The NAD(+)-dependent cytosolic glyceraldehyde-3-phosphate dehydrogenase (GAPDH, EC 1.2.1.

Relationship between posttranslational modification of transaldolase and catalase deficiency in UV-sensitive repair-deficient xeroderma pigmentosum fibroblasts and SV40-transformed human cells.

Xeroderma Pigmentosum (XP) is a rare recessively inherited human disease associated with a hypersensitivity to ultraviolet radiation. The ultraviolet component of sunlight can initiate and promote the formation of cutaneous tumors as seen in the skin cancer-prone XP patients. Previously, we have found that the low activity of the NADPH-dependent antioxydant enzyme, catalase, which we have observed in XP diploid fibroblasts and SV40-tranformed cells, could be restored by the addition of NADPH.

Advantages of a P-element construct containing MtnA sequences for the identification of patterning and cell determination genes in Drosophila melanogaster.

The P[MTW] transposon carries a functional MtnA (metallothionein) gene and a miniwhite reporter gene. When P[MTW] was transformed into Drosophila, many lines were found to show position-dependent expression patterns of the miniwhite or the MtnA transgene. Identification of several of the target genes indicated that this construct behaves as an enhancer or silencer trap.

Characterization of two promoters of the Xenopus laevis elrD gene.

The Xenopus laevis elrD gene belongs to the multigenic elav/Hu family. elrD is exclusively expressed in neural cells, where it could be involved in the posttranscriptional control of mRNAs. Here we report the isolation and characterization of the genomic elrD 5'-flanking region.

Expression of the Xenopus laevis metallothionein gene during ontogeny.

Expression of the Xenopus laevis metallothionein (MT) gene was studied by in situ hybridization throughout development. MT mRNA was detected from the tailbud stage onwards. MT expression was observed in bucco-pharyngeal epithelium, pronephros and liver anlagen, aswell as in lens and periventricular areas of the encephalon.

Xenopus elav-like genes are differentially expressed during neurogenesis.

In Xenopus, three neural-specific elav-like genes (ELGs) have been identified, elrB/Xel-1, elrC and elrD. With the aim to highlight possible differences in the regulation of these genes, we compared their expression patterns during development. We had previously shown that elrB is expressed from the early tailbud stage onwards, in both the central and peripheral nervous system.

Misexpression of the RNA-binding protein ELRB in Xenopus presumptive neurectoderm induces proliferation arrest and programmed cell death.

Proteins of the ELAV/Hu family share the presence of three RNA binding domains. In Xenopus, three nervous system-specific elav/Hu related genes, elrB, elrC and elrD, have been identified so far. The temporally regulated expression patterns of elrB, elrC and elrD suggest their involvement at different steps of neural differentiation.

Subcellular distribution of Xenopus XEL-1 protein, a member of the neuron-specific ELAV/Hu family, revealed by epitope tagging.

Drosophila and vertebrate elav/Hu genes are involved in the development and the maintenance of the nervous system. They all encode proteins that contain three RNA recognition motifs (RRM) and are thus expected to play a role in RNA metabolism. Drosophila ELAV and RBP9 proteins were reported to be exclusively distributed in nuclei of neurons, whereas known human Hu proteins display a bipartite nuclear and cytoplasmic distribution.

Distribution and evolution of introns in Drosophila amylase genes.

While the two amylase genes of Drosophila melanogaster are intronless, the three genes of D. pseudoobscura harbor a short intron. This raises the question of the common structure of the Amy gene in Drosophila species.

Thyroid hormone regulation of germ cell-specific EF-1 alpha expression during metamorphosis of Xenopus laevis.

In situ hybridization was used to follow the distribution of the mRNAs encoding the somatic form of elongation factor 1 alpha (EF-1 alpha S) and the germinal counterparts of this factor, thesaurin a and EF-1 alpha O, throughout metamorphosis in the gonads of Xenopus laevis tadpoles. EF-1 alpha S mRNA is detected before metamorphosis in both the somatic and germ cells of the gonads. In contrast, thesaurin a and EF-1 alpha O mRNAs are first detected in spermatogonia and oogonia at stages 60-62, corresponding to the climax of metamorphosis and to the peak of circulating thyroid hormone.

Response of Drosophila metallothionein promoters to metallic, heat shock and oxidative stresses.

The metallothionein system in Drosophila melanogaster is composed of two genes, Mtn and Mto. In order to compare the induction properties of these genes, we transformed D. melanogaster with P-element vectors containing Adh and lacZ reporter genes under the control of Mtn and Mto promoters, respectively.

Rearrangements involving repeated sequences within a P element preferentially occur between units close to the transposon extremities.

In a previous report we described rearrangements occurring at a high rate (30% of the progeny of dysgenic flies) within a cluster of 5S genes internal to a P element. These events were characterized as precise amplifications and deletions of 5S units. Here we analyze recombination events within P elements containing two repeated arrays of 5S genes flanking a central white gene.

Structural evolution of the Drosophila 5S ribosomal genes.

We compare the 5S gene structure from nine Drosophila species. New sequence data (5S genes of D. melanogaster, D.

Expression of metallothionein genes during the post-embryonic development of Drosophila melanogaster.

Expression of the two Drosophila melanogaster metallothionein genes, Mtn and Mto, has been analyzed by in situ hybridization during post-embryonic development. Mtn and Mto transcripts were detected exclusively in the digestive tract of larvae, pupae and adults reared on standard medium. Mtn and Mto expression domains overlap, but each gene is also expressed at unique sites.

Isolation and embryonic expression of Xel-1, a nervous system-specific Xenopus gene related to the elav gene family.

We have identified a new member of the elav gene family in Xenopus laevis. This gene, Xel-1, like the other elav-related genes, encodes a putative RNA-binding protein that contains three RNA Recognition Motifs and is solely expressed in the nervous system. Xel-1 is most likely the Xenopus homologue of Hel-N1, one of the three known human genes related to elav.

Developmental variability of metallothionein Mtn gene expression in the species of the Drosophila melanogaster subgroup.

Developmental expression of the Drosophila melanogaster metallothionein Mtn gene has been analysed. Transcripts of this gene accumulate during the vitellogenic phase of oogenesis in a ring of follicular cells at the oocyte-nurse cell margin and in the follicular cells surrounding the oocyte. There is also strong expression of the Mtn gene during the second half of embryogenesis in hemocytes, the endoderm midgut, and Malpighian tubules.

Deletions and amplifications of tandemly arranged ribosomal 5S genes internal to a P element occur at a high rate in a dysgenic context.

We observed unusual kinds of rearrangements within tandemly clustered 5S genes internal to a P element in dysgenic context. Rearranged P transposons, initially containing eight 5S genes, were found to display discrete numbers of 5S genes, from 4 up to 17 units. Precise deletions and amplifications occurred at a high rate (40%), at both original and new insertion sites.

Molecular cloning and expression of a metallothionein mRNA in Xenopus laevis.

Metallothioneins (MT) are expressed during early development in species of several groups. To understand MT function in developmental processes, we studied the MT system of Xenopus laevis, a model vertebrate species in experimental embryology. We first purified and sequenced the liver MT from copper-treated animals.

Molecular cloning and expression of ferritin mRNA in heavy metal-poisoned Xenopus laevis cells.

In a search for genes transcriptionally regulated by metal ions, we have isolated a Xenopus laevis ferritin cDNA clone, XL2-17, from cadmium-poisoned XL2 cells. The large size of the corresponding ferritin mRNA (1.4 kb) is due to the presence of a 629-nucleotide 5'-untranslated region.

Metallothionein Mto gene of Drosophila melanogaster: structure and regulation.

We report the sequence of the Mto gene, one of the two known metallothionein genes of Drosophila melanogaster, and compare its structure with that of the other metallothionein gene, Mtn. The main structural features are the presence of a small intron (61 base-pairs), the presence of four potential MREs (metal regulatory elements) and the absence of a TATA box in the promoter region. Of all metals tested, Hg2+, Cd2+ and Cu2+ are the most efficient ions for inducing an increase in Mto gene transcription.