Biomedical subjects

Christian Schön

Publications and source records attributed to Christian Schön.

3 recordsLinked to original sources

PubMed2006

The FoxP subclass in Xenopus laevis development.

We have investigated the sequences and the expression patterns of different members of the Xenopus laevis FoxP gene subfamily during embryogenesis. Low stringency hybridisation of a tadpole cDNA library with an xlFoxP2 fragment led to the isolation of several splice variants of xlFoxP1, xlFoxP2 and xlFoxP4. These variants do not only differ by utilisation of different leader exons, but also by alternative usage of coding exons thereby leading to functional alterations. For xlFoxP1b, we show that insertion of an additional exon disrupts binding to the co-repressor C-terminal binding protein1. Temporal and spatial expression patterns of xlFoxP2 and xlFoxP4 were analysed by RT-PCR and by whole mount in situ hybridisation. xlFoxP2 transcripts are detected from mid-gastrula to late tadpole stages and are found to be localised to pronephros, branchial arches and distinct structures of the hind-, mid- and forebrain, including the ciliary marginal zone of the retina. xlFoxP4 RNA is already present in early cleavage stage embryos and accumulates from midblastula until the end of embryogenesis. Localised expression is found within the anterior neural fold, in the mid- and hindbrain, in the branchial arches as well as in the pancreas.

Amino Acid Sequence↗

PubMed2004

A downstream enhancer is essential for Xenopus FoxD5 transcription.

We have isolated and sequenced the pseudo-allelic versions of FoxD5 genes in Xenopus laevis, xlFoxD5a and xlFoxD5b, and the xtFoxD5 gene of Xenopus tropicalis. These genes show a highly conserved structure, they are composed of only one exon, and they exhibit a high degree of sequence conservation within their flanking sequences. The X. tropicalis gene is expressed like its X. laevis orthologues in progenitor cells of the neural floor plate. Serial deletions of the 5'- and 3'-flanking region in combination with reporter gene assays demonstrate that a distal and a proximal upstream element as well as a downstream-located enhancer do mainly contribute to transcriptional activity. The downstream enhancer cooperates with the proximal upstream element and also contributes to the spatial expression. Transgenic animals express enhanced green fluorescent protein in a spatial pattern like xlFoxD5b, when the 5'- and 3'-flanking regions of the xlFoxD5b gene are used to direct transgene expression.

Amino Acid Sequence↗

PubMed2004

The FoxO-subclass in Xenopus laevis development.

Transcription factors of the Fox (fork head box) family are involved in cellular specification and determination processes. Here, we report on the isolation and first characterisation of two members of the FoxO subclass in Xenopus laevis, xFoxO1 and xFoxO3. These sequences exhibit 68% (67%) and 69% (70%) identity to their mouse (human) orthologues, respectively. Serine and threonine residues, which are phosphorylated upon insulin signalling, are evolutionarily conserved from frogs to mammals. xFoxO1 and xFoxO3 genes are maternally transcribed, but transcripts disappear during early cleavage stages. Zygotic transcription of both genes starts at the late neurula stages and transcripts accumulate at the end of organogenesis. While maternal transcripts of both genes are found within the animal half of the early embryo, zygotic transcripts show distinct patterns. xFoxO1 expression is observed in the pronephros, within head mesenchyme in front of the eye, within the branchial arches and in the liver primordium. At the late neurula, xFoxO3 is found to be specifically expressed in the anterior neural plate and in neural crest cells. Later, expression of xFoxO3 is observed in a variety of organs and tissues, like the head, the branchial arches and the somites.

Amino Acid Sequence↗