Biomedical subjects

Nicole Spieker

Publications and source records attributed to Nicole Spieker.

3 recordsLinked to original sources

PubMed2005

Cloning and functional characterization of a novel connexin expressed in somites of Xenopus laevis.

Connexin-containing gap junctions play an essential role in vertebrate development. More than 20 connexin isoforms have been identified in mammals. However, the number identified in Xenopus trails with only six isoforms described. Here, identification of a new connexin isoform from Xenopus laevis is described. Connexin40.4 was found by screening expressed sequence tag databases and carrying out polymerase chain reaction on genomic DNA. This new connexin has limited amino acid identity with mammalian (<50%) connexins, but conservation is higher (approximately 62%) with fish. During Xenopus laevis development, connexin40.4 was first expressed after the mid-blastula transition. There was prominent expression in the presomitic paraxial mesoderm and later in the developing somites. In adult frogs, expression was detected in kidney and stomach as well as in brain, heart, and skeletal muscle. Ectopic expression of connexin40.4 in HEK293 cells, resulted in formation of gap junction like structures at the cell interfaces. Similar ectopic expression in neural N2A cells resulted in functional electrical coupling, displaying mild, asymmetric voltage dependence. We thus cloned a novel connexin from Xenopus laevis, strongly expressed in developing somites, with no apparent orthologue in mammals.

Aging↗

PubMed2004

Analysis of the Tcf-3 promoter during early development of Xenopus.

XTcf-3 functions as a transcriptional regulator in the canonical Wnt signaling cascade and can repress or activate downstream target genes. Expression of XTcf-3 is differentially regulated in time and place during development (Molenaar et al. [1998] Mech Dev. 75:151-154), but little is known about the mechanisms that control transcriptional activation and repression. A 15-kb genomic fragment of Tcf-3 sequences from Xenopus tropicalis was cloned, including the 5' untranslated region; exons 1, 2, and 3; and intron sequences. We used 5' deletion constructs for transgenesis and episomal luciferase assays in Xenopus to examine temporal and spatial regulation of the promoter during early development. A -3054/+34-bp Tcf-3 upstream region was identified that drives a green fluorescent protein (GFP) reporter transgene in a pattern similar to endogenous expression of XtTcf-3 from gastrula to tail bud stages. At stage 12, expression of the reporter is restricted to the middle and posterior neurectoderm. At stage 22, expression is strongest in the neural plate, the eye anlagen and branchial arches. At stage 35/36, expression is found in the head mesenchyme, the branchial arches, the heart, the mesencephalon, eyes, otic vesicles, notochord, somites and the lateral plate mesoderm. Part of the cis-acting elements driving this GFP reporter transgene expression map between -372 and -95 bp of the transcription start site. Furthermore, two TCF/LEF sites are necessary for full activity of the promoter during gastrula stages in episomal luciferase assays.

5' Untranslated Regions↗

PubMed2003

Tcf-1 expression during Xenopus development.

We report the cloning and expression of Xenopus Tcf-1. The amino acid sequence of Tcf-1 of Xenopus laevis and Xenopus tropicalis is closely related to that of chicken, mouse and man. Thus, the family of Tcf/Lef proteins in the amphibian Xenopus comprises four members as in higher vertebrates. RT-PCR analysis revealed that Tcf-1 RNA encoding a beta-catenin binding isoform is maternally present as well as throughout early development. Different transcripts are expressed by alternative splicing. In cleavage and blastula stage embryos, Tcf-1 RNA is present at high levels in the animal hemisphere. During gastrulation Tcf-1 is differentially expressed with high levels in the animal cap and most of the marginal zone except for a narrow domain around the blastopore. At neurula stages expression is predominant in the neural plate. At tailbud stages expression is localized in specific areas of the brain, in the eyes, the otic vesicle, branchial arches and head mesenchyme, somites, tailbud, pronephros and pronephric duct.

Amino Acid Sequence↗