Biomedical subjects

Christoph Winkler

Publications and source records attributed to Christoph Winkler.

23 records · Page 2Linked to original sources

PubMed2003

Characterization of hey bHLH genes in teleost fish.

Hairy-related basic helix-loop-helix (bHLH) transcription factors are targets of Delta-Notch signaling and represent essential components for a number of cell fate decisions during vertebrate embryogenesis. Hey genes encode a subfamily of hairy-related proteins that have been implicated in processes like somitogenesis, blood vessel and heart development. We have identified and characterized hey genes in three teleost fish lineages using degenerate PCR and database searches. Phylogenetic analysis of Hey proteins suggests a complex pattern of evolution with high divergence of hey2 in Takifugu rubripes (Fugu, Japanese pufferfish) and possibly loss in the related Tetraodon nigroviridis (the freshwater pufferfish). In addition, duplication of hey1 in both pufferfishes, Fugu and Tetraodon, was observed. Conversely, zebrafish (Danio rerio) has the same complement of three hey genes as known from mammals. All three hey genes show much more restricted gene expression profiles in zebrafish when compared to mouse. Importantly, while all three murine Hey genes are expressed in overlapping patterns in the presomitic mesoderm (PSM) and somites, in zebrafish only hey1 shows PSM and somite expression in a highly dynamic fashion. Therefore, while overlapping expression might account for redundancy of hey function in higher vertebrates, this is unlikely to be the case in zebrafish. In deltaD (dlD) deficient after-eight zebrafish mutants, the dynamic expression of hey1 in the PSM is impaired and completely lost in newly formed somitomeres. Overexpression of dlD on the other hand results in the ectopic expression of hey1 in the axial mesoderm. Hence, hey1 represents a target of Delta-Notch signaling dynamically expressed during somite formation in zebrafish.

Amino Acid Sequence↗

PubMed2003

Functional divergence of two zebrafish midkine growth factors following fish-specific gene duplication.

In mammals, the unique midkine (mdk) gene encodes a secreted heparin-binding growth factor with neurotrophic activity. Here, we show the presence of two functional mdk genes named mdka and mdkb in zebrafish and rainbow trout. Both midkine proteins are clearly different from the related pleiotrophin, which was also identified in zebrafish and other fishes. Zebrafish mdka and mdkb genes map to linkage groups LG7 and LG25, respectively, both presenting synteny to human chromosome 11, in which the unique human ortholog mdk is located. At least four other genes unique in mammals are also present as duplicates on LG7 and LG25. Phylogenetic and divergence analyses suggested that LG7/LG25 paralogs including mdka and mdkb have been formed at approximately the same time, early during the evolution of the fish lineage. Hence, zebrafish and rainbow trout mdka and mdkb might have been generated by an ancient block duplication, and might be remnants of the proposed fish-specific whole-genome duplication. In contrast to the ubiquitous expression of their mammalian counterpart, zebrafish mdka and mdkb are expressed in spatially restricted, mostly nonoverlapping patterns during embryonic development and strongly in distinct domains in the adult brain. Ectopic ubiquitous expression of both mdk genes in early zebrafish embryos caused completely distinct effects on neural crest and floorplate development. These data indicate that mdka and mdkb underwent functional divergence after duplication. This provides an outstanding model to analyze the molecular mechanisms that lead to differences in pathways regulating the formation of homologous embryonic structures in different vertebrates.

Amino Acid Sequence↗

PubMed2003

The lamina-associated polypeptide 2 (LAP2) isoforms beta, gamma and omega of zebrafish: developmental expression and behavior during the cell cycle.

Zebrafish lamina-associated polypeptides 2 (ZLAP2) beta, gamma and omega have in common an N-terminal region with a LEM domain, and in the C-terminal half of the molecule a lamina binding domain and a membrane spanning sequence. The maternally synthesized omega is the largest isoform and the only LAP2 present in the rapidly dividing embryonic cells up to the gastrula stage. ZLAP2omega levels decrease during development, concomitant with the increase of the somatic isoforms ZLAP2beta and gamma. In somatic zebrafish cells ZLAP2gamma is the predominant isoform, whereas only small amounts of ZLAP2beta are present. During early embryonic development, ZLAP2omega becomes associated with mitotic chromosomes before anaphase. The surface of these chromosomes is decorated with vesicles, and each chromosome assembles its own nuclear envelope at the end of mitosis (karyomere formation). Ectopically expressed ZLAP2omega-green fluorescent protein (GFP) fusion protein targets vesicles to mitotic chromosomes in Xenopus A6 cells, suggesting that ZLAP2omega is involved in karyomere formation during early zebrafish development. When ZLAP2beta and gamma were expressed as GFP fusion proteins in Xenopus A6 cells, the beta- but not the gamma-isoform was found in association with mitotic chromosomes, and ZLAP2beta-containing chromosomes were decorated with vesicles. Further analysis of ZLAP2-GFP fusion proteins containing only distinct domains of the ZLAP2 isoforms revealed that the common N-terminal region in conjunction with beta- or omega-specific sequences mediate binding to mitotic chromosomes in vivo.

Amino Acid Sequence↗

PubMed2003

The pro-opiomelanocortin gene of the zebrafish (Danio rerio).

The cDNA and the gene for pro-opiomelanocortin (POMC) in the zebrafish (Danio rerio) were isolated and analyzed. The gene consists of three exons and two short introns and has a similar overall structural organization as in Homo sapiens. Intron 1 (339 bp) divides the 5(') untranslated region from the coding region while intron 2 (1522 bp) is located between the signal peptide and the sequence encoding ACTH. Transcription starts 26 bp downstream of a TATA box and there is one polyadenylation signal in the 3(') untranslated region. The cDNA comprises of 964 bp with an open reading frame encoding a 222 amino acid hormone prepropeptide that is split into six putative hormones. Sequence comparison of zebrafish POMC to sequences of various other vertebrate species reveals four regions that are highly conserved during the evolution of vertebrates-the N-terminal region, ACTH, beta-MSH, and beta-endorphin, whereas the connecting peptides show a much higher degree of variability. Phylogenetic analysis of the POMC sequences of various vertebrate species resulted in the expected pattern of species evolution. In situ hybridization demonstrated POMC expression in a cluster of cells (corticotrophs) in the pituitary of the zebrafish as early as 23 h after fertilization. These findings will facilitate the use of the zebrafish as a model organism in the study of the physiological role of POMC-derived peptides.

Amino Acid Sequence↗

PubMed2002

A duplicated copy of DMRT1 in the sex-determining region of the Y chromosome of the medaka, Oryzias latipes.

The genes that determine the development of the male or female sex are known in Caenorhabditis elegans, Drosophila, and most mammals. In many other organisms the existence of sex-determining factors has been shown by genetic evidence but the genes are unknown. We have found that in the fish medaka the Y chromosome-specific region spans only about 280 kb. It contains a duplicated copy of the autosomal DMRT1 gene, named DMRT1Y. This is the only functional gene in this chromosome segment and maps precisely to the male sex-determining locus. The gene is expressed during male embryonic and larval development and in the Sertoli cells of the adult testes. These features make DMRT1Y a candidate for the medaka male sex-determining gene.

Amino Acid Sequence↗