Biomedical subjects

Achim C Heinrich

Publications and source records attributed to Achim C Heinrich.

3 recordsLinked to original sources

PubMed2005

Fjx1: a notch-inducible secreted ligand with specific binding sites in developing mouse embryos and adult brain.

The mouse fjx1 gene was identified as a homologue to the Drosophila gene four-jointed (fj). Fj encodes a transmembrane type II glycoprotein that is partially secreted. The gene was found to be a downstream target of the Notch signaling pathway in leg segmentation and planar cell polarity processes during eye development of Drosophila. Here, we show that fjx1 is not only conserved in vertebrates, but we also identified the murine fjx1 gene as a direct target of Notch signaling. In addition to the previously described expression of fjx1 in mouse brain, we show here that fjx1 is expressed in the peripheral nervous system, epithelial cells of multiple organs, and during limb development. The protein is processed and secreted as a presumptive ligand. Through the use of an fjx1-AP fusion protein, we could visualize fjx1 binding sites at complementary locations, supporting the notion that fjx1 may function as a novel signaling molecule.

Aging↗

PubMed2004

A mouse model for visualization and conditional mutations in the erythroid lineage.

Hematologic disorders can be caused by sporadic or inherited mutations. However, the molecular mechanisms that lead to pathogenicity are only partially understood. An accurate method to generate mouse models is conditional gene manipulation facilitated by the Cre-loxP recombination system. To enable identification and genomic manipulation of erythroid progenitor cells, we established a knock-in mouse model (ErGFPcre) that expresses an improved GFPcre fusion protein controlled by the endogenous erythropoietin receptor (EpoR) promoter. We show that ErGFPcre mice enable the identification of GFP-positive erythroid progenitor cells and the highly specific genomic manipulation of the erythroid lineage. Analysis of GFP-positive erythroid progenitor cells suggests a developmental switch in lineage progression from the hematopoietic stem cell compartment to early erythroid progenitor cells that are stem cell antigen-1-negative (Sca-1(-)) and c-kit(high). Within the hematopoietic system, Cre-mediated recombination is limited to erythroid progenitor cells and occurs in the adult bone marrow at a frequency of up to 80% and in the fetal liver with an efficiency close to 100%. Differential transcriptional activity of the wild-type and the knock-in locus was observed in nonhematopoietic tissues. Thus, our ErGFPcre mouse model could promote the identification of regulatory elements controlling nonhematopoietic EpoR expression and facilitates the characterization and genomic manipulation of erythroid progenitor cells.

Animals↗

PubMed2002

A functional green fluorescent protein-erythropoietin receptor despite physical separation of JAK2 binding site and tyrosine residues.

Signaling through hematopoietic cytokine receptors such as the erythropoietin receptor (EpoR) depends on the activation of a receptor-bound Janus kinase (JAK) and tyrosine phosphorylation of the cytoplasmic domain. To visualize the EpoR and elucidate structural requirements coordinating signal transduction, we probed the EpoR by inserting the green fluorescent protein (GFP) at various positions. We show that insertion of GFP in proximity to the transmembrane domain, either in the extracellular or the cytoplasmic domain, results in EpoR-GFP receptors incompetent to elicit biological responses in a factor-dependent cell line or in erythroid progenitor cells. Surprisingly, a receptor harboring GFP insertion in the middle of the cytoplasmic domain, and thereby separating the JAK2 binding site from the tyrosine residues, is capable of supporting signal transduction in response to ligand binding. Comparable with the wild type EpoR, but more efficient than a C-terminal EpoR-GFP fusion, this chimeric receptor promotes the maturation of erythroid progenitor cells and is localized in punctated endosome-like structures. We conclude that the extracellular, transmembrane, and membrane-proximal segment of the cytoplasmic domain form a rigid structural entity whose precise orientation is essential for the initiation of signal transduction, whereas the cytoplasmic domain possesses flexibility in adopting an activated conformation.

Animals↗