Jürgen J. Heinisch

The frontotemporal dementia mutation R406W blocks tau’s interaction with the membrane in an annexin A2–dependent manner

The R406W mutation prevents tau from functioning as a linker between the membrane and the microtubule cytoskeleton.

How do I begin? Sensing extracellular stress to maintain yeast cell wall integrity.

The cell wall integrity (CWI) signalling pathway is necessary to remodel the yeast cell wall during normal morphogenesis and in response to cell surface stress. In the Bakers yeast Saccharomyces cerevisiae, a set of five membrane-spanning sensors, namely Wsc1, Wsc2, Wsc3, Mid2 and Mtl1, detect perturbations in the cell wall and/or the plasma membrane and activate a downstream signal transduction pathway with a central MAP kinase module. As a consequence, the expression of genes whose products are involved in cell wall structure and remodelling is induced. This review summarises our recent results on sensor structure and function, as well as the advances made regarding sensor mechanics.

Single-molecule tracking of tau reveals fast kiss-and-hop interaction with microtubules in living neurons

This is the first study in which the interaction of a microtubule-associated protein has been evaluated by direct single-molecule observations in living neurons. The data imply a novel kiss-and-hop mechanism of tau–microtubule interaction, rationalizing how tau can regulate microtubule dynamics without interfering with axonal transport.

STAT2 is an essential adaptor in USP18-mediated suppression of type I interferon signaling

Type I interferons (IFNs) are multifunctional cytokines that regulate immune responses and cellular functions but also can have detrimental effects on human health. A tight regulatory network therefore controls IFN signaling, which in turn may interfere with medical interventions. The JAK–STAT signaling pathway transmits the IFN extracellular signal to the nucleus, thus resulting in alterations in gene expression. STAT2 is a well-known essential and specific positive effector of type I IFN signaling. Here, we report that STAT2 is also a previously unrecognized, crucial component of the USP18-mediated negative-feedback control in both human and mouse cells. We found that STAT2 recruits USP18 to the type I IFN receptor subunit IFNAR2 via its constitutive membrane-distal STAT2-binding site. This mechanistic coupling of effector and negative-feedback functions of STAT2 may provide novel strategies for treatment of IFN-signaling-related human diseases.

Guidelines and recommendations on yeast cell death nomenclature

Elucidating the biology of yeast in its full complexity has major implications for science, medicine and industry. One of the most critical processes determining yeast life and physiology is cellular demise. However, the investigation of yeast cell death is a relatively young field, and a widely accepted set of concepts and terms is still missing. Here, we propose unified criteria for the definition of accidental, regulated, and programmed forms of cell death in yeast based on a series of morphological and biochemical criteria. Specifically, we provide consensus guidelines on the differential definition of terms including apoptosis, regulated necrosis, and autophagic cell death, as we refer to additional cell death routines that are relevant for the biology of (at least some species of) yeast. As this area of investigation advances rapidly, changes and extensions to this set of recommendations will be implemented in the years to come. Nonetheless, we strongly encourage the authors, reviewers and editors of scientific articles to adopt these collective standards in order to establish an accurate framework for yeast cell death research and, ultimately, to accelerate the progress of this vibrant field of research.

Proton-associated sucrose transport of mammalian solute carrier family 45: an analysis in Saccharomyces cerevisiae.

The members of the solute carrier 45 (SLC45) family have been implicated in the regulation of glucose homoeostasis in the brain (SLC45A1), with skin and hair pigmentation (SLC45A2), and with prostate cancer and myelination (SLC45A3). However, apart from SLC45A1, a proton-associated glucose transporter, the function of these proteins is still largely unknown, although sequence similarities to plant sucrose transporters mark them as a putative sucrose transporter family. Heterologous expression of the three members SLC45A2, SLC45A3 and SLC45A4 in Saccharomyces cerevisiae confirmed that they are indeed sucrose transporters. [(14)C]Sucrose-uptake measurements revealed intermediate transport affinities with Km values of approximately 5 mM. Transport activities were best under slightly acidic conditions and were inhibited by the protonophore carbonyl cyanide m-chlorophenylhydrazone, demonstrating an H(+)-coupled transport mechanism. Na(+), on the other hand, had no effect on sucrose transport. Competitive inhibition assays indicated a possible transport also of glucose and fructose. Real-time PCR of mouse tissues confirmed mRNA expression of SLC45A2 in eyes and skin and of SLC45A3 primarily in the prostate, but also in other tissues, whereas SLC45A4 showed a predominantly ubiquitous expression. Altogether the results provide new insights into the physiological significance of SLC45 family members and challenge existing concepts of mammalian sugar transport, as they (i) transport a disaccharide, and (ii) perform secondary active transport in a proton-dependent manner.

Triple mammalian/yeast/bacterial shuttle vectors for single and combined Lentivirus- and Sindbis virus-mediated infections of neurons

Today, a large variety of viral vectors is available for ectopic gene expression in mammalian cell cultures or in vivo. Among them, infection with Sindbis virus- or Lentivirus-derived constructs is often used to address biological questions or for applications in neuronal therapies. However, cloning of genes of interest is time consuming, since it relies on restriction and ligation, frequently of PCR-generated DNA fragments with suitable restriction sites introduced by the primers employed. We here take advantage of the unusually high capacity for homologous recombination in Saccharomyces cerevisiae to circumvent this problem, and introduce a new set of triple shuttle vectors, which can be shuffled between E. coli, yeast, and mammalian cells. The system allows the introduction of genes of interest largely independent of the target site in the vectors. It also allows the removal of the yeast selection marker by Cre-recombinase directed recombination in E. coli, if vector size limits transfection efficiency in the mammalian cells. We demonstrate the expression of genes encoding fluorescent proteins (EGFP and mCherry) both separately and in combination, using two different viral systems in mammalian cell lines, primary neurons and organotypic slices.

Milk and sugar: Regulation of cell wall synthesis in the milk yeast Kluyveromyces lactis

The milk yeast Kluyveromyces lactis is an alternative model yeast to the well established Saccharomyces cerevisiae. The cell wall of these fungi consists of polysaccharides (i.e. long chains of β-1,3- and β-1,6-linked sugar chains and some chitin) and mannoproteins, both of which are continually adapted to environmental conditions in terms of their abundance and organization. This implies the need to perceive signals at the cell surface and to transform them into a proper cellular response. The signal transduction cascade involved in this process is generally referred to as the cell wall integrity (CWI) pathway. CWI signaling and cell wall composition have been extensively studied in the Bakers yeast S. cerevisiae and are also of interest in other yeast species with commercial potential, such as K. lactis. We here summarize the results obtained in the past years on CWI signaling in K. lactis and use a comparative approach to the findings obtained in S. cerevisiae to highlight special adaptations to their natural environments.

The bHLH transcription factor hand is required for proper wing heart formation in Drosophila.

The Hand basic helix-loop-helix transcription factors play an important role in the specification and patterning of various tissues in vertebrates and invertebrates. Here, we have investigated the function of Hand in the development of the Drosophila wing hearts which consist of somatic muscle cells as well as a mesodermally derived epithelium. We found that Hand is essential in both tissues for proper organ formation. Loss of Hand leads to a reduced number of cells in the mature organ and loss of wing heart functionality. In wing heart muscles Hand is required for the correct positioning of attachment sites, the parallel alignment of muscle cells, and the proper orientation of myofibrils. At the protein level, α-Spectrin and Dystroglycan are misdistributed suggesting a defect in the costameric network. Hand is also required for proper differentiation of the wing heart epithelium. Additionally, the handC-GFP reporter line is not active in the mutant suggesting an autoregulatory role of Hand in wing hearts. Finally, in a candidate-based RNAi mediated knock-down approach we identified Daughterless and Nautilus as potential dimerization partners of Hand in wing hearts.

Identification of Dck1 and Lmo1 as upstream regulators of the small GTPase Rho5 in Saccharomyces cerevisiae

The exact function and regulation of the small GTPase Rho5, a putative homolog of mammalian Rac1, in the yeast Saccharomyces cerevisiae have not yet been elucidated. In a genetic screen initially designed to identify novel regulators of cell wall integrity signaling, we identified the homologs of mammalian DOCK1 (Dck1) and ELMO (Lmo1) as upstream components which regulate Rho5. Deletion mutants in any of the encoding genes (DCK1, LMO1, RHO5) showed hyper‐resistance to cell wall stress agents, demonstrating a function in cell wall integrity signaling. Live‐cell fluorescence microscopy showed that Dck1, Lmo1 and Rho5 quickly relocate to mitochondria under oxidative stress and cell viability assays indicate a role of Dck1/Lmo1/Rho5 signaling in triggering cell death as a response to hydrogen peroxide treatment. A regulatory role in autophagy/mitophagy is suggested by the colocalization of Rho5 with autophagic markers and the decreased mitochondrial turnover observed in dck1, lmo1 and rho5 deletion mutants. Rho5 activation may thus serve as a central hub for the integration of different signaling pathways.