Biology subjects

Pfeifer, K.

Publications and source records attributed to Pfeifer, K..

4 recordsLinked to original sources

bioRxiv2018

Characterization of Drosophila Nidogen/entactin reveals roles in basement membrane stability, barrier function and nervous system plasticity

Basement membranes (BMs) are specialized layers of extracellular matrix (ECM) mainly composed of Laminin, type IV Collagen, Perlecan and Nidogen/entactin (NDG). While the essential and evolutionary conserved functions of Laminin, Collagen and Perlecan are well documented in Drosophila and other species, the proposed role of NDG as the major ECM linker molecule has been challenged by several in vivo studies revealing that NDG is dispensable for viability and BM formation. Here, we report the characterization of the single Ndg gene in Drosophila. Embryonic Ndg expression differed from that of other BM components and was primarily observed in mesodermal tissues and the chordotonal organs, whereas NDG protein localized to all BMs. While loss of Laminin strongly affected BM-localization of NDG, Ndg null mutants exhibited no overt changes in the distribution of BM core components. However, loss of NDG led to ultrastructural BM defects compromising barrier function and stability in vivo. Although Ndg mutants were viable, loss of NDG led to decreased fecundity in flies as well as impaired crawling behavior and reduced response to vibrational stimuli in larvae. Further morphological analysis revealed accompanying defects in the larval peripheral nervous system especially in the chordotonal organs and the neuromuscular junction (NMJ), where Ndg genetically interacted with the Leukocyte-antigen-related-like (Lar) receptor gene to regulate NMJ extension and synaptic differentiation. Taken together, our analysis suggests that NDG is not essential for BM assembly but mediates BM stability and ECM-dependent neural plasticity during Drosophila development.\n\nSummary StatementIn this study we characterize Drosophila Nidogen/Entactin (Ndg) mutants revealing that loss of Ndg impairs basement membrane (BM) stability and permeability as well as proper function of the nervous system.

developmental biology↗

bioRxiv2017

Candidatus Nitrosocaldus cavascurensis, an ammonia oxidizing, extremely thermophilic archaeon with a highly mobile genome

Ammonia oxidizing archaea (AOA) of the phylum Thaumarchaeota are widespread in moderate environments but their occurrence and activity has also been demonstrated in hot springs. Here we present the first cultivated thermophilic representative with a sequenced genome, which allows to search for adaptive strategies and for traits that shape the evolution of Thaumarchaeota. Candidatus Nitrosocaldus cavascurensis has been cultivated from a hot spring in Ischia, Italy. It grows optimally at 68{degrees}C under chemolithoautotrophic conditions on ammonia or urea converting ammonia stoichiometrically into nitrite with a generation time of approximately 25h. Phylogenetic analyses based on ribosomal proteins place the organism as a sister group to all known mesophilic AOA. The 1.58 Mb genome of Ca. N. cavascurensis harbors an amoAXCB gene cluster encoding ammonia monooxygenase, genes for a 3-hydroxypropionate/4-hydroxybutyrate pathway for autotrophic carbon fixation, but also genes that indicate potential alternative energy metabolisms. Although a bona fide gene for nitrite reductase is missing, the organism is sensitive to NO-scavenging, underlining the importance of this compound for AOA metabolism. Ca. N. cavascurensis is distinct from all other AOA in its gene repertoire for replication, cell division and repair. Its genome has an impressive array of mobile genetic elements and other recently acquired gene sets, including conjugative systems, a provirus, transposons and cell appendages. Some of these elements indicate recent exchange with the environment, whereas others seem to have been domesticated and might convey crucial metabolic traits.

microbiology↗

bioRxiv2017

ALKALs are in vivo ligands for ALK family Receptor Tyrosine Kinases in the neural crest and derived cells.

Mutations in Anaplastic Lymphoma Kinase (ALK) are implicated in somatic and familial neuroblastoma, a paediatric tumour of neural crest-derived tissues. Recently, biochemical analyses have identified secreted small ALKAL proteins (FAM150, AUG) as potential ligands for human ALK and the related Leukocyte Tyrosine Kinase (LTK). In the zebrafish Danio rerio, DrLtk, which is similar to human ALK in sequence and domain structure, controls the development of iridophores, neural crest-derived pigment cells. Hence, the zebrafish system allows studying Alk/Ltk and Alkals involvement in neural crest regulation in vivo. Using zebrafish pigment pattern formation, Drosophila eye patterning, and cell culture-based assays, we show that zebrafish Alkals potently activate zebrafish Ltk and human ALK driving downstream signalling events. Overexpression of the three Dr Alkals cause ectopic iridophore development whereas loss of function alleles lead to spatially distinct patterns of iridophore loss in zebrafish larvae and adults. alkal loss of function triple mutants completely lack iridophores and are larval lethal as is the case for ltk null mutants. Our results provide the first in vivo evidence of (i) activation of ALK/LTK family receptors by ALKALs and (ii) an involvement of these ligand-receptor complexes in neural crest development.

developmental biology↗

bioRxiv2017

The scaffolding protein Cnk Interacts with Alk to Promote Visceral Founder Cell Specification in Drosophila

In Drosophila, the receptor tyrosine kinase Alk and its ligand Jeb are required to drive founder cell (FC) specification in the visceral mesoderm (VM). Alk-signalling activates downstream MAPK/ERK- and PI3K-pathways in human and Drosophila but little is known about immediate downstream signalling events. Here we report that the scaffolding protein Cnk interacts directly with Alk via a novel c-terminal binding motif. Cnk is required for Alk-signalling as ectopic expression of the minimal interaction motif as well as loss of maternal and zygotic cnk blocks visceral FC-formation, resembling the phenotype of jeb and Alk mutants. We also show that the Cnk-interactor Aveugle/Hyphen (Ave/HYP) is critical, while the (pseudo-) kinase Ksr is not required for Alk-signalling in the developing VM. Taken together, Cnk and Ave represent the first molecules downstream of Alk whose loss genocopies the lack of visceral FC-specification of Alk and jeb mutants indicating an essential role in Alk-signalling.

developmental biology↗