Characterizing a hybrid zone between a cryptic species pair of freshwater snails

Characterizing hybrid zones and their dynamics is a central goal in evolutionary biology, but this is particularly challenging for morphologically cryptic species. The lack of conspicuous divergence between parental types means intermediate hybrid forms often go undetected. We aimed to detect and characterize a suspected hybrid zone between a pair of morphologically cryptic lineages of the freshwater snail, Radix. We sampled Radix from across a contact zone between two mitochondrial lineages (Radix balthica and an undescribed lineage termed ‘MOTU3’) and detected admixture between two nuclear genotype clusters, which were significantly but not categorically associated with the mitochondrial lineages. Using a model selection approach, we show that the admixture cline is best explained by an interaction between precipitation and temperature gradients over the area, rather than geographic distance. We thus hypothesize that the correlation with climatic gradients suggests environmental selection has played a role in maintaining the hybrid zone. In a 2050 climate change scenario, we furthermore predict an expansion of one of the nuclear clusters and a widening of the hybrid zone as the climate warms and dries.     

The transition zone protein Rpgrip1l regulates proteasomal activity at the primary cilium

Mutations in RPGRIP1L result in severe human diseases called ciliopathies. To unravel the molecular function of RPGRIP1L, we analyzed Rpgrip1l^−/− mouse embryos, which display a ciliopathy phenotype and die, at the latest, around birth. In these embryos, cilia-mediated signaling was severely disturbed. Defects in Shh signaling suggested that the Rpgrip1l deficiency causes an impairment of protein degradation and protein processing. Indeed, we detected a cilia-dependent decreased proteasomal activity in the absence of Rpgrip1l. We found different proteasomal components localized to cilia and identified Psmd2, a component of the regulatory proteasomal 19S subunit, as an interaction partner for Rpgrip1l. Quantifications of proteasomal substrates demonstrated that Rpgrip1l regulates proteasomal activity specifically at the basal body. Our study suggests that Rpgrip1l controls ciliary signaling by regulating the activity of the ciliary proteasome via Psmd2.     

Trophic flexibility and opportunism in pike Esox lucius

The first comprehensive investigation of pike Esox lucius trophic ecology in a region (Ireland) where they have long been thought to be a non‐native species is presented. Diet was investigated across habitat types (lake, river and canal) through the combined methods of stable‐isotope and stomach content analyses. Variations in niche size, specialization and the timing of the ontogenetic dietary switch were examined, revealing pronounced opportunism and feeding plasticity in E. lucius, along with a high occurrence of invertivory (up to 60 cm fork length, L_F) and a concomitant delayed switch to piscivory. Furthermore, E. lucius were found to primarily prey upon the highly available non‐native roach Rutilus rutilus, which may alleviate predation pressure on brown trout Salmo trutta, highlighting the complexity of dynamic systems and the essential role of research in informing effective management.     

The Tyrosine Kinase c-Abl Promotes Homeodomain-interacting Protein Kinase 2 (HIPK2) Accumulation and Activation in Response to DNA Damage

The non-receptor tyrosine kinase c-Abl is activated in response to DNA damage and induces p73-dependent apoptosis. Here, we investigated c-Abl regulation of the homeodomain-interacting protein kinase 2 (HIPK2), an important regulator of p53-dependent apoptosis. c-Abl phosphorylated HIPK2 at several sites, and phosphorylation by c-Abl protected HIPK2 from degradation mediated by the ubiquitin E3 ligase Siah-1. c-Abl and HIPK2 synergized in activating p53 on apoptotic promoters in a reporter assay, and c-Abl was required for endogenous HIPK2 accumulation and phosphorylation of p53 at Ser⁴⁶ in response to DNA damage by γ- and UV radiation. Accumulation of HIPK2 in nuclear speckles and association with promyelocytic leukemia protein (PML) in response to DNA damage were also dependent on c-Abl activity. At high cell density, the Hippo pathway inhibits DNA damage-induced c-Abl activation. Under this condition, DNA damage-induced HIPK2 accumulation, phosphorylation of p53 at Ser⁴⁶, and apoptosis were attenuated. These data demonstrate a new mechanism for the induction of DNA damage-induced apoptosis by c-Abl and illustrate network interactions between serine/threonine and tyrosine kinases that dictate cell fate.     

The biodiversity‐dependent ecosystem service debt

Habitat destruction is driving biodiversity loss in remaining ecosystems, and ecosystem functioning and services often directly depend on biodiversity. Thus, biodiversity loss is likely creating an ecosystem service debt: a gradual loss of biodiversity‐dependent benefits that people obtain from remaining fragments of natural ecosystems. Here, we develop an approach for quantifying ecosystem service debts, and illustrate its use to estimate how one anthropogenic driver, habitat destruction, could indirectly diminish one ecosystem service, carbon storage, by creating an extinction debt. We estimate that c. 2–21 Pg C could be gradually emitted globally in remaining ecosystem fragments because of plant species loss caused by nearby habitat destruction. The wide range for this estimate reflects substantial uncertainties in how many plant species will be lost, how much species loss will impact ecosystem functioning and whether plant species loss will decrease soil carbon. Our exploratory analysis suggests that biodiversity‐dependent ecosystem service debts can be globally substantial, even when locally small, if they occur diffusely across vast areas of remaining ecosystems. There is substantial value in conserving not only the quantity (area), but also the quality (biodiversity) of natural ecosystems for the sustainable provision of ecosystem services.     

Cell type-specific and site directed N-glycosylation pattern of FcγRIIIa

Human leukocyte receptor IIIa (hFcγRIIIa) plays a prominent role in the elimination of tumor cells by antibody-based cancer therapies. In previous studies, a major impact of the presence of carbohydrates at Asn-162 on the binding between the receptor and the Fc part of wild type fucosylated or glycoengineered nonfucosylated antibodies has been shown. In this study, we performed a site directed carbohydrate analysis at hFcγRIIIa derived from human embryonic kidney (HEK) and Chinese hamster ovary (CHO) cells, respectively. Using mass spectrometry (MS) and a multienzyme protein digest, we analyzed the proteolysis-generated glycopeptides in detail. We could show that hFcγRIIIa expressed by HEK cells was mostly bearing multifucosylated biantennary Asn162-glycans with a major fraction terminating with GalNAc residues replacing the more common Gal. We could demonstrate that the glycan antennae with terminal GalNAc could be sialylated as indicated by a novel reporter ion HexNAcHexNAcNeuAc(+) (m/z 698.28) using a source induced dissociation (SID) scan in the MS cycle. In contrast to the hFcγRIIIa Asn-162 glycosylation pattern from HEK cells, the CHO cells derived receptor contains bi- and triantennary galactosylated and highly sialylated carbohydrates. Our data suggest that the type of expression host system was a dominating factor for formation of distinct glycopatterns of hFcγRIIIa, while the protein sequence and the site of glycosylation remained unchanged for both types of cells. Using surface plasmon resonance (SPR) interaction analysis, we show that the cell type and site specific glycosylation pattern of hFcγRIIIa influences its binding behavior to immunoglobulin molecules.     

Inhibition of eukaryotic translation elongation by the antitumor natural product Mycalamide B

Mycalamide B (MycB) is a marine sponge-derived natural product with potent antitumor activity. Although it has been shown to inhibit protein synthesis, the molecular mechanism of action by MycB remains incompletely understood. We verified the inhibition of translation elongation by in vitro HCV IRES dual luciferase assays, ribosome assembly, and in vivo [(35)S]methinione labeling experiments. Similar to cycloheximide (CHX), MycB inhibits translation elongation through blockade of eEF2-mediated translocation without affecting the eEF1A-mediated loading of tRNA onto the ribosome, AUG recognition, or dipeptide synthesis. Using chemical footprinting, we identified the MycB binding site proximal to the C3993 28S rRNA residue on the large ribosomal subunit. However, there are also subtle, but significant differences in the detailed mechanisms of action of MycB and CHX. First, MycB arrests the ribosome on the mRNA one codon ahead of CHX. Second, MycB specifically blocked tRNA binding to the E-site of the large ribosomal subunit. Moreover, they display different polysome profiles in vivo. Together, these observations shed new light on the mechanism of inhibition of translation elongation by MycB.