Interacting forces of predation and fishing affect species’ maturation size

1. Fishing is a strong selective force and is supposed to select for earlier maturation at smaller body size. However, the extent to which fishing‐induced evolution is shaping ecosystems remains debated. This is in part because it is challenging to disentangle fishing from other selective forces (e.g., size‐structured predation and cannibalism) in complex ecosystems undergoing rapid change.
2. Changes in maturation size from fishing and predation have previously been explored with multi‐species physiologically structured models but assumed separation of ecological and evolutionary timescales. To assess the eco‐evolutionary impact of fishing and predation at the same timescale, we developed a stochastic physiologically size‐structured food‐web model, where new phenotypes are introduced randomly through time enabling dynamic simulation of species'' relative maturation sizes under different types of selection pressures.
3. Using the model, we carried out a fully factorial in silico experiment to assess how maturation size would change in the absence and presence of both fishing and predation (including cannibalism). We carried out ten replicate stochastic simulations exposed to all combinations of fishing and predation in a model community of nine interacting fish species ranging in their maximum sizes from 10 g to 100 kg. We visualized and statistically analyzed the results using linear models.
4. The effects of fishing on maturation size depended on whether or not predation was enabled and differed substantially across species. Fishing consistently reduced the maturation sizes of two largest species whether or not predation was enabled and this decrease was seen even at low fishing intensities (F = 0.2 per year). In contrast, the maturation sizes of the three smallest species evolved to become smaller through time but this happened regardless of the levels of predation or fishing. For the four medium‐size species, the effect of fishing was highly variable with more species showing significant and larger fishing effects in the presence of predation.
5. Ultimately our results suggest that the interactive effects of predation and fishing can have marked effects on species'' maturation sizes, but that, at least for the largest species, predation does not counterbalance the evolutionary effect of fishing. Our model also produced relative maturation sizes that are broadly consistent with empirical estimates for many fish species.

     

Malaria Parasite-Infected Erythrocytes Secrete PfCK1, the Plasmodium Homologue of the Pleiotropic Protein Kinase Casein Kinase 1

Casein kinase 1 (CK1) is a pleiotropic protein kinase implicated in several fundamental processes of eukaryotic cell biology. Plasmodium falciparum encodes a single CK1 isoform, PfCK1, that is expressed at all stages of the parasite’s life cycle. We have previously shown that the pfck1 gene cannot be disrupted, but that the locus can be modified if no loss-of-function is incurred, suggesting an important role for this kinase in intra-erythrocytic asexual proliferation. Here, we report on the use of parasite lines expressing GFP- or His-tagged PfCK1 from the endogenous locus to investigate (i) the dynamics of PfCK1 localisation during the asexual cycle in red blood cells, and (ii) potential interactors of PfCK1, so as to gain insight into the involvement of the enzyme in specific cellular processes. Immunofluorescence analysis reveals a dynamic localisation of PfCK1, with evidence for a pool of the enzyme being directed to the membrane of the host erythrocyte in the early stages of infection, followed by a predominantly intra-parasite localisation in trophozoites and schizonts and association with micronemes in merozoites. Furthermore, we present strong evidence that a pool of enzymatically active PfCK1 is secreted into the culture supernatant, demonstrating that PfCK1 is an ectokinase. Our interactome experiments and ensuing kinase assays using recombinant PfCK1 to phosphorylate putative interactors in vitro suggest an involvement of PfCK1 in many cellular processes such as mRNA splicing, protein trafficking, ribosomal, and host cell invasion.     

Axial Diffusivity of the Corona Radiata at 24 Hours Post-Stroke: A New Biomarker for Motor and Global Outcome

Fractional anisotropy (FA) is an effective marker of motor outcome at the chronic stage of stroke yet proves to be less efficient at early time points. This study aims to determine which diffusion metric in which location is the best marker of long-term stroke outcome after thrombolysis with diffusion tensor imaging (DTI) at 24 hours post-stroke. Twenty-eight thrombolyzed patients underwent DTI at 24 hours post-stroke onset. Ipsilesional and contralesional FA, mean (MD), axial (AD), and radial (RD) diffusivities values were calculated in different Regions-of-Interest (ROIs): (1) the white matter underlying the precentral gyrus (M1), (2) the corona radiata (CoRad), (3) the posterior limb of the internal capsule (PLIC) and (4) the cerebral peduncles (CP). NIHSS scores were acquired at admission, day 1, and day 7; modified Rankin Scores (mRS) at 3 months. Significant decreases were found in FA, MD, and AD of the ipsilesional CoRad and M1. MD and AD were also significantly lower in the PLIC. The ratio of ipsi and contralesional AD of the CoRad (CoRad-rAD) was the strongest diffusion parameter correlated with motor NIHSS scores on day 7 and with the mRS at 3 months. A Receiver-Operator Curve analysis yielded a model for the CoRad-rAD to predict good outcome based on upper limb NIHSS motor scores and mRS with high specificity and sensitivity. FA values were not correlated with clinical outcome. In conclusion, axial diffusivity of the CoRad from clinical DTI at 24 hours post-stroke is the most appropriate diffusion metric for quantifying stroke damage to predict outcome, suggesting the importance of early axonal damage.     

Mechanisms of HIV-1 evasion to the antiviral activity of chemokine CXCL12 indicate potential links with pathogenesis

HIV-1 infects CD4 T lymphocytes (CD4TL) through binding the chemokine receptors CCR5 or CXCR4. CXCR4-using viruses are considered more pathogenic, linked to accelerated depletion of CD4TL and progression to AIDS. However, counterexamples to this paradigm are common, suggesting heterogeneity in the virulence of CXCR4-using viruses. Here, we investigated the role of the CXCR4 chemokine CXCL12 as a driving force behind virus virulence. In vitro, CXCL12 prevents HIV-1 from binding CXCR4 and entering CD4TL, but its role in HIV-1 transmission and propagation remains speculative. Through analysis of thirty envelope glycoproteins (Envs) from patients at different stages of infection, mostly treatment-naïve, we first interrogated whether sensitivity of viruses to inhibition by CXCL12 varies over time in infection. Results show that Envs resistant (RES) to CXCL12 are frequent in patients experiencing low CD4TL levels, most often late in infection, only rarely at the time of primary infection. Sensitivity assays to soluble CD4 or broadly neutralizing antibodies further showed that RES Envs adopt a more closed conformation with distinct antigenicity, compared to CXCL12-sensitive (SENS) Envs. At the level of the host cell, our results suggest that resistance is not due to improved fusion or binding to CD4, but owes to viruses using particular CXCR4 molecules weakly accessible to CXCL12. We finally asked whether the low CD4TL levels in patients are related to increased pathogenicity of RES viruses. Resistance actually provides viruses with an enhanced capacity to enter naive CD4TL when surrounded by CXCL12, which mirrors their situation in lymphoid organs, and to deplete bystander activated effector memory cells. Therefore, RES viruses seem more likely to deregulate CD4TL homeostasis. This work improves our understanding of the pathophysiology and the transmission of HIV-1 and suggests that RES viruses’ receptors could represent new therapeutic targets to help prevent CD4TL depletion in HIV+ patients on cART.     

Minimal exon sequence requirements for efficient in vitro splicing of mono-intronic nuclear pre-mRNA

Measurements of the in vitro splicing efficiency of deletion mutant RNA precursors containing the small intron of the rabbit beta-globin gene, which are truncated in the first or in the second exon, revealed that no more than approximately 20 nucleotides of either exon are necessary for efficient splicing. At least for the second exon, this minimal length requirement is globin sequence-independent. Reduction of the exon-2 length to 14 nucleotides resulted in very inefficient splicing, whereas further reduction to 5 nucleotides apparently abolished the second splicing step (3' cutting and ligation), whereas the first step (5' cutting and branching) still occurred. The splicing efficiency of a double-mutant substrate retaining approximately 20 nucleotides of each exon was reduced to 50%. A kinetic study indicated that in the reaction of this double-mutant substrate the second, but not the first, splicing step was delayed, in contrast to the reaction of the wild-type precursor. Duplication or triplication of the entire sequence of exon-1 did not affect the splicing efficiency, whereas elongation of this exon with approximately 100 nucleotides of 5'-flanking (nontranscribed) beta-globin sequence diminished the level of correct splicing with the simultaneous appearance of aberrant lariat forms. We conclude that for mono-intronic precursors in which there is only one choice of splice sites, most of the exon sequences are not mechanistically involved in the splicing process.     

Alzheimer's disease: study of the distribution of tau proteins constituting helical filament pairs in human central nervous tissue

Tau proteins are the major components of Paired Helical Filaments (PHF) of Alzheimer's disease. Using the immunoblot technique and an antiserum against PHF, we have studied the distribution of Tau proteins in the different areas of normal human brains and Alzheimer brains. Tau proteins were clearly present in cortical grey matter but were difficult to detect in the white matter. In Alzheimer brains, we observed two differences: first, there is an important background due to the partial dissociation of the lesions containing Tau aggregates. Second, the profile of Tau proteins is modified, due to abnormal phosphorylation. Thus, Tau proteins are found in large amounts in the grey matter of the cortical areas and are not exclusively distributed in the axonal domain. The normal cortical distribution of Tau in the human brain correlates well with the distribution of histological lesions that contain PHF (neurofibrillary tangles and neuritic plaques) in the Alzheimer cortex.     

A human histone H2B.1 variant gene, located on chromosome 1, utilizes alternative 3' end processing.

A variant human H2B histone gene (GL105), previously shown to encode a 2300 nt replication independent mRNA, has been cloned. We demonstrate this gene expresses alternative mRNAs regulated differentially during the HeLa S3 cell cycle. The H2B-Gl105 gene encodes both a 500 nt cell cycle dependent mRNA and a 2300 nt constitutively expressed mRNA. The 3' end of the cell cycle regulated mRNA terminates immediately following the region of hyphenated dyad symmetry typical of most histone mRNAs, whereas the constitutively expressed mRNA has a 1798 nt non-translated trailer that contains the same region of hyphenated dyad symmetry but is polyadenylated. The cap site for the H2B-GL105 mRNAs is located 42 nt upstream of the protein coding region. The H2B-GL105 histone gene was localized to chromosome region 1q21-1q23 by chromosomal in situ hybridization and by analysis of rodent-human somatic cell hybrids using an H2B-GL105 specific probe. The H2B-GL105 gene is paired with a functional H2A histone gene and this H2A/H2B gene pair is separated by a bidirectionally transcribed intergenic promoter region containing consensus TATA and CCAAT boxes and an OTF-1 element. These results demonstrate that cell cycle regulated and constitutively expressed histone mRNAs can be encoded by the same gene, and indicate that alternative 3' end processing may be an important mechanism for regulation of histone mRNA. Such control further increases the versatility by which cells can modulate the synthesis of replication-dependent as well as variant histone proteins during the cell cycle and at the onset of differentiation.     

Swainsonine treatment accelerates intracellular transport and secretion of glycoproteins in human hepatoma cells

We are interested in determining whether carbohydrates are important regulatory determinants in the intracellular transport and secretion of glycoproteins. In the present study, we have used swainsonine, an indolizidine alkaloid, to modify the structure of N-glycosidically linked complex oligosaccharides. By inhibiting Golgi mannosidase II, swainsonine prevents the trimming of GlcNAc(Man)5(GlcNAc)2 to GlcNAc-(Man)3(GlcNAc)2, resulting in the formation of hybrid-type oligosaccharides. We find, from pulse-chase experiments using [35S]methionine and immunoprecipitation of individual proteins from culture media, that swainsonine treatment (1 microgram/ml) accelerated the secretion of glycoproteins (transferrin, ceruloplasmin, alpha 2-macroglobulin, and alpha 1-antitrypsin) by decreasing the lag period by 10-15 min relative to untreated cultures. The enhanced secretion was specific for glycoproteins since the secretion of albumin, a nonglycoprotein, was unaffected. When alpha 1-antitrypsin was immunoprecipitated from the cell lysates, sodium dodecyl sulfate-polyacrylamide gel electrophoresis fluorographic analysis demonstrated that the conversion of the high-mannose precursor to the hybrid form in swainsonine-treated cells occurred more rapidly (by about 10 min) than the conversion to the complex form in control cells. Since both the hybrid and complex forms of alpha 1-antitrypsin are terminally sialylated by sialyltransferase in the trans-Golgi, these results suggest that swainsonine-modified glycoproteins traverse the Golgi more rapidly than their normal counterparts. Therefore, accelerated transport within this organelle may account for the decreased lag period of glycoprotein secretion in the swainsonine-treated cultures.     

Differential effects of 1-deoxynojirimycin on the intracellular transport of secretory glycoproteins of human hepatoma cells in culture

To investigate our earlier hypothesis that carbohydrates play a regulatory role in the intracellular transport of secretory glycoproteins, we used 1-deoxynojirimycin (DNJ), and inhibitor of glucosidase I and II of the rough endoplasmic reticulum (RER), to modify the structure of N-linked glycan moieties of secretory glycoproteins of human hepatoma (Hep G2) cells in culture. Using a pulse-chase protocol, we found that treatment of Hep G2 cultures with 1.25 mM DNJ markedly reduced the rate of secretion of ₁-protease inhibitor, ceruloplasmin, and ₂-macroglobulin, but had no effect on the export of fibronectin, -fetoprotein and transferrin, nor on albumin which lacks carbohydrate. For example, 50% of newly synthesized ₁-protease inhibitor, the glycoprotein most dramatically affected, was secreted by 27 min in control cultures versus 110 min in DNJ-treated cultures. Percoll gradient cell fractionation analyses revealed that DNJ inhibited transport of the affected secretory glycoproteins in the RER segment of the ER/Golgi pathway. For example, 50% of newly synthesized ₁-protease inhibitor was lost from the RER fraction by 10 min in untreated cells, but 70 min was required for the transport of a similar amount of protein in DNJ-treated cells. DNJ treatment also inhibited the rate at which the N-linked glycan moieties of the affected glycoproteins became resistant to endo H in the Golgi. Since the glycan moiety of secreted forms of the affected glycoproteins were fully processed to the complex structure, suggesting escape from DNJ inhibition, we concluded that removal of terminal glucose residues from the glycan chain of secretory glycoproteins is required for their transport from the RER to the Golgi. We suggest that the oligosaccharide moieties on ₁-protease inhibitor, ceruloplasmin and ₂-macroglobulin form part of the binding site for a receptor which regulates transport of these glycoproteins.