Strong genetic isolation despite wide distribution in a commercially exploited coastal shark

The common smoothhound, Mustelus mustelus, is an epibenthic species targeted by fisheries around the world driven by the increasing demand for shark products. Given the wide-spread occurrence of this species and corresponding lack of molecular data in many areas of said distribution, baseline molecular assessments of this commercially important shark may contribute to finer-scale analyses in areas in which this species is targeted. Therefore, population genetic analyses were conducted along the East Atlantic, from the Mediterranean Sea to the south-east coast of Africa, using microsatellite markers and the mitochondrial control region (mtCR). Overall, M. mustelus displayed low to moderate genetic diversity, with the Mediterranean populations appearing to exhibit the lowest mitochondrial diversity, and the west African populations displaying the lowest nuclear diversity. Microsatellite analysis indicated strong genetic differentiation between the three regions, with finer-scale population structure in each region, without correlation between genetic and geographical distance. For the mtCR sequences, a total of 18 haplotypes were identified, with a high degree of divergence discernable between the regions, largely in accordance with the microsatellite data. The study documents a remarkable level of population isolation across a vast area, suggesting little or no present-day connectivity among extant populations. The findings may serve as an essential baseline for global population management and commercial traceability of this threatened shark.

     

Light capture and pigment diversity in marine and freshwater cryptophytes

Phenotypic traits associated with light capture and phylogenetic relationships were characterized in 34 strains of diversely pigmented marine and freshwater cryptophytes. Nuclear SSU and partial LSU rDNA sequence data from 33 of these strains plus an additional 66 strains produced a concatenated rooted maximum likelihood tree that classified the strains into 7 distinct clades. Molecular and phenotypic data together support: (i) the reclassification of Cryptomonas irregularis NIES 698 to the genus Rhodomonas, (ii) revision of phycobiliprotein (PBP) diversity within the genus Hemiselmis to include cryptophyte phycocyanin (Cr‐PC) 569, (iii) the inclusion of previously unidentified strain CCMP 2293 into the genus Falcomonas, even though it contains cryptophyte phycoerythrin 545 (Cr‐PE 545), and (iv) the inclusion of previously unidentified strain CCMP 3175, which contains Cr‐PE 545, in a clade with PC‐containing Chroomonas species. A discriminant analysis‐based model of group membership correctly predicted 70.6% of the clades using three traits: PBP concentration · cell^?1, the wavelength of PBP maximal absorption, and habitat. Non‐PBP pigments (alloxanthin, chl‐a, chl‐c₂, α‐carotene) did not contribute significantly to group classification, indicating the potential plasticity of these pigments and the evolutionary conservation of the PBPs. Pigment data showed evidence of trade‐offs in investments in PBPs vs. chlorophylls (a +c₂).     

Whole community estimates of macroalgal pigment concentration within two southern New Zealand kelp forests1

Light availability is a fundamental factor that controls the productivity and distribution of macroalgae and is highly variable, both spatially and temporally, in subtidal coastal systems. Our comprehension of how macroalgae respond to such variability is a significant knowledge gap that limits our understanding of how light influences the structure and productivity of these environments. Here, we examined the pigment characteristics of individual species, and for the first time the whole community, within one low‐light, and one high‐light kelp‐forest system in southern New Zealand. The aim was to quantify the range of pigmentation seen within the two kelp‐forests which differed in irradiance regime. Light availability was 33% and 64% greater at the high‐light compared to the low‐light site at 2 and 10 m depth, respectively. Results suggested Phaeophyceae species at deeper depths in the low‐light site may be living at the edge of their photosynthetic ability and pigment synthesis appeared significantly restricted. Even with greater investment in the pigment fucoxanthin, biomass of Phaeophyceae species was significantly lower in the low‐light site. Highly pigmented Rhodophyceae species made a greater proportional contribution to community biomass within the low‐light site where they likely possessed a photosynthetic advantage. This work helps explain discrepancies in community structure between the two study sites and explores the complex relationship between irradiance and photoacclimation. The comparison of community pigment concentration holds potential as a tool for assessing the relative degree of photoacclimation occurring between sites and provides a proxy of photosynthetic cost under a specific light regime.     

Escherichia coli “TatExpress” strains export several g/L human growth hormone to the periplasm by the Tat pathway

Escherichia coli is a heavily used platform for the production of biotherapeutic and other high-value proteins, and a favored strategy is to export the protein of interest to the periplasm to simplify downstream processing and facilitate disulfide bond formation. The Sec pathway is the standard means of transporting the target protein but it is unable to transport complex or rapidly folding proteins because the Sec system can only transport proteins in an unfolded state. The Tat system also operates to transport proteins to the periplasm, and it has significant potential as an alternative means of recombinant protein production because it transports fully folded proteins. Here, we have tested the Tat system's full potential for the production of biotherapeutics for the first time using fed-batch fermentation. We expressed human growth hormone (hGH) with a Tat signal peptide in E. coli W3110 “TatExpress” strains that contain elevated levels of the Tat apparatus. This construct contained four amino acids from TorA at the hGH N-terminus as well as the initiation methionine from hGH, which is removed in vivo. We show that the protein is efficiently exported to the periplasm during extended fed-batch fermentation, to the extent that it is by far the most abundant protein in the periplasm. The protein was shown to be homogeneous, disulfide bonded, and active. The bioassay showed that the yields of purified periplasmic hGH are 5.4 g/L culture whereas an enzyme-linked immunosorbent assay gave a figure of 2.39 g/L. Separate analysis of a TorA signal peptide linked to hGH construct lacking any additional amino acids likewise showed efficient export to the periplasm, although yields were approximately two-fold lower.     

The molecular mechanism of induction of unfolded protein response by Chlamydia

The unfolded protein response (UPR) contributes to chlamydial pathogenesis, as a source of lipids and ATP during replication, and for establishing the initial anti-apoptotic state of host cell that ensures successful inclusion development. The molecular mechanism(s) of UPR induction by Chlamydia is unknown. Chlamydia use type III secretion system (T3SS) effector proteins (e.g, the Translocated Actin-Recruiting Phosphoprotein (Tarp) to stimulate host cell's cytoskeletal reorganization that facilitates invasion and inclusion development. We investigated the hypothesis that T3SS effector-mediated assembly of myosin-II complex produces activated non-muscle myosin heavy chain II (NMMHC-II), which then binds the UPR master regulator (BiP) and/or transducers to induce UPR. Our results revealed the interaction of the chlamydial effector proteins (CT228 and Tarp) with components of the myosin II complex and UPR regulator and transducer during infection. These interactions caused the activation and binding of NMMHC-II to BiP and IRE1α leading to UPR induction. In addition, specific inhibitors of myosin light chain kinase, Tarp oligomerization and myosin ATPase significantly reduced UPR activation and Chlamydia replication. Thus, Chlamydia induce UPR through T3SS effector-mediated activation of NMMHC-II components of the myosin complex to facilitate infectivity. The finding provides greater insights into chlamydial pathogenesis with the potential to identify therapeutic targets and formulations.     

A Biomechanical Model of Tumor-Induced Intracranial Pressure and Edema in Brain Tissue

Brain tumor growth and tumor-induced edema result in increased intracranial pressure (ICP), which, in turn, is responsible for conditions as benign as headaches and vomiting or as severe as seizures, neurological damage, or even death. Therefore, it has been hypothesized that tracking ICP dynamics may offer improved prognostic potential in terms of early detection of brain cancer and better delimitation of the tumor boundary. However, translating such theory into clinical practice remains a challenge, in part because of an incomplete understanding of how ICP correlates with tumor grade. Here, we propose a multiphase mixture model that describes the biomechanical response of healthy brain tissue—in terms of changes in ICP and edema—to a growing tumor. The model captures ICP dynamics within the diseased brain and accounts for the ability/inability of healthy tissue to compensate for this pressure. We propose parameter regimes that distinguish brain tumors by grade, thereby providing critical insight into how ICP dynamics vary by severity of disease. In particular, we offer an explanation for clinically observed phenomena, such as a lack of symptoms in low-grade glioma patients versus a rapid onset of symptoms in those with malignant tumors. Our model also takes into account the effects tumor-derived proteases may have on ICP levels and the extent of tumor invasion. This work represents an important first step toward understanding the mechanisms that underlie the onset of edema and ICP in cancer-afflicted brains. Continued modeling effort in this direction has the potential to make an impact in the field of brain cancer diagnostics.