Identification of functional domains in sarcoglycans essential for their interaction and plasma membrane targeting

Mutations in sarcoglycans have been reported to cause autosomal-recessive limb-girdle muscular dystrophies. In skeletal and cardiac muscle, sarcoglycans are assembled into a complex on the sarcolemma from four subunits (alpha, beta, gamma, delta). In this report, we present a detailed structural analysis of sarcoglycans using deletion study, limited proteolysis and co-immunoprecipitation. Our results indicate that the extracellular regions of sarcoglycans consist of distinctive functional domains connected by proteinase K-sensitive sites. The N-terminal half domains are required for sarcoglycan interaction. The C-terminal half domains of beta-, gamma- and delta-sarcoglycan consist of a cysteine-rich motif and a previously unrecognized conserved sequence, both of which are essential for plasma membrane localization. Using a heterologous expression system, we demonstrate that missense sarcoglycan mutations affect sarcoglycan complex assembly and/or localization to the cell surface. Our data suggest that the formation of a stable complex is necessary but not sufficient for plasma membrane targeting. Finally, we provide evidence that the beta/delta-sarcoglycan core can associate with the C-terminus of dystrophin. Our results therefore generate important information on the structure of the sarcoglycan complex and the molecular mechanisms underlying the effects of various sarcoglycan mutations in muscular dystrophies.     

Strabismus regulates asymmetric cell divisions and cell fate determination in the mouse brain

The planar cell polarity (PCP) pathway organizes the cytoskeleton and polarizes cells within embryonic tissue. We investigate the relationship between PCP signaling and cell fate determination during asymmetric division of neural progenitors (NPs) in mouse embryos. The cortex of Lp/Lp (Loop-tail) mice deficient in the essential PCP mediator Vangl2, homologue of Drosophila melanogaster Strabismus (Stbm), revealed precocious differentiation of neural progenitors into early-born neurons at the expense of late-born neurons and glia. Although Lp/Lp NPs were easily maintained in vitro, they showed premature differentiation and loss of asymmetric distribution of Leu-Gly-Asn–enriched protein (LGN)/partner of inscuteable (Pins), a regulator of mitotic spindle orientation. Furthermore, we observed a decreased frequency in asymmetric distribution of the LGN target nuclear mitotic apparatus protein (NuMa) in Lp/Lp cortical progenitors in vivo. This was accompanied by an increase in the number of vertical cleavage planes typically associated with equal daughter cell identities. These findings suggest that Stbm/Vangl2 functions to maintain cortical progenitors and regulates mitotic spindle orientation during asymmetric divisions in the vertebrate brain.     

The Ubiquitin-conjugating Enzyme (E2) Ube2w Ubiquitinates the N Terminus of Substrates

Attachment of ubiquitin to substrate is typically thought to occur via formation of an isopeptide bond between the C-terminal glycine residue of ubiquitin and a lysine residue in the substrate. In vitro, Ube2w is nonreactive with free lysine yet readily ubiquitinates substrate. Ube2w also contains novel residues within its active site that are important for its ability to ubiquitinate substrate. To identify the site of modification, we analyzed ubiquitinated substrates by mass spectrometry and found the N-terminal -NH₂ group as the site of conjugation. To confirm N-terminal ubiquitination, we generated lysine-less and N-terminally blocked versions of one substrate, the polyglutamine disease protein ataxin-3, and showed that Ube2w can ubiquitinate a lysine-less, but not N-terminally blocked, ataxin-3. This was confirmed with a second substrate, the neurodegenerative disease protein Tau. Finally, we directly sequenced the N terminus of unmodified and ubiquitinated ataxin-3, demonstrating that Ube2w attaches ubiquitin to the N terminus of its substrates. Together these data demonstrate that Ube2w has novel enzymatic properties that direct ubiquitination of the N terminus of substrates.     

Adaptive potential of northernmost tree populations to climate change, with emphasis on Scots pine (Pinus sylvestris L.)

The adaptive potential of the northernmost Pinus sylvestris L. (and other northern tree) populations is considered by examining first the current patterns of quantitative genetic adaptive traits, which show high population differentiation and clines. We then consider the postglacial history of the populations using both paleobiological and genetic data. The current patterns of diversity at nuclear genes suggest that the traces of admixture are mostly visible in mitochondrial DNA variation patterns. There is little evidence of increased diversity due to admixture between an eastern and western colonization lineage, but no signal of reduced diversity (due to sequential bottlenecks) either. Quantitative trait variation in the north is not associated with the colonizing lineages. The current clines arose rapidly and may be based on standing genetic variation. The initial phenotypic response of Scots pine in the north is predicted to be increased survival and growth. The genetic responses are examined based on quantitative genetic predictions of sustained selection response and compared with earlier simulation results that have aimed at more ecological realism. The phenotypic responses of increased growth and survival reduce the opportunity for selection and delay the evolutionary responses. The lengthening of the thermal growing period also causes selection on the critical photoperiod in the different populations. Future studies should aim at including multiple ecological and genetic factors in evaluating potential responses.     

Maintaining embryonic stem cell pluripotency with Wnt signaling

Wnt signaling pathways control lineage specification in vertebrate embryos and regulate pluripotency in embryonic stem (ES) cells, but how the balance between progenitor self-renewal and differentiation is achieved during axis specification and tissue patterning remains highly controversial. The context- and stage-specific effects of the different Wnt pathways produce complex and sometimes opposite outcomes that help to generate embryonic cell diversity. Although the results of recent studies of the Wnt/β-catenin pathway in ES cells appear to be surprising and controversial, they converge on the same conserved mechanism that leads to the inactivation of TCF3-mediated repression.     

Specific Microbiome Changes in a Mouse Model of Parenteral Nutrition Associated Liver Injury and Intestinal Inflammation

Background

Parenteral nutrition (PN) has been a life-saving treatment in infants intolerant of enteral feedings. However, PN is associated with liver injury (PN Associated Liver Injury: PNALI) in a significant number of PN-dependent infants. We have previously reported a novel PNALI mouse model in which PN infusion combined with intestinal injury results in liver injury. In this model, lipopolysaccharide activation of toll-like receptor 4 signaling, soy oil-derived plant sterols, and pro-inflammatory activation of Kupffer cells (KCs) played key roles. The objective of this study was to explore changes in the intestinal microbiome associated with PNALI.

Methodology and Principal Findings

Microbiome analysis in the PNALI mouse identified specific alterations within colonic microbiota associated with PNALI and further association of these communities with the lipid composition of the PN solution. Intestinal inflammation or soy oil-based PN infusion alone (in the absence of enteral feeds) caused shifts within the gut microbiota. However, the combination resulted in accumulation of a specific taxon, Erysipelotrichaceae (23.8% vs. 1.7% in saline infused controls), in PNALI mice. Moreover, PNALI was markedly attenuated by enteral antibiotic treatment, which also was associated with significant reduction of Erysipelotrichaceae (0.6%) and a Gram-negative constituent, the S24-7 lineage of Bacteroidetes (53.5% in PNALI vs. 0.8%). Importantly, removal of soy oil based-lipid emulsion from the PN solution resulted in significant reduction of Erysipelotrichaceae as well as attenuation of PNALI. Finally, addition of soy-derived plant sterol (stigmasterol) to fish oil-based PN restored Erysipelotrichaceae abundance and PNALI.

Conclusions

Soy oil-derived plant sterols and the associated specific bacterial groups in the colonic microbiota are associated with PNALI. Products from these bacteria may directly trigger activation of KCs and promote PNALI. Furthermore, the results indicate that lipid modification of PN solutions may alter specific intestinal bacterial species associated with PNALI, and thus suggest strategies for management of PNALI.     

Passing the Red Pen: EvoS Journal Offers an Early Education in Peer Review

EvoS Journal: The Journal of the Evolutionary Studies Consortium is the open-access, peer-reviewed journal borne of the EvoS (Evolutionary Studies) Consortium movement. The journal has two separate, yet related goals: to publish scholarly articles regarding the intersection of higher education and evolutionary theory, and to publish articles written and reviewed by undergraduates that incorporate an evolutionary perspective. Undergraduates who publish and review for EvoS Journal get the chance to see their work published alongside that of experts within the field of evolutionary studies, and to see the interdisciplinary and widespread applications of evolutionary theory to human life and beyond. The current study examines whether the interdisciplinary nature of EvoS Journal and its initiation of students into the peer-review process set EvoS Journal apart from more traditional undergraduate journals. EvoS Journal was compared to other journals listed by the Council for Undergraduate Research. While EvoS Journal mirrors many traditional undergraduate journals in their employment of student reviewers and publishing work originating from any U.S. institution, it differs by both its interdisciplinary focus and by serving as an outlet for both student and professional publications. The implications are discussed in terms of the benefits of interdisciplinary and peer-review training to students in the classroom, including improvements in writing, interpersonal relations, and real-world skills.