In vitro heterogeneity of osteogenic cell populations at various equine skeletal sites

Bone cell cultures were evaluated to determine if osteogenic cell populations at different skeletal sites in the horse are heterogeneous. Osteogenic cells were isolated from cortical and cancellous bone in vitro by an explant culture method. Subcultured cells were induced to differentiate into bone-forming osteoblasts. The osteoblast phenotype was confirmed by immunohistochemical testing for osteocalcin and substantiated by positive staining of cells for alkaline phosphatase and the matrix materials collagen and glycosaminoglycans. Bone nodules were stained by the von Kossa method and counted. The numbers of nodules produced from osteogenic cells harvested from different skeletal sites were compared with the use of a mixed linear model. On average, cortical bone sites yielded significantly greater numbers of nodules than did cancellous bone sites. Between cortical bone sites, there was no significant difference in nodule numbers. Among cancellous sites, the radial cancellous bone yielded significantly more nodules than did the tibial cancellous bone. Among appendicular skeletal sites, tibial metaphyseal bone yielded significantly fewer nodules than did all other long bone sites. This study detected evidence of heterogeneity of equine osteogenic cell populations at various skeletal sites. Further characterization of the dissimilarities is warranted to determine the potential role heterogeneity plays in differential rates of fracture healing between skeletal sites.     

The bacterial condensin MukBEF compacts DNA into a repetitive, stable structure

Condensins are conserved proteins containing SMC (structural maintenance of chromosomes) moieties that organize and compact chromosomes in an unknown mechanism essential for faithful chromosome partitioning. We show that MukBEF, the condensin in Escherichia coli, cooperatively compacts a single DNA molecule into a filament with an ordered, repetitive structure in an adenosine triphosphate (ATP) binding-dependent manner. When stretched to a tension of approximately 17 piconewtons, the filament extended in a series of repetitive transitions in a broad distribution centered on 45 nanometers. A filament so extended and held at a lower force recondensed in steps of 35 nanometers or its multiples; this cycle was repeatable even in the absence of ATP and free MukBEF. Remarkably, the pattern of transitions displayed by a given filament during the initial extension was identical in every subsequent extension. Hence, after being deformed micrometers in length, each filament returned to its original compact structure without the addition of energy. Incubation with topoisomerase I increased the rate of recondensation and allowed the structure to extend and reform almost reversibly, indicating that supercoiled DNA is trapped in the condensed structure. We suggest a new model for how MukBEF organizes the bacterial chromosome in vivo.     

Farmer-Community Connections and the Future of Ecological Agriculture in California

While questions about the environmental sustainability of contemporary farming practices and the socioeconomic viability of rural communities are attracting increasing attention throughout the US, these two issues are rarely considered together. This paper explores the current and potential connections between these two aspects of sustainability, using data on community members’ and farmers’ views of agricultural issues in California’s Central Valley. These views were collected from a series of individual and group interviews with biologically oriented and conventional farmers as well as community stakeholders. Local marketing, farmland preservation, and perceptions of sustainable agriculture comprised the primary topics of discussion. The mixed results indicate that, while many farmers and community members have a strong interest in these topics, sustainable community development and the use of sustainable farming practices are seldom explicitly linked. On the other hand, many separate efforts around the Valley to increase local marketing and agritourism, improve public education about agriculture, and organize grassroots farmland preservation initiatives were documented. We conclude that linking these efforts more explicitly to sustainable agriculture and promoting more engagement between ecologically oriented farmers and their communities could engender more economic and political support for these farmers, helping them and their communities to achieve greater sustainability in the long run. Sonja Brodt is a former program evaluation specialist with the University of California Integrated Pest Management Program. Her current research focuses on extension and adoption of integrated pest management strategies by California growers and the impacts of pesticide safety training programs on farmworkers. Gail Feenstra is a food systems analyst at the University of California Sustainable Agriculture Research and Education Program (SAREP). She coordinates SAREP’s Community Development and Public Policy grants program and conducts outreach and education to academic and community-based groups to build their capacity and leadership skills for developing sustainable community food systems. Robin Kozloff is a social science researcher and consultant in agricultural and land use policy. Karen Klonsky is an extension specialist at the University of California at Davis in the Department of Agricultural and Resource Economics. Her research focuses on the economic viability of organic and sustainable farming systems as well as the evolution of the organic market. Laura Tourte is county director and farm advisor at the University of California Cooperative Extension in Santa Cruz County. Her research and extension activities currently focus on farm management and marketing for small-scale growers.     

Angiogenesis-independent endothelial protection of liver: role of VEGFR-1

The vascular endothelium was once thought to function primarily in nutrient and oxygen delivery, but recent evidence suggests that it may play a broader role in tissue homeostasis. To explore the role of sinusoidal endothelial cells (LSECs) in the adult liver, we studied the effects of vascular endothelial growth factor (VEGF) receptor activation on mouse hepatocyte growth. Delivery of VEGF-A increased liver mass in mice but did not stimulate growth of hepatocytes in vitro, unless LSECs were also present in the culture. Hepatocyte growth factor (HGF) was identified as one of the LSEC-derived paracrine mediators promoting hepatocyte growth. Selective activation of VEGF receptor-1 (VEGFR-1) stimulated hepatocyte but not endothelial proliferation in vivo and reduced liver damage in mice exposed to a hepatotoxin. Thus, VEGFR-1 agonists may have therapeutic potential for preservation of organ function in certain liver disorders.     

Coiled-coil irregularities and instabilities in group A Streptococcus M1 are required for virulence

Antigenically variable M proteins are major virulence factors and immunogens of the human pathogen group A Streptococcus (GAS). Here, we report the approximately 3 angstrom resolution structure of a GAS M1 fragment containing the regions responsible for eliciting type-specific, protective immunity and for binding fibrinogen, which promotes M1 proinflammatory and antiphagocytic functions. The structure revealed substantial irregularities and instabilities throughout the coiled coil of the M1 fragment. Similar structural irregularities occur in myosin and tropomyosin, explaining the patterns of cross-reactivity seen in autoimmune sequelae of GAS infection. Sequence idealization of a large segment of the M1 coiled coil enhanced stability but diminished fibrinogen binding, proinflammatory effects, and antibody cross-reactivity, whereas it left protective immunogenicity undiminished. Idealized M proteins appear to have promise as vaccine immunogens.