Isolation of Osteoprogenitors from Human Jaw Periosteal Cells: A Comparison of Two Magnetic Separation Methods

Human jaw periosteum tissue contains osteoprogenitors that have potential for tissue engineering applications in oral and maxillofacial surgeries. To isolate osteoprogenitor cells from heterogeneous cell populations, we used the specific mesenchymal stem cell antigen-1 (MSCA-1) antibody and compared two magnetic separation methods. We analyzed the obtained MSCA-1⁺ and MSCA-1⁻ fractions in terms of purity, yield of positive/negative cells and proliferative and mineralization potentials. The analysis of cell viability after separation revealed that the EasySep method yielded higher viability rates, whereas the flow cytometry results showed a higher purity for the MACS-separated cell fractions. The mineralization capacity of the osteogenic induced MSCA-1⁺ cells compared with the MSCA-1⁻ controls using MACS was 5-fold higher, whereas the same comparison after EasySep showed no significant differences between both fractions. By analyzing cell proliferation, we detected a significant difference between the proliferative potential of the osteogenic cells versus untreated cells after the MACS and EasySep separations. The differentiated cells after MACS separation adjusted their proliferative capacity, whereas the EasySep-separated cells failed to do so. The protein expression analysis showed small differences between the two separation methods. Our findings suggest that MACS is a more suitable separation method to isolate osteoprogenitors from the entire jaw periosteal cell population.     

Neurotrophic and hepatotrophic stimulation of proliferation of embryonic chick muscle cells in vitro: Assay and partial characterization of mitogenic activity in chick embryonic organ and tissue extracts

Whole embryo extract is routinely employed as a growth-promoting supplement in chick embryonic muscle cell cultures. In assessing the effect of the extract on muscle cell cultures, extracts of various embryonic tissues and organs were substituted for whole embryo extract and the effects on proliferation of dissociated 12-day chick embryonic leg muscle cells were observed. The effects were measured according to [³H]thymidine incorporation into deoxyribonucleic acid (DNA) and were confirmed with total cell counts. Brain and liver extracts were found to be especially effective in stimulating muscle cell proliferation. The extracts were found to be heat and trypsin labile. Further analysis of activity in the extracts by dialysis and Sephadex G-25 fractionation revealed the presence of at least two classes of activity—one of high molecular weight (>5000) and one of low molecular weight (<5000)—which must be present together to yield the full activity of crude extracts from embryonic liver and brain. The results are discussed against the background of our interest in the neurotrophic phenomenon.     

When the same is not the same: phenotypic variation reveals different plant ecological strategies within species occurring in distinct Neotropical savanna habitats

Variations in abiotic characteristics such as soil water availability and fertility impose different selective pressures on plant populations. This may produce intraspecific variability in functional traits, even at a fine spatial scale. We investigated whether functional traits related to water-use efficiency, resource-retention strategy, soil nutrient acquisition, and fire tolerance differ in species that occur in two different habitats of Brazilian Cerrado: rocky savannas and savanna woodlands. Rocky savannas occur over sandstone, quartzite outcrops and have shallow nutrient-poor and low-moisture rocky soils, while savanna woodlands occur over well-drained and deep soils with frequent fire regimes. We measured nine functional traits of 40 tree species that occur in both habitats. Rocky savanna individuals exhibited a greater water-use efficiency strategy. The resource-retention strategy in rocky savanna individuals was corroborated by lower adult maximum height. However, despite the lower nutrient availability in rocky savanna soils, we only detected lower leaf phosphorus content in individuals from this habitat. Furthermore, individuals from both habitats had equally thick bark, suggesting that the fire-defense strategy is related to a stable, rather than plastic trait. Overall, our results highlight the central role of contrasting soil water availability patterns in driving phenotypic plasticity within species. We conclude that savanna species are responding to water and nutrient availabilities, via plasticity in traits related to the resource-retention strategy, and preparing for future fires, via uniformly thick bark. Wide plant distribution in contrasting habitats is possible for species that can shift ecological strategies to survive in nutrient- and water-limited habitats such as rocky savannas.     

West Nile Virus and California Breeding Bird Declines

Since it was first detected in 1999, West Nile virus (WNV) quickly spread, becoming the dominant vector-borne disease in North America. Sometimes fatal to humans, WNV is even more widespread among birds, with hundreds of species known to be susceptible to WNV infection in North America alone. However, despite considerable mortality and local declines observed in American crows (Corvus brachyrhynchos), there has been little evidence of a large regional association between WNV susceptibility and population declines of any species. Here we demonstrate a correlation between susceptibility to WNV measured by large-scale testing of dead birds and two indices of overall population change among bird species following the spread of WNV throughout California. This result was due primarily to declines in four species of Corvidae, including all species in this family except common ravens (Corvus corax). Our results support the hypothesis that susceptibility to WNV may have negative population consequences to most corvids on regional levels. They also provide confirmation that dead animal surveillance programs can provide important data indicating populations most likely to suffer detrimental impacts due to WNV.     

Evidence for template-specific sites in DNA polymerases

Using rabbit hemoglobin messenger RNA as template, $\text{E. coli}$ polymerase I produces poly (dT), poly (dA)·(dT) and antimessenger DNA products. Mild heating of the enzyme causes a differential loss in activity as indicated by three rates of inactivation for the three types of synthesis. Heat inactivation studies have also been carried out with DNA polymerases from oncogenic RNA viruses and mammalian sources using various homopolymer-oligomer pairs as primertemplates. In general, for any given enzyme these synthetic primer-templates reveal different extents of inactivation of the polymerase. These findings may be interpreted to suggest a) that the binding of DNA polymerase to various primer-templates produces conformational changes in the enzyme which are dependent on the type of template bound, or b) that many, if not all, DNA polymerases have different subsites for different templates.