Mechanical Restoration of California Mixed‐Conifer Forests: Does it Matter Which Trees Are Cut?

The montane ecosystems of northern California have been subjected to repeated manipulation and active fire suppression for over a century, resulting in changes in community structure that contribute to increased wildfire hazard. Ecosystem restoration via reduction of stand density for wildfire hazard mitigation has received substantial attention in recent years; however, many ecological questions remain unanswered. This study compares belowground effects of two alternative forest thinning treatments designed to restore the large, old tree component of late‐seral structure, one of which focuses on restoring Pinus ponderosa dominance (Pine‐preference) and the other of which promotes development of large trees regardless of species (Size‐preference). We evaluated forest floor and soil chemical and microbial parameters in six experimental thinning treatment units of 40 ha each in the Klamath National Forest of northern California 5–6 years after thinning. Inorganic N availability, soil organic C content, phenol oxidase activity, and forest floor C:N ratio were greater in the Size‐preference treatment, whereas forest floor N and soil pH were greater in the Pine‐preference treatment. Our results indicate that these two thinning strategies produce differences in the soil environment that has the potential to affect growth rates of trees that remain, as well as the growth and survivorship of newly established seedlings. Thus, which species/individuals are removed during structural restoration of these mixed‐conifer forests matters both to the belowground components of the ecosystem today and the vegetation and productivity of the ecosystem in future decades.     

Teaching animal habitat selection using wildlife tracking equipment

We present a hands-on outdoor activity coupled with classroom discussion to teach students about wildlife habitat selection, the process by which animals choose where to live. By selecting locations or habitats with many benefits (e.g., food, shelter, mates) and few costs (e.g., predators), animals improve their ability to survive and reproduce. Biologists track animal movement using radio telemetry technology to study habitat selection so they can better provide species with habitats that promote population growth. We present a curriculum in which students locate “animals” (transmitters) using radio telemetry equipment and apply math skills (use of fractions and percentages) to assess their “animal's” habitat selection by comparing the availability of habitat types with the proportion of “animals” they find in each habitat type.     

How Sugars Might Coordinate Chloroplast and Nuclear Gene Expression during Acclimation to High Light Intensities

The concept of retrograde control of nuclear gene expression assumes the generation of signals inside the chloroplasts, which are either released from or sensed inside of the organelle. In both cases, downstream signaling path- ways lead eventually to a differential regulation of nuclear gene expression and the production of proteins required in the chloroplast. This concept appears reasonable as the majority of the over 3000 predicted plastidial proteins are encoded by nuclear genes. Hence, the nucleus needs information on the status of the chloroplasts, such as during acclimation responses, which trigger massive changes in the protein composition of the thylakoid membrane and in the stroma. Here, we propose an additional control mechanism of nuclear- and plastome-encoded photosynthesis genes, taking advantage of pathways involved in sugar- or hormonal signaling. Sugars are major end products of photosynthesis and their con- tents respond very sensitively to changes in light intensities. Based on recent findings, we ask the question as to whether the carbohydrate status outside the chloroplast can be directly sensed within the chloroplast stroma. Sugars might syn- chronize the responsiveness of both genomes and thereby help to coordinate the expression of piastome- and nuclear- encoded photosynthesis genes in concert with other, more specific retrograde signals.     

Isochoric preservation: A novel characterization method

Isochoric (constant volume) preservation is an alternative to traditional cryopreservation methods because it requires less cryoprotectant and is simple to operate. In order to validate that this method automatically minimizes the pressure for a given temperature, pressure and temperature data were collected from a specially designed pressure vessel. This vessel was then used to examine the effect of an isochoric environment on freezing point nucleation in an aqueous antifreeze protein solution, and to generate pressure-temperature phase diagrams for various cryoprotectant solutions. Our results show that the isochoric pressure vessel follows the pressure-temperature phase diagram of water, thereby minimizing the pressure for the given temperature. We also show that the nucleation temperature of the antifreeze protein in an isochoric vessel is lower than that of the isobaric method. Furthermore, the nucleation temperature decreased with increasing concentration in the isochoric vessel while the isobaric nucleation temperature showed no change. These results indicate that the isochoric environment imposes additional constraints on ice formation and warrants further study as these results may change when a different type of cryoprotectant is used. Finally, all of the cryoprotectant phase diagrams exhibited a similar pressure-temperature slope indicating that, regardless of the cryoprotectant used or the mechanism by which it suppresses freezing, isochoric freezing affects the molecules in the same manner. Together, all of these results indicate that the isochoric method of preservation is a valuable tool for characterizing the thermodynamic properties of cryoprotectants and has great potential as a cryopreservation method in the field of cryobiology.     

CD36 signals to the actin cytoskeleton and regulates microglial migration via a p130Cas complex

The pattern recognition receptor CD36 initiates a signaling cascade that promotes microglial activation and recruitment to beta-amyloid deposits in the brain. In the present study we identify the focal adhesion-associated proteins p130Cas, Pyk2, and paxillin as novel members of the tyrosine kinase signaling pathway downstream of CD36 and show that assembly of this complex is essential for microglial migration. In primary microglia and macrophages exposed to beta-amyloid, the scaffolding protein p130Cas is rapidly tyrosine-phosphorylated and co-localizes with CD36 to membrane ruffles contemporaneous with F-actin polymerization. These beta-amyloid-stimulated events are not detected in CD36 null cells and are dependent on CD36 activation of Src family tyrosine kinases. Fyn, a Src kinase known to interact with CD36, co-precipitates with p130Cas and is an essential upstream intermediate in the signaling pathways leading to phosphorylation of the p130Cas substrate domain. Furthermore, the p130Cas-interacting kinase Pyk2 and the cytoskeletal adapter protein paxillin also demonstrate CD36-dependent phosphorylation, identifying these focal adhesion molecules as additional members of this beta-amyloid signaling cascade. Disruption of this p130Cas complex by small interfering RNA silencing inhibits p44/42 mitogen-activated protein kinase phosphorylation and microglial migration, illustrating the importance of this pathway in microglial activation and recruitment. Together, these data are the first to identify the signaling cascade that directly links CD36 to the actin cytoskeleton and, thus, implicates it in diverse processes such as cellular migration, adhesion, and phagocytosis.     

Structural Insights into Calmodulin-regulated L-selectin Ectodomain Shedding

The L-selectin glycoprotein receptor mediates the initial steps of leukocyte migration into secondary lymphoid organs and sites of inflammation. Following cell activation through the engagement of G-protein-coupled receptors or immunoreceptors, the extracellular domains of L-selectin are rapidly shed, a process negatively controlled via the binding of the ubiquitous eukaryotic calcium-binding protein calmodulin to the cytoplasmic tail of L-selectin. Here we present the solution structure of calcium-calmodulin bound to a peptide encompassing the cytoplasmic tail and part of the transmembrane domain of L-selectin. The structure and accompanying biophysical study highlight the importance of both calcium and the transmembrane segment of L-selectin in the interaction between these two proteins, suggesting that by binding this region, calmodulin regulates in an "inside-out" fashion the ectodomain shedding of the receptor. Our structure provides the first molecular insight into the emerging new role for calmodulin as a transmembrane signaling partner.