Sequential Subterranean Transport of Excavated Sand and Foraged Seeds in Nests of the Harvester Ant,Pogonomyrmex badius

During their approximately annual nest relocations, Florida harvester ants (Pogonomyrmex badius) excavate large and architecturally-distinct subterranean nests. Aspects of this process were studied by planting a harvester ant colony in the field in a soil column composed of layers of 12 different colors of sand. Quantifying the colors of excavated sand dumped on the surface by the ants revealed the progress of nest deepening to 2 m and enlargement to 8 L in volume. Most of the excavation was completed within about 2 weeks, but the nest was doubled in volume after a winter lull. After 7 months, we excavated the nest and mapped its structure, revealing colored sand deposited in non-host colored layers, especially in the upper 30 to 40 cm of the nest. In all, about 2.5% of the excavated sediment was deposited below ground, a fact of importance to sediment dating by optically-stimulated luminescence (OSL). Upward transport of excavated sand is carried out in stages, probably by different groups of ants, through deposition, re-transport, incorporation into the nest walls and floors and remobilization from these. This results in considerable mixing of sand from different depths, as indicated in the multiple sand colors even within single sand pellets brought to the surface. Just as sand is transported upward by stages, incoming seeds are transported downward to seed chambers. Foragers collect seeds and deposit them only in the topmost nest chambers from which a separate group of workers rapidly transports them downward in increments detectable as a "wave" of seeds that eventually ends in the seed chambers, 20 to 80 cm below the surface. The upward and downward transport is an example of task-partitioning in a series-parallel organization of work carried out by a highly redundant work force in which each worker usually completes only part of a multi-step process.     

The Role of ARF6 in Biliary Atresia

Background & Aims

Altered extrahepatic bile ducts, gut, and cardiovascular anomalies constitute the variable phenotype of biliary atresia (BA).

Methods

To identify potential susceptibility loci, Caucasian children, normal (controls) and with BA (cases) at two US centers were compared at >550000 SNP loci. Systems biology analysis was carried out on the data. In order to validate a key gene identified in the analysis, biliary morphogenesis was evaluated in 2-5-day post-fertilization zebrafish embryos after morpholino-antisense oligonucleotide knockdown of the candidate gene ADP ribosylation factor-6 (ARF6, Mo-arf6).

Results

Among 39 and 24 cases at centers 1 and 2, respectively, and 1907 controls, which clustered together on principal component analysis, the SNPs rs3126184 and rs10140366 in a 3’ flanking enhancer region for ARF6 demonstrated higher minor allele frequencies (MAF) in each cohort, and 63 combined cases, compared with controls (0.286 vs. 0.131, P = 5.94x10^-7, OR 2.66; 0.286 vs. 0.13, P = 5.57x10^-7, OR 2.66). Significance was enhanced in 77 total cases, which included 14 additional BA genotyped at rs3126184 only (p = 1.58x10^-2, OR = 2.66). Pathway analysis of the 1000 top-ranked SNPs in CHP cases revealed enrichment of genes for EGF regulators (p<1 x10^-7), ERK/MAPK and CREB canonical pathways (p<1 x10^-34), and functional networks for cellular development and proliferation (p<1 x10^-45), further supporting the role of EGFR-ARF6 signaling in BA. In zebrafish embryos, Mo-arf6 injection resulted in a sparse intrahepatic biliary network, several biliary epithelial cell defects, and poor bile excretion to the gall bladder compared with uninjected embryos. Biliary defects were reproduced with the EGFR-blocker AG1478 alone or with Mo-arf6 at lower doses of each agent and rescued with arf6 mRNA.

Conclusions

The BA-associated SNPs identify a chromosome 14q21.3 susceptibility locus encompassing the ARF6 gene. arf6 knockdown in zebrafish implicates early biliary dysgenesis as a basis for BA, and also suggests a role for EGFR signaling in BA pathogenesis.     

Vegetation succession among and within structural layers following wildfire in managed forests

Question: How does vegetation develop during the initial period following severe wildfire in managed forests? Location: Southwestern Oregon, USA. Methods: In severely burned plantations, dynamics of (1) shrub, herbaceous, and cryptogam richness; (2) cover; (3) topographic, overstory, and site influences were characterized on two contrasting aspects 2 to 4 years following fire. Analysis of variance was used to examine change in structural layer richness and cover over time. Non‐metric multidimensional scaling, multi‐response permutation procedure, and indicator species analysis were used to evaluate changes in community composition over time. Results: Vegetation established rapidly following wildfire in burned plantations, following an initial floristics model of succession among structural layers. Succession within structural layers followed a combination of initial and relay floristic models. Succession occurred simultaneously within and among structural layers following wildfire, but at different rates and with different drivers. Stochastic (fire severity and site history) and deterministic (species life history traits, topography, and pre‐disturbance plant community) factors determined starting points of succession. Multiple successional trajectories were evident in early succession. Conclusions: Mixed conifer forests are resilient to interacting effects of natural and human‐caused disturbances. Predicting the development of vegetation communities following disturbances requires an understanding of the various successional components, such as succession among and within structural layers, and the fire regime. Succession among and within structural layers can follow different successional models and trajectories, occurs at different rates, and is affected by multiple interacting factors.     

Estimating body size of fossil sirenians

Estimates of fossil sirenian body size are important for understanding niche partitioning among possibly sympatric species. Because of the paucity of complete fossil skeletons, we explored the utility of three morphometric predictors of body size: (condylobasal skull length [BSL]; occipital condyle width [OCW]; and foramen magnum width [FMW]) in extant sirenians—Florida manatees (Trichechus manatus latirostris) and dugongs (Dugong dugon)—and then applied these to obtain estimates of body size in extinct sirenian taxa. Condylobasal length of the skull is a more accurate predictor of body size in extant Florida manatees and dugongs than are width of the occipital condyles or width of the foramen magnum. Body length (BL) is predicted more accurately than is body weight (BW) for all three morphometric predictors. For our sample of fossil sirenians, BSL, OCW, and FMW were used to generate predicted BLs and BWs. Preliminary assessments of fossil sirenian faunas from Florida and India suggest that body mass could have been one of several possible important morphological parameters accounting for feeding niche separation.     

Methylene amine substituted arylindenopyrimidines as potent adenosine A2A/A1 antagonists

A novel series of arylindenopyrimidines were identified as A_2A and A₁ receptor antagonists. The series was optimized for in vitro activity by substituting the 8- and 9-positions with methylene amine substituents. The compounds show excellent activity in mouse models of Parkinson’s disease when dosed orally.     

Structure-based optimization of pyrazolo-pyrimidine and -pyridine inhibitors of PI3-kinase

Starting from HTS hit 1a, X-ray co-crystallization and molecular modeling were used to design potent and selective inhibitors of PI3-kinase. Bioavailablity in this series was improved through careful modulation of physicochemical properties. Compound 12 displayed in vivo knockdown of PI3K pharmacodynamic markers such as pAKT, pPRAS40, and pS6RP in a PC3 prostate cancer xenograft model.     

β-Arrestin-1 links mitogenic sonic hedgehog signaling to the cell cycle exit machinery in neural precursors

Development of the cerebellum, a brain region regulating posture and coordination, occurs post-natally and is marked by rapid proliferation of granule neuron precursors (CGNPs), stimulated by mitogenic Sonic hedgehog (Shh) signaling. β-Arrestin (βArr) proteins play important roles downstream of Smoothened, the Shh signal transducer. However, whether Shh regulates βArrs and what role it plays in Shh-driven CGNP proliferation remains to be determined. Here, we report that Shh induces βArr1 accumulation and localization to the nucleus, where it participates in enhancing expression of the cyclin dependent kinase (cdk) inhibitor p27, whose accumulation eventually drives CGNP cell cycle exit. βArr1 knockdown enhances CGNP proliferation and reduces p27 expression. Thus, Shh-mediated βArr1 induction represents a novel negative feedback loop within the Shh mitogenic pathway, such that ongoing Shh signaling, while required for CGNPs to proliferate, also sets up a cell-intrinsic clock programming their ultimate exit from the cell cycle.Key words: sonic hedgehog, cerebellum, neural precursor, β-arrestin 1, p27, differentiation