Understanding User Triads on Facebook

Contemporary approaches that analyze user behavior on online social networks only consider interactions among dyads, which are pairs of directly connected users. A large body of sociological work, however, suggests that mutual connections among users can influence their activities, leading to differences between two- and three-way interactions. This paper explores the dynamics of triads among Facebook users based on the wall posts from the New Orleans regional network. Initially, each connection is categorized as a close friendship or an acquiantance, contingent on the number of wall posts exchanged. Subsequently, the impact of different types of connections comprising triads is examined on the post volume and inter-post times. The analysis finds that these two properties are influenced by the number of close friendships constituting triads

Genome Evolution and the Emergence of Fruiting Body Development in Myxococcus xanthus

BACKGROUND: Lateral gene transfer (LGT) is thought to promote speciation in bacteria, though well-defined examples have not been put forward. METHODOLOGY/PRINCIPLE FINDINGS: We examined the evolutionary history of the genes essential for a trait that defines a phylogenetic order, namely fruiting body development of the Myxococcales. Seventy-eight genes that are essential for Myxococcus xanthus development were examined for LGT. About 73% of the genes exhibit a phylogeny similar to that of the 16S rDNA gene and a codon bias consistent with other M. xanthus genes suggesting vertical transmission. About 22% have an altered codon bias and/or phylogeny suggestive of LGT. The remaining 5% are unique. Genes encoding signal production and sensory transduction were more likely to be transmitted vertically with clear examples of duplication and divergence into multigene families. Genes encoding metabolic enzymes were frequently acquired by LGT. Myxobacteria exhibit aerobic respiration unlike most of the delta Proteobacteria. M. xanthus contains a unique electron transport pathway shaped by LGT of genes for succinate dehydrogenase and three cytochrome oxidase complexes. CONCLUSIONS/SIGNIFICANCE: Fruiting body development depends on genes acquired by LGT, particularly those involved in polysaccharide production. We suggest that aerobic growth fostered innovation necessary for development by allowing myxobacteria access to a different gene pool from anaerobic members of the delta Proteobacteria. Habitat destruction and loss of species diversity could restrict the evolution of new bacterial groups by limiting the size of the prospective gene pool

Structural basis for assembly and function of the Nup82 complex in the nuclear pore scaffold

Nuclear pore complexes (NPCs) are huge assemblies formed from ∼30 different nucleoporins, typically organized in subcomplexes. One module, the conserved Nup82 complex at the cytoplasmic face of NPCs, is crucial to terminate mRNA export. To gain insight into the structure, assembly, and function of the cytoplasmic pore filaments, we reconstituted in yeast the Nup82–Nup159–Nsp1–Dyn2 complex, which was suitable for biochemical, biophysical, and electron microscopy analyses. Our integrative approach revealed that the yeast Nup82 complex forms an unusual asymmetric structure with a dimeric array of subunits. Based on all these data, we developed a three-dimensional structural model of the Nup82 complex that depicts how this module might be anchored to the NPC scaffold and concomitantly can interact with the soluble nucleocytoplasmic transport machinery

Understanding User Triads on Facebook

Contemporary approaches that analyze user behavior on online social networks only consider interactions among dyads, which are pairs of directly connected users. A large body of sociological work, however, suggests that mutual connections among users can influence their activities, leading to differences between two- and three-way interactions. This paper explores the dynamics of triads among Facebook users based on the wall posts from the New Orleans regional network. Initially, each connection is categorized as a close friendship or an acquiantance, contingent on the number of wall posts exchanged. Subsequently, the impact of different types of connections comprising triads is examined on the post volume and inter-post times. The analysis finds that these two properties are influenced by the number of close friendships constituting triads

Characterizing the Activity of Friendship Triads on Facebook

Contemporary approaches to analyze user behavior on online social networks consider interactions among pairs of directly connected users or dyads. A large body of sociological work, however, suggests that mutual connections can influence the activity between two users, leading to differences between three-way and two-way interactions. This paper explores the dynamics of three-way relationships on Facebook. Categorizing each connection as a close friend or an acquaintance, contingent on the number of wall posts, this study examines how the different types of connections forming triads influence their characteristics embodied in posting activity, inter-post, reciprocation, and formation times, and activity decay. The analysis indicates that the number of constituent friendships primarily influences the characteristics of triads

Clinical, histopathologic, and genomic features of Spitz tumors with ALK fusions.

Activating kinase fusions have recently been described as early oncogenic events that are mutually exclusive with HRAS and BRAF mutations in Spitz tumors. Here, we report a series of 32 Spitz tumors with ALK fusions (6 Spitz nevi, 22 atypical Spitz tumors, and 4 spitzoid melanomas) in patients ranging from 5 months to 64 years (median=12 y) of age. The tumors typically presented as exophytic papules on the extremities and were occasionally darkly pigmented. In addition to ALK fusions previously described in other tumor types (NPM1-ALK, TPR-ALK), we identified 2 novel ALK fusions (CLIP1-ALK and GTF3C2-ALK) in our cohort of Spitz tumors. Array comparative genomic hybridization of 19 of these tumors demonstrated a high frequency of chromosome 2 aberrations (where ALK resides, 63%) and chromosome 1p loss in 37% of the cases. Spitz tumors with ALK fusions demonstrated unique histopathologic features. Clefts and small vesicle-like spaces were arrayed between plump spindled melanocytes with fibrillar cytoplasm and enlarged nuclei. These melanocytes were typically arrayed in elongated and fusiform nests with radial orientation. The tumors often had extension into the dermis or subcutis with a wedge-shaped or bulbous lower border (45% and 17%, respectively). An infiltrative growth pattern was often present at the periphery of the tumor and was highlighted by ALK immunohistochemistry. In conclusion, Spitz tumors with ALK rearrangement show distinct histopathologic features that should aid in improving classification of these diagnostically challenging tumors