Understanding variation in resource specialization is important for progress on issues that include coevolution, community assembly, ecosystem processes, and the latitudinal gradient of species richness. Herbivorous insects are useful models for studying resource specialization, and the interaction between plants and herbivorous insects is one of the most common and consequential ecological associations on the planet. However, uncertainty persists regarding fundamental features of herbivore diet breadth, including its relationship to latitude and plant species richness. Here, we use a global dataset to investigate host range for over 7,500 insect herbivore species covering a wide taxonomic breadth and interacting with more than 2,000 species of plants in 165 families. We ask whether relatively specialized and generalized herbivores represent a dichotomy rather than a continuum from few to many host families and species attacked and whether diet breadth changes with increasing plant species richness toward the tropics. Across geographic regions and taxonomic subsets of the data, we find that the distribution of diet breadth is fit well by a discrete, truncated Pareto power law characterized by the predominance of specialized herbivores and a long, thin tail of more generalized species. Both the taxonomic and phylogenetic distributions of diet breadth shift globally with latitude, consistent with a higher frequency of specialized insects in tropical regions. We also find that more diverse lineages of plants support assemblages of relatively more specialized herbivores and that the global distribution of plant diversity contributes to but does not fully explain the latitudinal gradient in insect herbivore specialization.
Little is known of molecular requirements for specification of human germ cells. However, it is likely that they are specified through the action of sequentially expressed genes just as in model organisms. We sought to determine whether human embryonic stem (ES) cell lines, like those of mice, might be capable of forming germ cells in vitro. We compared transcriptional profiles of three pluripotent human ES cells to those of isolated inner cell mass (ICM) cells. We found that ICM cells expressed NANOS1, STELLAR and OCT4, whereas undifferentiated human ES cells expressed these genes along with the germ cell-specific gene, DAZL. Upon ES cell differentiation into embryoid bodies (EBs), we observed a shift in expression from RNA and protein markers of immature germ cells to those indicative of mature germ cells, including expression of VASA, BOL, SCP1, SCP3, GDF9 and TEKT1. Although ability to test the function of these putative VASA positive germ cells is limited, these results demonstrate that differentiation of human ES cells into EBs in vitro results in formation of cells that express markers specific to gonocytes.
Early in development, a part of the embryo is set aside to become the germ cell lineage that will ultimately differentiate to form sperm and eggs and transmit genetic information to the next generation. Men with deletions encompassing the Y-chromosome DAZ genes have few or no germ cells but are otherwise healthy, indicating they harbor specific defects in formation or maintenance of germ cells. A DAZ homolog, DAZL (DAZ-Like), is found in diverse organisms, including humans and is required for germ cell development in males and͞or females. We identified proteins that interact with DAZ proteins to better understand their function in human germ cells. Here, we show that PUM2, a human homolog of Pumilio, a protein required to maintain germ line stem cells in Drosophila and Caenorhabditis elegans, forms a stable complex with DAZ through the same functional domain required for RNA binding, protein-protein interactions and rescue of Pumilio mutations in flies. We also show that PUM2 is expressed predominantly in human embryonic stem cells and germ cells and colocalizes with DAZ and DAZL in germ cells. These data implicate PUM2 as a component of conserved cellular machinery that may be required for germ cell development.A ll stem cells have potential to differentiate or proliferate mitotically. These potentials must be balanced for the stem cell population to be maintained. If differentiation exceeds proliferation, the stem cell population is not maintained. Evidence in humans suggests that the DAZ genes function early in the germ line stem cells. Men with deletions encompassing the Y-chromosome DAZ gene cluster have defects in spermatogenesis that are detected initially in the stem cell population. These men frequently lack all germ cells, including the spermatogonial stem cells, and only somatic cells are present in testicular tissue (1-3). In addition, expression of the DAZ gene and its ancestral, autosomal homolog, DAZL, only occurs in germ cells; DAZ is expressed in males, and DAZL is expressed in males and females (4, 5). Evidence from model organisms also suggests the DAZ genes function in germ cell maintenance. The Xenopus homolog of DAZ, Xdazl, is expressed in a region of the early oocyte that contains the germ plasm that is required for formation and maintenance of the germ cell lineage (6, 7). Inhibition of Xdazl leads to loss of the primordial germ cells (6, 7). Finally, the DAZ homolog in mice, Dazl, is most abundantly expressed in premeiotic germ cells; disruption of this gene causes depletion of germ cells beginning prenatally (8-10). DAZ and DAZL homologs may function interchangeably as suggested by the observation that a human DAZ transgene can partially rescue a mouse Dazl mutation (11). To shed light on how DAZ genes might function in human germ cells, we sought to identify proteins that interact with DAZ proteins. Materials and MethodsTwo-Hybrid Screening of DAZ-Interacting Proteins. The yeast two-hybrid system was used to identify proteins that interact with a DAZ:GAL4 DNA-binding domain fusion prot...
Abstract. The supply chain is a worldwide network of suppliers, factories, warehouses, distribution centers, and retailers through which raw materials are acquired, transformed, and delivered to customers. In recent years, a new software architecture for managing the supply chain at the tactical and operational levels has emerged. It views the supply chain as composed of a set of intelligent software agents, each responsible for one or more activities in the supply chain and each interacting with other agents in the planning and execution of their responsibilities. This paper investigates issues and presents solutions for the construction of such an agent-oriented software architecture. The approach relies on the use of an agent building shell, providing generic, reusable, and guaranteed components and services for communicative-act-based communication, conversational coordination, role-based organization modeling, and others. Using these components, we show two nontrivial agent-based supply-chain architectures able to support complex cooperative work and the management of perturbation caused by stochastic events in the supply chain.
The decline in estrogen levels during menopause is associated with increased cytokine production and inflammatory diseases. Estrogens exert anti-inflammatory effects by repressing cytokine genes, such as tumor necrosis factor-alpha (TNFalpha). The mechanisms involved in transcriptional repression by estrogens are virtually unknown. Here, we used chromatin immunoprecipitation to investigate how estrogens repress the autoinduction of the TNFalpha gene. TNFalpha assembled a transcriptional activation complex at the TNFalpha promoter that includes c-jun, p50-NFkappaB, p65-NFkappaB, CBP, Hsp90, and unliganded estrogen receptor (ER). Estradiol repressed TNFalpha gene expression by reversing the ligand-independent activation by ERalpha and the stimulatory actions of c-jun, NFkappaB, and CBP on transcription. Silencing of GRIP1 reversed the repression of TNFalpha and other cytokine genes by estradiol, demonstrating that GRIP1 is required for transcriptional repression and can act as a corepressor. Our study demonstrates that ERalpha is a TNFalpha-induced coactivator that becomes a repressor in the presence of estradiol by recruiting GRIP1.
We present a logical framework for representing activities, states, time, and cost in an enterprise integration architecture. We define ontologies for these concepts in first-order logic and consider the problems of temporal projection and reasoning about the occurrence of actions. We characterize the ontology with the use of competency questions. The ontology must contain a necessary and sufficient set of axioms to represent and solve these questions. These questions not only characterize existing ontologies for enterprise engineering, but also drive the development of new ontologies that are required to solve the competency questions.
Analysis of the job shop scheduling domain has indicated that the crux of the scheduling problem is the determination and satisfaction of a large variety of constraints. Schedules are influenced by such diverse and conflicting factors as due date requirements, cost restrictions, produdion levels. machine capab&bes and substitutability, alternative production processes, order characteristics, resource requirements, and resource availability. This paper describes ISIS. a scheduling system capable of incorporating all relevant constraints in the cowtrwbon ' ofjob shop schedules. We examine both the representation of constraints within ISIS, and the manner in which these constraints are used in conducting a constraintdirected search for an acceptable schedule. The important issues relating to the relaxation of constraints are addressed. Finally, the interawe scheduling faalities provided by lSlS are considered.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
334 Leonard St
Brooklyn, NY 11211
Copyright © 2023 scite Inc. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.