The cloning and expression of the cDNA for ovine stem cell factor (kit-ligand) and characterization of its in vitro haematopoietic activity.

The cDNA encoding the soluble form of ovine stem cell factor (SCF) has been cloned and expressed. The soluble protein is predicted to be 165/166 amino acids in length, one more than the human and murine SCFs with which it shares 87% and 81% identity respectively. Ovine SCF has 98.5%, 95% and 91% identity with cattle, pig and dog SCF, respectively. The recombinant ovine (rov) SCF protein has been expressed in Chinese hamster ovary (CHO) cells, purified, and its biological activity on ovine bone marrow cells compared with that of interleukin 3 (rovIL-3), granulocyte-macrophage colony-stimulating factor (rovGM-CSF), interleukin 5 (rovIL-5), human macrophage colony-stimulating factor (M-CSF) and human erythropoietin (epo). On its own rovSCF supported the development of small numbers of neutrophil, macrophage, eosinophil, granulocyte-macrophage, mixed cell phenotype, haemopoietic blast cell and basophilic granular cell colonies in a soft agar clonogenic assay. In combination with each of the above cytokines rovSCF supported an increase in the number and size of the lineage-specific colony types that were stimulated by the other cytokines on their own. In an assay for precursors of multipotential colony-forming cells (multi-CFC), rovSCF in combination with rovIL-3 (but neither cytokine alone) supported the development of these early haematopoietic progenitor cells.     

Live fast,die young: the life cycle of the brooding feather star Aporometra wilsoni (Echinodermata: Crinoidea)

We present here the first documentation of the entire life cycle of a crinoid. A population of the diminutive feather star Aporometra wilsoni, which broods larvae, was sampled near Adelaide, in the Gulf St Vincent, South Australia, every fortnight between February 2004 and February 2005. Body size, sex, and reproductive status were recorded for 30–50 individuals collected on each occasion. The population showed a sex ratio of 1:1, with unequivocal male and female specimens found in 10 of 13 months. The average size (arm length) of individuals increased until June, when it stabilized and females began to brood larvae. Females were found brooding larvae until November, when adults began senescing. By January, the majority of the population consisted of small recruits. The entire life cycle of this small ovoviviparous crinoid occurs over a single year, a life cycle that is unique among echinoderms.     

Divergent mating systems and parental conflict as a barrier to hybridization in flowering plants

Parental conflicts can lead to antagonistic coevolution of the sexes and of parental genomes. Within a population, the resulting antagonistic effects should balance, but crosses between populations can reveal conflict. Parental conflict is less intense in self-pollinating plants than in outcrossers because outcrossing plants are pollinated by multiple pollen donors unrelated to the seed parent, while a self-pollinating plant is primarily pollinated by one individual (itself). Therefore, in crosses between plants with differing mating systems, outcrossing parents are expected to "overpower" selfing parents. We call this the weak inbreeder/strong outbreeder (WISO) hypothesis. Prezygotically, such overpowering can alter pollination success, and we argue that our hypothesis explains a common pattern of unilateral incompatibility, in which pollen from self-incompatible populations fertilizes ovules of self-compatible individuals but the reciprocal cross fails. A postzygotic manifestation of overpowering is aberrant seed development due to parent-of-origin effects such as genomic imprinting. We evaluate evidence for the WISO hypothesis by reviewing published accounts of crosses between plants of different mating systems. Many, but not all, of such reports support our hypothesis. Since parental conflicts can perturb fertilization and development, such conflicts may strengthen reproductive barriers between populations, contributing to speciation.     

Identifying shared genetic structure patterns among Pacific Northwest forest taxa: insights from use of visualization tools and computer simulations

Background

Identifying causal relationships in phylogeographic and landscape genetic investigations is notoriously difficult, but can be facilitated by use of multispecies comparisons.

Methodology/Principal Findings

We used data visualizations to identify common spatial patterns within single lineages of four taxa inhabiting Pacific Northwest forests (northern spotted owl: Strix occidentalis caurina; red tree vole: Arborimus longicaudus; southern torrent salamander: Rhyacotriton variegatus; and western white pine: Pinus monticola). Visualizations suggested that, despite occupying the same geographical region and habitats, species responded differently to prevailing historical processes. S. o. caurina and P. monticola demonstrated directional patterns of spatial genetic structure where genetic distances and diversity were greater in southern versus northern locales. A. longicaudus and R. variegatus displayed opposite patterns where genetic distances were greater in northern versus southern regions. Statistical analyses of directional patterns subsequently confirmed observations from visualizations. Based upon regional climatological history, we hypothesized that observed latitudinal patterns may have been produced by range expansions. Subsequent computer simulations confirmed that directional patterns can be produced by expansion events.

Conclusions/Significance

We discuss phylogeographic hypotheses regarding historical processes that may have produced observed patterns. Inferential methods used here may become increasingly powerful as detailed simulations of organisms and historical scenarios become plausible. We further suggest that inter-specific comparisons of historical patterns take place prior to drawing conclusions regarding effects of current anthropogenic change within landscapes.     

Intragenomic politics

The mammalian genome contains multiple genetic factions with distinct interests in the outcomes of interactions among kin. In the context of an offspring's relations with its mother, these factions are proposed to align into two 'parties', one favoring increased demand by offspring and the other favoring reduced demand. A possible alignment has inhibitors of demand located on the X chromosome and enhancers of demand located on autosomes, because X-linked loci are maternally derived two-thirds of the time by contrast to autosomal loci which are maternally derived half of the time.     

The Broad-Spectrum Antiviral Protein ZAP Restricts Human Retrotransposition

Intrinsic immunity describes the set of recently discovered but poorly understood cellular mechanisms that specifically target viral pathogens. Their discovery derives in large part from intensive studies of HIV and SIV that revealed restriction factors acting at various stages of the retroviral life cycle. Recent studies indicate that some factors restrict both retroviruses and retrotransposons but surprisingly in ways that may differ. We screened known interferon-stimulated antiviral proteins previously untested for their effects on cell culture retrotransposition. Several factors, including BST2, ISG20, MAVS, MX2, and ZAP, showed strong L1 inhibition. We focused on ZAP (PARP13/ZC3HAV1), a zinc-finger protein that targets viruses of several families, including Retroviridae, Tiloviridae, and Togaviridae, and show that ZAP expression also strongly restricts retrotransposition in cell culture through loss of L1 RNA and ribonucleoprotein particle integrity. Association of ZAP with the L1 ribonucleoprotein particle is supported by co-immunoprecipitation and co-localization with ORF1p in cytoplasmic stress granules. We also used mass spectrometry to determine the protein components of the ZAP interactome, and identified many proteins that directly interact and colocalize with ZAP, including MOV10, an RNA helicase previously shown to suppress retrotransposons. The detection of a chaperonin complex, RNA degradation proteins, helicases, post-translational modifiers, and components of chromatin modifying complexes suggest mechanisms of ZAP anti-retroelement activity that function in the cytoplasm and perhaps also in the nucleus. The association of the ZAP ribonucleoprotein particle with many interferon-stimulated gene products indicates it may be a key player in the interferon response.     

Cellular mechanisms governing synaptic development in Drosophila melanogaster

The neuromuscular connections of Drosophila are ideally suited for studying synaptic function and development. Hypotheses about cell recognition can be tested in a simple array of pre-and postsynaptic elements. Drosophila muscle fibers are multiply innervated by individually identifiable motoneurons. The neurons express several synaptic cotransmitters, including glutamate, proctolin, and octopamine, and are specialized by their synaptic morphology, neurotransmitters, and connectivity. During larval development the initial motoneuron endings grow extensively over the surface of the muscle fibers, and differentiate synaptic boutons of characteristic morphology. While considerable growth occurs postembryonically, the initial wiring of motoneurons to muscle fibers is accomplished during mid-to-late embryogenesis (stages 15–17). Efferent growth cones sample multiple muscle fibers with rapidly moving filopodia. Upon reaching their target muscle fibers, the growth cones rapidly differentiate into synaptic contacts whose morphology prefigures that of the larval junction. Mismatch experiments show that growth cones recognize specific muscle fibers, and can do so when the surrounding musculature is radically altered. However, when denied their normal targets, motoneurons can establish functional synapses on alternate muscle fibers. Blocking synaptic activity with either injected toxins or ion channel mutants does not derange synaptogenesis, but may influence the number of motor ending processes. The molecular mechanisms governing cellular recognition during synaptogenesis remain to be identified. However, several cell surface glycoproteins known to mediate cellular adhesion events in vitro are expressed by the developing synapses. Furthermore, enhancer detector lines have identified genes with expression restricted to small subsets of muscle fibers and /or motoneurons during the period of synaptogenesis. These observations suggest that in Drosophila a mechanism of target chemoaffinity may be involved in the genesis of stereotypic synaptic wiring. © 1993 John Wiley & Sons, Inc.     

Adaptive evolution of Toll-like receptor 5 in domesticated mammals

ABSTRACT: BACKGROUND: Previous studies have proposed that mammalian toll like receptors (TLRs) have evolved under diversifying selection due to their role in pathogen detection. To determine if this is the case, we examined the extent of adaptive evolution in the TLR5 gene in both individual species and defined clades of the mammalia. RESULTS: In support of previous studies, we find evidence of adaptive evolution of mammalian TLR5. However, we also show that TLR5 genes of domestic livestock have a concentration of single nucleotide polymorphisms suggesting a specific signature of adaptation. Using codon models of evolution we have identified a concentration of rapidly evolving codons within the TLR5 extracellular domain a site of interaction between host and the bacterial surface protein flagellin. CONCLUSIONS: The results suggest that interactions between pathogen and host may be driving adaptive change in TLR5 by competition between species. In support of this, we have identified single nucleotide polymorphisms (SNP) in sheep and cattle TLR5 genes that are co-localised and co-incident with the predicted adaptive codons suggesting that adaptation in this region of the TLR5 gene is on-going in domestic species.     

THE DARK ADAPTATION OF RETINAL FIELDS OF DIFFERENT SIZE AND LOCATION

The decrease in threshold shown by the eye during dark adaptation proceeds in two steps. The first is rapid, short in duration, and small in extent. The second is slow, prolonged, and large. The first is probably due to cone function; the second to rod function. In centrally located fields the two parts of adaptation change differently with area. With small, foveal fields the first part dominates and only traces of the second part appear. As the area increases the first part changes a little, while the second part covers an increasing range of intensities and appears sooner in time. Measurements with an annulus field covering only the circumference of a 20° circle show most of the characteristics of a 20° whole field centrally located. Similarly a 2° field located at different distances from the center shows dark adaptation characteristics essentially like those of large centrally located fields whose edges correspond to the position of the central field. Evidently the behavior in dark adaptation of centrally located fields of different size is determined in the main not by area as area, but by the fact that the retina gradually changes in sensitivity from center to periphery, and therefore the larger the field the farther it reaches into peripheral regions of permanently greater sensibility.