{gamma}-Tubulin and microtubule organization during meiosis in the liverwort Ricciocarpus natans (Ricciaceae)

Extant liverworts are "living fossils" considered sister to all other plants and as such provide clues to the evolution of the microtubule organizing center (MTOC) in anastral cells. This report is the first on microtubule arrays and their γ-tubulin-nucleating sites during meiosis in a member of the Ricciales, a specialized, species-rich group of complex thalloid (marchantioid) liverworts. In meiotic prophase, γ-tubulin becomes concentrated at several sites adjacent to the nuclear envelope. Microtubules organized at these foci give rise to a multipolar prometaphase spindle. By metaphase I, the spindle has matured into a bipolar structure with truncated poles. In both first and second meiosis, γ-tubulin forms box-like caps at the spindle poles. γ-Tubulin moves from spindle poles to the proximal surfaces of telophase chromosomes where interzonal microtubules are nucleated. Although a phragmoplast is organized, no cell plate is deposited, and second division occurs simultaneously in the undivided sporocyte. γ-Tubulin surrounds each of the tetrad nuclei, and phragmoplasts initiated between both sister and nonsister nuclei direct simultaneous cytokinesis. The overall pattern of meiosis (unlobed polyplastidic sporocytes, nuclear envelope MTOC, multipolar spindle origin, spindles with box-like poles, and simultaneous cytokinesis) more closely resembles that of Conocephalum than other marchantiod liverworts.     

The single transmembrane domains of ErbB receptors self-associate in cell membranes.

Members of the epidermal growth factor receptor, or ErbB, family of receptor tyrosine kinases have a single transmembrane (TM) alpha-helix that is usually assumed to play a passive role in ligand-induced dimerization and activation of the receptor. However, recent studies with the epidermal growth factor receptor (ErbB1) and the erythropoietin receptor have indicated that interactions between TM alpha-helices do contribute to stabilization of ligand-independent and/or ligand-induced receptor dimers. In addition, not all of the expected ErbB receptor ligand-induced dimerization events can be recapitulated using isolated extracellular domains, suggesting that other regions of the receptor, such as the TM domain, may contribute to dimerization in vivo. Using an approach for analyzing TM domain interactions in Escherichia coli cell membranes, named TOXCAT, we find that the TM domains of ErbB receptors self-associate strongly in the absence of their extracellular domains, with the rank order ErbB4-TM > ErbB1-TM equivalent to ErbB2-TM > ErbB3-TM. A limited mutational analysis suggests that dimerization of these TM domains involves one or more GXXXG motifs, which occur frequently in the TM domains of receptor tyrosine kinases and are critical for stabilizing the glycophorin A TM domain dimer. We also analyzed the effect of the valine to glutamic acid mutation in ErbB2 that constitutively activates this receptor. Contrary to our expectations, this mutation reduced rather than increased ErbB2-TM dimerization. Our findings suggest a role for TM domain interactions in ErbB receptor function, possibly in stabilizing inactive ligand-independent receptor dimers that have been observed by several groups.     

Sporogenesis in Eusporangiate Ferns: II. Polyplastidic Meiosis in Ophioglossum (Ophioglossales)

Ophioglossum petiolatum . Unlike Angiopteris (Marattiales), which is monoplastidic, Ophioglossum undergoes polyplastidic meiosis like members of the fern-seed plant clade. The meiotic spindle is distinctly multipolar in origin and is consolidated into a bipolar spindle that is variously twisted and curved to accommodate the large number of chromosomes. Although a phragmoplast forms after first meiosis, no wall is deposited. Instead, an organelle band consisting of intermingled plastids and mitochondria is formed in the equatorial region between the dyad domains. Following second meiosis, a complex of phragmoplasts forms among sister and non-sister nuclei. Cell plates are deposited first between sister nuclei and then in the region of the organelle band resulting in a tetrad of spores each with a equal allotment of organelles. Received 30 January 2001/ Accepted in revised form 24 April 2001     

Ultrastructure of meiosis in the mossRhynchostegium serrulatum I. Prophasic microtubules and spindle dynamics

Summary An extensive system of microtubules develops during meiotic prophase in the mossRhynchostegium serrulatum (Hedw.)Jaeg. &Sauerb. Development of the cytoskeleton can be traced to early prophase when the nucleus is acentric and the single plastid divides into four plastids. The cytoskeletal microtubules are associated with equidistant positioning of the four plastids at the distal tetrad poles and with migration of the nucleus to a central position in the sporocyte. The cytoskeleton, which interconnects plastids and encloses the nucleus, contributes to the establishment of moss sporocyte polarity. Just prior to metaphase I evidence of the prophase cytoskeleton is lost as the bipolar metaphase I spindle develops in association with discrete polar organizers located in opposite cleavage furrows between plastids.     

Inverse dispersal patterns in a group of ant parasitoids (Hymenoptera: Eucharitidae: Oraseminae) and their ant hosts

When postulating evolutionary hypotheses for diverse groups of taxa using molecular data, there is a tradeoff between sampling large numbers of taxa with a few Sanger-sequenced genes or sampling fewer taxa with hundreds to thousands of next-generation-sequenced genes. High taxon sampling enables the testing of evolutionary hypotheses that are sensitive to sampling bias (i.e. dating, biogeography and diversification analyses), whereas high character sampling improves resolution of critical nodes. In a group of ant parasitoids (Hymenoptera: Eucharitidae: Oraseminae), we analyse both of these types of datasets independently (203 taxa with five Sanger loci, 92 taxa with 348 anchored hybrid enrichment loci) and in combination (229 taxa, 353 loci) to explore divergence dating, biogeography, host relationships and differential rates of diversification. Oraseminae specialize as parasitoids of the immature stages of ants in the subfamily Myrmicinae (Hymenoptera: Formicidae), with ants in the genus Pheidole being their most common and presumed ancestral host. A general assumption is that the distribution of the parasite must be limited by any range contraction or expansion of its host. Recent studies support a single New World to Old World dispersal pattern for Pheidole at c. 11–27 Ma. Using multiple phylogenetic inference methods (parsimony, maximum likelihood, dated Bayesian and coalescent analyses), we provide a robust phylogeny showing that Oraseminae dispersed in the opposite direction, from Old World to New World, c. 24–33 Ma, which implies that they existed in the Old World before their presumed ancestral hosts. Their dispersal into the New World appears to have promoted an increased diversification rate. Both the host and parasitoid show single unidirectional dispersals in accordance with the presence of the Beringian Land Bridge during the Oligocene, a time when the changing northern climate probably limited the dispersal ability of such tropically adapted groups.     

A deeper meaning for shallow-level phylogenomic studies: nested anchored hybrid enrichment offers great promise for resolving the tiger moth tree of life (Lepidoptera: Erebidae: Arctiinae)

Anchored hybrid enrichment (AHE) has emerged as a powerful tool for uncovering the evolutionary relationships within many taxonomic groups. AHE probe sets have been developed for a variety of insect groups, though none have yet been shown to be capable of simultaneously resolving deep and very shallow (e.g., intraspecific) divergences. In this study, we present NOC1, a new AHE probe set (730 loci) for Lepidoptera specialized for tiger moths and assess its ability to deliver phylogenetic utility at all taxonomic levels. We test the NOC1 probe set with 142 individuals from 116 species sampled from all the major lineages of Arctiinae (Erebidae), one of the most diverse groups of noctuoids (>11 000 species) for which no well-resolved, strongly supported phylogenetic hypothesis exists. Compared to previous methods, we generally recover much higher branch support (BS), resulting in the most well-supported, well-resolved phylogeny of Arctiinae to date. At the most shallow-levels, NOC1 confidently resolves species-level and intraspecific relationships and potentially uncovers cryptic species diversity within the genus Hypoprepia. We also implement a ‘sensitivity analysis’ to explore different loci combinations and site sampling strategies to determine whether a reduced probe set can yield results similar to those of the full probe set. At both deep and shallow levels, only 50–175 of the 730 loci included in the complete NOC1 probe set were necessary to resolve most relationships with high confidence, though only when the more rapidly evolving sites within each locus are included. This demonstrates that AHE probe sets can be tailored to target fewer loci without a significant reduction in BS, allowing future studies to incorporate more taxa at a lower per-sample sequencing cost. NOC1 shows great promise for resolving long-standing taxonomic issues and evolutionary questions within arctiine lineages, one of the most speciose clades within Lepidoptera.     

Soft-tissue injuries of the fingertip: methods of evaluation and treatment. An algorithmic approach

LEARNING OBJECTIVES: After studying this article, the participant should be able to: 1. Understand the anatomy of the fingertip. 2. Describe the methods of evaluating fingertip injuries. 3. Discuss reconstructive options for various tip injuries. SUMMARY: The fingertip is the most commonly injured part of the hand, and therefore fingertip injuries are among the most frequent injuries that plastic surgeons are asked to treat. Although microsurgical techniques have enabled replantation of even very distal tip amputations, it is relatively uncommon that a distal tip injury will be appropriate for replantation. In the event that replantation is not pursued, options for distal tip soft-tissue reconstruction must be considered. This review presents a straightforward method for evaluating fingertip injuries and provides an algorithm for fingertip reconstruction.     

Clathrin Functions in the Absence of the Terminal Domain Binding Site for Adaptor-associated Clathrin-Box Motifs

Clathrin is involved in vesicle formation in the trans-Golgi network (TGN)/endosomal system and during endocytosis. Clathrin recruitment to membranes is mediated by the clathrin heavy chain (HC) N-terminal domain (TD), which forms a seven-bladed β-propeller. TD binds membrane-associated adaptors, which have short peptide motifs, either the clathrin-box (CBM) and/or the W-box; however, the importance of the TD binding sites for these motifs has not been tested in vivo. We investigated the importance of the TD in clathrin function by generating 1) mutations in the yeast HC gene (CHC1) to disrupt the binding sites for the CBM and W-box (chc1-box), and 2) four TD-specific temperature-sensitive alleles of CHC1. We found that TD is important for the retention of resident TGN enzymes and endocytosis of α-factor; however, the known adaptor binding sites are not necessary, because chc1-box caused little to no effect on trafficking pathways involving clathrin. The Chc1-box TD was able to interact with the endocytic adaptor Ent2 in a CBM-dependent manner, and HCs encoded by chc1-box formed clathrin-coated vesicles. These data suggest that additional or alternative binding sites exist on the TD propeller to help facilitate the recruitment of clathrin to sites of vesicle formation.