Protein kinase Akt2/PKBβ is involved in blastomere proliferation of preimplantation mouse embryos

Activation of Akt/Protein Kinase B (PKB) by phosphatidylinositol-3-kinase (PI3K) controls several cellular functions largely studied in mammalian cells, including preimplantation embryos. We previously showed that early mouse embryos inherit active Akt from oocytes and that the intracellular localization of this enzyme at the two-cell stage depends on the T-cell leukemia/lymphoma 1 oncogenic protein, Tcl1. We have now investigated whether Akt isoforms, namely Akt1, Akt2 and Akt3, exert a specific role in blastomere proliferation during preimplantation embryo development. We show that, in contrast to other Akt family members, Akt2 enters male and female pronuclei of mouse preimplantation embryos at the late one-cell stage and thereafter maintains a nuclear localization during later embryo cleavage stages. Depleting one-cell embryos of single Akt family members by microinjecting Akt isoform-specific antibodies into wild-type zygotes, we observed that: (a) Akt2 is necessary for normal embryo progression through cleavage stages; and (b) the specific nuclear targeting of Akt2 in two-cell embryos depends on Tcl1. Our results indicate that preimplantation mouse embryos have a peculiar regulation of blastomere proliferation based on the activity of the Akt/PKB family member Akt2, which is mediated by the oncogenic protein Tcl1. Both Akt2 and Tcl1 are essential for early blastomere proliferation and embryo development.     

Malaria Parasite-Infected Erythrocytes Secrete PfCK1, the Plasmodium Homologue of the Pleiotropic Protein Kinase Casein Kinase 1

Casein kinase 1 (CK1) is a pleiotropic protein kinase implicated in several fundamental processes of eukaryotic cell biology. Plasmodium falciparum encodes a single CK1 isoform, PfCK1, that is expressed at all stages of the parasite’s life cycle. We have previously shown that the pfck1 gene cannot be disrupted, but that the locus can be modified if no loss-of-function is incurred, suggesting an important role for this kinase in intra-erythrocytic asexual proliferation. Here, we report on the use of parasite lines expressing GFP- or His-tagged PfCK1 from the endogenous locus to investigate (i) the dynamics of PfCK1 localisation during the asexual cycle in red blood cells, and (ii) potential interactors of PfCK1, so as to gain insight into the involvement of the enzyme in specific cellular processes. Immunofluorescence analysis reveals a dynamic localisation of PfCK1, with evidence for a pool of the enzyme being directed to the membrane of the host erythrocyte in the early stages of infection, followed by a predominantly intra-parasite localisation in trophozoites and schizonts and association with micronemes in merozoites. Furthermore, we present strong evidence that a pool of enzymatically active PfCK1 is secreted into the culture supernatant, demonstrating that PfCK1 is an ectokinase. Our interactome experiments and ensuing kinase assays using recombinant PfCK1 to phosphorylate putative interactors in vitro suggest an involvement of PfCK1 in many cellular processes such as mRNA splicing, protein trafficking, ribosomal, and host cell invasion.     

Localization of Phenolic Compounds in the Covering Tissues of the Embryo of Brassica napus (L.) during Different Stages of Embryogenesis and Seed Maturation

During embryogenesis and maturation of an embryo the tissuescovering it produce phenolic compounds the localization of whichchanges during maturation of the embryo. In the ovary containinga globular embryo, phenolics are located in the epidermis ofthe integumentum externum and the innermost layer of the integumentuminternum. In the ovule at the stage at which heart- and torpedo-shapedembryos are present, phenolic compounds are visible in the stellarcells, the innermost cells of the integumentum internum andthe endosperm. In hard, green seeds, after the integumentuminternum and layers over the stellar cells gradually disappear,the remaining tissue contains cell walls impregnated with phenolics.Mature, black seeds contain only one distinct layer of cells—stellarcells, which, like the other compressed cell walls, are impregnatedwith phenolics. In this way they constitute a barrier betweenthe embryo and its environment.Copyright 1994, 1999 AcademicPress Brassica napus, seed coat, integumentum, phenolic compounds     

Vertical plankton transport due to self-induced convection

The slightly increased density of Chlorella over that of purewater is shown to be capable of driving convective water motionswhich lead to very efficient vertical transport.     

Tomato genetic resources and activities in Poland

The vegetables germplasm conservation programme in Poland was started in 1982, activities under this program resulted up to this date in building up a tomato germplasm collection of 782 accessions that are available for distribution to breeders and researchers in Poland and abroad. Between 1990 and 1999 we distributed 651 tomato seed samples to breeders and scientists in Poland, and 95 samples to users abroad. During 1990 – 1999 the 652 tomato accessions were evaluated for 43 traits of plants and fruits. Work is in progress to expand the collection and identify useful characteristics of the collected material, and to make use of them in breeding and other research works.     

Phosphorus-mediated changes in life history traits of the invasive New Zealand mudsnail (Potamopyrgus antipodarum)

The longer soil has to stay moist to allow germination the more likely that seedlings experience favourable moisture conditions. Since theory predicts that fitness variance-reducing traits will be negatively correlated, we tested the hypothesis that time to germination is negatively correlated with the ability of radicle growth to keep up with the drying front. We measured time to germination and root elongation rate (RER) in 14 Kalahari annuals. We controlled for habitat (canopy association and sand content), germinability, median base water potential for germination (ψ ₅₀), seed mass and seed shape as a persistence surrogate. For species and phylogenetically independent contrasts (PICs), we did not find a relationship between time to germination and RER. However, we found a negative relationship of time to germination with RER for PICs when controlling for sand content and ψ ₅₀. Seed shape increased with time to germination which can be explained by reduced opportunities for germination in slow-germinating species that select for persistence. We found a positive relationship between time to germination and ψ ₅₀, suggesting a continuum of risky to cautious germination. ψ ₅₀ was not correlated with RER suggesting that variation in ψ ₅₀ reflects different drought-adapted traits. Probably the relationship of time to germination with RER is not mediated by seed mass, which was not correlated with time to germination as found by others, though RER was positively correlated with seed mass. Instead of the seed size-seed number trade-off, a trade-off with resource capture may explain variation in RER: more root hairs or rootlets may increase resource capturing surface while reducing RER. For habitat, we found a (positive) relationship with time to germination only for canopy association. This may be explained by maximization of resource capture at the expense of RER being favoured by the higher nutrient and water availability under canopies. Future studies should clarify which trade-offs govern variation in time to germination, focussing on a possible resource capture-RER trade-off.     

Transcontinental Phylogeography of the Daphnia pulex Species Complex

Daphnia pulex is quickly becoming an attractive model species in the field of ecological genomics due to the recent release of its complete genome sequence, a wide variety of new genomic resources, and a rich history of ecological data. Sequences of the mitochondrial NADH dehydrogenase subunit 5 and cytochrome c oxidase subunit 1 genes were used to assess the global phylogeography of this species, and to further elucidate its phylogenetic relationship to other members of the Daphnia pulex species complex. Using both newly acquired and previously published data, we analyzed 398 individuals from collections spanning five continents. Eleven strongly supported lineages were found within the D. pulex complex, and one lineage in particular, panarctic D. pulex, has very little phylogeographical structure and a near worldwide distribution. Mismatch distribution, haplotype network, and population genetic analyses are compatible with a North American origin for this lineage and subsequent spatial expansion in the Late Pleistocene. In addition, our analyses suggest that dispersal between North and South America of this and other species in the D. pulex complex has occurred multiple times, and is predominantly from north to south. Our results provide additional support for the evolutionary relationships of the eleven main mitochondrial lineages of the D. pulex complex. We found that the well-studied panarctic D. pulex is present on every continent except Australia and Antarctica. Despite being geographically very widespread, there is a lack of strong regionalism in the mitochondrial genomes of panarctic D. pulex – a pattern that differs from that of most studied cladocerans. Moreover, our analyses suggest recent expansion of the panarctic D. pulex lineage, with some continents sharing haplotypes. The hypothesis that hybrid asexuality has contributed to the recent and unusual geographic success of the panarctic D. pulex lineage warrants further study.     

Serosa membrane plays a key role in transferring vitellin polypeptides to the perivitelline fluid in insect embryos

In mid-embryogenesis, the stick insect Carausius morosus comes to be comprised of three distinct districts: the embryo proper, the yolk sac and the perivitelline fluid. A monolayered epithelium, the so-called serosa membrane, encloses the yolk sac and its content of vitellophages and large yolk granules. During embryonic development, the yolk sac declines gradually in protein concentration due to Vt polypeptides undergoing limited proteolysis to yield a number of Vt cleavage products of lower molecular weights. mAbs 1D1 and 5H11 are monoclonal antibodies raised against some of the Vt cleavage products generated by this process in the yolk sac. At the confocal microscope, antibody fluorescence is initially associated with a few yolk granules, while it is gradually displaced in the cytosolic spaces of the vitellophages. With the proceeding of embryonic development, label appears also in the serosa membrane in the form of clustered dots. At the ultrastructural level, gold particles are initially associated with the vitellophages that are labeled on a few yolk granules and in the cytosolic space flanking the yolk granules. Subsequently, the serosa cells become labeled on vesicles close to the yolk granules or just underneath the plasma membrane. Inside the serosa cells, label is also associated with granules budding from the Golgi apparatus, but never with the intercellular channels percolating the serosa membrane. These observations are interpreted as indicating that Vt cleavage products leak out from the yolk granules into the cytosolic spaces of the vitellophages and are eventually transferred to the perivitelline fluid via transcytosis through the serosa cells.     

Antifungal sordarins. Synthesis and structure-activity relationships of 3'-O-substituted derivatives.

A number of novel 3'-O-acyl and alkyl sordarins were synthesised for structure-activity relationship studies. Many of these derivatives exhibit high activity against Candida albicans, Candida pseudotropicalis, Candida tropicalis and Cryptococcus neoformans.