The relative importance of architecture and resource competition in allocation to pollen and ovule number within inflorescences of Hosta ventricosa varies with the resource pools

Background and Aims

Allocation of resources to floral traits often declines distally within inflorescences in flowering plants. Architecture and resource competition have been proposed as underlying mechanisms. The aim of the present study is to assess the relative importance of resource competition and architectural effects in pollen and ovule production on racemes of Hosta ventricosa, an apomictic perennial herb.

Methods

Combinations of two defoliation treatments (intact and defoliated) and two fruit-set treatments (no-fruit and fruit) were created, and the roles of architecture and resource competition at each resource level were assessed.

Key Results

Pollen and ovule number per flower increased after defoliation, but pollen to ovule ratio per flower did not change. Pollen, ovules and the pollen to ovule ratio per flower declined distally on racemes at each resource level. In the intact treatment, fruit development of early flowers did not affect either pollen or ovule number of late flowers. In the defoliated treatment, fruit development of early flowers reduced both pollen and ovule numbers of late flowers due to over-compensation caused by defoliation. Late flowers on defoliated fruit racemes produced less pollen than intact fruit racemes but the same number of ovules; therefore, the reduction in pollen number was not caused by over-compensation. In addition, the fruit-set rate of early flowers during flowering was higher in intact racemes than in defoliated racemes.

Conclusions

In flowering plants, the relative importance of architecture and resource competition in allocation to pollen and ovules may vary with the resource pools or the overall resource availability of maternal plants.     

Nxf3 is expressed in Sertoli cells, but is dispensable for spermatogenesis

In eukaryotes, mRNA is actively exported to the cytoplasm by a family of nuclear RNA export factors (NXF). Four Nxf genes have been identified in the mouse: Nxf1, Nxf2, Nxf3, and Nxf7. Inactivation of Nxf2, a germ cell-specific gene, causes defects in spermatogenesis. Here we report that Nxf3 is expressed exclusively in Sertoli cells of the postnatal testis, in a developmentally regulated manner. Expression of Nxf3 coincides with the cessation of Sertoli cell proliferation and the beginning of their differentiation. Continued expression of Nxf3 in mature Sertoli cells of the adult is spermatogenesis stage-independent. Nxf3 is not essential for spermatogenesis, however, suggesting functional redundancy among Nxf family members. With its unique expression pattern in the testis, the promoter of Nxf3 can be used to drive postnatal Sertoli cell-specific expression of other proteins such as Cre recombinase.     

Novel symmetric and asymmetric DNA scission determinants for Streptococcus pneumoniae topoisomerase IV and gyrase are clustered at the DNA breakage site

Topoisomerase (topo) IV and gyrase are bacterial type IIA DNA topoisomerases essential for DNA replication and chromosome segregation that act via a transient double-stranded DNA break involving a covalent enzyme-DNA "cleavage complex." Despite their mechanistic importance, the DNA breakage determinants are not understood for any bacterial type II enzyme. We investigated DNA cleavage by Streptococcus pneumoniae topo IV and gyrase stabilized by gemifloxacin and other antipneumococcal fluoroquinolones. Topo IV and gyrase induce distinct but overlapping repertoires of double-strand DNA breakage sites that were essentially identical for seven different quinolones and were augmented (in intensity) by positive or negative supercoiling. Sequence analysis of 180 topo IV and 126 gyrase sites promoted by gemifloxacin on pneumococcal DNA revealed the respective consensus sequences: G(G/c)(A/t)A*GNNCt(T/a)N(C/a) and GN4G(G/c)(A/c)G*GNNCtTN(C/a) (preferred bases are underlined; disfavored bases are in small capitals; N indicates no preference; and asterisk indicates DNA scission between -1 and +1 positions). Both enzymes show strong preferences for bases clustered symmetrically around the DNA scission site, i.e. +1G/+4C, -4G/+8C, and particularly the novel -2A/+6T, but with no preference at +2/+3 within the staggered 4-bp overhang. Asymmetric elements include -3G and several unfavored bases. These cleavage preferences, the first for Gram-positive type IIA topoisomerases, differ markedly from those reported for Escherichia coli topo IV (consensus (A/G)*T/A) and gyrase, which are based on fewer sites. However, both pneumococcal enzymes cleaved an E. coli gyrase site suggesting overlap in gyrase determinants. We propose a model for the cleavage complex of topo IV/gyrase that accommodates the unique -2A/+6T and other preferences.     

Natural and engineered biosynthesis of nucleoside antibiotics in Actinomycetes

Journal of Industrial Microbiology & Biotechnology - Nucleoside antibiotics constitute an important family of microbial natural products bearing diverse bioactivities and unusual structural...     

Inhibition of the Inositol Kinase Itpkb Augments Calcium Signaling in Lymphocytes and Reveals a Novel Strategy to Treat Autoimmune Disease

Emerging approaches to treat immune disorders target positive regulatory kinases downstream of antigen receptors with small molecule inhibitors. Here we provide evidence for an alternative approach in which inhibition of the negative regulatory inositol kinase Itpkb in mature T lymphocytes results in enhanced intracellular calcium levels following antigen receptor activation leading to T cell death. Using Itpkb conditional knockout mice and LMW Itpkb inhibitors these studies reveal that Itpkb through its product IP4 inhibits the Orai1/Stim1 calcium channel on lymphocytes. Pharmacological inhibition or genetic deletion of Itpkb results in elevated intracellular Ca²⁺ and induction of FasL and Bim resulting in T cell apoptosis. Deletion of Itpkb or treatment with Itpkb inhibitors blocks T-cell dependent antibody responses in vivo and prevents T cell driven arthritis in rats. These data identify Itpkb as an essential mediator of T cell activation and suggest Itpkb inhibition as a novel approach to treat autoimmune disease.     

Microencapsulation of Neuroblastoma Cells and Mesenchymal Stromal Cells in Collagen Microspheres: A 3D Model for Cancer Cell Niche Study

There is a growing trend for researchers to use in vitro 3D models in cancer studies, as they can better recapitulate the complex in vivo situation. And the fact that the progression and development of tumor are closely associated to its stromal microenvironment has been increasingly recognized. The establishment of such tumor supportive niche is vital in understanding tumor progress and metastasis. The mesenchymal origin of many cells residing in the cancer niche provides the rationale to include MSCs in mimicking the niche in neuroblastoma. Here we co-encapsulate and co-culture NBCs and MSCs in a 3D in vitro model and investigate the morphology, growth kinetics and matrix remodeling in the reconstituted stromal environment. Results showed that the incorporation of MSCs in the model lead to accelerated growth of cancer cells as well as recapitulation of at least partially the tumor microenvironment in vivo. The current study therefore demonstrates the feasibility for the collagen microsphere to act as a 3D in vitro cancer model for various topics in cancer studies.