Pollen and gene flow in fragmented habitats

Abstract. Habitat fragmentation affects both plants and pollinators. Habitat fragmentation leads to changes in species richness, population number and size, density, and shape, thus to changes in the spatial arrangement of flowers. These changes influence the amount of food for flower-visiting insects and the quantity and quality of pollinations. Seed set in small populations is often reduced and genetic variation is expected but not always found to be low. The majority of studies show that low flower densities have reduced pollination success and higher inbreeding. Density effects are stronger than size effects. Most studies concluded that species richness in flower-visiting insects is directly related to richness in plant species. However, the consequences of low insect species richness for pollination are not always clear, depending on the studied pollinator-plant relationship. The effects of the presence of simultaneously flowering species are highly dependent on the circumstances and may range from competition to facilitation. Other flowering plant species may play a role as stepping stones or corridor in the connection between populations. In the absence of stepping stones even short distances between populations act as strong barriers for gene flow. We illustrate the present review paper with own data collected for three plant species, rare in The Netherlands: Phyteuma spicatum ssp. nigrum (Campanulaceae), Salvia pratensis (Labiatae) and Scabiosa columbaria (Dipsacaceae). The species differ in their breeding systems and in the assemblage of visitor species. Data are shown on the effects of population size on species richness with consequences for seed set. Effects of flower density and isolation on pollen exchange are given. Since plant reproduction depends on the behaviour of individual insects and not on the overall behaviour of the species, the examples all point to individual insects and extrapolate to effects at the species level.     

Specific Labeling of Stem Cell Activity in Human Colorectal Organoids Using an ASCL2-Responsive Minigene

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Allogeneic Non-Adherent Bone Marrow Cells Facilitate Hematopoietic Recovery but Do Not Lead to Allogeneic Engraftment

Background

Non adherent bone marrow derived cells (NA-BMCs) have recently been described to give rise to multiple mesenchymal phenotypes and have an impact in tissue regeneration. Therefore, the effects of murine bone marrow derived NA-BMCs were investigated with regard to engraftment capacities in allogeneic and syngeneic stem cell transplantation using transgenic, human CD4⁺, murine CD4^−/−, HLA-DR3⁺ mice.

Methodology/Principal Findings

Bone marrow cells were harvested from C57Bl/6 and Balb/c wild-type mice, expanded to NA-BMCs for 4 days and characterized by flow cytometry before transplantation in lethally irradiated recipient mice. Chimerism was detected using flow cytometry for MHC-I (H-2D[b], H-2K[d]), mu/huCD4, and huHLA-DR3). Culturing of bone marrow cells in a dexamethasone containing DMEM medium induced expansion of non adherent cells expressing CD11b, CD45, and CD90. Analysis of the CD45⁺ showed depletion of CD4⁺, CD8⁺, CD19⁺, and CD117⁺ cells. Expanded syngeneic and allogeneic NA-BMCs were transplanted into triple transgenic mice. Syngeneic NA-BMCs protected 83% of mice from death (n = 8, CD4⁺ donor chimerism of 5.8±2.4% [day 40], P<.001). Allogeneic NA-BMCs preserved 62.5% (n = 8) of mice from death without detectable hematopoietic donor chimerism. Transplantation of syngeneic bone marrow cells preserved 100%, transplantation of allogeneic bone marrow cells 33% of mice from death.

Conclusions/Significance

NA-BMCs triggered endogenous hematopoiesis and induced faster recovery compared to bone marrow controls. These findings may be of relevance in the refinement of strategies in the treatment of hematological malignancies.     

Novel nuclear and mitochondrial glycosylases revealed by disruption of the mouse Nth1 gene encoding an endonuclease III homolog for repair of thymine glycols

Endonuclease III, encoded by nth in Escherichia coli, removes thymine glycols (Tg), a toxic oxidative DNA lesion. To determine the biological significance of this repair in mammals, we established a mouse model with mutated mNth1, a homolog of nth, by gene targeting. The homozygous mNth1 mutant mice showed no detectable phenotypical abnormality. Embryonic cells with or without wild-type mNth1 showed no difference in sensitivity to menadione or hydrogen peroxide. Tg produced in the mutant mouse liver DNA by X-ray irradiation disappeared with time, though more slowly than in the wild-type mouse. In extracts from mutant mouse liver, we found, instead of mNTH1 activity, at least two novel DNA glycosylase activities against Tg. One activity is significantly higher in the mutant than in wild-type mouse in mitochondria, while the other is another nuclear glycosylase for Tg. These results underscore the importance of base excision repair of Tg both in the nuclei and mitochondria in mammals.     

Nest preference of laying hens (Gallus gallus domesticus) and their motivation to exert themselves to gain nest access

In connection with the development of a test method for the attractiveness and appropriateness of nests for laying hens, we carried out an investigation by using a preference test and motivation measuring with the help of push doors. Hens were offered two different nest sites either consisting of a tray filled with wood shavings (litter tray) or a wooden nest box plus wood shavings (nest box). Hens were individually housed in pens (2.0 m × 2.0 m) and had free access to the nest sites until they laid their 15th egg. From that day the hens had to overcome a push door to reach the nest sites. Resistance for entrance was also increased stepwise at the door leading to the hens’ nest. The experiment ended when a hen stopped to lay in her usual nest site for four consecutive days (postexperimental period). The behaviour during the last hour before oviposition was video taped at a level of resistance of 3.5, 6.0, 7.5 and 10.0 N.The hens were categorized into nest and litter layers depending on nest choice. All but one hen pushed maximum resistances between 11.5 and 18.0 N with no differences between nest and litter layers. Behaviour did not significantly change with increasing levels of resistance, but there were significant differences between nest and litter layers. Nest layers spent more time nesting than litter layers while the latter showed a strong tendency to more exploring behaviour. For litter layers, more entries through the push door leading to their nest site and more unsuccessful pushes were detected than for nest layers. According to our results, two types of layers could be distinguished whereas the two were equally motivated to access their nest site.     

Precise and economic FIB/SEM for CLEM: with 2 nm voxels through mitosis

A portfolio is presented documenting economic, high-resolution correlative focused ion beam scanning electron microscopy (FIB/SEM) in routine, comprising: (i) the use of custom-labeled slides and coverslips, (ii) embedding of cells in thin, or ultra-thin resin layers for correlative light and electron microscopy (CLEM) and (iii) the claim to reach the highest resolution possible with FIB/SEM in xyz. Regions of interest (ROIs) defined in light microscope (LM), can be relocated quickly and precisely in SEM. As proof of principle, HeLa cells were investigated in 3D context at all stages of the cell cycle, documenting ultrastructural changes during mitosis: nuclear envelope breakdown and reassembly, Golgi degradation and reconstitution and the formation of the midzone and midbody.     

TLR2 and TLR7 mediate distinct immunopathological and antiviral plasmacytoid dendritic cell responses to SARS‐CoV‐2 infection

Understanding the molecular pathways driving the acute antiviral and inflammatory response to SARS‐CoV‐2 infection is critical for developing treatments for severe COVID‐19. Here, we find decreasing number of circulating plasmacytoid dendritic cells (pDCs) in COVID‐19 patients early after symptom onset, correlating with disease severity. pDC depletion is transient and coincides with decreased expression of antiviral type I IFNα and of systemic inflammatory cytokines CXCL10 and IL‐6. Using an in vitro stem cell‐based human pDC model, we further demonstrate that pDCs, while not supporting SARS‐CoV‐2 replication, directly sense the virus and in response produce multiple antiviral (interferons: IFNα and IFNλ1) and inflammatory (IL‐6, IL‐8, CXCL10) cytokines that protect epithelial cells from de novo SARS‐CoV‐2 infection. Via targeted deletion of virus‐recognition innate immune pathways, we identify TLR7‐MyD88 signaling as crucial for production of antiviral interferons (IFNs), whereas Toll‐like receptor (TLR)2 is responsible for the inflammatory IL‐6 response. We further show that SARS‐CoV‐2 engages the receptor neuropilin‐1 on pDCs to selectively mitigate the antiviral interferon response, but not the IL‐6 response, suggesting neuropilin‐1 as potential therapeutic target for stimulation of TLR7‐mediated antiviral protection.