Biomedical subjects

E van der Meijden

Publications and source records attributed to E van der Meijden.

7 recordsLinked to original sources

PubMed2005

Herbivory and abiotic factors affect population dynamics of Arabidopsis thaliana in a sand dune area.

Population dynamics of the annual plant Arabidopsis thaliana (L.) Heynh. were studied in a natural habitat of this species on the coastal dunes of the Netherlands. The main objective was to elucidate factors controlling population dynamics and the relative importance of factors affecting final population density. Permanent plots were established and plants were mapped to obtain data on survival and reproductive performance of each individual, with special attention to herbivore damage. In experimental plots we studied how watering, addition of nutrients, artificial disturbance, and natural herbivores affected survival and growth. Mortality was low during autumn and early winter and high at the time of stem elongation, between February and April. A key factor analysis showed a high correlation between mortality from February to April and total mortality. The specialist weevils Ceutorhyncus atomus and C. contractus (Curculionidae) were identified as the major insect herbivores on A. thaliana, reducing seed production by more than 40 %. These herbivores acted in a plant size-dependent manner, attacking a greater fraction of the fruits on large plants. While mortality rates were not affected by density, fecundity decreased with density, although the effect was small. Adding water reduced mortality in rosette and flowering plant stages. Soil disturbance did not increase seed germination, but did have a significant positive effect on survival of rosette and flowering plants. Seed production of A. thaliana populations varied greatly between years, leading to population fluctuations, with a small role for density-dependent fecundity and plant size-dependent herbivory.

Animals↗

PubMed2004

Sex ratio of some long-lived dioecious plants in a sand dune area.

In dioecious plants the fraction of males among flowering plants in the field (the secondary sex ratio) is the result of the fraction of males in the seeds (the primary sex ratio) and the subsequent survival and age at first reproduction of the two genders. It has been assumed that survival and age at first reproduction are the main determinants of biased secondary sex ratio but, especially for long-lived perennials, few data are available. We address this issue for natural populations of four long-lived perennials in a dune area. In Asparagus officinale and Bryonia dioica, the secondary sex ratio was unbiased. In Salix repens the secondary sex ratio was female-biased (0.337). Hippophae rhamnoides populations were male-biased; the average sex ratio of flowering plants was 0.658, while the fraction of males varied between 0.39 near the sea to 0.84 at the inland side of the dunes. The primary sex ratio was estimated by germinating seeds and growing plants under favourable conditions with minimal mortality. In S. repens the primary sex ratio in seeds was variable among mother plants and was, on average, female-biased (0.289). This is close to the secondary sex ratio, suggesting that the female bias already originates in the seed stage. In Hippophae rhamnoides the primary sex ratio was slightly male-biased (0.564). We argue that in this species, apart from the primary sex ratio, higher mortality and a later age at first reproduction for females contribute to the strong male bias among flowering plants in the field.

Asparagus Plant↗

PubMed2003

Contrasting dynamics in the same plant-herbivore interaction.

Long-term studies of two-species interactions under field conditions are unusual; most long-term field studies are of single species dynamics (1-6). Concurrent long-term studies on the dynamics of the same two interacting species in different locations are very rare. This result has led to the tacit assumption that different cases of the same two-species interaction would involve essentially quantitative differences (e.g., context-specific differences in the numeric values of demographic parameters like fecundity or death rates). Here, we show that for one of the best-known two-species systems (ragwort and cinnabar moth), this finding does not hold. The interaction between the plant and its herbivore is fundamentally different in coastal dunes in The Netherlands and in grasslands in Southeast England. In the first case, the dynamics are cyclic and the interaction involves both direct and delayed density dependence; in the second case, the insect has little impact on plant dynamics and there are no time lags in density dependence. The difference is caused by differences in the importance of seed-limitation in plant recruitment in the two locations.

Animals↗

PubMed2001

Inhibition of human papillomavirus-16 long control region activity by interferon-gamma overcome by p300 overexpression.

Although interferons (IFNs) are currently used in the treatment of various human papillomavirus (HPV)-associated lesions, their mechanisms of action are still unclear. In this study, we clearly demonstrated that IFN-gamma was a strong inhibitor of HPV-16 long control region (LCR) activity in two human cervical carcinoma cell lines. The effect of IFN-gamma was dose dependent. We investigated whether the effect of IFN-gamma on HPV-16 LCR could involve the inhibition of the CREB-binding protein (CBP)/p300 family of transcriptional coactivators. In support of this model, we demonstrated by transfection experiments that a 12S E1A mutant (RG2), which interacts poorly with p300 and CBP in comparison to wild-type E1A, was less able to repress human papillomavirus (HPV) 16 long control region (LCR) than wild-type E1A. More important, overexpression of p300 was able to increase the HPV-16 LCR activity and to overcome inhibition by IFN-gamma. Finally, we demonstrated that p300 could cooperate with c-jun to activate HPV-16 LCR. According to our results, IFN-gamma might inhibit HPV-16 LCR transcription by activating the signal transducer and activator of transcription 1alpha, which in turn might compete for p300/CBP binding with specific transcription factors involved in LCR activation.

Adenovirus E1A Proteins↗

PubMed2000

A functional NF-kappaB binding site in the human papillomavirus type 16 long control region.

By computer search, we identified one potential NF-kappaB binding site in the HPV16 long control region (LCR) at position 7554-7563 having two mismatches in comparison to the consensus NF-kappaB binding site of the Igkappa L promoter. Bandshift experiments with nuclear extracts from HeLa cells or purified glutathione S-transferase-p65 fusion protein clearly demonstrated that NF-kappaB is able to bind to this region of the LCR. However, in comparison to NF-kappaB binding on a consensus probe, the affinity of NF-kappaB for this site is about 250-fold reduced. When mutations were introduced into this NF-kappaB binding site, the activity of the LCR was increased, strongly suggesting that NF-kappaB was acting as a transcriptional repressor in the context of the HPV16 LCR. In addition, overexpression of NF-kappaB p65 repressed the activity of the HPV16 LCR, strengthening this conclusion.

Base Sequence↗

PubMed2000

Transcriptional regulation of human papillomavirus type 16 LCR by different C/EBPbeta isoforms.

During genital human papillomavirus (HPV) infection several cytokines are released, such as interleukin-1 (IL-1), tumor necrosis factoralpha (TNFalpha), IL-6, and IL-8. These cytokines may play a role in the immune surveillance against viral infection. Two of these cytokines, IL-1 and TNFalpha, suppress the transcription of the HPV16 early genes. CAATT/ enhancer binding protein, (C/EBPbeta), which is activated by IL-1 and TNFalpha, has been suggested to act as a mediator of this transcriptional downregulation. C/EBPbeta contains three different translation initiation sites that can lead probably by leaky ribosome scanning to the generation of three isoforms of C/EBPbeta, namely full-length C/EBPbeta, liver enriched transcriptional activator protein (LAP), and liver enriched inhibitory protein (LIP). When transiently expressed in C33A and HeLa cells, the first two C/EBPbeta isoforms activate the HPV16 long control region (LCR). LIP, which acts as an antagonist of C/EBPbeta, represses the HPV16 LCR activity. Our observation that treatment of HeLa cells with IL-1 leads to induction of LIP supports the hypothesis that the LCR downregulation by IL-1 is mediated by LIP.

CCAAT-Enhancer-Binding Proteins↗

PubMed1999

Evolutionary dynamics of seed size and seedling competitive ability.

We present a model for the evolutionary dynamics of seed size when there is a trade-off between seed size and seed number, and seedlings from large seeds are better competitors and have a higher precompetitive survival than seedlings from small seeds. We find that strong competitive asymmetry, high resource levels, and intermediate harshness of the precompetitive environment favor coexistence of plants with different seed sizes. If the evolution of seed size is mutation-limited and single mutations have only a small phenotypic effect, then an initially monomorphic population reaches the final evolutionarily stable polymorphic state through one or more discrete evolutionary branching events. At each such branching event, a given lineage already present in the population divides into two phenotypically diverging daughter lines, each with its own seed size. If the precompetitive survival of seeds and seedlings is high for small and large seeds alike, however, evolutionary branching may be followed by the extinction of one or more lineages. Various results presented here are model-independent and point the way to a more general evolutionary bifurcation theory describing how the number and stability properties of evolutionary equilibria may change as a consequence of changes in model parameters.

Biological Evolution↗