Phenological behavior of the tree Elaeagia uxpanapensis (Rubiaceae), in a premontane rain forest of Costa Rica

Phenology of the tree Elaeagia uxpanapensis was studied from March 1994 to March 1998. This species is a canopy emergent in the A.M. Brenes Biological Reserve, Alajuela, Costa Rica. Fifteen mature trees were marked in order of appearance and observed every month using bionculars. A platform was built on one three better distinguished the transition from flowering to fruiting. Leaf abscission and budding were continuous throughout the year with several peaks, while flowering and fruit production occurred every 28 and 25 months, respectively. Leaf-fall was positively correlated with a ir temperature (n = 13, r = 0.44, p < 0.05), and fruiting with precipitation (n = 13, r = 0.37, p < 0.05) and relative humidity (n = 13, r = 0.44, p < 0.05). Bud formation was in inversely associated with precipitation (n = 13, r = 0.66 p < 0.05) and relative humidity ( n = 13, r = 0.61, p < 0.05).     

Internalization of factor J and cellular signalization after factor J-cell interaction

Factor J (FJ) is a cationic glycoprotein with inhibitory activity in vitro against both classical and alternative pathways of complement activation. Recently FJ has been implicated in adhesion to several cell lines, through a membrane receptor identified as nucleolin. In the present work we study the events that follow the binding of FJ to cells. After incubation of K562 with FJ, this protein was internalized actively and localized in the cytoplasm and nucleus. Adhesion to immobilized FJ induced tyrosine phosphorylation of several intracellular proteins in Jurkat cell line with a similar pattern to that induced by fibronectin (FN), an extracellular matrix protein. This effect was maximal at 5 min and decreased after 10 min, and inhibited by anti-FJ monoclonal antibody (mAb). These results suggest that the binding of FJ to cells may play an important role in transduction of biochemical signals across the plasma membrane to the cell interior.     

Up-regulation of IL-12 in monocytes: a fundamental defect in common variable immunodeficiency

We show that LPS-stimulated circulating CD14-positive monocytes from patients with common variable immunodeficiency (CVID) express a higher proportion of intracellular IL-12-positive cells than monocytes from patients with X-linked agammaglobulinemia or normal subjects. We used four-color flow cytometry and measured IL-12 with an Ab to the p40 subunit following stimulation with LPS. The raised IL-12 is associated with an increased frequency of IFN-gamma-positive T cells, but not of IFN-gamma-positive CD56+ NK cells. These increases in frequency of cytokine-positive cells are due to a decrease in the absolute numbers of circulating monocytes and T cells that are negative for IL-12 and IFN-gamma, respectively. The increased frequency of IL-12-positive monocytes appears to be selective because TNF-alpha was not increased, and is thus unlikely to reflect a general activation. Chronic infection is also unlikely to explain our data since cells from X-linked agammaglobulinemia patients with a similar Ig deficiency do not show these changes. Our data suggest a fundamental abnormality in the IL-12/IFN-gamma circuit in CVID, with up-regulation of IL-12 being the "primary" factor. This imbalance is likely to skew the immune response away from Ab production and also explains the failure of CVID T cells to make Ag-specific memory cells and the chronic inflammatory and granulomatous complications that are a feature of CVID. This disease appears to be a rare example of a polarized Th1-type response and may in part be due to a genetic defect in the control of IL-12 production.     

Expression of Hoxa2 in rhombomere 4 is regulated by a conserved cross-regulatory mechanism dependent upon Hoxb1

The Hoxa2 gene is an important component of regulatory events during hindbrain segmentation and head development in vertebrates. In this study we have used sequenced comparisons of the Hoxa2 locus from 12 vertebrate species in combination with detailed regulatory analyses in mouse and chicken embryos to characterize the mechanistic basis for the regulation of Hoxa2 in rhombomere (r) 4. A highly conserved region in the Hoxa2 intron functions as an r4 enhancer. In vitro binding studies demonstrate that within the conserved region three bipartite Hox/Pbx binding sites (PH1-PH3) in combination with a single binding site for Pbx-Prep/Meis (PM) heterodimers co-operate to regulate enhancer activity in r4. Mutational analysis reveals that these sites are required for activity of the enhancer, suggesting that the r4 enhancer from Hoxa2 functions in vivo as a Hox-response module in combination with the Hox cofactors, Pbx and Prep/Meis. Furthermore, this r4 enhancer is capable of mediating a response to ectopic HOXB1 expression in the hindbrain. These findings reveal that Hoxa2 is a target gene of Hoxb1 and permit us to develop a gene regulatory network for r4, whereby Hoxa2, along with Hoxb1, Hoxb2 and Hoxa1, is integrated into a series of auto- and cross-regulatory loops between Hox genes. These data highlight the important role played by direct cross-talk between Hox genes in regulating hindbrain patterning.     

Pristine but metal-rich Río Sucio (Dirty River) is dominated by Gallionella and other iron-sulfur oxidizing microbes

Whether the extreme conditions of acidity and heavy metal pollution of streams and rivers originating in pyritic formations are caused primarily by mining activities or by natural activities of metal-oxidizing microbes living within the geological formations is a subject of considerable controversy. Most microbiological studies of such waters have so far focused on acid mine drainage sites, which are heavily human-impacted environments, so it has been problematic to eliminate the human factor in the question of the origin of the key metal compounds. We have studied the physico-chemistry and microbiology of the Río Sucio in the Braulio Carrillo National Park of Costa Rica, 22 km from its volcanic rock origin. Neither the remote origin, nor the length of the river to the sampling site, have experienced human activity and are thus pristine. The river water had a characteristic brownish-yellow color due to high iron-dominated minerals, was slightly acidic, and rich in chemolithoautotrophic iron- and sulfur-oxidizing bacteria, dominated by Gallionella spp. Río Sucio is thus a natural acid-rock drainage system whose metal-containing components are derived primarily from microbial activities.

     

Temporal genetic stability in natural populations of the waterflea Daphnia magna in response to strong selection pressure

Studies monitoring changes in genetic diversity and composition through time allow a unique understanding of evolutionary dynamics and persistence of natural populations. However, such studies are often limited to species with short generation times that can be propagated in the laboratory or few exceptional cases in the wild. Species that produce dormant stages provide powerful models for the reconstruction of evolutionary dynamics in the natural environment. A remaining open question is to what extent dormant egg banks are an unbiased representation of populations and hence of the species’ evolutionary potential, especially in the presence of strong environmental selection. We address this key question using the water flea Daphnia magna, which produces dormant stages that accumulate in biological archives over time. We assess temporal genetic stability in three biological archives, previously used in resurrection ecology studies showing adaptive evolutionary responses to rapid environmental change. We show that neutral genetic diversity does not decline with the age of the population and it is maintained in the presence of strong selection. In addition, by comparing temporal genetic stability in hatched and unhatched populations from the same biological archive, we show that dormant egg banks can be consulted to obtain a reliable measure of genetic diversity over time, at least in the multidecadal time frame studied here. The stability of neutral genetic diversity through time is likely mediated by the buffering effect of the resting egg bank.     

Possible influence of ramets on the population structure and distribution of the giant tree Warszewiczia uxpanapensis, Tilarán Mountain Range, Costa Rica

The distribution and population structure of Warszewiczia (=Elaeagia) uxpanapensis, a tree that reaches a height of 45 m, a DBH of 1.40 m and 8 m tall buttresses, was studied on two 1-ha plots of premontane pluvial forest. It had a frequency of 49 % and a mean dominance of 6.5 %. The adult distribution was random (mean distance to the nearest neighboring tree in plot 1, it was 14.26 m, n = 15; Clark-Evans Index (IC-E) = 1.07; in plot 2, it was 15.33 m, n = 18, IC-E = 1.34,). The seedlings represented 60.3 % of the sampled population (plot 1, n = 94; plot 2, n = 85). This species has a very high capability of propagating itself vegetatively through clones ("ramets"), which influence its distribution and population structure. With a ramet density in plot 1 of 0.8 and in plot 2 of 0.3/100 m2, its propagation could be from fallen trees or branches (which also create clearings in the forest) or from standing trees and even live branches that produce adventitious roots.     

Hoxb1 enhancer and control of rhombomere 4 expression: complex interplay between PREP1-PBX1-HOXB1 binding sites

The Hoxb1 autoregulatory enhancer directs segmental expression in vertebrate hindbrain. Three conserved repeats (R1, R2, and R3) in the enhancer have been described as Pbx-Hoxb1 (PH) binding sites, and one Pbx-Meinox (PM) binding site has also been characterized. We have investigated the importance and relative roles of PH and PM binding sites with respect to protein interactions and in vivo regulatory activity. We have identified a new PM site (PM2) and found that it cooperates with the R3 PH site to form ternary Prep1-Pbx1-Hoxb1 complexes. In vivo, the combination of the R3 and PM2 sites is sufficient to mediate transgenic reporter activity in the developing chick hindbrain. In both chicken and mouse transgenic embryos, mutations of the PM1 and PM2 sites reveal that they cooperate to modulate in vivo regulatory activity of the Hoxb1 enhancer. Furthermore, we have shown that the R2 motif functions as a strong PM site, with a high binding affinity for Prep1-Pbx1 dimers, and renamed this site R2/PM3. In vitro R2/PM3, when combined with the PM1 and R3 motifs, inhibits ternary complex formation mediated by these elements and in vivo reduces and restricts reporter expression in transgenic embryos. These inhibitory effects appear to be a consequence of the high PM binding activity of the R2/PM3 site. Taken together, our results demonstrate that the activity of the Hoxb1 autoregulatory enhancer depends upon multiple Prep1-Pbx1 (PM1, PM2, and PM3) and Pbx1-Hoxb1 (R1 and R3) binding sites that cooperate to modulate and spatially restrict the expression of Hoxb1 in r4 rhombomere.     

Adrenalectomy does not change CRF secretion induced by interleukin-1 from rat perifused hypothalami.

Interleukin-1 (IL-1) is a potent hypothalamic-pituitary-adrenal (H-P-A) axis activator. The hypothalamus is considered one of the main sites of action of IL-1 on the H-P-A axis, inducing CRF secretion, which is modulated by glucocorticoids. Glucocorticoids, which modulate CRF release by a negative feedback inhibition, have been postulated to exert a permissive action on the IL-1 effect on CRF secretion. Using a continuous perifusion system of rat hypothalami, the results of the present study indicate that at the same concentrations, IL-1 beta exerted a more potent effect than IL-1 alpha stimulating CRF secretion. The increase in hypothalamic CRF release induced by IL-1 was rapidly inhibited by both dexamethasone and corticosterone. However, adrenalectomy 2 or 8 days before did not modify CRF secretion induced by IL-1 from the in vitro perifused hypothalami. These data indicate that IL-1 does not seem to induce CRF secretion by interfering with an impeding action of glucocorticoids, although the cytokine effect is negatively modulated by corticosteroids.