Do Healthy Monarchs Migrate Farther? Tracking Natal Origins of Parasitized vs. Uninfected Monarch Butterflies Overwintering in Mexico

Long-distance migration can lower parasite prevalence if strenuous journeys remove infected animals from wild populations. We examined wild monarch butterflies (Danaus plexippus) to investigate the potential costs of the protozoan Ophryocystis elektroscirrha on migratory success. We collected monarchs from two wintering sites in central Mexico to compare infection status with hydrogen isotope (δ ²H) measurements as an indicator of latitude of origin at the start of fall migration. On average, uninfected monarchs had lower δ ²H values than parasitized butterflies, indicating that uninfected butterflies originated from more northerly latitudes and travelled farther distances to reach Mexico. Within the infected class, monarchs with higher quantitative spore loads originated from more southerly latitudes, indicating that heavily infected monarchs originating from farther north are less likely to reach Mexico. We ruled out the alternative explanation that lower latitudes give rise to more infected monarchs prior to the onset of migration using citizen science data to examine regional differences in parasite prevalence during the summer breeding season. We also found a positive association between monarch wing area and estimated distance flown. Collectively, these results emphasize that seasonal migrations can help lower infection levels in wild animal populations. Our findings, combined with recent declines in the numbers of migratory monarchs wintering in Mexico and observations of sedentary (winter breeding) monarch populations in the southern U.S., suggest that shifts from migratory to sedentary behavior will likely lead to greater infection prevalence for North American monarchs.     

Plant ontogenetic changes in vein and stomatal traits and their relationship with economic traits in leaves of three Mediterranean oaks

3种地中海橡树在叶脉和气孔性状上的个体发育性变化及其与叶片经济性状的关系 我们比较了3个地中海栎属(Quercus)树种幼苗和成龄树的叶脉和气孔性状。之前的研究表明,幼苗的气体交换率往往比成龄树的要高。我们的研究目标是确认叶脉和气孔的性状在整个植物个体发育过程中是否会随着气体交换率的变化而同步改变。我们提出了以下两个备选假设：幼苗比成龄树有着更高的叶脉和气孔密度(假设1);幼苗在维管组织上的投资更少,从而降低了建设成本(假设2)。本研究是在西班牙中西部进行的,我们对每个树种不同生长阶段的植株随机采集了10个样本。我们测量了气孔和叶脉的平均性状(单位叶面积里的气孔大小和数量、叶脉密度、叶脉体积、叶脉到表皮的距离),比叶质量和叶片厚度。研究结果表明,细脉密度和单位面积叶脉体积随着树龄的增加而增加,这似乎与气体交换率方面的个体发育趋势不一致。这种差异支持了我们的假设2,说明植株在幼苗阶段减少对维管组织的投资以最大限度地提高生长速度是其当务之急。幼苗叶片中较大的叶脉间距可以由叶脉到表皮的较短距离所补偿。因此,薄叶片可能是幼苗的一个必要性状,它可以让水分沿较短路径输送到蒸发点,而无需对高成本的维管组织进行大量投资。     

Assessment of Zoonotic Transmission of Giardia and Cryptosporidium between Cattle and Humans in Rural Villages in Bangladesh

Giardia and Cryptosporidium are important causes of diarrhoea in Bangladesh. The high prevalence of both parasites in humans and cattle in rural Bangladesh and the common use of water ponds by village inhabitants and their animals suggest a potential for zoonotic transmission. Direct transmission of Giardia and Cryptosporidium between cattle and their handlers and indirect transmission through water ponds was investigated. Faecal/stool samples were collected from 623 calves and 125 calf handlers in a cross-sectional survey. In two villages, water samples were collected monthly from water ponds and faecal/stool samples were collected monthly from inhabitants and their cattle. Giardia cysts and Cryptosporidium oocysts were detected in water samples and in faecal/stool samples and positive samples were genotyped, to determine their human or animal origin. The prevalence of Giardia and Cryptosporidium in calves was 22% and 5% respectively. In calf handlers, the prevalence of Giardia and Cryptosporidium was 11.2% and 3.2% respectively. Both in the cross-sectional survey and in the longitudinal study in the villages, G. duodenalis assemblage E was most prevalent in calves, while in humans assemblage AII, BIII and BIV were found. In cattle, Cryptosporidium parvum, C. bovis and C. andersoni were identified, but no Cryptosporidium sequences were obtained from humans. Giardia and Cryptosporidium were detected in 14/24 and 12/24 water samples respectively. G. duodenalis assemblage E and BIV (-like), as well as C. andersoni and C. hominis were identified. Although the presence of Giardia and Cryptosporidium in both water ponds suggests that water-borne transmission of Giardia and Cryptosporidium is possible, the genotyping results indicate that there is no significant direct or indirect (water-borne) transmission of Giardia between cattle and people in this area of rural Bangladesh. No conclusions could be drawn for Cryptosporidium, because of the low number of sequences that were obtained from human and water samples.     

Involvement of miRNAs in the Differentiation of Human Glioblastoma Multiforme Stem-Like Cells

Glioblastoma multiforme (GBM)-initiating cells (GICs) represent a tumor subpopulation with neural stem cell-like properties that is responsible for the development, progression and therapeutic resistance of human GBM. We have recently shown that blockade of NFκB pathway promotes terminal differentiation and senescence of GICs both in vitro and in vivo, indicating that induction of differentiation may be a potential therapeutic strategy for GBM. MicroRNAs have been implicated in the pathogenesis of GBM, but a high-throughput analysis of their role in GIC differentiation has not been reported. We have established human GIC cell lines that can be efficiently differentiated into cells expressing astrocytic and neuronal lineage markers. Using this in vitro system, a microarray-based high-throughput analysis to determine global expression changes of microRNAs during differentiation of GICs was performed. A number of changes in the levels of microRNAs were detected in differentiating GICs, including over-expression of hsa-miR-21, hsa-miR-29a, hsa-miR-29b, hsa-miR-221 and hsa-miR-222, and down-regulation of hsa-miR-93 and hsa-miR-106a. Functional studies showed that miR-21 over-expression in GICs induced comparable cell differentiation features and targeted SPRY1 mRNA, which encodes for a negative regulator of neural stem-cell differentiation. In addition, miR-221 and miR-222 inhibition in differentiated cells restored the expression of stem cell markers while reducing differentiation markers. Finally, miR-29a and miR-29b targeted MCL1 mRNA in GICs and increased apoptosis. Our study uncovers the microRNA dynamic expression changes occurring during differentiation of GICs, and identifies miR-21 and miR-221/222 as key regulators of this process.     

SV40 immortalizes myogenic cells: DNA synthesis and mitosis in differentiating myotubes

Primary skeletal muscle myoblasts have a limited proliferative capacity in cell culture and cease to proliferate after several passages. We examined the effects of several oncogenes on the immortalization and differentiation of primary cultures of rat skeletal muscle myoblasts. Retroviruses containing a SV40 large T antigen (LT) gene very efficiently immortalize myogenic cells. The immortalized cell lines retain a very high differentiation capacity and form, in the appropriate culture conditions, a very dense network of muscle fibers. As in primary culture, cell fusion is associated with the synthesis of large amounts of muscle-specific proteins. However, unlike normal myoblasts (and previously established myogenic cell lines), nuclei in the multinucleated fibers of SV40-immortalized cells synthesize DNA and enter mitosis. Thus, withdrawal from DNA synthesis is not obligatory for cell fusion and biochemical differentiation. Using a retrovirus coding for a temperature-sensitive SV40 LT, myogenic cell lines were produced in which the SV40 LT could be inactivated by a shift from 33 degrees C to 39 degrees C. The inactivation of LT induced massive cell fusion and synthesis of muscle proteins. The nuclei in those fibers did not synthesize DNA, nor did they undergo mitosis. This approach enabled the reproducible establishment of myogenic cell lines from very small populations of myoblasts or single primary myogenic clones. Activated p53 also readily immortalized cells in primary muscle cultures, however the cells of eight out of the nine cell lines isolated had a fibroblastic morphology and could not be induced to form multinucleated fibers.     

Landscape and Ecosystem-Level Controls on Net Carbon Dioxide Exchange along a Natural Moisture Gradient in Canadian Low Arctic Tundra

Our understanding of the controls and magnitudes of regional CO₂ exchanges in the Arctic are limited by uncertainties due to spatial heterogeneity in vegetation across the landscape and temporal variation in environmental conditions through the seasons. We measured daytime net ecosystem CO₂ exchange and each of its component fluxes in the three major tundra ecosystem-types that typically occur along natural moisture gradients in the Canadian Low Arctic biweekly during the full snow-free season of 2004. In addition, we used a plant-removal treatment to compare the contribution of bulk soil organic matter to total respiratory CO₂ loss among these ecosystems. Net CO₂ exchange rates varied strongly, but not consistently, among ecosystems in the spring and summer phases as a result of ecosystem-specific and differing responses of gross photosynthesis and respiration to temporal variation in environmental conditions. Overall, net carbon gain was largest in the wet sedge ecosystem and smallest in the dry heath. Our measures of CO₂ flux variation within each ecosystem were frequently most closely correlated with air or soil temperatures during each seasonal phase. Nevertheless, a particularly large rainfall event in early August rapidly decreased respiration rates and stimulated gross photosynthetic rates, resulting in peak rates of net carbon gain in all ecosystems. Finally, the bulk soil carbon contribution to total respiration was relatively high in the birch hummock ecosystem. Together, these results demonstrate that the relative influences of moisture and temperature as primary controls on daytime net ecosystem CO₂ exchange and its component fluxes differ in fundamental ways between the landscape and ecosystem scales. Furthermore, they strongly suggest that carbon cycling responses to environmental change are likely to be highly ecosystem-specific, and thus to vary substantially across the low arctic landscape. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.