Showing 31 - 40 of 257 Items
Lake water chemistry and local adaptation shape NaCl toxicity in Daphnia ambigua
Date: 2024-01-01
Creator: Mary Alta Rogalski, Elizabeth S Baker, Clara M Benadon
Access: Open access
- Increasing application of road deicing agents (e.g., NaCl) has caused widespread salinization of freshwater environments. Chronic exposure to toxic NaCl levels can impact freshwater biota at genome to ecosystem scales, yet the degree of harm caused by road salt pollution is likely to vary among habitats and populations. The background ion chemistry of freshwater environments may strongly impact NaCl toxicity, with greater harm occurring in ion-poor, soft water conditions. In addition, populations exposed to salinization may evolve increased NaCl tolerance. Notably, if organisms are adapted to their natal lake water chemistry, toxicity responses may also vary among populations in a given test medium. We examined how this evolutionary and environmental context may interact in shaping NaCl toxicity with a pair of laboratory reciprocal transplant toxicity experiments, using natural populations of the water flea Daphnia ambigua from three lakes differing in ion availability. The lake water environment strongly influenced NaCl toxicity in both trials. NaCl greatly reduced reproduction and r in lake water from a low-ion/ calcium-poor environment compared with water from both a calcium-rich lake and an ion-rich coastal lake. Daphnia from this coastal lake were most robust to the effects of NaCl. A significant population x environment interaction shaped survival in both trials, suggesting that local adaptation to the test waters used contributed to toxicity responses. Our findings that the lake water environment, adaptation to that environment, and adaptation to a focal contaminant may shape toxicity demonstrate the importance of considering environmental and biological complexity in mitigating pollution impacts.
Genetic interactions of yeast eukaryotic translation initiation factor 5a (eIF5A) reveal connections to poly(A)-binding protein and protein kinase C signaling
Date: 2002-03-14
Creator: Sandro R. Valentini, Jason M. Casolari, Carla C. Oliveira, Pamela A. Silver, Anne E., McBride
Access: Open access
- The highly conserved eukaryotic translation initiation factor eIF5A has been proposed to have various roles in the cell, from translation to mRNA decay to nuclear protein export. To further our understanding of this essential protein, three temperature-sensitive alleles of the yeast TIF51A gene have been characterized. Two mutant eIF5A proteins contain mutations in a proline residue at the junction between the two eIFSA domains and the third, strongest allele encodes a protein with a single mutation in each domain, both of which are required for the growth defect. The stronger tif51A alleles cause defects in degradation of short-lived mRNAs, supporting a role for this protein in mRNA decay. A multicopy suppressor screen revealed six genes, the overexpression of which allows growth of a tif51A-1 strain at high temperature; these genes include PAB1, PKC1, and PKC1 regulators WSC1, WSC2, and WSC3. Further results suggest that eIFSA may also be involved in ribosomal synthesis and the WSC/PKC1 signaling pathway for cell wall integrity or related processes.
Arginine methyltransferase affects interactions and recruitment of mRNA processing and export factors
Date: 2004-08-15
Creator: Michael C. Yu, François Bachand, Anne E. McBride, Suzanne Komili, Jason M., Casolari, Pamela A. Silver
Access: Open access
- Hmt1 is the major type I arginine methyltransferase in the yeast Saccharomyces cerevisiae and facilitates the nucleocytoplasmic transport of mRNA-binding proteins through their methylation. Here we demonstrate that Hmt1 is recruited during the beginning of the transcriptional elongation process. Hmt1 methylates Yra1 and Hrp1, two mRNA-binding proteins important for mRNA processing and export. Moreover, loss of Hmt1 affects interactions between mRNA-binding proteins and Tho2, a component of the TREX (transcription/export) complex that is important for transcriptional elongation and recruitment of mRNA export factors. Furthermore, RNA in situ hybridization analysis demonstrates that loss of Hmt1 results in slowed release of HSP104 mRNA from the sites of transcription. Genome-wide location analysis shows that Hmt1 is bound to specific functional gene classes, many of which are also bound by Tho2 and other mRNA-processing factors. These data suggest a model whereby Hmt1 affects transcriptional elongation and, as a result, influences recruitment of RNA-processing factors.
Data associated with Walter-McNeill et al. (2021) Oecologia https://doi.org/10.1007/s00442-021-05038-y
Date: 2021-01-01
Creator: Barry Logan
Access: Open access
Bilateral consequences of chronic unilateral deafferentation in the auditory system of the cricket gryllus bimaculatus
Date: 2011-04-01
Creator: Hadley Wilson Horch, Elizabeth Sheldon, Claire C. Cutting, Claire R. Williams, Dana M., Riker, Hannah R. Peckler, Rohit B. Sangal
Access: Open access
- The auditory system of the cricket has the unusual ability to respond to deafferentation by compensatory growth and synapse formation. Auditory interneurons such as ascending neuron 2 (AN-2) in the cricket Gryllus bimaculatus possess a dendritic arbor that normally grows up to, but not over, the midline of the prothoracic ganglion. After chronic deafferentation throughout larval development, however, the AN-2 dendritic arbor changes dramatically, and medial dendrites sprout across the midline where they form compensatory synapses with the auditory afferents from the contralateral ear. We quantified the extent of the effects of chronic, unilateral deafferentation by measuring several cellular parameters of 3 different neuronal components of the auditory system: the deafferented AN-2, the contralateral (or nondeafferented) AN-2 and the contralateral auditory afferents. Neuronal tracers and confocal microscopy were used to visualize neurons, and double-label experiments were performed to examine the cellular relationship between pairs of cells. Dendritic complexity was quantified using a modified Sholl analysis, and the length and volume of processes and presynaptic varicosities were assessed under control and deafferented conditions. Chronic deafferentation significantly influenced the morphology of all 3 neuronal components examined. The overall dendritic complexity of the deafferented AN-2 dendritic arbor was reduced, while both the contralateral AN-2 dendritic arbor and the remaining, intact, auditory afferents grew longer. We found no significant changes in the volume or density of varicosities after deafferentation. These complex cellular changes after deafferentation are interpreted in the light of the reported differential regulation of vesicle-associated membrane protein and semaphorin 2a. Copyright © 2011 S. Karger AG, Basel.
Hedgehog signaling regulates dental papilla formation and tooth size during zebrafish odontogenesis
Date: 2015-04-01
Creator: Jeffrey C. Yu, Zachary D. Fox, James L. Crimp, Hana E. Littleford, Andrea L., Jowdry, William R. Jackman
Access: Open access
- Intercellular communication by the hedgehog cell signaling pathway is necessary for tooth development throughout the vertebrates, but it remains unclear which specific developmental signals control cell behavior at different stages of odontogenesis. To address this issue, we have manipulated hedgehog activity during zebrafish tooth development and visualized the results using confocal microscopy. Results: We first established that reporter lines for dlx2b, fli1, NF-κB, and prdm1a are markers for specific subsets of tooth germ tissues. We then blocked hedgehog signaling with cyclopamine and observed a reduction or elimination of the cranial neural crest derived dental papilla, which normally contains the cells that later give rise to dentin-producing odontoblasts. Upon further investigation, we observed that the dental papilla begins to form and then regresses in the absence of hedgehog signaling, through a mechanism unrelated to cell proliferation or apoptosis. We also found evidence of an isometric reduction in tooth size that correlates with the time of earliest hedgehog inhibition. Conclusions: We hypothesize that these results reveal a previously uncharacterized function of hedgehog signaling during tooth morphogenesis, regulating the number of cells in the dental papilla and thereby controlling tooth size.
Evolution of the interaction between Hox genes and a downstream target
Date: 1998-05-07
Creator: Michael F. Palopoli, Nipam H. Patel
Access: Open access
- Segmental identifies along the insect body depend on the activities of Hox genes [1,2]. In Drosophila melanogaster, one well-studied Hox regulatory target is Distal-less (DII), which Is required for the development of distel limb structures [3]. In abdominal segments, DII transcription is prevented when Hox proteins of the Bithorax Complex (BX-C) bind to cis-regulatory elements upstream of the DII transcription start site [4,5]. Previous evolutionary comparisons of gene expression patterns suggest that this direct repression is conserved between Diptera and Lepidoptera, but is absent in the Crustacea [6,7]. We examined gene expression patterns in three orders of hexapods, all of which develop abdominal appendages, in order to determine when the strong repressive interaction between BX-C proteins and DII appeared during evolution. In each of the species examined, DII expression was initiated in abdominal cells despite the presence of high levels of BX-C proteins. It appears that the strong repressive effects of BX-C proteins on DII expression arose relatively late in insect evolution. We suggest that the regulatory interaction between the BX-C genes and DII has evolved within the hexapods in a complex, segment-specific manner.
Are melanized feather barbs stronger?
Date: 2004-01-01
Creator: Michael Butler, Amy S. Johnson
Access: Open access
- Melanin has been associated with increased resistance to abrasion, decreased wear and lowered barb breakage in feathers. But, this association was inferred without considering barb position along the rachis as a potentially confounding variable. We examined the cross-sectional area, breaking force, breaking stress, breaking strain and toughness of melanized and unmelanized barbs along the entire rachis of a primary feather from an osprey (Pandion haliaetus). Although breaking force was higher for melanized barbs, breaking stress (force divided by cross-sectional area) was greater for unmelanized barbs. But when position was considered, all mechanical differences between melanized and unmelanized barbs disappeared. Barb breaking stress, breaking strain and toughness decreased, and breaking stiffness increased, distally along the rachis. These proximal-distal material property changes are small and seem unlikely to affect flight performance of barbs. Our observations of barb bending, breaking and morphology, however, lead us to propose a design principle for barbs. We propose that, by being thicker-walled dorso-ventrally, the barb's flexural stiffness is increased during flight; but, by allowing for twisting when loaded with dangerously high forces, barbs firstly avoid failure by bending and secondly avoid complete failure by buckling rather than rupturing.
Consequences of a flattened morphology: effects of flow on feeding rates of the scleractinian coral Meandrina meandrites
Date: 1993-01-01
Creator: A. S. Johnson, K. P. Sebens
Access: Open access
- Per polyp feeding rate was independent of the horizontal planform area of colonies. At the lowest velocities, most particles were captured on the upstream edge or in the middle of colonies, but all positional bias in capture rate disappeared at higher velocities. Particle capture and increasing flow speed were negatively associated. There were small, but measurable, differences in mean tentacle length between corals feeding at different velocities. Velocity-dependent feeding rate at most velocities was thus related to changes in flow rather than to changes in feeding behavior. Experiments in which corals were turned upside down revealed that the increased capture rate for rightside-up corals feeding at low velocity could be almost entirely accounted for by gravitational deposition of particles on the corals' tentacles. The tentacles form a canopy within which water movement was slowed, possibly facilitating gravitational deposition of non-buoyant or sinking food particles. -from Authors
Chloroplasts of Arabidopsis thaliana homozygous for the ch-1 locus lack chlorophyll b, lack stable LHCPII and have stacked thylakoids
Date: 1991-07-01
Creator: David L. Murray, Bruce D. Kohorn
Access: Open access