Showing 231 - 240 of 274 Items
Functional redundancy of a non-native foundation species (eelgrass, Zostera japonica) across intertidal stress gradients
Date: 2023-01-01
Creator: S. Maria Garcia
Access: Open access
- Non-native species foundation species can alter ecosystems in both positive and negative ways. The creation of habitat can be beneficial to native species when they provide a limiting resource or in a stressful environment. Yet this creation of habitat can also be detrimental by replacing native species and/or facilitating the presence of more non-native species. In Willapa Bay, WA, a non-native foundation species, Zostera japonica, co-exists with the native foundation species Zostera marina. Zostera japonica persists at the higher intertidal in monocultures, the two species overlap in the mid intertidal, and Z. marina persists in monocultures in the low intertidal. Epifaunal invertebrates, the organisms that live on eelgrass blades, connect eelgrass to higher trophic levels. Through a series of transplants and removals, I used this zonation pattern to ask if the two species can fulfill a similar functional role in respect to epifaunal invertebrates (functional redundancy), and if this was due to the identity of the foundation species or a response to the stress gradient of the intertidal. My results suggest that the epifaunal invertebrate community is responding more to the physiological stress gradient, and the functional redundancy of the two species depends on the location they are found. Z. japonica is expanding the range of vegetated habitat into to the physiologically stressful high zone, which supports a different community. This experiment highlights that the impacts of non- native species are highly localized and that abiotic and biotic factors are important to trophic interactions.
Fitness and sex effects of a novel microsporidian parasite on its Daphnia host
Date: 2025-01-01
Creator: Gracie Scheve
Access: Open access
- Parasitism can influence host ecology and evolution in powerful ways, although the specific impacts on host fitness and life history may be context dependent and involve complex trade-offs. In this study, I investigated the effects of a novel microsporidian gut parasite on Daphnia ambigua, a freshwater zooplankton with a cyclical parthenogenetic life cycle. Combining extensive field sampling at Sewall Pond, Maine, with chronic exposure experiments in the lab, I assessed the parasite's impact on Daphnia fitness and propensity to shift from asexual to sexual reproduction. Field observations revealed a correlation between gut parasite prevalence and increased production of males and sexual females, independent of known sex inducers such as crowding, food limitation, and photoperiod. Lab experiments confirmed that chronic spore exposure significantly reduced Daphnia survival and reproductive output, particularly in clones previously naïve to this strain of the parasite. However, no induction of sex or male offspring was observed in response to parasite exposure under laboratory conditions. This suggests that more complex environmental interactions might be triggering sex in Daphnia. While sex provides the benefit of increased genetic diversity for future generations, I hypothesize that while Daphnia undergo sexual reproduction their ability to resist or tolerate parasite infection is diminished. Phylogenetic analyses indicate the parasite is closely related to the less virulent microsporidian Ordospora pajunii but genetically distinct, potentially constituting a new species or genus. These findings provide insight into the ecological and evolutionary tradeoffs involved in host-parasite interactions and introduce a new host-parasite system for this study.
Building (Cellular) Barriers: Identifying cellularization dynamics involving somatic Xchromosome eliminations in Bradysia coprophila embryonic development This record is embargoed.
Date: 2025-01-01
Creator: Aale J. Agans
Access: Permanent restriction
Modulation of migratory and breeding phenologies by Maine’s common loons (Gavia immer) in response to climate conditions Access to this record is restricted to members of the Bowdoin community. Log in here to view.
Date: 2025-01-01
Creator: Henry Grant Marriott
Access: Access restricted to the Bowdoin Community
Identification of methylated proteins in the yeast small ribosomal subunit: A role for SPOUT methyltransferases in protein arginine methylation
Date: 2012-06-26
Creator: Brian D. Young, David I. Weiss, Cecilia I. Zurita-Lopez, Kristofor J. Webb, Steven G., Clarke, Anne E. McBride
Access: Open access
- We have characterized the posttranslational methylation of Rps2, Rps3, and Rps27a, three small ribosomal subunit proteins in the yeast Saccharomyces cerevisiae, using mass spectrometry and amino acid analysis. We found that Rps2 is substoichiometrically modified at arginine-10 by the Rmt1 methyltransferase. We demonstrated that Rps3 is stoichiometrically modified by ω- monomethylation at arginine-146 by mass spectrometric and site-directed mutagenic analyses. Substitution of alanine for arginine at position 146 is associated with slow cell growth, suggesting that the amino acid identity at this site may influence ribosomal function and/or biogenesis. Analysis of the three-dimensional structure of Rps3 in S. cerevisiae shows that arginine-146 makes contacts with the small subunit rRNA. Screening of deletion mutants encoding potential yeast methyltransferases revealed that the loss of the YOR021C gene results in the absence of methylation of Rps3. We demonstrated that recombinant Yor021c catalyzes ω-monomethylarginine formation when incubated with S-adenosylmethionine and hypomethylated ribosomes prepared from a YOR021C deletion strain. Interestingly, Yor021c belongs to the family of SPOUT methyltransferases that, to date, have only been shown to modify RNA substrates. Our findings suggest a wider role for SPOUT methyltransferases in nature. Finally, we have demonstrated the presence of a stoichiometrically methylated cysteine residue at position 39 of Rps27a in a zinc-cysteine cluster. The discovery of these three novel sites of protein modification within the small ribosomal subunit will now allow for an analysis of their functional roles in translation and possibly other cellular processes. © 2012 American Chemical Society.
Specific sequences within arginine-glycine-rich domains affect mRNA-binding protein function
Date: 2009-08-05
Creator: Anne E. McBride, Ana K. Conboy, Shanique P. Brown, Chaiyaboot Ariyachet, Kate L., Rutledge
Access: Open access
- The discovery of roles for arginine methylation in intracellular transport and mRNA splicing has focused attention on the methylated arginine-glycine (RG)-rich domains found in many eukaryotic RNA-binding proteins. Sequence similarity among these highly repetitive RG domains, combined with interactions between RG-rich proteins, raises the question of whether these regions are general interaction motifs or whether there is specificity within these domains. Using the essential Saccharomyces cerevisiae mRNA-binding protein Npl3 (ScNpl3) as a model system, we first tested the importance of the RG domain for protein function. While Npl3 lacking the RG domain could not support growth of cells lacking Npl3, surprisingly, expression of the RG domain alone supported partial growth of these cells. To address the specificity of this domain, we created chimeric forms of ScNpl3 with RG-rich domains of S. cerevisiae nucleolar proteins, Gar1 and Nop1 (ScGar1, ScNop1), or of the Candida albicans Npl3 ortholog (CaNpl3). Whereas the CaNpl3 RG chimeric protein retained nearly wild-type function in S. cerevisiae, the ScGar1 and ScNop1 RG domains significantly reduced Npl3 function and self-association, indicating RG domain specificity. Nuclear localization of Npl3 also requires specific RG sequences, yet heterologous RG domains allow similar modulation of Npl3 transport by arginine methylation.
Protein arginine methylation in Candida albicans: Role in nuclear transport
Date: 2007-07-01
Creator: Anne E. McBride, Cecilia Zurita-Lopez, Anthony Regis, Emily Blum, Ana, Conboy, Shannon Elf, Steven Clarke
Access: Open access
- Protein arginine methylation plays a key role in numerous eukaryotic processes, such as protein transport and signal transduction. In Candida albicans, two candidate protein arginine methyltransferases (PRMTs) have been identified from the genome sequencing project. Based on sequence comparison, C. albicans candidate PRMTs display similarity to Saccharomyces cerevisiae Hmt1 and Rmt2. Here we demonstrate functional homology of Hmt1 between C. albicans and S. cerevisiae: CaHmt1 supports growth of S. cerevisiae strains that require Hmt1, and CaHmt1 methylates Npl3, a major Hmt1 substrate, in S. cerevisiae. In C. albicans strains lacking CaHmt1, asymmetric dimethylarginine and ω-monomethylarginine levels are significantly decreased, indicating that Hmt1 is the major C. albicans type I PRMT1. Given the known effects of type I PRMTs on nuclear transport of RNA-binding proteins, we tested whether Hmt1 affects nuclear transport of a putative Npl3 ortholog in C. albicans. CaNpl3 allows partial growth of S. cerevisiae npl3Δ strains, but its arginine-glycine-rich C terminus can fully substitute for that of ScNpl3 and also directs methylation-sensitive association with ScNpl3. Expression of green fluorescent protein-tagged CaNpl3 proteins in C. albicans strains with and without CaHmt1 provides evidence for CaHmt1 facilitating export of CaNpl3 in this fungus. We have also identified the C. albicans Rmt2, a type IV fungus- and plant-specific PRMT, by amino acid analysis of an rmt2Δ/rmt2Δ strain, as well as biochemical evidence for additional cryptic PRMTs. Copyright © 2007, American Society for Microbiology. All Rights Reserved.
Human protein Sam68 relocalization and interaction with poliovirus RNA polymerase in infected cells
Date: 1996-03-19
Creator: A. E. Mcbride, A. Schlegel, K. Kirkegaard
Access: Open access
- A HeLa cDNA expression library was screened for human polypeptides that interacted with the poliovirus RNA-dependent RNA polymerase, 3D, using the two-hybrid system in the yeast Saccharomyces cerevisiae. Sam68 (Src- associated in mitosis, 68 kDa) emerged as the human cDNA that, when fused to a transcriptional activation domain, gave the strongest 3D interaction signal with a LexA-3D hybrid protein. 3D polymerase and Sam68 coimmunoprecipitated from infected human cell lysates with antibodies that recognized either protein. Upon poliovirus infection. Sam68 relocalized from the nucleus to the cytoplasm, where poliovirus replication occurs. Sam68 was isolated from infected cell lysates with an antibody that recognizes poliovirus protein 2C, suggesting that it is found on poliovirus-induced membranes upon which viral RNA synthesis occurs. These data, in combination with the known RNA- and protein-binding properties of Sam68, make Sam68 a strong candidate for a host protein with a functional role in poliovirus replication.
Xanthophyll cycle activity in two prominent arctic shrub species
Date: 2017-01-01
Creator: T.S. Magney, B.A. Logan, J.S. Reblin, N.T. Boelman, J.U.H., Eitel, H.E. Greaves, K.L. Griffin, C.M. Prager, L.A. Vierling
Access: Open access
Live imaging and biophysical modeling support a button-based mechanism of somatic homolog pairing in Drosophila
Date: 2021-06-01
Creator: Myron Child, Jack R. Bateman, Amir Jahangiri, Armando Reimer, Nicholas C., Lammers, Nica Sabouni, Diego Villamarin, Grace C. McKenzie-Smith, Justine E. Johnson, Daniel Jost, Hernan G. Garcia
Access: Open access
- 3D eukaryotic genome organization provides the structural basis for gene regulation. In Drosophila melanogaster, genome folding is characterized by somatic homolog pairing, where homologous chromosomes are intimately paired from end to end; however, how homologs identify one another and pair has remained mysterious. Recently, this process has been proposed to be driven by specifically interacting “buttons” encoded along chromosomes. Here, we turned this hypothesis into a quantitative biophysical model to demonstrate that a button-based mechanism can lead to chromosome-wide pairing. We tested our model using live-imaging measurements of chromosomal loci tagged with the MS2 and PP7 nascent RNA labeling systems. We show solid agreement between model predictions and experiments in the pairing dynamics of individual homologous loci. Our results strongly support a button-based mechanism of somatic homolog pairing in Drosophila and provide a theoretical framework for revealing the molecular identity and regulation of buttons.