Publications by authors named "Robert J Scott"

7 Publications

  • Page 1 of 1

Virus shedding kinetics and unconventional virulence tradeoffs.

PLoS Pathog 2021 May 10;17(5):e1009528. Epub 2021 May 10.

Department of Biology, University of Washington, Seattle, Washington, United States of America.

Tradeoff theory, which postulates that virulence provides both transmission costs and benefits for pathogens, has become widely adopted by the scientific community. Although theoretical literature exploring virulence-tradeoffs is vast, empirical studies validating various assumptions still remain sparse. In particular, truncation of transmission duration as a cost of virulence has been difficult to quantify with robust controlled in vivo studies. We sought to fill this knowledge gap by investigating how transmission rate and duration were associated with virulence for infectious hematopoietic necrosis virus (IHNV) in rainbow trout (Oncorhynchus mykiss). Using host mortality to quantify virulence and viral shedding to quantify transmission, we found that IHNV did not conform to classical tradeoff theory. More virulent genotypes of the virus were found to have longer transmission durations due to lower recovery rates of infected hosts, but the relationship was not saturating as assumed by tradeoff theory. Furthermore, the impact of host mortality on limiting transmission duration was minimal and greatly outweighed by recovery. Transmission rate differences between high and low virulence genotypes were also small and inconsistent. Ultimately, more virulent genotypes were found to have the overall fitness advantage, and there was no apparent constraint on the evolution of increased virulence for IHNV. However, using a mathematical model parameterized with experimental data, it was found that host culling resurrected the virulence tradeoff and provided low virulence genotypes with the advantage. Human-induced or natural culling, as well as host population fragmentation, may be some of the mechanisms by which virulence diversity is maintained in nature. This work highlights the importance of considering non-classical virulence tradeoffs.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1371/journal.ppat.1009528DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8109835PMC
May 2021

Replication and shedding kinetics of infectious hematopoietic necrosis virus in juvenile rainbow trout.

Virus Res 2017 01 19;227:200-211. Epub 2016 Oct 19.

USGS Western Fisheries Research Center, 6505 NE 65th St., Seattle, WA 98115, United States.

Viral replication and shedding are key components of transmission and fitness, the kinetics of which are heavily dependent on virus, host, and environmental factors. To date, no studies have quantified the shedding kinetics of infectious hematopoietic necrosis virus (IHNV) in rainbow trout (Oncorhynchus mykiss), or how they are associated with replication, making it difficult to ascertain the transmission dynamics of this pathogen of high agricultural and conservation importance. Here, the replication and shedding kinetics of two M genogroup IHNV genotypes were examined in their naturally co-evolved rainbow trout host. Within host virus replication began rapidly, approaching maximum values by day 3 post-infection, after which viral load was maintained or gradually dropped through day 7. Host innate immune response measured as stimulation of Mx-1 gene expression generally followed within host viral loads. Shedding also began very quickly and peaked within 2days, defining a generally uniform early peak period of shedding from 1 to 4days after exposure to virus. This was followed by a post-peak period where shedding declined, such that the majority of fish were no longer shedding by day 12 post-infection. Despite similar kinetics, the average shedding rate over the course of infection was significantly lower in mixed compared to single genotype infections, suggesting a competition effect, however, this did not significantly impact the total amount of virus shed. The data also indicated that the duration of shedding, rather than peak amount of virus shed, was correlated with fish mortality. Generally, the majority of virus produced during infection appeared to be shed into the environment rather than maintained in the host, although there was more retention of within host virus during the post-peak period. Viral virulence was correlated with shedding, such that the more virulent of the two genotypes shed more total virus. This fundamental understanding of IHNV shedding kinetics and variation at the individual fish level could assist with management decisions about how to respond to disease outbreaks when they occur.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.virusres.2016.10.011DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5206995PMC
January 2017

Analysis of host genetic diversity and viral entry as sources of between-host variation in viral load.

Virus Res 2012 Apr 30;165(1):71-80. Epub 2012 Jan 30.

U.S. Geological Survey, Western Fisheries Research Center, 6505 NE 65th Street, Seattle, WA 98115-5016, USA.

Little is known about the factors that drive the high levels of between-host variation in pathogen burden that are frequently observed in viral infections. Here, two factors thought to impact viral load variability, host genetic diversity and stochastic processes linked with viral entry into the host, were examined. This work was conducted with the aquatic vertebrate virus, Infectious hematopoietic necrosis virus (IHNV), in its natural host, rainbow trout. It was found that in controlled in vivo infections of IHNV, a suggestive trend of reduced between-fish viral load variation was observed in a clonal population of isogenic trout compared to a genetically diverse population of out-bred trout. However, this trend was not statistically significant for any of the four viral genotypes examined, and high levels of fish-to-fish variation persisted even in the isogenic trout population. A decrease in fish-to-fish viral load variation was also observed in virus injection challenges that bypassed the host entry step, compared to fish exposed to the virus through the natural water-borne immersion route of infection. This trend was significant for three of the four virus genotypes examined and suggests host entry may play a role in viral load variability. However, high levels of viral load variation also remained in the injection challenges. Together, these results indicate that although host genetic diversity and viral entry may play some role in between-fish viral load variation, they are not major factors. Other biological and non-biological parameters that may influence viral load variation are discussed.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.virusres.2012.01.010DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3314121PMC
April 2012

A role for the karyopherin Kap123p in microtubule stability.

Traffic 2009 Nov 22;10(11):1619-34. Epub 2009 Aug 22.

Department of Cell Biology, University of Alberta, Edmonton, AB T6G 2H7 Canada.

Several components of the nuclear transport machinery play a role in mitotic spindle assembly in higher eukaryotes. To further investigate the role of this family of proteins in microtubule function, we screened for mutations in Saccharomyces cerevisiae that confer sensitivity to microtubule-destabilizing drugs. One mutant exhibiting this phenotype lacked the gene encoding the karyopherin Kap123p. Analysis of kap123Delta cells revealed that the drug sensitivity was caused by a defect in microtubule stability and/or assembly. In support of this idea, we demonstrated genetic interactions between the kap123Delta mutation and mutated alleles of genes encoding alpha-tubulins and factors controlling microtubule dynamics. Moreover, kap123Delta cells exhibit defects in spindle structure and dynamics as well as nuclear positioning defects during mitosis. Cultures of kap123Delta strains are enriched for mononucleated large-budded cells often containing short spindles and nuclei positioned away from the budneck, phenotypes indicative of defects in both cytoplasmic and nuclear microtubules. Finally, we identified a gene, CAJ1, which when deleted in combination with KAP123 exacerbated the microtubule-related defects of the kap123Delta mutants. We propose that Kap123p and Caj1p, a member of the Hsp40 family of proteins, together play an essential role in normal microtubule function.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/j.1600-0854.2009.00978.xDOI Listing
November 2009

The nuclear export factor Xpo1p targets Mad1p to kinetochores in yeast.

J Cell Biol 2009 Jan;184(1):21-9

Department of Cell Biology, University of Alberta, Edmonton, Alberta, Canada.

Nuclear pore complexes (NPCs) mediate all nucleocytoplasmic traffic and provide docking sites for the spindle assembly checkpoint (SAC) protein Mad1p. Upon SAC activation, Mad1p is recruited onto kinetochores and rapidly cycles between NPCs and kinetochores. We examined the mechanism of Mad1p movement onto kinetochores and show that it is controlled by two components of the nuclear transport machinery, the exportin Xpo1p and Ran-guanosine triphosphate (GTP). Mad1p contains a nuclear export signal (NES) that is recognized by Xpo1p. The NES, Xpo1p, and RanGTP are all required for Mad1p recruitment onto kinetochores in checkpoint-activated cells. Consistent with this function, Xpo1p also accumulates on kinetochores after SAC activation. We have also shown that Xpo1p and RanGTP are required for the dynamic cycling of Mad1p between NPCs and kinetochores in checkpoint-arrested cells. These results reveal an important function for Xpo1p in mediating intranuclear transport events and identify a signaling pathway between kinetochores and NPCs.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1083/jcb.200804098DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2615093PMC
January 2009

Interactions between Mad1p and the nuclear transport machinery in the yeast Saccharomyces cerevisiae.

Mol Biol Cell 2005 Sep 6;16(9):4362-74. Epub 2005 Jul 6.

Department of Cell Biology, University of Alberta, Edmonton, Alberta, Canada, T6G 2H7.

In addition to its role in nucleocytoplasmic transport, the nuclear pore complex (NPC) acts as a docking site for proteins whose apparent primary cellular functions are unrelated to nuclear transport, including Mad1p and Mad2p, two proteins of the spindle assembly checkpoint (SAC) machinery. To understand this relationship, we have mapped domains of yeast Saccharomyces cerevisiae Mad1p that interact with the nuclear transport machinery, including further defining its interactions with the NPC. We showed that a Kap95p/Kap60p-dependent nuclear localization signal, positioned in the C-terminal third of Mad1p, is required for its efficient targeting to the NPC. At the NPC, Mad1p interacts with Nup53p and a presumed Nup60p/Mlp1p/Mlp2p complex through two coiled coil regions within its N terminus. When the SAC is activated, a portion of Mad1p is recruited to kinetochores through an interaction that is mediated by the C-terminal region of Mad1p and requires energy. We showed using photobleaching analysis that in nocodazole-arrested cells Mad1p rapidly cycles between the Mlp proteins and kinetochores. Our further analysis also showed that only the C terminus of Mad1p is required for SAC function and that the NPC, through Nup53p, may act to regulate the duration of the SAC response.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1091/mbc.e05-01-0011DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1196344PMC
September 2005

The yeast nuclear pore complex functionally interacts with components of the spindle assembly checkpoint.

J Cell Biol 2002 Dec 9;159(5):807-19. Epub 2002 Dec 9.

Department of Cell Biology, University of Alberta, Edmonton, Alberta, T6G 2H7 Canada.

Aphysical and functional link between the nuclear pore complex (NPC) and the spindle checkpoint machinery has been established in the yeast Saccharomyces cerevisiae. We show that two proteins required for the execution of the spindle checkpoint, Mad1p and Mad2p, reside predominantly at the NPC throughout the cell cycle. There they are associated with a subcomplex of nucleoporins containing Nup53p, Nup170p, and Nup157p. The association of the Mad1p-Mad2p complex with the NPC requires Mad1p and is mediated in part by Nup53p. On activation of the spindle checkpoint, we detect changes in the interactions between these proteins, including the release of Mad2p (but not Mad1p) from the NPC and the accumulation of Mad2p at kinetochores. Accompanying these events is the Nup53p-dependent hyperphosphorylation of Mad1p. On the basis of these results and genetic analysis of double mutants, we propose a model in which Mad1p bound to a Nup53p-containing complex sequesters Mad2p at the NPC until its release by activation of the spindle checkpoint. Furthermore, we show that the association of Mad1p with the NPC is not passive and that it plays a role in nuclear transport.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1083/jcb.200205068DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2173375PMC
December 2002