Characterization of Avian Leukosis Virus Evolution in Culture.
infection in vivo is characterized by rapid population turnover that, when coupled with
a high mutation rate, allows the virus to quickly adapt to the immune system and
antiretroviral therapy. To date, all known antiretroviral therapy has been met with the
emergence of drug resitance mutations causing therapy to fail. The large number of
infected cells imply that drug resistant ... read moremutations might preexist in the population and
predictions of the emergence or clearance of mutations should be modeled
deterministically. The effective population size, a population genetics concept that
accounts for factors that make a population more or less sensitive to genetic drift, may
be much smaller than the census population size for HIV infections. Directly measuring
the effective population size of HIV infection is difficult given the complexities of
natural infections. We developed a simple tissue culture system to examine the
relationship between the census population size and effective population size of an
evolving retrovirus population. We initiated competition experiments between wild-type
ALV subgroup B virus (WT) and two previously described mutants, LS and LSTI, which were
found to confer a host range extension phenotype [Rainey et al., 2003,Taplitz and
Coffin, 1997]. We developed a measure for genetic drift in these cultures by initiating
replicate competition experiments and measuring the variance in the time of emergence of
WT virus. We found that under the relatively simple conditions of tissue culture,
genetic drift plays a significant role in the evolution of the population, a role that
was a function of the initial starting frequency of WT virus and the strength of
selection between WT and mutant virus. To define the idealized expectations of the
competition experiments, we experimentally measured the parameters relevant to the
evolution of the viral populations. We found that WT virus is 4.6 fold more fit that LS
and 10.9 fold more fit than LSTI viruses under the conditions of the competition
experiments. The generation time of the virus, defined as the time that elapses from one
point in the replication cycle to the same point in daughter virus, was found to be
greater than 96 hours. Target cell doubling times were unaffected by infection with all
viruses used in this study. We supplied these parameters to simulations based on our
simple model and found that the theoretical expectations underestimate the role of
drift. These results highlight the complexities that exist even under the relatively
homogenous conditions of tissue culture.
Thesis (Ph.D.)--Tufts University, 2011.
Submitted to the Dept. of Molecular Microbiology.
Advisor: John Coffin.
Committee: Naomi Rosenberg, Joan Mecsas, and Katya Heldwein.
Keywords: Virology, Molecular biology, and Microbiology.read less
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