Analysis of genetic variation in Pediculus humanus and Populus trichocarpa

Olds, Brett

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https://hdl.handle.net/2142/44336 Copy

Description

Title

Analysis of genetic variation in Pediculus humanus and Populus trichocarpa

Author(s)

Olds, Brett

Issue Date

2013-05-24T22:08:14Z

Director of Research (if dissertation) or Advisor (if thesis)

• Paige, Ken N.
• Pittendrigh, Barry R.

Doctoral Committee Chair(s)

• Paige, Ken N.
• Pittendrigh, Barry R.

Committee Member(s)

• Hudson, Matthew E.
• Malhi, Ripan S.

Department of Study

School of Integrative Biology

Discipline

Biology

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• body louse
• Pediculus humanus
• Bartonella quintana
• disease vector competency
• black cottonwood
• Populus trichocarpa
• somatic mutation

Abstract

With the advent of sequencing technologies that are both affordable and readily available, biologists are now able to address questions that were previously intractable. New species are having their genomes mapped at an increasing rate, including non-model organisms. Two such organisms are the human body louse, Pediculus humanus corporis and the black cottonwood, Populus trichocarpa. While unrelated, these two organisms each represent a study system with questions that challenge our current understanding of each organism. Body and head lice, while closely related, are thought to be separate species with their most important difference being that only body lice vector disease to humans. The first question is: Are body lice (Pediculus humanus coporis) and head lice (Pediculus humanus capitis) the same species? A total of 10,771 body louse and 10,770 head louse transcripts were predicted from a combined assembly of Roche 454 and Illumina sequenced cDNAs from whole body tissues collected at all life stages and during pesticide exposure and bacterial infection treatments. Illumina reads mapped to the 10,775 draft body louse gene models from the whole genome assembly predicted nine presence/absence differences, but PCR confirmation resulted in a single gene difference. One novel microRNA was predicted in both lice species and 99% of the 544 transcripts from Candidatus riesia indicate that they share the same endosymbiont. Overall, few differences exist, which supports the hypothesis that these two organisms are ecotypes of the same species. A second question is: Are there gene expression differences between these two organisms that cause the body louse to vector disease to humans while head lice do not? We utilized an RNAseq analysis on 7-day old head and body lice fed blood infected with Bartonella quintana, the bacterium that causes trench fever, and control individuals to elicit gene expression differences. Eight immunoresponse genes came out significant, many associated with the Toll pathway; Fibrinogen-related protein (PHUM500950), Spaetzle (PHUM595260), Defensin 1 (PHUM365700) and 2 (PHUM595870), Serpin (PHUM311330), Cactus (PHUM345810), Scavenger receptor A (ScavA; PHUM066640) and Apolipoprotein D (PHUM427700). Increased expression of Fibrinogen-related protein and Spaetzle, both related to the Toll pathway, in treated body lice supports the hypothesis that body lice are fighting infection from B. quintana. But conflicting results in Defensin 1 and 2 based upon validation method suggest another mechanism in head lice alternative to the Toll pathway might be involved. Additionally, Scavenger receptor A was higher in both control and treated head lice, suggesting higher phagocytotic activity in head lice to curb infection. In 1981, Whitham and Slobodchikoff hypothesized that long-lived plant species, like black cottonwood, that propagate both asexually and sexually, might develop, through accumulation of somatic mutations, as genetic mosaics, providing the potential to respond to or even outrun their insect herbivores. The initial question to assess this hypothesis is: What is the level of somatic variation that exists with an individual tree and its clonally derived offspring? We show that on the average there are 4,840 unique amino acid changes in 2,569 genes within each tissue sampled within an individual parental tree and its clonally derived offspring. In addition, genetic variation within a parental tree, and between a parental tree and its clonally derived offspring, show about half as much genetic variation among tissues as exists between genetically unrelated trees within a population. These results support the long-standing hypothesis that some tree species exist as mosaics of genetic variability and can evolve (i.e., genetic differentiation between parent and clonally derived offspring).

Graduation Semester

2013-05

Permalink

http://hdl.handle.net/2142/44336

Copyright and License Information

Copyright 2013 Brett Olds. Chapter 2 appeared in its entirety in the journal, Insect Molecular Biology and is referred to later in this dissertation as Olds et al. 2012. Olds B.P., B.S. Coates, L.D. Steele, W. Sun, T.A. Agunbiade, K.S. Yoon, J.P. Strycarz, S.H. Lee, K.N. Paige, L.M. Clark and B.R. Pittendrigh. 2012. Comparison of the transcriptional profiles of head and body lice. Insect Molecular Biology 21(2): 257-268.

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