Date of Award

Summer 2006

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Biological Sciences

Program/Concentration

Biology

Committee Director

Wayne L. Hynes

Committee Member

Christopher Osgood

Committee Member

Daniel Sonenshine

Call Number for Print

Special Collections LD4331.B46 T66 2006

Abstract

A number of bacterial, viral, and protozoan diseases are transmitted to humans via arthropods. Arthropods possess an innate immune system to destroy invading microorganisms. However, arthropods unable to rid their systems of pathogens function as disease vectors. The American dog tick, Dermacentor variabilis, destroys invading Borrelia burgdorferi spirochetes, preventing transmission. In contrast, the black-legged tick, Ixodes scapularis, which is unable to destroy acquired B. burgdorferi, successfully vectors the pathogen. The Lone Star tick, Amblyomma americanum, vectors a similar pathogen called Borrelia lonestari. The distribution of defensin, an antimicrobial peptide of the innate immune system, was examined in A. americanum and/. Scapularis to determine whether differences in defensin expression correlate with ability to vector Borrelia species.

The defensin transcript sequence of A. americanum was ascertained and found to contain a 219 base pair open reading frame encoding a 72 amino acid prepropeptide with a proposed 37 amino acid mature peptide. The gene, amercin (amn), displays similarity to other tick defensins including the/. scapularis defensin, scapularisin (sin), and the D. variabilis defensin, varisin (vsn). Amino acid similarity is 73.7% between mature amercin and mature scapularisin and 71.1 % between amercin and varisin. Nucleotide similarity is 67.1 % between amn and sin but only 61.3% between amn and vsn.

Amercin transcript was detected by reverse-transcription polymerase chain reaction (RT-PCR) in the hemocytes, midgut, fat body, and salivary glands of adult A. americanum. Scapularisin transcript was detected in J. scapularis salivary glands and has previously been identified in hemocytes, midgut, and fat body. These results parallel transcript distribution in D. variabilis. Additionally, transcript was identified in early and late stage eggs, larvae, and nymphs of both A. americanum and J. scapularis. Notably, defensin transcript in D. variabilis is absent from early stage eggs although it is present in all other life stages.

Since defensin transcript distributions of A. americanum, I. scapularis, and D. variablis are identical, excepting the lack of transcript in D. variabilis early stage eggs, the difference in vector competence may result from post-translational regulation of defensin or from the activity of other immune-related proteins.

Rights

In Copyright. URI: http://rightsstatements.org/vocab/InC/1.0/ This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).

DOI

10.25777/8fq6-3f07

Download

Share

COinS