David G Besselsen

David G Besselsen

Veterinary Specialist
Adjunct Associate Professor, Animal and Comparative Biomedical Sciences
Member of the Graduate Faculty
Associate Research Scientist, BIO5 Institute
Primary Department
(520) 626-6702

Research Interest

David Besselsen, DVM, PhD, is the Director of University Animal Care (UAC), the Attending Veterinarian. He is a board-certified veterinary specialist (Diplomate) in the American College of Laboratory Animal Medicine and the American College of Veterinary Pathology, and served as Interim Dean for the College of Veterinary Medicine from 2017-2019. In addition to his administrative and service responsibilities, Dr. Besselsen is actively engaged in research through the provision of comparative pathology support for rodent models and oversight of the gnotobiotic mouse service. He has directed UAC Pathology Services since his arrival in 1995 and has over 80 peer-reviewed publications. UAC Pathology Services provides diagnostic and comparative pathology support for the research animals and research animal facilities at the University of Arizona. Capabilities include hematology, blood chemistry, necropsy, histologic preparation and interpretation, and others.


Watson, J. M., Marion, S. L., Rice, P. F., Bentley, D. L., Besselsen, D. G., Utzinger, U., Hoyer, P. B., & Barton, J. K. (2014). In vivo time-serial multi-modality optical imaging in a mouse model of ovarian tumorigenesis. Cancer Biology and Therapy, 15(1), 42-60.
BIO5 Collaborators
Jennifer Kehlet Barton, David G Besselsen


Identification of the early microscopic changes associated with ovarian cancer may lead to development of a diagnostic test for high-risk women. In this study we use optical coherence tomography (OCT) and multiphoton microscopy (MPM) (collecting both two photon excited fluorescence [TPEF] and second harmonic generation [SH G]) to image mouse ovaries in vivo at multiple time points. We demonstrate the feasibility of imaging mouse ovaries in vivo during a longterm survival study and identify microscopic changes associated with early tumor development. These changes include alterations in tissue microstructure, as seen by OCT, alterations in cellular fluorescence and morphology, as seen by TPEF, and remodeling of collagen structure, as seen by SH G. These results suggest that a combined OCT-MPM system may be useful for early detection of ovarian cancer. © 2014 Landes Bioscience.

Barton, J., Hariri, L. P., Qiu, Z., Tumlinson, A. R., Besselsen, D. G., Gerner, E. W., Ignatenko, N. A., Povazay, B., Hermann, B., Sattmann, H., McNally, J., Unterhuber, A., Drexler, W., & Barton, J. K. (2007). Serial endoscopy in azoxymethane treated mice using ultra-high resolution optical coherence tomography. Cancer biology & therapy, 6(11).
BIO5 Collaborators
Jennifer Kehlet Barton, David G Besselsen

Optical coherence tomography (OCT) is a minimally invasive, depth-resolved imaging tool that can be implemented in a small diameter endoscope for imaging mouse models of colorectal cancer (CRC). In this study, we utilized ultrahigh resolution (UHR) OCT to serially image the lower colon of azoxymethane (AOM) treated A/J mouse models of CRC in order to monitor the progression of neoplastic transformations and determine if OCT is capable of identifying early disease.

Barton, J., Hariri, L. P., Tumlinson, A. R., Wade, N. H., Besselsen, D. G., Utzinger, U., Gerner, E. W., & Barton, J. K. (2007). Ex vivo optical coherence tomography and laser-induced fluorescence spectroscopy imaging of murine gastrointestinal tract. Comparative medicine, 57(2).
BIO5 Collaborators
Jennifer Kehlet Barton, David G Besselsen

Optical coherence tomography (OCT) and laser-induced fluorescence (LIF) spectroscopy each have clinical potential in identifying human gastrointestinal (GI) pathologies, yet their diagnostic capability in mouse models is unknown. In this study, we combined the 2 modalities to survey the GI tract of a variety of mouse strains and ages and to sample dysplasias and inflammatory bowel disease (IBD) of the intestines. Segments (length, 2.5 cm) of duodenum and lower colon and the entire esophagus were imaged ex-vivo with combined OCT and LIE We evaluated 30 normal mice (A/J and 10- and 21-wk-old and retired breeder C57BL/6J) and 10 mice each of 2 strains modeling colon cancer and IBD (Apc(Min) and IL2-deficient mice, respectively). Histology was used to classify tissue regions as normal, Peyer patch, dysplasia, adenoma, or IBD. Features in corresponding OCT images were analyzed. Spectra from each category were averaged and compared via Student t tests. OCT provided structural information that led to identification of the imaging characteristics of healthy mouse GI. With histology as the 'gold standard,' we developed preliminary image criteria for early disease in the form of adenomas, dysplasias, and IBD. LIF characterized the endogenous fluorescence of mouse GI tract, with spectral features corresponding to collagen, NADH, and hemoglobin. In the IBD sample, LIF emission spectra displayed potentially diagnostic peaks at 635 and 670 nm, which we attributed to increased porphyrin production by bacteria associated with IBD. OCT and LIF appear to be useful and complementary modalities for ex vivo imaging of mouse GI tissues.

Besselsen, D., Wagner, A. M., Loganbill, J. K., & Besselsen, D. G. (2004). Detection of lactate dehydrogenase-elevating virus by use of a fluorogenic nuclease reverse transcriptase-polymerase chain reaction assay. Comparative medicine, 54(3).

Lactate dehydrogenase-elevating virus (LDEV) induces persistent infections in laboratory mice, alters in vivo physiology, and is a common contaminant of biological materials such as transplantable tumor cell lines. The fluorogenic nuclease reverse transcriptase polymerase chain reaction (fnRT-PCR) assay combines RT-PCR analysis with an internal fluorogenic hybridization probe, thereby eliminating post-PCR processing and potentially enhancing specificity. An fnRT-PCR assay specific for LDEV was therefore developed by targeting primer and probe sequences to a unique region of the LDEV nucleocapsid (VP1) gene. Using the LDEV fnRT-PCR assay, we detected only LDEV and did not detect other RNA viruses that are capable of naturally infecting rodents. Using this assay, we detected as little as 10 fg of LDEV RNA; the assay was 10-fold less sensitive when directly compared with the mouse bioassay (measurement of serum LD after inoculation), without the problematic false-positive serum LD enzyme elevations associated with the mouse bioassay. Using the fnRT-PCR assay, we also were able to detect viral RNA in numerous tissues and in feces collected from experimentally inoculated C3H/HeN mice, but we did not detect any viral RNA in similar samples collected from age- and strain-matched mock-infected mice. Finally, using the fnRT-PCR assay, we were able to detect LDEV RNA in biological samples that had previously been determined to be contaminated with LDEV by use of the mouse bioassay and an RT-PCR assay at another laboratory. In conclusion, the LDEV fnRT-PCR assay is a potentially high-throughput diagnostic assay for detection of LDEV in mice and contaminated biological materials.

Flowers, M., Schroeder, J. A., Borowsky, A. D., Besselsen, D. G., Thomson, C. A., Pandey, R., & Thompson, P. A. (2010). Pilot study on the effects of dietary conjugated linoleic acid on tumorigenesis and gene expression in PyMT transgenic mice. Carcinogenesis, 31(9).

Conjugated linoleic acid (CLA) is a class of commercially available fatty acids that have been associated with anticancer properties in rodent models of chemical carcinogenesis. We conducted a pilot study to examine the antitumor effect of dietary CLA in a polyoma virus-middle T antigen (PyMT) mouse model of invasive breast cancer. Virgin 4-week-old PyMT mice were administered a mixed-isomer CLA diet (1% wt/wt) or control AIN-93G diet for 4 weeks (N = 6 and 5, respectively) and tumor burden was assessed at 8 weeks of age. Thoracic mammary glands were prepared as whole mounts with other glands being formalin fixed and paraffin embedded for histology and immunohistochemistry (IHC). Total RNA was prepared for microarray and real-time reverse transcription-polymerase chain reaction analysis. Western blots were performed for protein expression analysis. Tumor incidence was significantly increased in CLA-treated animals compared with controls (P = 0.009) and occurred with extensive lobular-alveolar expansion and loss of mammary adipose tissue. More than 100 genes were downregulated > or = 2-fold in the CLA-treated group compared with controls, including adipose-specific markers, as wells as cytoskeletal and adhesion-related genes. This was supported by dramatic decreases in the epithelial adherens E-cadherin and beta-catenin as demonstrated by IHC. Taken together, these results suggest that dietary CLA affects the mammary stromal environment, leading to tumor progression and cellular expansion in the PyMT mouse model. Further studies of the potential for cancer promotion are needed, especially because mixed-isomer CLA formulations are sold commercially as a nutritional supplement.