title: A Mouse Ear Model for Bystander Studies Induced by Microbeam Irradiation.
abstract: Radiation-induced bystander effects have been observed in vitro and in cell and tissue culture models, however, there are few reported studies showing these effects in vivo. To our knowledge, this is the first reported study on bystander effects induced by microbeam irradiation in an intact living mammal. The mouse ear was used to investigate radiation-induced bystander effects in keratinocytes, utilizing a 3 MeV proton microbeam (LET 13.1 keV/μm) with a range in skin of about 135 μm. Using a custom-designed holder, the ear of an anesthetized C57BL/6J mouse was flattened by gentle suction and placed over the microbeam port to irradiate cells along a 35 μm wide, 6 mm long path. Immunohistochemical analysis of γ-H2AX foci formation in tissue sections revealed, compared to control tissue, proton-induced γ-H2AX foci formation in one of the two epidermal layers of the mouse ear. Strikingly, a higher number of cells than expected showed foci from direct irradiation effects. Although the proton-irradiated line was ~35 μm wide, the average width spanned by γ-H2AX-positive cells exceeded 150 μm. Cells adjacent to or in the epidermal layer opposite the γ-H2AX-positive region did not exhibit foci. These findings validate this mammalian model as a viable system for investigating radiation-induced bystander effects in an intact living organism.
authors.affiliation: a  Radiological Research Accelerator Facility, Columbia University, Irvington, New York 10533;
authors.forename: M
authors.initials: M
authors.lastname: Buonanno
authors.affiliation: a  Radiological Research Accelerator Facility, Columbia University, Irvington, New York 10533;
authors.forename: G
authors.initials: G
authors.lastname: Randers-Pehrson
authors.affiliation: b  Center for Radiological Research and.
authors.forename: L B
authors.initials: LB
authors.lastname: Smilenov
authors.affiliation: c  Mailman School of Public Health, Columbia University Medical Center, New York, New York 10032.
authors.forename: N J
authors.initials: NJ
authors.lastname: Kleiman
authors.affiliation: b  Center for Radiological Research and.
authors.forename: E
authors.initials: E
authors.lastname: Young
authors.affiliation: a  Radiological Research Accelerator Facility, Columbia University, Irvington, New York 10533;
authors.forename: B
authors.initials: B
authors.lastname: Ponnayia
authors.affiliation: b  Center for Radiological Research and.
authors.forename: D J
authors.initials: DJ
authors.lastname: Brenner
mesh_terms: D000818:Animals; D024201:Bystander Effect; D004249:DNA Damage / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D004423:Ear / Q000528:radiation effects*; D015870:Gene Expression / Q000528:radiation effects; D006657:Histones / Q000096:biosynthesis; D015603:Keratinocytes / Q000528:radiation effects; D051379:Mice; D011522:Protons; D011827:Radiation
chemical_list: D006657:Histones; D011522:Protons; C475961:gamma-H2AX protein, mouse