Intracellular localization of dietary and naked DNA in intestinal tissue of Atlantic salmon, Salmo salar L. using in situ hybridization

Abstract

There is a continuing interest in the fate of DNA from genetically modified organisms (GMO) in the food chain including the uptake of DNA by intestinal cells from dietary sources containing GM feed ingredients. The objective of this study was to elucidate the uptake and persistence of foreign DNA in the intestinal tract of Atlantic salmon Salmo salar L. using in situ hybridization (ISH) that enables the intracellular localization of the DNA, and polymerase chain reaction (PCR) to verify the ISH results qualitatively. Two salmon intestinal models were employed for the investigations; intestinal tissues were sampled in two models namely (a) in vivo from salmon-fed diets containing 30% GM soybeans or 30% nonGM (nGM) soybeans, and (b) ex vivo from intestinal sleeves incubated using different concentrations of PCR-amplified test DNAs (211 and 305 bp) designed from the 35S promoter/plant DNA junction of the RoundupReady soybean (RRS) genome. Additionally, for the incubation study, the effect of a mucolytic agent dithiothreitol (DTT) and a permeability enhancer sodium deoxycholate (SDA) on DNA uptake were investigated. Both treatments were found to enhance DNA uptake ex vivo. Dietary DNA and PCR-amplified DNA could be visualized by ISH in the salmon intestine with more frequently observed signals in the ex vivo model compared to the in vivo model. All results could be verified by PCR. Dietary DNA was localized in the cell vacuolar system and in lamina propria of the mid intestine. Thus, based on the investigated DNA fragment lengths, this study shows that foreign DNA, can be taken up by Atlantic salmon intestinal tissue.