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

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.     

Influence of dietary fatty acids on the glycerophospholipid composition in organs of cod (gadus morhua)

Cod (mean start weight of 26 g) were fed three diets for 15 months, each based on a dry pellet coated at a level of 9g/100 g with soybean oil, capelin oil or sardine oil. The fatty acid compositions of neutral lipids and four glycerophospholipids of white muscle, liver, gills and heart were determined. The fatty acid composition of dietary lipids influenced the composition of neutral lipids in all organs. Linoleic acid (18∶2n−6) from soybean oil was selectively incorporated into phosphatidylcholine of the four tissues. Similar levels of 20∶5n−3 and 22∶6n−3 in phosphatidylcholine and phosphatidylethanolamine were found in all organs from cod fed capelin oil and sardine oil in spite of highly differentiated feed fatty acid levels. The polyunsaturated fatty acid (PUFA) composition of phosphatidylinositol was least influenced by dietary lipids. The preferred monoenic fatty acid in phospholipids of cod was 18∶1n−9, independent of dietary intake, whereas the longer chain monoenoic acids seemed to be preferentially catabolized. The results suggest that 20∶4n−6 as well as 20∶5n−3 and 22∶6n−3 fatty acids are essential for cod.     

Effects of different dietary fat levels in cage‐fed Atlantic mackerel (Scomber scombrus)

In wild Atlantic mackerel, Scomber scombrus, the lipid content of the lateral muscle varies according to the season from around 30% in autumn to less than 5% in spring. To be able to offer mackerel with optimal quality on the market during spring or early summer after overwintering, it is necessary that the muscle lipid content is close to 30%, which is favoured by the customers. Wild caught mackerel were kept in salmon cages fed a high energy (300 g fat kg^{– 1} ) salmon diet rich in n‐3 polyunsaturated fatty acids from October 1997 to April 1998. Fish were submerged at 20—40 m at a temperature above 5 °C from January until April. Then the fish were brought to the surface and randomly divided into three duplicate groups, i.e., non‐fed, 150 g fat kg ^{– 1}, and 300 g fat kg ^{– 1} and kept until August 1998. The mortality was very low and the body weight doubled concomitant with an increased muscle lipid content from 19.5% to 30.9% during the first six months. Both groups receiving feed further increased the body weight and muscle lipid content at the same magnitude towards the end of the experiment. During the first six months the cross sectional area (CSA) of red muscle fibres increased 3.3fold and this size was maintained throughout the experiment. In contrast, in non‐fed mackerel the increase in CSA of red muscle fibres was 1.5fold. White muscle fibres revealed a much weaker response in fed mackerel and were not affected in mackerel deprived of feed. In wild mackerel the fatty acid oxidation (β‐oxidation) capacity dominated in the red part of the lateral muscle. During the winter an increased β‐oxidation capacity was found in heart and liver, whereas both red and white part of the lateral muscle showed a low fatty acid catabolism. In contrast, during summer red and white part of the lateral muscle possessed high β‐oxidation capacities, particularly in high energy‐fed and non‐fed mackerel. It is concluded that it is possible to feed captive mackerel during the winter and produce mackerel with a high quality for the market in early spring.