Todorčević et al. BMC Genomics 2010, 11:39 http://www.biomedcentral.com/1471-2164/11/39 Page 4 of 17 Figure 3 Atlantic salmon aSVF primary cell culture. A, B: Electron micrographs of representative salmon adipocytes day 15 (A) and day 30 (B). Three weeks after induction of differentiation (day 30), a large portion of cytoplasmic space was filled with LDs, the number mitochondria was reduced and the nuclei were located between LDs and cell membranes. Bars: 5 μm. Arrows points to mitochondria and arrowheads to lipid droplets chondrocytes and osteoblasts [25,26]. In contrast, TNFa and related genes were down-regulated (Fig. 5 and 6). Terminal differentiation and the late phase of white adipocyte maturation (days 12-30) The increase in intracellular lipid levels measured by Oil Red O (Fig. 4A) was in line with the up-regulation of genes for several proteins of lipid metabolism (Fig. 5), including lipoprotein lipase (LPL) (Fig. 7). The expres- sion of fatty acid synthase (FAS) was highest from day 15 to day 30 (Fig. 7) in agreement with the profile of FAS observed in murine adipocytes [27]. Metabolic alterations were also supported by the regulation of key genes from major carbohydrate pathways (Fig. 8). Glu- cose-6-phosphate dehydrogenase (G6PD) and 6- phosphogluconate dehydrogenase (PGD) from the oxi- dative pentose phosphate pathway (PPP) were up-regu- lated from day 12 to the end of adipogenic differentiation indicating increased need for NADPH that is required for TAG biosynthesis. To synthesise nucleotides, cells need large amounts of ribose-5-phos- phate (R5P). The PPP uses glucose to provide R5P and NADPH, however, the output can be modified accord- ing to the cells’ current needs, towards the production of either one of the products. The increase of phospho- fructokinase (PFK) and pyruvate kinase (PK) expression from day 15 could be an evidence for the importance of glycolysis in TAG-accumulating adipocytes. In addition to glycolysis and contrary to what was earlier believed,