Todorčević et al. BMC Genomics 2010, 11:39 http://www.biomedcentral.com/1471-2164/11/39 Page 10 of 17 Figure 9 Genes for antioxidants and proteins involved in unfolded protein responses analyzed with real-time qPCR. PRDX1 - peroxiredoxin 1, GPx2 - glutathione peroxidase 2, ATF6 - activating transcription factor 6, XBP1 - x-box binding protein 1, GRP78 - glucose- regulated protein 78, 18S. adipogenic regulator, which simultaneously inhibits myogenesis, osteogenesis and chondrogenesis [44,46,47]. Thus, high expression of PPARg observed long before confluence with the peak at day 6 probably posed a bar- rier to the induction of non-adipogenic mesenchymal cell lineages. Non-adipogenic developmental pathways are expected to be strongly suppressed by the addition of hormones. Yet, we did not find any noticeable changes in the markers of different cell types after day 9 Figure 10 Ribosomal proteins analyzed with microarrays. Data are mean log-(ER) ± SEM of twenty and ten genes involved in 60S and 40S subunit assembly respectively. and earliest increased level of the anti-osteogenic GAS6 was observed at day 15. Our PCNA results suggested the highest proliferative activity during the first days of culture followed by a moderate reduction of mitotic activity at day 6 and much greater decrease by day 30. Overall, the expres- sion patterns of genes involved in cell cycle were in concordance with these changes. Highest levels of the key negative cell cycle regulators (e.g. RBL1, p53-like, GADD45g) were observed during days 15-30. An addi- tional evidence for the anti-proliferative status was the up-regulation of several pro-apoptotic genes, including retinoic acid-regulated apoptosis-related protein 3 (APR3). APR3 arrests cell cycle by suppressing the activity of cyclin D1 [48], which was also induced at the latest stage. Differentiation of adipocytes in mam- mals is associated with a reduction in proliferation at confluence followed by subsequent activation or clonal expansion and eventually with cell cycle arrest at term- inal differentiation [49]. Our results revealed the diver- sity of mechanisms potentially employed in the execution of the similar stage of events that occur dur- ing Atlantic salmon adipogenesis. Given that WAT is a highly specialized organ that functions to regulate