Delta-like protein 1 (DLK1) is involved in adipose and muscle development as shown by the reduction of fat mass in DLK1 transgenic mice and in muscle hypertrophy of callipyge sheep. However, no study on DLK1 has been investigated in avian species. Cloning and sequencing of a full length of chicken DLK1 (gDLK1) complementary DNA revealed that gDLK1 contains a total of 1,161 bp, encoding 386 amino acids. The similarity of gDLK1 nucleotide and protein sequences was over 50% compared with other mammalian species. In addition, chickens only express one full length of gDLK1 in various tissues at different ages without the alternative splicing variants of DLK1 found in mammalian species. This suggests that the full-length form of gDLK1 may be sufficient for normal development in the chicken. In adipose tissue, the gDLK1 gene was highly expressed in preadipocytes as compared with adipocytes (P < 0.05), whereas expression levels of adipogenic marker genes such as stearoyl-coenzyme A desaturase 1 (SCD-1) and fatty acid binding protein 4 (FABP4) were higher in mature adipocytes than in preadipocytes (P < 0.05 and P < 0.01, respectively). Expression of gDLK1 in adipose tissue tends to decrease with age. The expression of gDLK1 gene in the pectoralis major muscle was significantly higher in 13- and 17-d-old embryos (P < 0.05), decreased in 1- and 5-d-old chicks (P < 0.05), and further decreased in 11- and 33-d-old chickens (P < 0.05). This expression pattern of gDLK1 was very similar to the expression patterns of myogenin and Pax7 genes, suggesting a close association with myogenic activities. In conclusion, the developmental regulation of gDLK1 expression might play an important role in the early stages of adipose and muscle tissue development.

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The effects of genistein on cell proliferation and adipogenesis were examined in mouse 3T3-L1 preadipocyte cells. Genistein decreased viability of 3T3-L1 pre-adipocytes in a dose-dependent manner. Oil Red O staining of these cells also indicated that adipogenesis was inhibited by 50 μM genistein treatment. We investigated the molecular mechanisms involved in the decrease in cell viability in genistein-treated 3T3-L1 cells by conducting an oligo DNA microarray analysis. We selected the sirtuin-1 gene, one of the upregulated genes, for further experimentation because sirtuin-1 belongs to the sirtuin family, which is associated with anti-obesity and anti-inflammation activities. We found that four phytochemicals (resveratrol, capsaicin, daidzein, and genistein) could increase sirtuin-1 expression. Genistein was the strongest inducer of sirtuin-1 among the tested phytochemicals. The inhibition of adipogenesis by genistein was recovered by surtuin-1 siRNA transfection. Overall, these results may further our understanding of the molecular mechanisms underlying the inhibition of proliferation and adipogenesis by genistein in mouse 3T3-L1 cells.

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