Cloning and expression of delta-like protein 1 messenger ribonucleic acid during development of adipose and muscle tissues in chickens.

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.