The Relationship Between Cell Division And Cell Differentiation And Differentiation Expressed Genes In Chromosomal Localization

Upon the differentiation induction of 3T3-L1 preadipocytes by hormone cocktail containing 1-isobutyl-3-methylxanthine, dexamethasone and insulin, the preadipocytes undergo ~2 rounds of mitotic clonal expansion, which just precedes the adipogenic gene expression program and has been thought to be an essential early step for differentiation initiation. By inducing 3T3-L1 preadipocyte with individual hormone, it was identified that the mitotic clonal expansion was induced only by insulin, not by 1-isobutyl-3-methylxanthine or dexamethasone. However, significant fraction of 3T3-L1 preadipocytes differentiated into adipocytes without the mitotic clonal expansion when the preadipocytes were induced with the combination of 1-isobutyl-3-methylxanthine and dexamethasone. Furthermore, when normally induced 3T3-L1 preadipocytes were treated with PD98059 (an inhibitor of MEK-1), to block the activation of Erk1 and 2, the mitotic clonal expansion was blocked, while adipocyte differentiation was not affected. These observations were confirmed by BrdU labeling. It was found that the differentiated adipocytes induced with 1-isobutyl-3-methylxanthine and dexamethasone or standard hormone cocktail plus PD98059 were not labeled by BrdU. Cell number counting and FACS analysis indicated that in these conditions there was no cell division either. Thus, it is evident that 3T3-L1 preadipocytes could differentiate into adipocytes without DNA synthesis and mitotic clonal expansion.