A novel myocyte-specific gene Midori promotes the differentiation of P19CL6 cells into cardiomyocytes

Although several cardiac-specific transcription factors have been shown to play vital roles in various steps during the heart formation, the precise m echanism of the early stage of cardiogenesis has yet to be elucidated. By d ifferential display technique, we tried to identify molecules that are expr essed earlier than cardiac transcription factors such as CSX-/NKX2-5 and GA TA-4 and are involved in cardiomyocyte differentiation using the P19CL6 cel l line, which efficiently differentiates into cardiomyocytes when treated w ith dimethyl sulfoxide. We isolated a novel gene designated Midori. Its ded uced amino acid sequence contained an ATP/GTP-binding site, Ig-like domain, and Kringle-like domain. Northern blot analysis revealed that expression o f Midori was restricted to the fetal and adult heart and adult skeletal mus cle in mice. In whole mount in situ hybridization, Midori was expressed in cardiac crescent and developing heart but not in somites. The MIDORI protei n was localized in the nucleus and overexpression of Midori induced express ion of endogenous Midori itself, suggesting that MIDORI may act as a transc riptional regulator. Permanent P19CL6 cell lines overexpressing Midori more efficiently differentiated into cardiomyocytes than did parental cells, wh ereas those overexpressing the antisense Midori less efficiently differenti ated. These results suggest that Midori may promote the differentiation of P19CL6 into cardiomyocytes.