Ultrabithorax inhibits the expression of myc by directly binding to its 5′-UTR in the posterior silk gland of Bombyx mori

Abstract

Ultrabithorax (Ubx) is a famous gene for insect body segment determination and c-myc plays a crucial role in cell fate and is well-known as proto-oncogene. As two pivotal transcription factors, whether there is a regulatory relationship between them has not yet been reported. In our previous research, we found that excess Ubx can strongly repress the expression of Myc in the posterior silk gland of Bombyx mori (B. mori). One unresolved question is whether Ubx inhibits the Myc expression directly or indirectly. In our current study, multiple Ubx binding sites were identified from the upstream sequence and 5′-UTR of Myc. Meanwhile, the expression profile data in silkDB 3.0 showed that Ubx and Myc were expressed simultaneously in multiple tissues and developmental stages of B. mori. Luciferase reporter assay results indicated that overexpressed Ubx down-regulated the activity of luciferase which was activated by the upstream sequence and 5′-UTR of Myc in BmN cells. Electrophoretic Mobility Shift Assay (EMSA) confirmed that Ubx bound to the 5′-UTR of Myc directly. Prediction results and ChIP-Seq data suggested that this interaction might be widespread in insects. In conclusion, our study uncovered the relationship between two famous gene, Ubx and Myc, which play critical regulatory roles in insect growth and development.