XMam1, Xenopus Mastermind1, induces neural gene expression in a Notch-independent manner

Mastermind, which is a Notch signal component, is a nuclear protein and is thought to contribute to the transactivation of target genes. Previously we showed that XMam1, Xenopus Mastermind1, was essential in the transactivation of a Notch target gene, XESR-1, and was involved in primary neurogenesis. To examine the function of XMam1 during Xenopus early development in detail, XMam1-overexpressed embryos were analyzed. Overexpression of XMam1 ectopically caused the formation of a cell mass with pigmentation on the surface of embryos and expressed nrp-1. The nrp-1-positive cell mass was produced by XMam1 without expression of the Notch target gene, XESR-1, and not by the activation form of Notch, NICD. The ectopic expression of nrp-1 was not inhibited by co-injection of XMam1 with a molecule known to inhibit Notch signaling. The nrp-1 expression was also recognized in the animal cap injected with XMam1ΔN, which lacks the basic domain necessary for interacting with NICD and Su(H). These results show that XMam1 has the ability to induce the cell fate into the neurogenic lineage in a Notch-independent manner.