Makorin-2 is a neurogenesis inhibitor downstream of PI3k/AKT signal

Makorin-2 (MKRN2) belongs to makorin RING zinc-finger gene family which encodes putative ribonucleoproteins. Here we cloned the Xenopus homolog of human MKRN2 (XMR2) and characterized its function in Xenopus neurogenesis. We showed that forced overexpression of XMR2 via microinjection of XMR2 mRNA produced tadpoles with dorso-posterior deficiencies and small-head/short-tail phenotype, while knockdown of XMR2 by microinjecting morpholino antisense oligonucleotides induced double axis in tadpoles. These results are consistent with the comparatively low expression level of XMR2 in the brain. Using Xenopus animal cap (AC) explant assay, we further demonstrated that XMR2 inhibited activin plus retinonic-acid induced AC neutralization, concurrent with the suppression of pan neural marker NCAM. To our surprise, the anti-neurogenic activity of XMR2 is independent of the BMP-4 and Wnt8 signaling pathways. We showed that XMR2 worked specifically through blocking phosphatidylinositol 3-kinase (PI3K) and Akt mediated neurogenesis. Furthermore, overexpression of XMR2 completely abrogated constitutively active PI3K- and Akt-induced, but not dominant negative GSK-3ss-induced NCAM expression, indicating that XMR2 acts downstream of PI3K and Akt and upstream of GSK-3ss. These results reveal for the first time the important role of XMR2 as a new player in PI3K/Akt mediated neurogenesis during Xenopus embryonic development.