Makorin-2 belongs to the makorin RING zinc finger gene family, which encodes putative ribonucleoproteins. Here we cloned the Xenopus makorin-2 (mkrn2) and characterized its function in Xenopus neurogenesis. Forced overexpression of mkrn2 produced tadpoles with dorso-posterior deficiencies and small-head/shorttail phenotype, whereas knockdown of mkrn2 by morpholino antisense oligonucleotides induced double axis in tadpoles. In Xenopus animal cap explant assay, mkrn2 inhibited activin, and retinoic acid induced animal cap neuralization, as evident from the suppression of a pan neural marker, neural cell adhesion molecule. Surprisingly, the anti-neurogenic activity of mkrn2 is independent of the two major neurogenesis signaling cascades, BMP-4 and Wnt8 pathways. Instead, mkrn2 works specifically through the phosphatidylinositol 3-kinase (PI3K) and Akt-mediated neurogenesis pathway. Overexpression of mkrn2 completely abrogated constitutively active PI3K-and Akt-induced, but not dominant negative glycogen synthase kinase-3␤ (GSK-3␤)-induced, neural cell adhesion molecule expression, indicating that mkrn2 acts downstream of PI3K and Akt and upstream of GSK-3␤. Moreover, mkrn2 upregulated the mRNA and protein levels of GSK-3␤. These results revealed for the first time the important role of mkrn2 as a new player in PI3K/Akt-mediated neurogenesis during Xenopus embryonic development. Makorin RING zinc finger (MKRN)3 gene family encodes putative ribonucleoproteins with a distinctive array of zinc finger domains. To date, nine MKRN family loci scattered throughout the human genome have been identified (1). The most studied member of this family is makorin-1 gene (MKRN1), which was recently documented to modulate telomere length homeostasis (2) and RNA polymerase II-dependent transcription (3). MKRN1 is widely transcribed in mammals, particularly in murine embryonic nervous system and adult testis (1). Such expression pattern suggests that members of this gene family may play an important role in embryonic development and neurogenesis.We had previously identified a new gene makorin-2 (MKRN2), formerly designated as HSPC070, from human CD34ϩ hematopoietic stem/progenitor cells (4). The nucleotide sequence of this gene shares 105 bp in the 3Ј-untranslated region with an oncogene c-RAF in reversed transcription orientation (4, 5). However, the function of MKRN2 remains elusive.Here we report the cloning of the Xenopus ortholog of human MKRN2 (mkrn2) and the characterization of its functions in Xenopus neurogenesis. In both gain-of-function and loss-of-function studies, we showed that dysregulation of mkrn2 produced morphological defects in neural development. To elucidate the underlying mechanism, we employed animal cap (AC) explant culture system to examine the effect of mkrn2 on the expression of a key neural marker, neural cell adhesion molecule (NCAM) (6). Xenopus AC is a unique model system for studying neural and mesodermal induction as it is capable of giving rise to either neural or mesodermal tissues in the presence o...

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