Evolutionary mechanisms of the gastrula organizer and blastopore formation by focusing on the gene regulatory network

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Secreted proteins in the extracellular space and transcription factors functioning in the nuclei do not appear to be related, but they have similarity not only in biochemical characters but also in other features so that some secreted proteins are functioning in the nucleus, and some transcription factors are secreted from the cell. To explore the meaning of these phenomena, we focused on Otx2, which is a transcription factor and reported to be secreted from the cell. We made an Otx2 construct containing a signal peptide and a fluorescent protein, Venus, at the N-terminus, but we could not detect this construct in the extracellular space in the Xenopus embryo. One possibility might be the fact that Otx2 is modified, which we found recently. We revealed that Otx2 is phosphorylated at three serines in the region C-terminal to the homeodomain. Thus, it is important in future to examine whether modifications of Otx2 affect its secretion from the cell.