Jak1/Stat3 signaling acts as a positive regulator of pluripotency in chicken pre-gastrula embryos

Pluripotent cells emerging at very early stages of development are the founders of differentiated cells. It has been established in mouse that the LIF/Jak/Stat-Nanog axis acts as a positive regulator to support the pluripotent state of cells whereas Fgf/Erk signaling acts as a negative regulator to direct cells to enter the differentiating state. In chicken, although Fgf/Erk signaling is known to act as a negative regulator, positive regulators remained unknown. Here, to identify positive regulator(s) of chicken pluripotency, we selected Jak1/Stat3 signaling as a candidate based on transcriptome analyses. Jak1/Stat3 signaling was activated specifically at stages before gastrulation: Stat3 protein was localized in nuclei at blastodermal stages, but translocated to cytoplasm after gastrulation. We conducted pharmacological and gene transfection analyses in the blastoderm-derived colony formation assay, in which Nanog-positive dense colonies represent a hallmark of the undifferentiated state, and found that Jak1/Stat3 signaling supports pluripotency in chicken early embryos. Jak1 inhibition abolished the formation of dense colonies, but the colony formation was restored when Stat3ER was artificially activated. We propose that the molecular mechanisms regulating pluripotency are conserved at the signaling network level between mouse and chicken, and possibly among a wider range of species.