Activin/Nodal signaling in mouse embryonic stem cells

Members of the transforming growth factor (TGF)- superfamily play essential roles in the pluripotency, self-renewal, and differentiation of embryonic stem cells. While bone morphogenic proteins maintain pluripotency of undifferentiated mouse ES cells, the role of Activin/Nodal signaling is less clear. To determine the target genes of Activin/Nodal-Smad2 signaling in undifferentiated embryonic stem cells, changes in gene expression were examined following stimulation with recombinant Activin (2 hours) or after inhibition of Activin/Nodal with SB431542 (24 hours) using defined media culture conditions with LIF and 20 ng/mL BMP4. SB431542 is a specific inhibitor of ALK4/5/7 receptors and antagonizes both Activin and Nodal signaling. Via western analysis, Activin stimulation increased pSmad2 in ES cells after 2 hours, and treatment with SB431542 for 24 hours virtually eliminated pSmad2. Total Smad2 expression remained unchanged through these manipulations. RNA from cells treated with Activin or SB431542 was extracted by standard methods with Qiagen RNeasy columns. The RNA was analyzed with the Mouse Genome 430A Array from Affymetrix. Samples were performed in duplicate, and RNA from cells treated with Activin or SB431542 was compared to untreated embryonic stem cells.

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