- Serum response factor is required for immediate-early gene activation yet is dispensable for proliferation of embryonic stem cells. Schratt, G., Weinhold, B., Lundberg, A.S., Schuck, S., Berger, J., Schwarz, H., Weinberg, R.A., Rüther, U., Nordheim, A. Mol. Cell. Biol. (2001)