- Expression of type I and type IB receptors for activin in midgestation mouse embryos suggests distinct functions in organogenesis. Verschueren, K., Dewulf, N., Goumans, M.J., Lonnoy, O., Feijen, A., Grimsby, S., Vandi Spiegle, K., ten Dijke, P., Morén, A., Vanscheeuwijck, P. Mech. Dev. (1995)