- A novel member of the transmembrane serine/threonine kinase receptor family is specifically expressed in the gonads and in mesenchymal cells adjacent to the müllerian duct. Baarends, W.M., van Helmond, M.J., Post, M., van der Schoot, P.J., Hoogerbrugge, J.W., de Winter, J.P., Uilenbroek, J.T., Karels, B., Wilming, L.G., Meijers, J.H. Development (1994)