1. Departments of Cell Biology and Physiology (S.R., T.M.P.), University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261
2. Duquesne University School of Health Sciences (C.R.P.), Pittsburgh, Pennsylvania 15282
3. Medical Research Council Reproductive Biology Unit, University of Edinburgh (A.S.M.), Edinburgh, United Kingdom EH3 9EW
4. Medicine (S.J.W.), University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261