[1] HARVARD UNIV, SCH MED, NERPRC, DIV REPROD BIOL, BOSTON, MA 02115 USA
[2] MASSACHUSETTS GEN HOSP, SURG RES LAB, BOSTON, MA 02114 USA
[3] TUFTS UNIV, DEPT ANAT & CELLULAR BIOL, BOSTON, MA 02111 USA
[4] HARVARD UNIV, SCH MED, LHRRB, BOSTON, MA 02115 USA
[5] HARVARD UNIV, SCH MED, DEPT CELLULAR & MOLEC PHYSIOL, BOSTON, MA 02115 USA