A naturally occurring hormone that plays an important role in fetal development may be the basis for a new type of reversible contraceptive that can protect ovaries from the damage caused by chemotherapy drugs. In their report receiving online publication in PNAS, a team from the Pediatric Surgical Research Laboratories in the Massachusetts General Hospital (MGH) Department of Surgery describes using Mullerian Inhibiting Substance (MIS) to halt, in a mouse model, the early development of the ovarian follicles in which oocytes mature, an accomplishment that protects these primordial follicles from chemotherapy-induced damage.  “MIS has long been suspected as an inhibitor of the initial stages of follicular development, but the complete blockade of the process was unexpected and opened up a number of new applications for the hormone,” says corresponding author David Pepin, PhD. “Because most of what we know about female reproduction is focused on the late stages of follicle maturation, our current therapies – including contraceptive drugs – are all targeted at those processes. ...