How do hermaphrodites initiate the switch from spermatogenesis to oogenesis?
We suggested above that the crucial factor controlling whether germ cells become sperm or oocytes is the ratio of TRA-2 activity to FEM-3 activity, and described several regulatory pathways that influence these activities. However, we do not yet know why hermaphrodites make sperm early in life, and oocytes later on, since we don’t know which regulatory activities change at the appropriate time. For example, GLD-1 and FOG-2 are expressed in both larval and adult hermaphrodites, so it seems unlikely that repression of tra-2 ends when animals reach sexual maturity, thus allowing the switch to oogenesis, although it remains possible that the activity of a third factor, or a modification to either FOG-2 or GLD-1, might be responsible for the switch. As proposed by Goodwin and Ellis (2002), three explanations might account for this puzzle. First, one of these regulatory proteins might be modified to change its activity in a manner that could not be detected by RNA or protein cytological anal
