ROLE-PLAY IN X-INACTIVATION

Initiation of X-inactivation is known to depend on the presence of a u nique region or locus known as the X-inactivation center, or Xic, defi ned by the study of chromosomal rearrangements. Its mode of action is currently unknown but is the scene of much research effort. This revie w explores the recent literature concerning the definition of Xic and its relationship both to Xist and to another genetic entity thought to play a role in the initiation of X-inactivation, the X-controlling el ement, or Xce.