Apoptosis plays a major role in normal organism development, tissue homeostasis, and removal of damaged cells. Disruption of this process has been implicated in a variety of diseases such as cancer. The Bcl-2 family of proteins is comprised of critical regulators of apoptosis that can be divided into two classes: those that inhibit apoptosis and those that promote cell death. BOK, a pro-apoptotic Bcl-2 family member, was initially identified in the ovary, and was found to interact with other Bcl-2 family members such as Mcl-1 and Bfl-1. BOK expression is high during early placental development, suggesting that it may also play a role in regulating trophoblast cell proliferation.