Expression of bcl-2 in fetal tissues suggests a role in morphogenesis.

We have studied the distribution of the bcl-2 protein in fetal tissues, in an effort to uncover patterns of expression that may elucidate the potential role of bcl-2 during development. We find that bcl-2 is expressed in many hematolymphoid and non-hematolymphoid tissues, most abundantly in placental trophoblast. In tissues of endocrine and neural derivation and in stem-cell populations of colonic and some stratified epithelia, bcl-2 seems to be involved in tissue homeostasis. However, in developing proximal nephrons of the kidney and other sites characterized by inductive interactions between epithelium and mesenchyme, bcl-2 is apparently involved in morphogenesis, possibly by mediating the formation of condensations of cells that are "committed" to the formation of more differentiated structures. The distribution of bcl-2-protein expression in fetal tissues is consistent with its previously described role in promoting cell survival, presumably by preventing apoptosis in lymphoid and other tissues where cell death represents an active regulatory process. Expression of bcl-2 protein is more widespread in fetal than adult tissues. Our observations therefore represent supportive evidence for the importance of inducible cell survival as a regulatory process in normal homeostasis and morphogenesis in many fetal tissues and structures.