Mechanisms of syncytial fusion: a review

Syncytial fusion of trophoblast is a key process in placental morphogenesis and physiology. Disturbed syncytial fusion may lead to a number of pregnancy-associated pathologies. The mechanisms regulating syncytial fusion are only partly understood. This review tries to summarize the available knowledge on trophoblast fusion, originating from different scientific disciplines. Among the themes addressed in this paper are: morphogenesis and functions of syncytiotrophoblast; early apoptotic events and changes in plasmalemmal phospholipid orientation; proteins involved in membrane fusion: ADAMs and retrovirally-derived proteins and short-lived proteolipid intermediates in membrane fusion. Deeper understanding of syncytiotrophoblast fusion in future studies is only to be anticipated from collaborative studies focusing in parallel on physicochemical events in the participating plasmalemmas, early apoptotic/differentiation events preceding the fusion and role of the fusogenic membrane proteins.