The plasma membrane transformation facilitates pregnancy in both reptiles and mammals

Mechanisms of placentation are very diverse in mammals and range from types in which the uterine epithelium is breached by the implanting blastocyst to those where the epithelium remains intact. Despite these differences in mechanisms? the initial response of the plasma membrane of uterine epithelial cells is remarkably similar across mammalian species which has led to the term 'plasma membrane transformation' to encapsulate the concept of a common beginning to implantation. Membrane phenomena similar to those of mammals have now been observed in some viviparous lizards at the ultrastructural level during early pregnancy, and we propose extending the concept of 'plasma membrane transformation' to lizards with live birth. (C) 2000 Elsevier Science Inc. All rights reserved.