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 t o those where the epithelium remains intact. Despite these differences in m echanisms? the initial response of the plasma membrane of uterine epithelia l cells is remarkably similar across mammalian species which has led to the term 'plasma membrane transformation' to encapsulate the concept of a comm on beginning to implantation. Membrane phenomena similar to those of mammal s have now been observed in some viviparous lizards at the ultrastructural level during early pregnancy, and we propose extending the concept of 'plas ma membrane transformation' to lizards with live birth. (C) 2000 Elsevier S cience Inc. All rights reserved.