The plasma membrane transformation

The plasma membrane transformation is a concept introduced by Christopher R. Murphy of The University of Sydney to encapsulate the idea that a series of changes in the plasma membrane of uterine epithelial cells is essential to the development of the receptivity of the uterus (womb) for attachment of the (fertilized egg) and the beginning of a pregnancy.

Originally advanced in 1993 (Murphy 1993) and subsequently elaborated in 1994 (Murphy and Shaw 1994), the concept has gained widespread acceptance as a useful way to think about changes in the epithelial cells which line the uterus as they progress towards becoming receptive for blastocyst implantation.

Subsequent reviews in 2000 and 2004 elaborated on the concept which has been extended to encompass all placental animals with live birth.

The final section of Murphy 2004 is a good summary of the concept and reads (slightly edited for this forum):

The many changes which take place in the uterine epithelium during early pregnancy have been suggested to represent a loss of polarity in these cells and this thought has been extended to suggest further that an epithelial-mesenchymal transition may occur in the cells during this time. These perceptive insights highlight the critical importance of uterine epithelial cells in uterine receptivity and in one sense recall earlier suggestions on events in uterine epithelial cells. These early thoughts on uterine epithelial cells highlighted the apical plasma membrane flattening and led to the term ‘attachment reaction’ being used to describe some of the membrane changes which occur during early pregnancy. This term was used to apply to those changes in the apical membrane of uterine epithelial cells upon contact with the blastocyst itself, or when opposing uterine epithelial cells came into physical contact at around the same time of early pregnancy in rats and mice. In particular, the term indicated that in those species with an ‘attachment reaction’, closure of the uterine lumen was involved such that little or no luminal space remained. However, as is now known, considerable change occurs in all compartments of the plasma membrane of uterine epithelial cells and these changes occupy most of early pregnancy in the rat and mouse with long, regular microvilli being converted into short, irregular structures as early as d 3, 2 to 3 days before the blastocyst even enters the uterus. As we have also seen, in a wide diversity of species, there are changes in the apical plasma membrane which have features in common with those seen in rats and mice and in many of these other species, closure of the uterine lumen does not occur.

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