Actin-binding proteins undergo major alterations during the plasma membrane transformation in uterine epithelial...

The apical surface of uterine epithelial cells undergoes a dramatic transformation during early pregnancy. Previous studies have shown that cytoskeletal actin microfilaments are associated with this transformation, but little is known of the role played by actin-binding proteins or which of the many described in other cell types are present in uterine epithelial cells.

Immunohistochemical staining using monoclonal antibodies raised against four different actin-binding proteins (alpha-actinin, tropomyosin, gelsolin, and vinculin) was used to study the changing distribution of these proteins in uterine epithelium during early pregnancy in the rat.

Findings indicated the presence of all four of the actin-binding proteins in the uterine epithelium. The distribution of tropomyosin remained unchanged over the period of early pregnancy. Gelsolin and alpha-actinin displayed similarity in distribution. Day 1 showed an apicobasal localisation of reaction product, which by day 6 of pregnancy had concentrated into a thick band across the luminal surface of the cells. Vinculin staining was a diffuse band at the level of the basal plasma membrane at day 1 and became a diffuse faint band across the apical part of the cells on day 6.

This study confirms the presence of actin-binding proteins in uterine epithelial cells, and these findings are discussed in light of known ultrastructural alterations in the uterine epithelium during early pregnancy. Elucidation of the role of the actin-based cytoskeleton in the uterine epithelium may further our understanding of the dynamics of this unique environment that allows the implantation of a blastocyst.