Luminal uterine epithelial cells (UECs) undergo extensive remodelling of the actin cytoskeleton during early pregnancy to become receptive to implantation by the invading blastocyst.  Filamin A is an actin cross linking protein with links to focal adhesions, integrins and is also a substrate of calpain activity.

This study investigates the localisation and expression of filamin A in the rat uterus on fertilisation (day 1) and implantation (day 6) of pregnancy, pseudo-pregnancy and also its hormonal control in ovariectomised rats  by means of immunofluorescence and western blotting of isolated luminal epithelial cells. We also investigate whether its localisation and expression on day 6 of pregnancy is dependent on calpain activity by using calpeptin - a calpain inhibiting molecule.

Filamin A localises basally in UECs at fertilisation and is concentrated in the first two to three stromal cell layers which form the primary decidua.   At the time of implantation filamin A is localised apically, and throughout the primary decidualisation zone.  Protein expression of filamin A does not change during early pregnancy in UECs, with a calpain cleaved fragment present on both days of pregnancy.  Expression and localisation of filamin A in pseudo-pregnant rats is the same on day 6 of pregnancy. The apical localisation of filamin A in luminal UECs is progesterone dependent.  However, expression is greater in oestrogen than progesterone treated rats.  Day 6 rats treated with calpeptin express filamin A apically in luminal UECs and spread throughout the primary decidualisation zone.  However, the expression of the calpain cleaved fragment of filamin A is reduced. 

In summary filamin A expression and localisation was found to be altered during early pregnancy in response to maternal factors, with its apical localisation being progesterone dependent.  Calpain activity may be a contributing factor for its apical localisation and role in cytoskeletal remodelling.