Uterine epithelial cells undergo extensive morphological and molecular remodelling to prepare for implantation; these changes are collectively termed ‘the plasma membrane transformation’. These changes are likely mediated by vesicular trafficking and indeed there is a large increase in the number of apical vesicles as well as an increase in vesicular activity at the time of receptivity.
This study examined the role of VAMP2 and Syntaxin 3 in the uterus during early pregnancy. Vesicle associated membrane protein 2 (VAMP2) is known to travel in vesicle membranes that constitutively fuse with the plasma membrane. Syntaxin 3 is a crucial protein involved in the delivery of proteins from the trans-golgi network to the apical surface of polarized epithelia.
Uterine tissues were collected from pregnant rats during early pregnancy for immunofluorescence and uterine epithelial cells were isolated for western blot analysis.
Immunofluorescence microscopy at the time of fertilisation (non-receptive) has demonstrated that VAMP2 and Syntaxin 3 are diffusely distributed throughout the cytoplasm of uterine epithelial cells. At the initial stage of implantation (apposition), VAMP2 remains diffused throughout the cytoplasm with granular staining in the perinuclear region. During adhesion, VAMP2 becomes restricted to the cytoplasm region above the nucleus but below the localisation of Syntaxin 3, which is found immediately below the apical plasma membrane. Western blot analysis of isolated uterine epithelial cells reveals an overall increase in the amount of VAMP2 and Syntaxin 3 from the non-receptive phase to the time of implantation.
This increase in VAMP2 and Syntaxin 3 as well as the more confined localisation at the apical cytoplasmic region of uterine epithelial cells suggests that these proteins are involved in vesicle regulation. This may play a role in maintaining directional vesicle traffic to the apical plasma membrane at the time of uterine receptivity.