Uterine epithelial cells undergo extensive morphological and molecular remodeling to prepare for implantation; these changes are collectively termed the plasma membrane transformation. During the time of receptivity there is a large increase in the number of apical vesicles that is correlated with increased endocytotic activity in uterine epithelial cells. However the mechanism involved in this change in vesicle distribution is unclear. This study examined the role of Syntaxin 3 in the uterus during early pregnancy. Syntaxin 3 is a crucial protein involved in delivery of proteins from the trans-golgi network to the apical surface of polarized epithelia. Syntaxin 3 also plays a role in determining the specificity of membrane targeting by permitting fusion only with the apical membrane.
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 fertilization (non-receptive) has demonstrated Syntaxin 3 diffusely throughout the cytoplasm of uterine epithelial cells. At the time of implantation, Syntaxin 3 is concentrated in the apical cytoplasmic portion of uterine epithelial cells. Western blot analysis of isolated uterine epithelial cells reveals an overall increase in Syntaxin 3 expression from the non-receptivfe phase to the time of implantation.
This increase in Syntaxin 3 as well as the more confined localization at the apical cytoplasmic region of uterine epithelial cells at the time of implantation suggests that this key vesicular regulatory protein may play a role in directing important receptivity markers to the apical plasma membrane at the time of uterine receptivity.