The luminal uterine epithelial cells (UECs) are the first point of contact with the implanting blastocyst and are only receptive for a narrow period of time. Specific changes in UECs are required for receptivity, termed the Plasma Membrane Transformation. These include deepening of the lateral tight junctions, a loss of adherens junctions and a redistribution of desmosomes to the apical part of the lateral plasma membrane (pm). While these morphological changes are important for uterine receptivity, mechanisms of regulation are currently unknown.
Rab13, a member of the Rab (Ras-related in the brain) family of GTPases, has a critical role in endosomal trafficking. While individual members of the Rab family have specific sub-cellular localizations, Rab13 is associated with endosomal trafficking to the lateral pm and is involved with modulation of tight junctions in several cell types. The aim of this study is to investigate the role of Rab13 in UECs during early pregnancy and to determine if Rab13 is involved in modification of the lateral junctional complex at the time of receptivity.
Confocal microscopy localised Rab13 along the entire lateral pm at the time of fertilization, which was shifted to the apical part of the lateral pm at the time of receptivity. Rab13 was consistently found below ZO-1 staining, an integral tight junction protein. There was no colocalisation between Rab13 and E-cadherin, a component of adherens junctions. Our modified immunofluorescence protocol demonstrated colocalisation between Rab 13 and desmoglein, a component of desmosomes at the time of fertilization and receptivity.
This is the first study to localize a member of the Rab family of GTPases, Rab 13, in the uterus. Rab13 was localized to the lateral pm where it colocalised with Dsg. We speculate that Rab13 is involved in the redistribution of desmosomes, which is an essential component of uterine receptivity.