Claudin 7 is reduced in uterine epithelial cells during early pregnancy in the rat
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ORIGINAL PAPER
Claudin 7 is reduced in uterine epithelial cells during early pregnancy in the rat Connie E. Poon • Romanthi J. Madawala Margot L. Day • Christopher R. Murphy
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Accepted: 5 November 2012 / Published online: 21 November 2012 Ó Springer-Verlag Berlin Heidelberg 2012
Abstract The non-receptive uterine luminal epithelium forms an intact polarised epithelial barrier that is refractory to blastocyst invasion. During implantation, organised dismantling of this barrier leads to a receptive state promoting blastocyst attachment. Claudins are tight junction proteins that increase in the uterine epithelium at the time of implantation. Claudin 7 is a member of this family but demonstrates a basolateral localisation pattern that is distinct from other claudins. The present study investigated the localisation, abundance and hormonal regulation of claudin 7 to elucidate a role for the protein during implantation. The results showed that claudin 7 demonstrates a distinct basal and lateral localisation in the uterine luminal and glandular epithelium throughout early pregnancy. On day 1, claudin 7 is abundantly present in response to ovarian estrogen. At the time of implantation, claudin 7 decreases in abundance. This decrease is not dependent on blastocyst presence, as shown by results in pseudopregnant animals. We propose that claudin 7 mediates intercellular adhesions in the uterine epithelium and also may be responsible for stabilising adhesion proteins at the basolateral cell surface. Thus, claudin 7 may function under the maintenance of the uterine luminal
C. E. Poon (&) R. J. Madawala C. R. Murphy Cell and Reproductive Biology Laboratory, School of Medical Sciences (Discipline of Anatomy and Histology) and The Bosch Institute, The University of Sydney, N364, F13 Anderson Stuart Building, Sydney, NSW 2006, Australia e-mail: [email protected] M. L. Day School of Medical Sciences (Discipline of Physiology) and The Bosch Institute, The University of Sydney, The Medical Foundation Building, Sydney, NSW 2050, Australia
epithelial barrier, in the non-receptive state preventing implantation from occurring. Keywords Rat Hormones Ovariectomy Uterus Pseudopregnancy
Introduction Blastocyst implantation is a delicately orchestrated event that is highly dependent on hormonal and temporal inputs (Carson et al. 2000; Kennedy et al. 2007; Lopata 1996; Psychoyos 1976). A key player is the uterine luminal epithelium which when non-receptive forms a normal intact epithelial barrier that is refractory to invasive elements, including blastocysts (Murphy and Shaw 1994; Psychoyos 1976, 1986; Short and Yoshinaga 1967). During implantation under the conditioning of the ovarian hormones, progesterone and estrogen, this barrier undergoes major structural and morphological changes to form an altered epithelium receptive to blastocyst attachment and subsequent access to the underlying endometrial stroma (Fain et al. 1973; Psychoyos 1976). At the plasma membrane level this process is known as the plasma membrane tr
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