Reduction of Mucin-1 Expression during the Receptive Phase in the Rat Uterus1

Abstract

Mucin-1 (Muc1), an integral membrane mucin, is expressed on the apical surface of uterine epithelial cells (UE) of various species. Loss of Muc1 is believed to be necessary for embryo attachment. Muc1 expression is markedly reduced in luminal epithelia during the receptive phase in mice, baboons, and pigs. In the present study, we examined Muc1 expression during the rat estrous cycle and at Day 5 of pregnancy, the time of embryo attachment. In contrast to findings in the mouse, indirect immunofluorescence revealed that uterine Muc1 protein expression was unaltered during the estrous cycle. However, similar to what is observed in the mouse and other species, Muc1 protein decreased at Day 5 of pregnancy in luminal UE. The decrease in Muc1 expression was specific to luminal UE and did not occur in glandular UE. A partial cDNA corresponding to the cytoplasmic tail region of rat Muc1 was generated by a reverse transcription-polymerase chain reaction (RT-PCR) strategy. This cDNA sequence is 89% and 91% identical to the corresponding region of mouse Muc1 at the nucleotide and amino acid levels, respectively. The predicted sequence of rat Muc1 protein has 70-90% identity to the Muc1 protein sequence obtained in other species. Semiquantitative RT-PCR experiments indicated that the mRNA encoding rat Muc1 decreased 57% at Day 5 as compared with the levels found at estrus. This value included mRNA from both luminal and glandular UE and so may underestimate the relative decrease in mRNA in the luminal compartment. In conclusion, we have determined that the levels of rat Muc1 protein and mRNA decrease in the luminal UE at the time of implantation, a pattern similar to that seen in the mouse, baboon, and pig. This supports the general theory that reduction of Muc1 expression is necessary for embryo implantation.

Integrins and Extracellular Matrix Proteins at the Maternal-Fetal Interface in Domestic Animals

“…These heavily glycosylated mucins are thought to project above the apical surface of LE cells to sterically block cell-cell and cell-ECM adhesion [Wesseling et al, 1995;Komatsu et al, 1995] and thereby, Tr access to the uterine LE. The implantation adhesion cascade in rodents is initiated following down-regulation of MUC1 [Surveyor et al, 1995;Carson et al, 1998;DeSouza et al, 1998]. This pattern of MUC1 contrasts with that reported in rabbits and humans where MUC1 expression increases during the receptive phase under the influence of progesterone.…”

Uterine receptivity and the plasma membrane transformation

“…A reduction in surface negativity as well as a reduction in the presence of the morphological glycocalyx in most species so far studied including rats, mice, rabbits, monkeys and humans now seems to be reasonably well accepted [3,6,44,[63][64][65]. Much recent interest has been focussed on one molecular component of the glycocalyx, the large mucin, MUC-1, which is reduced generally on the apical plasma membrane in rats [66], mice [67], monkeys [68], pigs [69] and sheep [97] and is also reduced locally in the region of the blastocyst in rabbits [70]. In the human clinical situation considerable interest has been shown in this molecule because of its possible involvement in idiopathic infertility [71].…”

CCL20/Macrophage Inflammatory Protein 3α and Tumor Necrosis Factor Alpha Production by Primary Uterine Epithelial Cells in Response to Treatment with Lipopolysaccharide or Pam3Cys

“…Alternatively, uterine epithelial cells are known to produce mucin and surfactants that act as physical or chemical barriers to prevent bacteria from interacting with epithelial cell receptors (2,9,36,39). Purified antigens (PAMPs) such as LPS, LTA, and Pam 3 Cys may pass through this barrier to interact with the cell surface receptors.…”