Progesterone stimulates calcitonin gene expression in the uterus during implantation.

Abstract

Implantation of the mammalian embryo into the wall of the uterus is regulated by a timely interplay of the ovarian hormones, estrogen and progesterone. These hormones orchestrate a set of modifications in the uterine endometrium that transforms it from a nonreceptive to a receptive phase allowing the implantation of the developing blastocyst. The molecular and cellular mechanisms underlying this complex process, however, remain largely unknown. To investigate the endocrine basis of uterine receptivity, we employed a gene expression screen technique to identify factors whose expressions are modulated in the rat uterus in response to estrogen and progesterone at the onset of implantation. Here we report that the expression of calcitonin, a peptide hormone involved in calcium homeostasis, is markedly enhanced in the uterus during pregnancy. By Northern blot analysis, we show that the synthesis of calcitonin messenger RNA is induced at the time of implantation. Immunocytochemistry with calcitonin antibody demonstrates further that the peptide is localized in the glandular epithelial cells of the uterus. The antiprogestin drug RU486, which is known to block implantation, abolishes calcitonin expression, suggesting a regulatory role for progesterone in this process. Consistent with this observation, progesterone significantly stimulates calcitonin messenger RNA and protein synthesis in the uteri of ovariectomized animals. Our study, therefore, identifies calcitonin as a stage- and cell-specific marker of progesterone action in the uterus during pregnancy. Estrogen exhibits no significant effect on calcitonin expression when administered alone to ovariectomized animals. However, a low dose of estrogen synergizes with progesterone, and a high dose antagonizes progesterone-mediated gene induction. Both estrogen and progesterone, therefore, modulate calcitonin gene expression in the uterus. The stage-specific regulation of calcitonin is apparently determined by the relative concentrations and the sequences of appearance of these two hormones and possibly other as yet unknown regulatory factors during pregnancy. We propose that calcitonin, a known regulator of calcium levels in the bone and kidney, may play an important regulatory role in the uterus of pregnant animals during the early events leading to implantation of the embryo.

Subfertility, Uterine Hypoplasia, and Partial Progesterone Resistance in Mice Lacking the Krüppel-like Factor 9/Basic Transcription Element-binding Protein-1 (Bteb1) Gene

“…Importantly, the relative abundance of the mRNAs for cyclin D3 and Hoxa10, both of which are normally expressed by stromal cells and known to be intimately involved in P-dependent stromal cell proliferation (46 -48), were reduced in Bteb1-null uteri. By contrast, the mRNA abundance for calcitonin, which is localized exclusively to luminal epithelial cells (45) where Bteb1 expression was essentially undetected, was not altered by Bteb1 ablation. Because up-regulation of cyclin D3 and Hoxa10 genes at the implantation site is tightly associated with decidualization (47,52) and the level of Hoxa10 expression in the endometrium is directly associated with litter size in mice (65), our findings of reduced implantation sites in Bteb1-null uteri, independent of embryo genotype, suggest that Bteb1 in partnership with ligand-bound PR-A likely regulates the stromal expression of these genes.…”

“…To examine whether alterations in expression of specific uterine genes at 6.5 dpc accompany the reduced number of implantation sites noted in Bteb1 Ϫ/Ϫ mice, uteri from WT and Bteb1 Ϫ/Ϫ mice at 6.5 dpc were evaluated by QPCR for expression of progesterone-responsive, Bteb1-regulated, and/or implantation-specific genes (37,38,44,45) (Fig. 7).…”

Adrenomedullin in mammalian embryogenesis

“…Finally, it is of interest that calcitonin-a peptide belonging to the same family as AM, although with lower homology degree than CGRP or amylin (Wimalawansa, 1997)-is markedly induced in the pregnant rat uterus during implantation (Ding et al, 1994). In fact, the loss of calcitonin gene expression upon antisense treatment is accompanied by a severe impairment in the implantation of embryos (Zhu et al, 1998).…”

Expression Profile and Localization of Mouse Calcitonin (CT) Sense/Antisense Transcripts in Pre- and Postnatal Tissue Development

“…Expression of CT in tissue from the brain, prostate and uterus has been reported [3][4][5], and this suggests that it has additional functions other than those for osteoclasts and the kidney. As supporting evidence for additional functions, the CT expression levels have been shown to be related with tumorigenicity of prostate cancer [15] and to be increased in the pregnant rat uterus during implantation [4]. Furthermore, treatment with antisense olignucleotide of CT mRNA severely impairs embryo implantation [18].…”

“…Currently, CT is a therapeutic agent for treatment of bone diseases such as osteoporosis and Paget's disease [10,16]. Expression of CT in tissue from the brain, prostate and uterus has been reported [3][4][5], and this suggests that it has additional functions other than those for osteoclasts and the kidney. As supporting evidence for additional functions, the CT expression levels have been shown to be related with tumorigenicity of prostate cancer [15] and to be increased in the pregnant rat uterus during implantation [4].…”