Archive for the ‘Menstrual Cycle’ Category


We have localized anti-UCRP-immunoreactive protein to decidual cells that have high levels of secretory activity and that contain, and are known to secrete, IGFBP-1. UCRP appears also to be present in cells containing CD45. However, we do not know what the relationship may be between the appearance of UCRP-conjugates and the release of free UCRP from the endometrium. For ethical reasons it is less easy to obtain human uterine flushings to test whether, as in the cow, UCRP is present. It will be of great interest to determine whether UCRP in decidual cells is localized to the secretory apparatus. We have employed qualitative methods of immunohistochemistry and immu-noblotting to study changes in levels and distribution of ubiquitin and UCRP within the endometrium of humans and baboons during pregnancy and, even allowing for the limitations of these methods, the perceived changes appear striking.

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  • DISCUSSION(4)

    Ubiquitin appears to exist in a far greater number of conjugated species as compared to UCRP. This may reflect a greater number of polypeptide targets for ubiquitylation as compared to modification by UCRP and may indicate different cellular roles for these related proteins. The results from im-munoblots again suggest that UCRP-protein conjugates are largely confined to decidual cells. Therefore, we conclude that UCRP, certainly in the conjugated form, is up-regulated in the decidua during pregnancy. Anti-UCRP immunore-activity also appears in the baboon endometrium accompanying decidualization during pregnancy or induced by hCG. The appearance of anti-UCRP immunoreactivity in decidual cells at the beginning of pregnancy indicates that it may play an important role in the establishment of the conceptus.

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  • These novel results suggest that UCRP has a role in decidualization or in the function of the decidual cell. Anti-ubiquitin antibody immunoreactivity in decidual cells is stronger within the nucleus than in the cytoplasm (Fig. 1, e and f), this pattern being reversed with anti-UCRP antibody (Fig. 3g), which suggests that nuclear immunoreactivity in decidual cells may be largely due to the presence of ubiquitin alone. The absence of immuno-reactivity from postmenopausal endometrium would further indicate a role for this system in the activities of this dynamic tissue. We cannot exclude the possibility that UCRP is present in the stroma or epithelial gland cells of nonpregnant tissue, as it is possible that the concentrations are too low to be detected by the antibody employed.

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  • DISCUSSION(2)

    In some cases, anti-ubiquitin immunoreactivity is seen in the region of stroma underlying the luminal epithelium of nonpregnant women (Fig. 1a, labeled ‘‘p’’). Interestingly, these tissues were taken from women in the late secretory phase of the menstrual cycle and may represent cells undergoing pseudo-decidual-ization; together with the observations of immunoreactivity in pregnant tissue (Fig. 1, c, e, and f), the results indicate that decidualization is accompanied by an increase in anti-ubiquitin immunoreactivity. The pattern of anti-ubiquitin-immunoreactive polypeptides after electrophoresis and im-munoblotting (Fig. 2) of nonpregnant and pregnant human endometrium probably represents the presence of many different polypeptides conjugated to multi-ubiquitin chains of different sizes.

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  • Previous studies have established that ubiquitin and UCRP are present in bovine uterine washings, and UCRP is found conjugated to other cellular proteins in bovine endometrium during pregnancy; we have previously reported preliminary data on the distribution of ubiq-uitin in human endometrium. In this paper we report the presence of ubiquitin and UCRP in the human and baboon endometrium, as well as changes in the distribution of these proteins in the endometrium during pregnancy that may provide clues as to their possible specialized roles in this organ.

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  • RESULTS(6)

    The study of baboon tissues allowed us to observe protein distribution in tissue that is not available from humans for practical or ethical reasons. A range of tissues were examined, including those from cycling animals from the follicular (n = 3) and luteal (n = 3) phases. Tissues from pregnant animals were also studied (n = 6). This allowed us to collect decidua from as early as Day 17 of pregnancy and to compare maternal tissues collected from the site of implantation with that from other regions of the uterus at that time. The true decidual reaction in the baboon usually occurs later in pregnancy than in the human, and only in response to a conceptus. Study of specimens from later in pregnancy was therefore important. Tissue was also available from an animal treated with hCG to mimic pregnancy in the absence of invading trophoblast. In contrast to observations in the human tissues (Fig. 1, a and b), there was some anti-ubiquitin immunoreactivity in the stroma of the endometrium from Day 13 after ovulation (Fig. 6a), but no intense staining was observed until Day 71 of pregnancy (Fig. 6b), increasing into the later specimens (decidua from Day 176 of pregnancy showed clear immu-noreactivity, results not shown).

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  • Decidual cells secrete IGFBP-1 and can therefore be readily identified with an antibody to IGFBP-1. Pregnant endometrium simultaneously probed with mouse monoclonal anti-IGFBP-1 and antibody to ubiquitin exhibited IGFBP-1 immunoreactivity in what appeared to be perinuclear vesicles (Fig. 5a, arrow labeled ‘‘v’’). The nucleus of the same cell exhibited anti-ubiquitin antibody immu-noreactivity (Fig. 5b, arrow labeled ‘‘n’’). Anti-ubiquitin immunoreactivity was also visible in cells with much lower levels of IGFBP-1, and indeed the intensity of anti-ubiq-uitin antibody immunoreactivity did not directly correlate with the apparent cellular content of IGFBP-1. Anti-UCRP antibody immunoreactivity (Fig. 5d, arrow) was present in cells also immunoreactive to anti-IGFBP-1 (Fig. 5c, arrow). Anti-UCRP antibody immunoreactivity appeared to be distributed in a granular fashion throughout the cell (Fig. 5d, arrow).

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  • RESULTS(4)

    Incubation of anti-UCRP antibody with recombinant human UCRP (5 ^g/ml antibody) prior to application to sections abolished immunoreactivity (Fig. 3e). In contrast, preincubation of anti-UCRP antibody with ubiquitin (10 ^g/ml antibody) did not significantly alter the levels of anti-UCRP immunoreactivity seen in tissue sections (Fig. 3d). These controls suggest that anti-UCRP im-munoreactivity in tissue sections specifically indicates the presence of UCRP. Insignificant immunoreactivity was observed in fetal membranes (data not shown).

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