Cell kinetic study of the endometrium by nonisotopic in situ hybridization for histone H3 messenger RNA and immunohistochemistry for Ki-67 and for estrogen and progesterone receptors

We investigated the cell kinetics of the endometrium in hysterectomy specimens taken for leiomyoma from 22 women with regular ovulatory menstrual cycles. Formalin-fixed, paraffin-embedded tissue sections were examined for proliferating activity using histone H3 messenger RNA in situ hybridization (H3 mRNA-ISH) and immunostaining for the Ki-67 antigen. The relationship of the proliferative activity of endometrial cells to the immunohistochemical expression of the estrogen receptor (ER) and the progesterone receptor (PR) was also examined. During the menstrual cycle, H3 mRNA expression was observed in both the epithelial cells and the stromal cells of the endometrium. In the functional layer, the labeling indices for H3 mRNA (H3 mRNA-LIs) in the epithelial cells peaked in the late proliferative phase, decreased sharply in the early secretory phase, and remained unchanged thereafter. On the other hand, H3 mRNA-LIs of stromal cells displayed two peaks: one in the midproliferative phase and the other in the late secretory phase, the former peak being the greater. In the basal layer, epithelial cells and stromal cells showed low H3 mRNA-LIs and no significant variation throughout the menstrual cycle. The H3 mRNA-LIs correlated well with the Ki-67-LIs and were lower than the corresponding Ki-67-LIs. The regression coefficient (H3 mRNA-LIs against the Ki-67-LIs) was 0.33 for epithelial cells and 0.49 for stromal cells, suggesting that the cell cycle time was longer for epithelial cells than for stromal cells. The proliferative activity of endometrial cells showed close relationships with the expressions of ER and PR in the endometrium. When used in combination with other proliferative markers in paraffin-embedded tissue sections, H3 mRNA-ISH could open broader perspectives on the cell kinetics of the endometrium.     

Proliferative activity in endometrial stromal granulocytes throughout menstrual cycle and early pregnancy.

The proliferative activity in endometrial stromal granulocytes was studied using two approaches. Firstly, mitotic activity was studied in paraffin wax embedded sections of normal non-pregnant endometrium and early pregnancy decidua stained with phloxine-tartrazine. Secondly, the monoclonal antibody Ki67 was applied to cryostat sections of similar tissues. Endometrial stromal granulocytes were identified by their labelling with NKH1, Dako T11, UCHL1 or Dako-LC. The percentage of cases in which endometrial stromal granulocytes showed mitosis was 25%, 75%, 86%, and 93%, respectively in proliferative, early secretory, mid secretory, and late secretory phases, and 14% in early decidua. There were at most one or two endometrial stromal granulocytes in mitosis per 10 high power fields. Double labelled cells were present in small numbers in proliferative endometrium and in moderate numbers in secretory endometrium. Only a few cells in early decidua double labelled with Ki67/T11; moderate numbers of cells double labelled with Ki67/Dako-LC. It is concluded that proliferative activity does occur in endometrial stromal granulocytes and is particularly prominent in the late secretory phase.     

Telomerase activity is found in the epithelial cells but not in the stromal cells in human endometrial cell culture

Telomerase activity is associated with the proliferative activity of cells. In the endometrium, telomerase activity is higher in the proliferative phase than in the secretory phase of the menstrual cycle, suggesting that telomerase activity may occur primarily in the glandular epithelial cells. To test this, a dissociated cell culture of the endometrium was performed, and the telomerase activity in each cell fraction was analysed. Telomerase activity was found in all 10 endometrial tissues of the proliferative phase of the menstrual cycle. Both the fragments of epithelial glands and single cells, which were prepared by enzymatic dissociation, showed telomerase activity. In the 7 day cell culture, it was found in nine out of 10 epithelial cell enriched fractions, but in none of the stromal cell enriched fractions. Flow cytometric analysis showed that the epithelial enriched fraction was contaminated with a predominant number of stromal cells, while the stromal cell enriched fraction was comprised mostly of stromal cells with apparent proliferative activity. Our results suggest that telomerase activity of the endometrium occurs primarily in the epithelial cells in the endometrium and that the stromal cells do not express telomerase activity regardless of their potent proliferative activity.      

Oestrogen receptor alpha and beta mRNA expression in human endometrium throughout the menstrual cycle.

We examined the localization of oestrogen receptor (ER) beta mRNA in the human endometrium throughout the menstrual cycle using non-radioactive in-situ hybridization with Brigati-tailed oligonucleotides. The findings were compared with those of ERalpha in order to examine the possible biological significance of ERbeta in the human endometrium. Both ERalpha and ERbeta mRNA expression were detected in all major human uterine cell types, including glandular epithelial cells, stromal cells and smooth muscle cells of the uterine wall, at every menstrual cycle stage. However, ERalpha mRNA expression was more prominent than that of ERbeta in all cell types throughout the menstrual cycle. In proliferative phase endometrium, ERalpha mRNA was expressed in both glandular epithelial and stromal cells, while ERbeta mRNA was expressed predominantly in glandular epithelial cells. Although the same pattern was observed in the secretory phase, both the ERalpha and ERbeta mRNA expression was relatively weaker. These results suggest that oestrogenic effects occur predominantly through ERalpha, but that ERbeta may also play a role in the modulation of oestrogenic action, especially on glandular epithelial cells in the human endometrium throughout the menstrual cycle.     

Regulation of TNF-alpha mRNA expression in endometrial cells by TNF-alpha and by oestrogen withdrawal

During each menstrual cycle, the human endometrium undergoes a series of orchestrated and well controlled changes in anticipation of the arrival of the blastocyst. In the absence of implantation, the endometrium is shed. The underlying basis of the menstrual bleeding is not clear, however, it seems to be related to steroid hormone withdrawal. We showed that tumour necrosis factor-alpha (TNF-alpha) is released by human endometrium and that endometrial epithelial cells are a major source of TNF-alpha mRNA and protein. We show here that TNF-alpha mRNA shows a specific menstrual cycle-dependent expression. The expression of TNF-alpha is mostly minimal throughout the proliferative, early and mid-secretory phases. Expression of TNF-alpha mRNA, however, is increased in the human endometrium in the late secretory phase and during endometrial bleeding. Such a menstrual cycle-dependent expression suggests that specific signals regulate the expression of TNF-alpha mRNA in the human endometrium. In vitro, the expression of TNF-alpha mRNA in endometrial epithelial cells could be regulated by exogenous TNF-alpha. This induced expression was both time- and dose-dependent. In vitro, the TNF-alpha mRNA expression was not altered by oestrogen, progesterone, or both, in the endometrial epithelial cells under conditions that maintain the steroid hormone receptors. However, in vivo, oestrogen withdrawal led to an enhanced expression of TNF-alpha in endometrial epithelial cells. These findings suggest that the up-regulation of TNF-alpha in human endometrium in the late secretory phase may be related to the falling serum oestrogen concentration at the end of the menstrual cycle as well as the potentiating effect of released TNF-alpha on its own mRNA expression.     

Endothelin synthesis and receptors in human endometrium throughout the normal menstrual cycle

This study was undertaken to investigate the presence of messengerRNA (mRNA) for prepro-endothelin-l (ET-1) and the known receptorsubtypes (ET_A and ET_B) in human endometrium at different stagesof the menstrual cycle obtained at hysterectomy. Northern blotanalysis revealed expression of ET-1 mRNA in human endometriumduring the normal menstrual cycle. The concentration of ET-1mRNA in endometrial tissue was greater during the menstrualand proliferative phases than during the ovulatory and secretoryphases. Immunoreactive ET-1 was secreted into the medium ofisolated endometrial stromal cells. Oestradiol and progesteronesignificantly attenuated ET-1 release in endometrial stromalcells cultured for 6 days. ET_A and ET_B mRNA were also presentin endometrial tissue of the normal cycle. The concentrationof ET_A receptor mRNA was greater in the proliferative phasethan in the secretory phase, whereas expression of ET_B mRNAincreased in menstrual phase. ET-1 significantly increased extracellularaccumulation of cyclic AMP (cAMP), intracellular generationof inositol phosphates and significantly enhanced DNA synthesisin cultured endometrial stromal cells from the proliferativephase. Our results showed that human endometrial cells synthesizedand released ET-1, and contained ET_A and ET_B receptors whichwere functionally coupled to phosphoinosttide breakdown andto adenylate cyclase with the increase of cAMP by ET-1 stimulation.Our findings suggest that ET-1 may have a potential autocrineand/or paracrine function in human endometrial stromal cells. cyclic AMP/endothelin-l synthesis/human endometrium/inositol phosphate/receptors     

Molecular aspects of implantation: Variation in the expression of cellular retinoid binding proteins in human endometrium throughout the menstrual cycle

Human endometrium is a glandular epithelial tissue with a substantialunderlying stroma. Under the influence of ovarian steroids,endometrium undergoes a cyclical pattern of proliferation followedby secretory differentiation. Since retinoids promote the differentiationof many epithelia to secretory phenotypes they may be involvedin controlling the secretory differentiation of human endometrialepithelium. Cytosolic binding proteins for retinol (cellularretinol binding protein) and retinoic acid (cellular retinoicacid binding protein) may play an important part in regulatingthe availability of retinoic acid to its nuclear receptors andwe have therefore asked whether expression of mRNA for theseproteins varies in relation to endometrial differentiation.In a series of 54 endometrial biopsies, both endometrial epithelialand stromal cells expressed mRNA for cellular retinol bindingprotein type I at a constant level throughout the menstrualcycle. Cellular retinoic acid binding protein type II was alsoexpressed but the level of expression varied dramatically, beingelevated in the proliferative phase and depressed during thesecretory phase of the menstrual cycle in both epithelial andstromal cells. These data suggest that cytosolic binding proteinsmodulate the supply of retinoic acid to the nuclei of endometrialcells during the menstrual cycle and that retinoic acid is involvedin the cyclical control of endometrial differentiation.     

Tenascin expression in the human endometrium and in endometrial adenocarcinomas.

To investigate the involvement of tenascin, an extracellular matrix glycoprotein, in epithelial growth and malignancy, its specific distribution pattern in the human uterus was examined immunohistochemically. During the proliferative phase of the menstrual cycle, this antigen was found as a sharp band around the endometrial glands. The immunoreactivity persisted until the early postovulatory phase of the menstrual cycle, but was not detectable in the glandular or stromal compartment during this later secretory stage, instead endometrial arterioles were immunostained. In marked contradistinction, when antibodies directed against tenascin were applied to sections of endometrial adenocarcinoma, almost the entire extracellular space stained, whereas the neoplastic cells themselves were nonreactive, whatever the degree of tumor differentiation. In precancerous proliferative lesions of the endometrium, tenascin's presence was variable. It was detectable around some superficial glands demonstrating cystic hyperplasia and around all deeply situated glands at the endometrial/myometrial interface. In cases of adenomatous hyperplasia, tenascin immunolocalized throughout the extracellular space of the stroma and the staining intensity was increased as the hyperplasia became more atypical. We therefore conclude that tenascin may be a stromal marker for epithelial proliferative states including those associated with malignancies of the endometrium.     

Expression of Telomerase Activity in Human Endometrium Is Localized to Epithelial Glandular Cells and Regulated in a Menstrual Phase-Dependent Manner Correlated with Cell Proliferation

Telomerase activity is observed in most malignant tumors and germ cells, whereas normal somatic cells usually do not express it. Human endometrium is composed of glandular and stromal components and exhibits dramatic changes in proliferative activity during the menstrual cycle, which is exquisitely regulated by estrogen function. We previously reported that normal human endometrium expresses telomerase activity. However, it remains unclear which of the above components are the major sources of telomerase activity and how levels of telomerase activity are regulated over the menstrual cycle. Quantitative analysis of telomerase activity revealed that it changes dramatically over the course of the menstrual cycle and is strictly regulated in a menstrual-phase-dependent manner. Maximal activity equivalent to that in endometrial cancer was present in late proliferative phase, and minimal activity in late secretory phase. Postmenopausal endometrium and endometrium treated with anti-estrogen drugs exhibited decreased telomerase activity. Testing isolated epithelial glandular cells and stromal cells, we found that telomerase activity was localized to epithelial glandular cells. In situ RNA hybridization analysis also revealed epithelial-specific expression of human telomerase RNA. In vitro analysis of cultured epithelial cells demonstrated that telomerase activity is correlated with epithelial proliferation but not affected by estrogen treatment. These findings suggest that expression of telomerase activity is specific to epithelial cells and linked to cell proliferative status. The involvement of estrogen in telomerase regulation remains to be elucidated.     

Secretory endometrium highly expresses urocortin messenger RNA and peptide: possible role in the decidualization process

BACKGROUND: Urocortin (UCN) gene expression and synthesis have been reported in epithelial and stromal cells of the human endometrium. In this study we evaluated (i) UCN messenger RNA (mRNA) expression and peptide production in uterine specimens collected throughout the endometrial cycle, (ii) UCN secretion after decidualization of cultured human endometrial stromal cells (HESCs) and (iii) the effect of UCN on endometrial decidualization. METHODS: HESCs were isolated from samples of human endometrium collected from healthy patients with normal menstrual cycle and cultured in presence of cAMP, 17-beta-estradiol (E(2)) + medroxyprogesterone acetate (MPA) and UCN. UCN levels were measured in endometrial extracts by an enzyme immunoassay, and changes of endometrial UCN mRNA expression were measured by RT-PCR analysis. RESULTS: UCN peptide concentrations and mRNA expression were highest in the secretory phase of the menstrual cycle (P < 0.001, late secretory versus early and late proliferative phase) and higher in the late than the early secretory phase (P < 0.01). After decidualization of HESC with cAMP or E(2) + MPA, UCN levels rose in parallel with prolactin concentrations by days 6 (P < 0.01, for all). Finally, the addition of UCN to HESCs, with or without E(2) + MPA, induced the release of prolactin. CONCLUSIONS: The evidence that (i) UCN is highly expressed in the secretory phase of the endometrial cycle; (ii) cAMP and E(2) + MPA modulate secretion of UCN and (iii) UCN induces HESCs decidualization together suggest a possible role for UCN in endometrial physiology.     

Cytomorphologic appearances of normal endometrial cells during different phases of the menstrual cycle: A cytologic approach to endometrial dating

From 1988 to 1992, 156 endometrial cytologic preparations were procured by directly brushing hysterectomy specimens from premenopausal women with normal endometrium and regular menstruation. These brushing smears were obtained by using the cyto-brush and/or the endometrial brush. The cytologic findings were correlated with histologic endometrial dating. Of these, 56 cases were classified as proliferative phase endometrium; 89, secretory phase; and 11, menstrual phase. The cytomorphologic features of endometrial glandular and stromal cells at different stages of the menstrual cycle are summarized and compared. On the basis of the different cytomorphologic features of glandular and stromal cells seen during various phases of the cycle, cytologic differentiation between proliferative phase and secretory phase endometria can be readily established. It appears possible to date the endometrium by direct endometrial brushing technique. It is also possible to determine if the glandular and/or stromal cells seen in the endocervical smears procured by the cytobrush are normal endometrial cells from cytobrush extraction, and are consistent with the date of the menstrual cycle, which should be made clear in the cytology report. © 1995 Wiley-Liss, Inc.     

Plasma membrane and vesicular monoamine transporters in normal endometrium and early pregnancy decidua

The uterus is innervated by adrenergic sympathetic fibres, and the endometrium has a capability for endogenous monoamine synthesis. Extracellular monoamine levels are regulated primarily through re-uptake by specific membrane-bound transporter proteins dopamine transporter (DAT), norepinephrine transporter (NET) and serotonin transporter (SERT). Intracellular storage of monoamines involves vesicular transporter proteins (VMAT1 and VMAT2). This study explored gene expression of the monoamine transporters in normal endometrium throughout the menstrual cycle and early decidua. In-situ hybridization histochemistry revealed three general classes of expression patterns: (i). epithelial expression of NET mRNA; (ii). increasing stromal expression of VMAT2 mRNA in the proliferative phase; and (iii). increasing epithelial expression of VMAT2 mRNA during the secretory phase. Real time PCR showed low expression levels of NET in all phases of the endometrial cycle and a higher expression of VMAT2 mRNA in the mid-secretory phase. Our results suggest that several monoamine transporters may have menstrual cycle phase-specific functions in endometrial biology by maintaining adequate levels of monoamines. Re-uptake and regulated release of monoamines may also modulate several steps of the reproductive processes such as embryo implantation and decidua formation.     

Tissue inhibitor of metalloproteinases (TIMP)-1, -2 and -3 in human endometrium during the menstrual cycle

The extensive remodelling of the human endometrium throughout the menstrual cycle is accompanied by changes in production of matrix metalloproteinases, the activity of which can be inhibited by specific tissue inhibitors or by tissue inhibitors of metalloproteinases (TIMP)s with a 1:1 stoichiometry. This study immunolocalized TIMP-1, TIMP-2 and TIMP-3 in dated normal human endometrium across the menstrual cycle and examined cultured endometrial cells for their production. All three TIMPs were present in the major cellular compartments, luminal epithelium, glands, stroma, endothelial cells and vascular smooth muscle cells with the most intense immunoreactivity in the luminal epithelium. TIMP-1 and -3 were lower in the mid-to-late proliferative phase with a nadir of TIMP-3 particularly in the late proliferative phase. Decidualized stromal cells stained strongly positive for TIMP-1, -2 and -3. Cells of haematopoietic origin never stained. Monensin treatment of tissue resulted in accumulation of TIMPs in all cellular compartments but particularly of TIMP-1 in epithelium. Cultured endometrial stromal cells released more TIMP-1 than TIMP-2 or TIMP-3 into culture medium and all were increased following decidualization in vitro. Epithelial cells in culture produced less TIMPs than stromal cells, and only a few epithelial cells in each culture were immunopositive for TIMP-1. The ubiquitous distribution of TIMPs implicates them in maintenance of endometrial integrity, with changes in the matrix metalloproteinases without concomitant changes in TIMPs determining endometrial matrix degradation.      

Endothelin synthesis and receptors in human endometrium throughout the normal menstrual cycle

This study was undertaken to investigate the presence of messengerRNA (mRNA) for prepro-endothelin-I (ET-1) and the known receptorsubtypes (ETA and ETB) in human endometrium at different stagesof the menstrual cycle obtained at hysterectomy. Northern blotanalysis revealed expression of ET-1 mRNA in human endometriumduring the normal menstrual cycle. The concentration of ET-1mRNA in endometrial tissue was greater during the menstrualand proliferative phases than during the ovulatory and secretoryphases. Immunoreactive ET-1 was secreted into the medium ofisolated endometrial stromal cells. Oestradiol and progesteronesignificantly attenuated ET-1 release in endometrial stromalcells cultured for 6 days. ETA and ETB mRNA were also presentin endometrial tissue of the normal cycle. The concentrationof ETA receptor mRNA was greater in the proliferative phasethan in the secretory phase, whereas expression of ETB mRNAincreased in menstrual phase. ET-1 significantly increased extracellularaccumulation of cyclic AMP (cAMP), intracellular generationof inositol phosphates and significantly enhanced DNA synthesisin cultured endometrial stromal cells from the proliferativephase. Our results showed that human endometrial cells synthesizedand released ET-1, and contained ETA and ETB receptors whichwere functionally coupled to phosphoinositide breakdown andto adenylate cyclase with the increase of cAMP by ET-1 stimulation.Our findings suggest that ET-1 may have a potential autocrineand/or paracrine function in human endometrial stromal cells.     

Urocortin 2 and urocortin 3 in endometriosis: evidence for a possible role in inflammatory response

Urocortin 2 (Ucn 2) and urocortin 3 (Ucn 3) are neuropeptides expressed by human endometrium. This study evaluated (i) the expression of Ucn 2 and Ucn 3 mRNA in endometriotic lesions and in endometrium of women with endometriosis; (ii) the effect of Ucn 2 and Ucn 3 on cytokines secretion from cultured endometrial stromal cells. Endometriotic tissue was collected from endometrioma (n=39); endometrial specimens were obtained from women with (n=39) and without (n=41) endometriosis throughout menstrual cycle. Tissue specimens were analysed for Ucn 2 and Ucn 3 mRNA expression and peptide localization; the effects of Ucn 2 or Ucn 3 on tumour necrosis factor (TNF-α) and interleukin (IL-4) secretion from cultured endometrial stromal cells was studied. Ucn 2 and Ucn 3 mRNA expression and localization were assessed by RT-PCR and by immuohistochemistry, respectively; cytokines secretion were measured by ELISA. Results showed that endometriotic tissue expressed both Ucn 2 and Ucn 3, with Ucn 3 expression higher in ectopic than in eutopic endometrium. Endometrial Ucn 2 mRNA expression in controls showed peak values at early proliferative phase, while in endometriotic patients low expression and no significant changes throughout menstrual cycle were observed. Endometrial Ucn 3 mRNA expression was highest in late secretory phase in controls, while in endometriotic patients low levels and no menstrual-cycle-related changes were found. When added to cultured endometrial cell cultures, Ucn 2 significantly increased TNF-α (P<0.01) and IL-4 (P<0.001), while Ucn 3 induced an increase of IL-4 secretion (P<0.01). In conclusion, endometriotic tissue expressed and localized Ucn 2 and Ucn 3; patients with endometriosis showed Ucn 2 and Ucn 3 mRNA expression in eutopic endometrium lower than in control group, with no endometrial cycle-related changes. Ucn 2 and Ucn 3-modulated TNF-α and IL-4 secretion from culture endometrial cells. These data suggest a possible involvement of Ucn 2 and Ucn 3 in the mechanisms of endometriosis.     

Thioredoxin expression in the human endometrium during the menstrual cycle

Human thioredoxin, a cellular disulphide reducing protein, is known to be secreted by some types of cells and to display unique extracellular activities including modulation of cytokine actions and protection of the cell against damage from oxidative stress. This study has been undertaken to investigate the pattern of expression and tissue distribution of thioredoxin in human endometrium during the menstrual cycle. Immunohistochemical studies showed increased thioredoxin immunoreactivity in the glands of the secretory phase compared to those of the proliferative phase. Although the staining of thioredoxin was relatively intense in predecidual stromal cells, the most prominent staining of thioredoxin was present in both glands and stroma of the endometrium in the early secretory phase of the menstrual cycle. Northern hybridization analyses revealed that expression of thioredoxin mRNA in the endometrium of the early secretory phase was approximately 3-fold compared to the other phases of the menstrual cycle, consistent with the results of the immunohistochemical studies. These results suggest that both protein and gene expression of thioredoxin in the endometrium are menstrual cycle phase-specific and highly active in the phase of endometrial differentiation which occurs in preparation for implantation (early secretory phase of the menstrual cycle). Thioredoxin expressed in the early secretory phase of the menstrual cycle may be advantageous for blastocyst implantation.      

Expression patterns of cathepsins B, H, K, L and S in the human endometrium

Cathepsins B, H, K, L and S belong to the family of lysosomal cysteine proteinases and participate in a variety of proteolytic processes, including degradation of the extracellular matrix (ECM). In the present study, we used Northern hybridization to demonstrate the presence of mRNAs for cathepsins B, H, K, L and S in human endometrium during both the proliferative and secretory phases of menstrual cycle. The mRNA levels for cathepsins H and K were significantly lower in secretory phase endometrium in comparison with proliferative phase endometrium. Immunohistochemical localization of the different cathepsins revealed widespread distribution of all cathepsins in both stroma and epithelial cells. The immunoreactivity for cathepsins B, H and K exhibited changes related to endometrial location and/or to the phase of the cycle. The strongest immunoreactivity for cathepsins B, H, L and S was observed in the surface epithelium of the endometrium. The staining for cathepsins was predominantly intracellular, but immunoreactivity was also detected on the surface of small lymphoid cells in the stroma. The findings of the present study suggest that cysteine cathepsins are needed for normal development and function of human endometrium during both the proliferative and secretory phases.     

Expression of interleukin-11 during the human menstrual cycle: coincidence with stromal cell decidualization and relationship to leukaemia inhibitory factor and prolactin

Interleukin-11 (IL-11) is crucial in the decidualization response of the uterine stroma to the implanting blastocyst in the mouse. This study examined the localization and expression of IL-11 in human endometrium throughout the menstrual cycle and of prolactin and leukaemia inhibitory factor (LIF) in secretory phase endometrium. The mRNA expression of IL-11 receptor alpha and the signalling component, gp130, in endometrial tissue were also determined. Immunoreactive IL-11 was highest in the secretory phase and present in decidualized stromal cells, glandular epithelial cells, endothelial and smooth muscle cells, and the mRNA expression was verified by in-situ hybridization. Decidual cells showed the most intense staining. IL-11 receptor alpha and gp130 mRNA were detected throughout the cycle with minimal variation. Expression of IL-11 mRNA and protein preceded that of prolactin. While immunoreactive prolactin was found in stromal, decidual and glandular epithelial cells, prolactin mRNA was confined to decidual cells. In contrast, endometrial LIF expression preceded IL-11 but was largely confined to the glandular epithelium. The sequence of appearance of LIF, IL-11 and prolactin suggests a synchronized role for each in the differentiation of the endometrium. The cyclical changes and cell type specific expression of IL-11 suggests a potential role in the decidualization of stromal cells.