In the course of experiments to identify and characterize the factors that function in bovine conceptuses during peri-attachment periods, various transcripts related to the epithelial-mesenchymal transition (EMT) were found. In this study, RNA was extracted from different sets of days 17, 20, and 22 (day 0Zday of estrous) bovine conceptuses and subjected to real-time PCR analysis as well as Western blotting, from which abundances of N-cadherin (CDH2), vimentin, matrix metalloproteinase 2 (gelatinase A, 72 kDa gelatinase, 72 kDa type IV collagenase) (MMP2), and matrix metallopeptidase 9 (gelatinase B, 92 kDa gelatinase, 92 kDa type IV collagenase) (MMP9) mRNAs were determined on day 22, concurrent with (CDH1) mRNA and protein downregulation. Transcription factors in EMT processes were then analyzed and changes in snail homolog 2 (Drosophila) (SNAI), zinc finger E-box binding homeobox 1 (ZEB1), zinc finger E-box binding homeobox 2 (ZEB2), twist homolog 1 (Drosophila) (TWIST1), twist homolog 2 (Drosophila) (TWIST2), and Kruppel-like factor 8 (KLF8) transcripts were found in day 22 conceptuses, while confirming SNAI2 expression by Western blotting. Immunohistochemical analysis revealed that the day 22 trophectoderm expressed the mesenchymal markers N-cadherin and vimentin as well as the epithelial marker cytokeratin. In attempts to identify the molecular mechanisms by which the trophectoderm expressed EMT-related genes, growth factor receptors associated with EMT were analyzed. Upregulation of the growth factor receptor transcripts, fibroblast growth factor receptor 1 (FGFR1), platelet-derived growth factor receptor, alpha polypeptide (PDGFRA), platelet-derived growth factor receptor, beta polypeptide (PDGFRB), and transforming growth factor, beta receptor II (70/80 kDa) (TGFBR2) mRNAs, was found on day 22. The analysis was extended to determine the integrin (ITG) transcripts and found high levels of integrin, alpha 4 (antigen CD49D, alpha 4 subunit of VLA-4 receptor) (ITGA4), integrin, alpha 8 (ITGA8), integrin, beta 3 (platelet glycoprotein IIIa, antigen CD61) (ITGB3), and integrin, beta 5 (ITGB5) mRNAs on day 22. These observations indicate that after the conceptus-endometrium attachment, EMT-related transcripts as well as the epithelial marker cytokeratin were present in the bovine trophectoderm and suggest that the implantation process for noninvasive trophoblasts requires not only extracellular matrix expression but also partial EMT.

Expression of interferon-tau (IFNT), necessary for pregnancy establishment in ruminant ungulates, is regulated in a temporal and spatial manner. However, molecular mechanisms by which IFNT gene transcription is regulated in this manner have not been firmly established. In this study, DNA microarray/RT-PCR analysis between bovine trophoblast CT-1 and Mardin-Darby bovine kidney (MDBK) cells was initially performed, finding that transcription factors GATA2, GATA3, and GATA6 mRNAs were specific to CT-1 cells. These mRNAs were also found in Days 17, 20, and 22 (Day 0 = day of estrus) bovine conceptuses. In examining other bovine cell lines, ovary cumulus granulosa (oCG) and ear fibroblast (EF) cells, GATA2 and GATA3, but not GATA6, were found specific to the bovine trophoblast cells. In transient transfection analyses using the upstream region (-631 to +59 bp) of bovine IFNT gene (bIFNT, IFN-tau-c1), over-expression of GATA2/GATA3 did not affect the transcription of bIFNT-reporter construct in human choriocarcinoma JEG3 cells. Transfection of GATA2, GATA3, ETS2, and/or CDX2, however, was effective in the up-regulation of the bIFNT construct transfected into bovine oCG and EF cells. One Point mutation studies revealed that among six potential GATA binding sites located on the upstream region of the bIFNT gene, the one next to ETS2 site exhibited reduced luciferase activity. In CT-1 cells, endogenous bIFNT gene transcription was up-regulated by over-expression of GATA2 or GATA3, but down-regulated by siRNA specific to GATA2 mRNA. These data suggest that GATA2/3 is involved in trophoblast-specific regulation of bIFNT gene transcription.

No abstract

The transcription factor caudal-related homeobox 2 (CDX2) regulates trophectoderm differentiation, but its function beyond trophectoderm differentiation is not well characterized. CDX2 was shown to regulate a trophoblast-specific gene, interferon τ (IFNT), in the ruminants. However, its regulatory mechanism has not been determined. Here, we report a new role of CDX2 in histone modifications of the IFNT gene. Chromatin immunoprecipitation assays using ovine conceptuses obtained from d 14, 16, 16.5, or 20 of pregnancy (d 0, day of mating) revealed that H3K18 acetylation was highly detectable at the upstream and open reading frame regions of the IFNT gene on d 14 and 16, when CDX2 reached its peak expression. From d 16.5, when the conceptus initiates attachment to uterine epithelial cells, histone acetylation along with CDX2 expression declines. Two candidate CDX2 binding sites (-300 to -294 bp and -293 to -287 bp) of the bovine IFNT gene promoter region were detected from chromatin immunoprecipitation and luciferase assay. When Cdx2 constructs were transfected into bovine ear-derived fibroblast cells, histone acetylation was increased, concurrent with the recruitment of cAMP response element binding protein-binding protein, which has histone acetyltransferase activity. H3K18 acetylation was seen in the proximity of the CDX2 binding region located at the IFNT gene's upstream region in CT-1 cells, but when these cells were treated with specific CDX2 small interfering RNA, H3K18 acetylation was decreased. These findings suggest that CDX2 regulates its targeted gene through cAMP response element binding protein-binding protein recruitment, which correlates with greater histone acetylation.

Following bidirectional communication, the conceptus and the uterine epithelium must establish a proper cell-cell interaction, resulting in the progression of implantation processes. To clarify the mechanism of conceptus attachment to the uterine endometrium, we studied whether vascular cell adhesion molecule (VCAM1) was expressed in bovine conceptuses or endometrium during the peri-attachment period. Uterine VCAM1 expression was minimal in day 17 (day 0Zday of estrus) cyclic and pregnant animals, but increased between days 20 and 22 of pregnancy. In the intercaruncular regions, VCAM1 protein was localized to the luminal and glandular epithelia, whereas in the caruncular regions, VCAM1 protein was detected in the stroma and endothelia of the uterine endometrium. In cultured endometrial epithelial cells (EECs), VCAM1 expression was up-regulated when treated with uterine flushings or growth factor and further increased when EECs were cocultured with bovine trophoblast CT1 cells. VCAM1 expression in CT1 cells was also up-regulated with the use of uterine flushings, and further increased when these cells were cocultured with EECs. Expression of VCAM1 receptor, integrin a 4 (ITGA4) mRNA, increased significantly in day 22 conceptuses. In day 22 pregnant uteri, VCAM1 protein was found in both EECs and conceptuses, but ITGA4 was localized only to trophoblasts. These observations indicate that cell-cell interactions between conceptuses and uterine epithelial cells are required for sufficient VCAM1 and ITGA4 expression in the bovine species and suggest that uterine VCAM1 and conceptus ITGA4 play a role in the establishment of conceptus adhesion to the uterine endometrium.