Identification of trophoblast-specific binding sites for GATA-2 that are essential for rat placental lactogen-I gene expression

Tracing the cis-regulatory changes underlying the endometrial control of placental invasion

Among eutherian (placental) mammals, placental embedding into the maternal endometrium exhibits great differences, from being deeply invasive (e.g., humans) to noninvasive (e.g., cattle). The degree of invasion of placental trophoblasts is positively correlated with the rate of cancer malignancy. Previously, we have shown that fibroblasts from different species offer different levels of resistance to the invading trophoblasts as well as to cancer cell invasion. Here we present a comparative genomic investigation revealing cis-regulatory elements underlying these interspecies differences in invasibility. We identify transcription factors that regulate proinvasibility and antiinvasibility genes in stromal cells. Using an in vitro invasibility assay combined with CRISPR-Cas9 gene knockout, we found that the transcription factors GATA2 and TFDP1 strongly influence the invasibility of endometrial and skin fibroblasts. This work identifies genomic mechanisms explaining species differences in stromal invasibility, paving the way to therapies targeting stromal characteristics to regulate placental invasion, wound healing, and cancer dissemination.

Transcriptional regulation of the chicken CRHR2 gene by pituitary transcription factors

Corticotropin-releasing hormone (CRH) is known to act as a potent thyrotropin-releasing factor in non-mammalian species such as chicken and bullfrog. This interaction is mediated by type 2 CRH receptors (CRHR2) expressed by the thyrotropes in the pituitary gland. However, the response elements (REs) and their corresponding transcription factors (TFs) that control CRHR2 expression in thyrotropes are not known. Since thyrotrope-specific expression of the β-subunit of thyrotropin is synergistically stimulated by the co-expression of POU1F1 and GATA2, we hypothesised that in non-mammalian vertebrates like chicken, CRHR2 expression is controlled by the same TFs and that their REs are present in the chicken CRHR2 gene promoter. In situ hybridisation and immunohistochemistry suggest that chicken thyrotropes, like those of mammals, express the mRNAs for the TFs GATA2, POU1F1 and PITX1, but not NR5A1. Using luciferase reporter assays, we show that both GATA2 and PITX1 can activate the promoter of CRHR2, but PITX1 requires a functional GATA2 RE to be present. POU1F1 alone did not affect promoter activity, but synergistically increased the effect of GATA2. Promoter deletion analysis and mutagenesis showed that essential GATA2 and PITX1 REs are located between 116 and 198 bp upstream of the start codon. These REs are highly conserved in non-mammalian species. Additionally, NR5A1 (steroidogenic factor 1) suppressed both GATA2- and PITX1-induced promoter activity and may therefore play a role in restricting CRHR2 expression in gonadotropes. We conclude that the expression of CRHR2 in chicken thyrotropes is stimulated by GATA2 with interactions with POU1F1 and PITX1, in the absence of NR5A1.

Extracellular glucose levels in cultures of undifferentiated mouse trophoblast stem cells affect gene expression during subsequent differentiation with replicable cell line-dependent variation

Mouse trophoblast stem cells (TSCs) have been established and maintained using hyperglycemic conditions (11 mM glucose) for no apparent good reason. Because glucose metabolites are used as resources for cellular energy production, biosynthesis, and epigenetic modifications, differences in extracellular glucose levels may widely affect cellular function. Since the hyperglycemic culture conditions used for TSC culture have not been fully validated, the effect of extracellular glucose levels on the properties of TSCs remains unclear. To address this issue, we investigated the gene expression of stemness-related transcription factors in TSCs cultured in the undifferentiated state under various glucose concentrations. We also examined the expression of trophoblast subtype markers during differentiation, after returning the glucose concentration to the conventional culture concentration (11 mM). As a result, it appeared that the extracellular glucose conditions in the stem state not only affected the gene expression of stemness-related transcription factors before differentiation but also affected the expression of marker genes after differentiation, with some line-to-line variation. In the TS4 cell line, which showed the largest glucose concentration-dependent fluctuations in gene expression among all the lines examined, low glucose (1 mM glucose, LG) augmented H3K27me3 levels. An Ezh2 inhibitor prevented these LG-induced changes in gene expression, suggesting the possible involvement of H3K27me3 in the changes in gene expression seen in LG. These results collectively indicate that the response of the TSCs to the change in the extracellular glucose concentration is cell line-dependent and a part of which may be epigenetically memorized.

Expression and potential role of GATA factors in trophoblast development

Despite exhaustive studies, molecular mechanisms governing blastocyst formation, implantation to the uterine endometrium and placentation have not been definitively characterized. GATA family proteins are a group of zinc finger transcription factors, for which gene ablations eventually result in embryonic death later in pregnancy. These findings suggested that GATA factors are not essential for early embryonic development. However, recent studies from our laboratory and others have revealed that GATA proteins are involved in the regulation of key genes expressed by the trophectoderm that underpin the transition from the morula to trophoblast, and trophectoderm maintenance. Consequently, it is important to consider the current understanding how GATA factors govern early trophectoderm development.

DNA methylation contributes to the tissue-specific expression of the rPL-Iv gene

To understand the tissue-specific expression of the rat placental lactogen-I variant (rPL-Iv) gene, we investigated the methylation pattern of the 5'-flanking region of this gene in various rat tissues. We report that the 5'-flanking region of the rPL-Iv gene was hypomethylated in placenta that expressed the gene and hypermethylated in those tissues that did not express the gene. Moreover, the intron region of the rPL-Iv gene was hypomethylated in the placenta, but hypermethylated in the liver, kidney and pituitary. Although there are 5 CpG sites and the density of CpG dinucleotide is lower within 2 kb of the rPL-Iv 5'-flanking region, the methylated promoter reporter gene produced strong repression in the transcriptional activity of the gene. In addition, the 5'-flanking and intron regions of the rPL-Iv gene were hypomethylated on day 12 of gestation, and the methylation pattern in the placenta remained unchanged from mid-pregnancy until term. The entire genomic region of the rPL-Iv gene might be hypermethylated in tissues other than the placenta, within which its methylated status repress expression of the placenta-specific rPL-Iv gene. Interestingly, the methylation status of the intron region of the rPL-Iv in proliferating Rcho-1 cells was changed to the unmethylated status on day 8 and 12 of differentiation of Rcho-1 cells. These results demonstrate that demethylation in the rPL-Iv upstream region was induced at an early stage of placental development, and once the 5'-flanking region of the rPL-Iv had been demethylated, its status on the rPL-Iv genomic region was continued during pregnancy. Taken together, these results suggest that DNA methylation is responsible for the silencing of tissue-specific genes in non-expressing cells, while defined combinations of trophoblast factors dictate the expression of unmethylated rPL-Iv gene in placenta trophoblast cells.