Estrogen Receptor β (ERβ) Is Expressed Differently From ERα in Bovine Placentomes

Abstract

The functions of placental estrogens in cattle are still poorly understood. In order to investigate a putative role as local regulators of placental growth, differentiation and functions via estrogen receptor β (ERβ), the expression of this ER isoform was determined in bovine placentomes obtained from cows at midgestation (days 110 - 150; n = 7), late gestation (days 180 - 280; n = 9), from prepartal cows (sampling immediately after the prepartal decline in maternal progesterone blood levels became obvious; n = 3) and from cows at normal term (n = 5) on the protein and mRNA level. By means of immunohistochemistry using a monoclonal antibody against human ERβ (clone PPG5/10), nuclear signals were found in numerous cell types of the fetal (cotyledon) and maternal (caruncle) component of the placentomes with highest intensities in mature trophoblast giant cells (TGC), fetal and maternal vascular cells and caruncular stromal cells, in which the percentage of positive cells increased from 58.9 ± 2.3 and 59.1 ± 3.3 at mid- and late gestation to 65.1 ± 4.9 and 69.4 ± 4.2 in prepartal and parturient cows, resp. (p < 0.0001). Clear staining of uninucleated trophoblast cells was only observed in prepartal and parturient animals. Conventional RT-PCR confirmed ERβ expression in caruncles and cotyledons at all phases under investigation. With semi-quantitative real-time RT-PCR higher levels of ERβ-specific mRNA were measured in cotyledons compared to caruncles (p < 0.01). The results show that in contrast to ERα, which is only expressed in the caruncle, ERβ is also extensively expressed in the cotyledon and suggest a role of ERβ primarily in TGC differentiation and placental angiogenesis and/or vascular functions.

Key words

Cattle - placenta - estrogen receptor beta - trophoblast giant cells

References

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