Placental development during early pregnancy in sheep: nuclear estrogen and progesterone receptor mRNA expression in the utero-placental compartments

Abstract

Sex steroid hormones are major regulators of uterine and placental growth and functions, as well as many other biological processes. To examine the mRNA expression of nuclear estrogen (ESR1 and 2) and progesterone (PGRAB and B) receptors in different compartments of the uterus and placenta, tissues were collected in experiment 1, on days 16, 20 and 28 after natural mating (NAT) and on day 10 after estrus (non-pregnant controls [NP]); and in experiment 2, on day 22 of NAT, and pregnancies established after transfer of embryos generated through mating of FSH-treated ewes (NAT-ET), in vitro fertilization (IVF), or in vitro activation (IVA; parthenotes). In experiment 1, ESR1 expression in endometrial stroma (ES), endometrial glands (EG) and myometrial blood vessels (MBV), ESR2 in endometrial blood vessels (EBV), PGRAB in ES, and PGRB in ES, EG and MBV was greater in pregnant than NP depending on day of pregnancy. Day of pregnancy affected expression of ESR1 in MBV, ESR2 in EBV and MBV, and PGRAB in ES. In experiment 2, ESR1, PGRAB and PGRB in EG, but not in other compartments, was greater in NAT-ET than NAT, and PGRB was greater in NAT-ET than the IVF. These data demonstrated that the ESR and PGR expression was different in pregnant vs. NP ewes in selected compartments, and was affected by pregnancy stage or embryo origin in selected utero-placental compartments. Thus, sex steroid hormone mRNA expression is differentially regulated in a spatio-temporal manner in uterus and placenta, and is affected by application of assisted reproductive technology in sheep.

Differential Expression of Circular RNAs in Polytocous and Monotocous Uterus during the Reproductive Cycle of Sheep

“…The GnRH/GnRHR system might play a key role in promoting trophoblast invasion of the maternal endometrium during embryo implantation [62,63]. Estrogen is the major regulator of placental growth and uterine functions in sheep [64]. In the luteal phase, estrogen plays a regulatory role in vascular functions of the uterus and placenta, such as regulation of blood flow, vascular tone, promoting angiogenesis, and vascular remodeling [65,66,67].…”

Programming of Embryonic Development

“…In sheep, we, and others, have recently demonstrated that utero-placental vascularization, expression of several angiogenic factors, receptors for progesterone and estrogen, and DNA methyl transferases, as well as global DNA methylation and markers of growth all were altered in the developing placenta during early pregnancy after transfer of embryos obtained through IVF or in vitro activation (IVA; parthenotes, which have only a maternal genome [9,24,[32][33][34][35]58]). One of the very interesting observations from this work is that even when they are derived from naturally mated ewes and transferred to recipients, the embryos show many of the same defects as IVP embryos [9,24,32,35], implying that improvements in embryo collection, culturing, and transfer methods are sorely needed.…”

“…Comparison of placental development in natural pregnancies and pregnancies achieved by various ART, such as after transfer of embryos created through cloning or IVF, has demonstrated numerous significant effects of ART on placental and fetal growth and development, as well as offspring outcomes in several species [9,11,34]. In various animals, including mice, cattle, and sheep, impaired placental steroid metabolism, abnormal offspring syndrome, increased duration of gestation, and altered placental vascular development, have been reported with the use of ART [9,11,23,24,[32][33][34][35]. In addition, in sheep, use of ART significantly decreased fetal size at the third week of pregnancy and this was accompanied by decreased placental vascularity and cell proliferation, and altered expression of genes involved in epigenetic processes (e.g., 5-methyl cytosine and DNA methyl transferases), as well as factors involved in regulation of placental growth (e.g., steroid hormone receptors) and angiogenesis (e.g., several angiogenic and growth factors [24,32,33,35,55]).…”

“…In various animals, including mice, cattle, and sheep, impaired placental steroid metabolism, abnormal offspring syndrome, increased duration of gestation, and altered placental vascular development, have been reported with the use of ART [9,11,23,24,[32][33][34][35]. In addition, in sheep, use of ART significantly decreased fetal size at the third week of pregnancy and this was accompanied by decreased placental vascularity and cell proliferation, and altered expression of genes involved in epigenetic processes (e.g., 5-methyl cytosine and DNA methyl transferases), as well as factors involved in regulation of placental growth (e.g., steroid hormone receptors) and angiogenesis (e.g., several angiogenic and growth factors [24,32,33,35,55]). For early pregnancy in cows, both greater and lesser crown-rump length have been reported for fetuses created in vitro and then transferred compared to fetuses created in vivo [56,57].…”

“…Importantly for the topic of this review, functional defects due to maternal underor overnutrition or ART that have been documented during the periconceptual period include reduced embryonic development to blastocyst stage after IVF and embryo culture [23], reduced embryo-fetal growth [23,24], and altered nutrient supply to the developing fetus [25][26][27][28][29]. Assisted reproductive techniques also altered placental angiogenesis [9,[30][31][32], global DNA methylation [24], and expression of steroid receptor mRNA and proteins [11,[33][34][35]. Additionally, assisted reproductive techniques and moderate maternal nutrient restriction altered expression of gap junctions and chemokines and chemokine receptors in placenta [36,37]; altered expression of endogenous retroviruses, interferon-tau, and pregnancy-specific protein-B, as well as nutrient transporters, in placenta [25,27,38,39]; and altered gene expression during early development of fetal organs [40].…”