Establishment of pregnancy in mammals requires coordinated conceptus-maternal interactions involving numerous hormones, growth factors and cytokines acting via specific receptors in the uterus. Uterine secretions play an important role in establishing synchrony between development of the conceptus and uterine receptivity, as well as in conceptus remodeling, adhesion, implantation and placentation in domestic species. Studies of non-invasive implantation in domestic livestock provide valuable opportunities to investigate fundamental processes of the initial events of apposition, attachment and adhesive interactions that are shared among species. In pigs and sheep, it appears that integrins play a dominant role in these fundamental processes via interactions with extracellular matrix molecules and other ligands to transduce cellular signals in uterine epithelial cells and conceptus trophectoderm. This review considers several of the potential integrin-binding ligands involved in the complex implantation adhesion cascade in pigs and sheep along with in vitro evidence for the transduction of cytoplasmic signals that may be required to sustain fetal and maternal contributions to the formation of the epitheliochorial placenta.
"Both constitutive and cyclical expression of integrins has been observed in the uterus, and they are now considered to be the most decisive criteria for determining uterine receptivity (Lessey et al., 1996). Apical localization of ␣ V ␤ 3 and ␣ V ␤ 5 integrins in the mouse, human, baboon, rabbit, pig and sheep luminal epithelium makes these specific integrin pairs appropriate candidates for mediating trophoblast/epithelial interactions (Bowen et al., 1996; Lessey et al., 1996; Fazleabas et al., 1997; Burghardt et al., 2002; Illera et al., 2003). Moreover, the ␣ V ␤ 3 integrin has also been shown on the surface of the blastocyst (Sutherland et al., 1993), so a reciprocal and cooperative role in attachment is suggested. "
[Show abstract][Hide abstract] ABSTRACT: Summary Prenatal losses are a complex problem. Pregnancy requires orchestrated communication between the embryo and the uterus that includes secretions from the embryo to signal pregnancy recognition and secretion and remodelling from the uterine epithelium. Most of these losses are characterized by asynchronization between embryo and uterus. To better understand possible causes, an analysis was conducted of gene expression of a set of transcripts related to maternal recognition and establishment of rabbit pregnancy (uteroglobin, SCGB1A1; integrin α1, ITGA1; interferon-γ, IFNG; vascular endothelial growth factor, VEGF) in oviduct and uterine tissue at 16, 72 or 144 h post-ovulation and insemination. In the oviduct tissue, a significant decrease in the level of SCGB1A1 mRNA expression was observed from 144 h post-ovulation. In the case of ITGA1, the transcript abundance was initially lower, but mRNA expression increased significantly at 72 and 144 h post-ovulation. For IFNG, a huge decrease was observed from 16 to 72 h post-ovulation. Finally, no significant differences were observed in the VEGF transcript. For the endometrium, the results showed a significant decline in the level of SCGB1A1 mRNA expression from 16 to 144 h post-ovulation induction. The highest levels of ITGA1 transcript were detected at 144 h, followed by the 16 h group and lower at 72 h post-ovulation. For IFNG there were no significant differences among post-ovulation induction times. Finally, it was possible to observe that VEGF mRNA abundance was present at low levels at 16 h post-ovulation and remained low at 72 h, but increased at 144 h. The functional significance of these observations may provide new insights into the maternal role in prenatal losses.
"At this interface there is also expression of multiple integrin subunits that potentially form heterodimeric receptors for SPP1 including ITGAV:ITGB3, ITGAV:ITGB1, ITGAV:ITGB5, and ITGA4:ITGB1 [21,35]. The interaction between the integrin heterodimers and SPP1 likely induces changes in morphology of trophectoderm and mediates adhesion between trophectoderm and uterine LE essential for implantation and placentation [34,93]. "
[Show abstract][Hide abstract] ABSTRACT: There is a dialogue between the developing conceptus (embryo-fetus and associated placental membranes) and maternal uterus which must be established during the peri-implantation period for pregnancy recognition signaling, implantation, regulation of gene expression by uterine epithelial and stromal cells, placentation and exchange of nutrients and gases. The uterus provide a microenvironment in which molecules secreted by uterine epithelia or transported into the uterine lumen represent histotroph required for growth and development of the conceptus and receptivity of the uterus to implantation. Pregnancy recognition signaling mechanisms sustain the functional lifespan of the corpora lutea (CL) which produce progesterone, the hormone of pregnancy essential for uterine functions that support implantation and placentation required for a successful outcome of pregnancy. It is within the peri-implantation period that most embryonic deaths occur due to deficiencies attributed to uterine functions or failure of the conceptus to develop appropriately, signal pregnancy recognition and/or undergo implantation and placentation. With proper placentation, the fetal fluids and fetal membranes each have unique functions to ensure hematotrophic and histotrophic nutrition in support of growth and development of the fetus. The endocrine status of the pregnant female and her nutritional status are critical for successful establishment and maintenance of pregnancy. This review addresses the complexity of key mechanisms that are characteristic of successful reproduction in sheep and pigs and gaps in knowledge that must be the subject of research in order to enhance fertility and reproductive health of livestock species.
Journal of Animal Science and Biotechnology 07/2012; 3(1):23. DOI:10.1186/2049-1891-3-23 · 1.68 Impact Factor
"Besides its role in cell proliferation and differentiation, steroidogenesis, apoptosis, angiogenesis and tissue remodelling, TGFb stimulates the expression of ECM (e.g. fibronectin, SPP1), activates integrin receptors, as well as modulates the activity of proteases and protease inhibitors to facilitate the establishment of a stable connection between uterine LE and trophectoderm (Burghardt et al. 2002; Jaeger et al. 2005). Cells secrete TGFb as a complex with LAP, which contains RGD sequence. "
[Show abstract][Hide abstract] ABSTRACT: Establishment of pregnancy in pigs requires continuous function of corpora lutea and endometrial preparation for embryo implantation. Progesterone regulates expression of many proteins necessary for endometrial remodelling and embryo-maternal communications. Attaining the uterine receptivity involves progesterone priming and loss of progesterone receptors in the uterine epithelium before days 10-12 after oestrus. Spermatozoa and oocytes in oviduct alter secretion of specific proteins that exert beneficial effect on gametes and embryos. Moreover, an appropriate leucocyte activation and maintenance of delicate cytokine balance within the oviduct and uterus are important for early pregnancy. This early local immune response is rather mediated by seminal plasma components. These components also influence prostaglandin (PG) synthesis in the oviduct that is important for gamete and embryo transport. Pregnancy establishment requires the biphasic pattern of oestrogen secretion by conceptuses on days 11-12 and 15-30. Conceptus affects lipid signalling system consisting of prostaglandins and lysophosphatic acid. PG synthesis is changed by conceptus signals in favour of luteoprotective PGE(2) . Additionally, existence of PGE(2) positive feedback loop in the endometrium contributes to increased PGE(2) /PGF(2α) ratio during the peri-implantation period. PGE(2) through endometrial PGE(2) receptor (PTGER2) elevates the expression of enzymes involved in PGE(2) synthesis. Higher PGE(2) secretion in uterine lumen coincides with the elevated expression of HOXA10 transcription factor critical for implantation. A stable adhesion between conceptus and endometrium requires reduction in mucin-1 on the apical surface of epithelium and integrin activation by extracellular matrix proteins. Furthermore, growth factors, cytokines and its receptors are involved in embryo-maternal interactions.
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