F OPN mRNA- and protein-positive cells in the stratum compactum of

F OPN mRNA- and protein-positive cells in the stratum compactum of the stroma on DayJohnson (2-methoxy-5-methylphenyl)boronic acid et al. Journal of Animal Science and Biotechnology 2014, 5:56 http://www.jasbsci.com/content/5/1/Page 5 ofof the estrous cycle and pregnancy suggest that these are immune cells. Certainly Eta-1/OPN, is an established component of the immune system that is secreted by activated T lymphocytes [15]. It is reasonable to speculate that because insemination in pigs is intrauterine, OPN expressing immune cells may protect against pathogens introduced during mating. A similar pattern of distribution of OPN-producing cells is also evident in the allantois of the placenta beginning between Days PubMed ID:https://www.ncbi.nlm.nih.gov/pubmed/14960617 20 and 25 of pregnancy, and the number of these cells increases as gestation progresses [58]. The identity of these cells remains to be determined. OPN expression in uterine LE increases markedly during the peri-implantation period of pigs, but is never observed in uterine LE during the estrous cycle [59]. OPN mRNA is initially induced by conceptus estrogens in discrete regions of the LE juxtaposed to the conceptus just prior to implantation on Day 13, then expands to the entire LE by Day 20 when firm adhesion of conceptustrophectoderm to uterine LE occurs [58]. However, OPN mRNA is not present in pig conceptuses [58,59]. In contrast to mRNA, OPN protein is abundant along the apical surfaces of LE and trophectoderm/chorion, but only in areas of direct contact between the uterus and conceptus [58,59]. Remarkably, OPN mRNA and protein are not present in uterine LE and chorion of areolae where the chorion does not attach to LE, but rather forms a "pocket" of columnar epithelial cells that take up and transport secretions of uterine GE into the placental vasculature by fluid phase pinocytosis (S)-3-(tert-Butoxycarbonyl)-2,2-dimethyloxazolidine-4-carboxylic acid [114] (Figure 1). OPN levels remain high at this interface throughout pregnancy [59], as do multiple integrin subunits that potentially form heterodimeric receptors that bind OPN [8,84,90]. All experimental and surgical procedures were in compliance with the Guide for Care and Use of Agricultural Animals in Teaching and Research and approved by the Institutional Animal Care and Use Committee of Texas A M University.Figure 1 OPN is synthesized and secreted from the luminal epithelium (LE) only at sites of direct attachment of uterus to placenta. A) H E stained paraffin embedded thin section of the uterine/placental interface of a Day 80 pregnant gilt illustrating an areola containing histotroph (note the intense red eosin protein staining) secreted by the glandular epithelium (GE). B) OPN mRNA (top panels) and protein (bottom panels) is expressed in the uterus of a Day 80 pregnant gilt (expression begins in luminal epithelium (LE) on Day 13, in GE by Day 35, and then in both cell types to term). Note that OPN is not detectable in uterine LE associated with areolae where PubMed ID:https://www.ncbi.nlm.nih.gov/pubmed/21715270 there is no direct attachment of uterine LE to placental trophectoderm/chorion). This precise spatial distribution for OPN expression strongly suggests that it plays a role for attaching uterus to placenta during epitheliochorial placentation.Johnson et al. Journal of Animal Science and Biotechnology 2014, 5:56 http://www.jasbsci.com/content/5/1/Page 6 ofAffinity chromatography and immunoprecipitation experiments were performed to test whether the integrin subunits v, 4, 5, 1, 3, 5, and 6, expressed by porcine trophectoderm cells (pTr2) and porcine uterine epithelial (pUE) cells, directly bind OPN. Detergent extracts.