Chorionic expression of heterogeneous products of the PAG (Pregnancy-Associated Glycoprotein) gene family secreted in vitro throughout embryonic and foetal development in the pig

Identification of pregnancy-associated glycoprotein family (PAG) in the brown bear (Ursus arctos L.)

Pregnancy-associated glycoproteins (PAGs) are abundant embryo-originated products expressed in the pre-placental trophoblast and, later, in the post-implantational chorionic epithelium of some mammalian species. This paper describes the identification and cellular immunolocalization of the chorionic PAG family in the discoidal-type placenta of the brown bear (Ursus arctos L. - Ua), in which the PAGs were named 'UaPAG-Ls'. The study used: 1) Western blot for total placental glycoproteins; and 2) cross-species heterologous double fluorescent immunohistochemistry (IHC) for cellular immune-localization of the PAGs. This is the first study reporting the identification and immunolocalization of the UaPAG-L family in placental cells during early pregnancy in the brown bear. Our Western analysis revealed a dominant mature 72 kDa UaPAG-L isoform was expressed in all Ua placentas during early pregnancy. Various other UaPAG-L isoforms (16-66 kDa) were also identified. Using IHC, the UaPAG-L proteins were localized to trophectodermal cells (TRD), where signal intensity resembled intense TRD proliferation within developing placenta. The data increases our general knowledge of PAG proteins localized in discoidal-type placenta during early pregnancy in the brown bear.

Identification of Placental Aspartic Proteinase in the Eurasian Beaver (Castor fiber L.)

Aspartic proteinases (AP) form a multigenic group widely distributed in various organisms and includes pepsins (pep), cathepsins D and E, pregnancy associated glycoproteins (PAGs) as well as plant, fungal, and retroviral proteinases. This study describes the transcript identification and expression localization of the AP within the discoid placenta of the Castor fiber. We identified 1257 bp of the AP cDNA sequence, encoding 391 amino acids (aa) of the polypeptide precursor composed of 16 aa signal peptide, 46 aa pro-piece, and 329 aa of the mature protein. Within the AP precursor, one site of potential N-glycosylation (NPS^119–121) and two Asp residues (D) specific for the catalytic cleft of AP were identified (VLFDTGSSNLWV^91–102 and GIVDTGTSLLTV^277–288). The highest homology of the identified placental AP nucleotide and aa sequence was to mouse pepsinogen C (75.8% and 70.1%, respectively). Identified AP also shared high homology with other superfamily members: PAGs, cathepsins, and napsins. The AP identified in this study was named as pepsinogen/PAG-Like (pep/PAG-L). Diversified pep/PAG-L protein profiles with a dominant 58 kDa isoform were identified. Immune reactive signals of the pep/PAG-L were localized within the trophectodermal cells of the beaver placenta. This is the first report describing the placental AP (pep/PAG-L) in the C. fiber.

Identification of Novel Placentally Expressed Aspartic Proteinase in Humans

This study presents pioneering data concerning the human pregnancy-associated glycoprotein-Like family, identified in the genome, of the term placental transcriptome and proteome. RNA-seq allowed the identification of 1364 bp hPAG-L/pep cDNA with at least 56.5% homology with other aspartic proteinases (APs). In silico analyses revealed 388 amino acids (aa) of full-length hPAG-L polypeptide precursor, with 15 aa-signal peptide, 47 aa-blocking peptide and 326 aa-mature protein, and two Asp residues (D), specific for a catalytic cleft of the APs (VVFDTGSSNLWV91-102 and AIVDTGTSLLTG274-285). Capillary sequencing identified 9330 bp of the hPAG-L gene (Gen Bank Acc. No. KX533473), composed of nine exons and eight introns. Heterologous Western blotting revealed the presence of one dominant 60 kDa isoform of the hPAG-L amongst cellular placental proteins. Detection with anti-pPAG-P and anti-Rec pPAG2 polyclonals allowed identification of the hPAG-L proteins located within regions of chorionic villi, especially within the syncytiotrophoblast of term singleton placentas. Our novel data extend the present knowledge about the human genome, as well as placental transcriptome and proteome during term pregnancy. Presumably, this may contribute to establishing a new diagnostic tool for examination of some disturbances during human pregnancy, as well as growing interest from both scientific and clinical perspectives.

Placentation in different mammalian species

The placenta is a complex, transient organ associated with viviparity, which is located at the interface of the dam and fetus during pregnancy. It is formed after attachment, or implantation, of the blastocyst on the uterine lining and derives from complex cellular and molecular interactions between uterine and embryonic tissues. In mammals, there are many forms of placentation but this organ has the same function in all species: it is responsible for orchestrating materno-fetal exchanges, together with endocrine and immunological functions.

Expression of pregnancy-associated glycoprotein family in the epitheliochorial placenta of two Camelidae species (C. dromedarius and C. bactrianus)

This study describes placental morphology and immunolocalization of the placental pregnancy associated glycoprotein-like family (PAGs) identified in two selected taxa of Old-World camels of the Camelidae family: Camelus dromedarius (Cd) and Camelus bactrianus (Cb). Placental tissues of Cd from days 140-293 post-coitum (dpc), term (404 dpc); and of Cb from term (440 dpc) were examined. Histological staining (hematoxylin/eosin and propidium iodine) revealed the development of the placental structure, while chorionic folding increased the feto-placental surface during the progress of pregnancy. The camelid placenta during early pregnancy is similar to the diffuse epitheliochorial type, and during later stages of pregnancy resembles the synepitheliochorial (cotyledonary) type. Placental expression of the PAGs was detected (Alexa 488 - green) within camelid trophectoderm cells (TRD - chorionic epithelium as outer layer of embryonic cells) among all placental cells with nuclei stained by propidium iodide (red). The PAGs, identified in both Camelidae taxa, were named CbPAGs and CdPAGs. Placental CbPAG and CdPAG expression is restricted to the TRD cells, which are differentially developed throughout gestation. Cross-reactivity of polyvalent anti-pPAG polyclonals with the CbPAGs and CdPAGs revealed high structural similarities of the PAG-like epitopes in pigs and camels. This is the first study identifying PAG expression in chorionic cells of the camel placenta.

Pregnancy-associated glycoprotein (PAG) family localized in chorionic cells within the epitheliochorial/diffuse placenta of the alpaca (Lama pacos)

Pregnancy-associated glycoproteins (PAGs) are abundant embryo-originated products expressed in the pre-placental trophoblast and later in the post-implantational chorionic epithelium of some ungulate species. This paper describes the cellular immunolocalization of the chorionic PAG family in the epitheliochorial placenta type of the alpaca (Lama pacos-Lp), in which the PAGs were named 'LpPAGs'. Placental Lp sections (5 μm) of different females near mid-pregnancy (150 days post coitum; dpc), advanced pregnancy (244-263 dpc) and late pregnancy (347 dpc) were used for cross-species (heterologous-ht) double fluorescent immunohistochemistry (htdF-IHC). The htdF-IHC was performed with primary rabbit polyvalent anti-porcine PAG polyclonals. The LpPAG immuno-complexes were visualized with secondary goat anti-rabbit immunoglobulins-conjugated with Alexa 488 fluorophore (green), among all nuclei of placental cells stained with propidium iodide (red). This is the first study reporting the immunolocalization of the LpPAG family identified by htdF-IHC at the feto/maternal interface during different pregnancy stages of the alpaca. The most dominant and strongest immune-positive LpPAG signals were found in the well-developed chorionic cell layer. Our htdF-IHC indicated relatively high epitope resemblance to that of the PAGs in camelids and pigs. These data increase our general knowledge of chorionic PAG localization during pregnancy-stage dependent development of the epitheliochorial diffuse placenta type in the alpaca.

Pregnancy-associated glycoprotein (PAG) family: transcripts and gene amplicons in camelids

In this study, the placental localization of PAG-like transcripts and genomic existence of PAG-like amplicons in new-world (Lp, Lama pacos, alpaca) and old-world camelids (Cb, Camelus bactrianus, bactrian; Cd, Camelus dromedarius; dromedary) are reported for the first time. Sections of Lp (150-347 days post coitum), Cd (43-90 cm crown-rump length) and Cb (term) placentas were used for heterologous (ht; cross-species) autoradiographic in situ hybridization (aISH) with single-stranded diagnostic (antisense) or control (sense) [alpha-(35)S]dATP-labeled 323 nt porcine PAG8 (pPAG8) cDNA probes produced by asymmetric PCRs. The aISH with antisense (35)S-pPAG8 probe identified camelid PAG-like (LpPAG, CbPAG and CdPAG) mRNA expression restricted to chorionic epithelium cells within placentas of camelids. In addition, genomic DNA (gDNA), isolated from placental sections were used as templates for camelid PAG-like gene amplicon production by PCR. Specificity of the obtained multiple camelid gDNA PAG-like amplicons was confirmed by double ht-Southern hybridizations with [alpha-(32)P]dATP-labeled 611 bp pPAG5 and pPAG10 double-stranded cDNA probes. The double ht-Southern hybridizations of camelid gDNA amplicons (with pPAG5 and -10 probes) allowed the identification of length-polymorphism of LpPAG, CbPAG and CdPAG genes, coding catalytically active and potentially inactive forms. Such an application of porcine PAG probes may be advantageous for future identification of still undiscovered PAG-like families in other eutherian species.

Characterization of the peptidase activity of recombinant porcine pregnancy-associated glycoprotein-2

The pregnancy-associated glycoproteins (PAGs) belong to the aspartic peptidase family. They are expressed exclusively in trophoblasts of even-toed ungulates such as swine, cattle, sheep, etc. In pigs, two distinct PAG transcripts (and some variants) have been described. One of the transcripts, porcine PAG-1 (poPAG-1) may not be capable of acting as a peptidase. The second transcript, poPAG-2, possesses a conserved catalytic centre and has been predicted, but not shown, to have proteolytic activity. The thrust of this work was to test such a possibility. PoPAG-2 was expressed as a recombinant protein with an amino-terminal 'FLAG-tag' in a Baculoviral expression system. The expressed proteins were affinity purified by using an anti-FLAG antibody. The purified preparations were then analysed for proteolytic activity against a fluorescent substrate. Porcine PAG-2 had optimal proteolytic activity around pH 3.5. Against this substrate, it had a k(cat)/K(m) of 1.2 microM(-1) s(-1) and was inhibited by the aspartic peptidase inhibitor, pepstatin A, with a K(i) of 12.5 nM. Since the proteolytic activity of PAGs in the pig has now been established, the search for putative substrates to gain insight into the physiological role of PAGs will likely be the focus of future investigations.

Cellular localisation of the pregnancy-associated glycoprotein family (PAGs) in the synepitheliochorial placenta of the European bison

This paper describes the cellular immuno-localisation of the PAG family in synepitheliochorial (cotyledonary) placenta of the European bison (Eb). Uteri were harvested from pregnant wild Eb (n=4; 45-150 days post coitum-dpc); and additionally from cattle (30, 45 dpc) and pigs (42 dpc)--both domestic species were used as positive controls for cellular PAG immunodetection. Placentas were sectioned, fixed, dehydrated and subjected to double fluorescent immunohistochemistry (dF-IHC) with the use of Alexa 488 fluorochrom (A488) and propidium iodide (PI). Native positive EbPAG signals were detected by heterologous (ht; cross-species) dF-IHC with primary rabbit anti-PAG polyclonals against native or recombinant porcine PAG antigens (anti-pPAG); then visualised with secondary anti-rabbit goat immunoglobulins--conjugated to A488. Our htdF-IHC indicated an unequivocal localisation to the mono- and bi-nuclear trophectoderm (chorionic epithelium) cells expressing the PAGs (A488-green) among all placental cells, in which PI (red) stained nuclei. This is the first paper reporting the EbPAG family expression examined by htdF-IHC at the feto-maternal interface in wild Pecoran species. The cross-reactivity of anti-pPAG polyclonals with the EbPAGs suggests that shared epitopes are present in these molecules. It seems that the EbPAG family, which is robustly expressed in mono- and bi-nucleated trophectoderm cells, is associated with events taking place during placenta development. Our study also provided a proficient ht-system to identify various PAGs that could be useful as prenatal protein markers for pregnancy diagnoses, which is essential for effective reproductive management of endangered mammals.

Isolation of pregnancy-associated glycoproteins from placenta of the American bison (Bison bison) at first half of pregnancy

This paper describes the successful purification and characterisation of pregnancy-associated glycoproteins (PAG) extracted from placenta (3-4 months) of American bisons (Amb). Chorionic AmbPAG proteins were purified from foetal cotyledonary tissues (CT) and liquid cotyledonary-carrying proteins (LCP) leaking from damaged cells. Our protocols successfully indicated the usefulness of AmbPAG protein identification, especially from LCP fraction. The AmbPAGs were extracted, precipitated and eluted during DEAE cellulose chromatography. The richest protein fractions were further chromatographed on VVA (Vicia villosa agglutinin affinity column), then characterised by mono- and bi-dimensional electrophoresis, Western blot and N-terminal amino acid (aa) sequence. After being transferred to PVDF membranes, three selected VVA-purified AmbPAG isoforms differing in molecular masses and isoelectric points (Ip 4-4.6) were selected for sequencing. One identified N-terminal 25aa sequence of AmbPAG72kDa CT form was identified as completely new (RGSNLTSLPLQNVIDLFYVGNITIG). Two other AmbPAG proteins purified from different sources (74kDa CT and 76kDa LCP forms; RGSNLTIHPLRNIRDIFYVGNITIG) were identical or corresponded to N-terminus of various bovine PAGs (boPAG). The two AmbPAGs (74kDa CT and 76kDa LCP) revealed identical micro-sequence to boPAG7; and were similar mainly to bovine PAG4, -6, -15 and -17 precursors that were identified by full-length sequencing derived from cDNA cloning. The novel sequence of the AmbPAG (72kDa CT) was related to some boPAG and various other ruminant PAG precursors (caprine and ovine). All three identified AmbPAG sequences were also relatively similar to mature forms of purified native boPAG(56-75kDa) proteins. This is the first report indicating aa sequences of native AmbPAG proteins purified from placenta (CT and LCP) of bison species. The N-terminal sequences of the AmbPAGs have been deposited in the EMBL-EBI database (UniProtKB; Accession Nos.: P84916, P84917 and P84918).

Western analyses of pregnancy-associated glycoprotein family (PAG) in placental extracts of various mammals

The present study was conducted in order to analyze the immunoreactivity of placental extracts of several animal species and humans against the following three groups of PAG antisera: anti-boPAG-I (R#497), -boPAG-II (R#435), and -caPAG (R#706). Placental proteins were obtained after extraction at neutral pH, followed by ammonium sulfate (A.S.) precipitation, dialysis, and lyophilization. The immunoreactivity of different placental extracts was revealed by the use of monodimensional SDS-PAGE, followed by blotting on nitrocellulose membrane and the identification of immunoreactive proteins after incubation with PAG antisera (Western blot technique). A strong immunoreactivity of proteins from synepitheliochorial placenta (cattle, sheep, goat, bison, buffalo, and deer) was demonstrated in both 20-50% and 50-80% A.S. fractions using the three antisera. Proteins from species with epitheliochorial placenta presented variable profiles of detected PAG-like proteins: in the sow, many immunoreactive forms were revealed by antisera boPAG-I and boPAG-II, whereas in the dromedary, only two forms were revealed by anti-boPAG-II. Concerning other species, our protocols showed for the first time a cross-reaction between PAG antisera with proteins extracted from dog, alpaca, dromedary, sea lion, and human placenta.

Pregnancy-associated glycoprotein family (PAG)--as chorionic signaling ligands for gonadotropin receptors of cyclic animals

The chorionic pregnancy-associated glycoprotein (PAG) family was identified in pigs, cattle and other eutherian mammals. The objective of this study was to examine whether secretory chorionic proteins (including PAGs), produced in vitro by explants of porcine and bovine placental membranes, may interact with other proteins, i.e. gonadal and extragonadal binding sites. Trophoblast (TRF) and trophectoderm (TRD) explants of pigs (n=38; 14-61 dpc-day post coitum) or cotyledons (CT) of cows (n=5; 40-110 dpc) were long-term cultured. Released chorionic proteins were ultra-fractionated from media (>10 kDa) or precipitated [20-75% of (NH(4))(2)SO(4)]. The PAGs were monitored by Western/PAGE (30-73 kDa). Secretory TRF/TRD/CT (+PAG) proteins (0.78-25 microg/ligand) were examined by radioreceptor assay (RRA) with iodinated hCG ((125)I-hCG) for binding-effectiveness by gonadotropin receptors of cyclic pigs and cows (cRc). Gonadal and extragonadal cRc isolated from luteal-phase corpora lutea and uteri (cCLRc, cMYORc and cENDRc) were tested with positive control ligands: porcine LH and hCG (0.39-50 ng/ml). Control proteins produced in vitro by endometrial (END) explants of cyclic (cEND), pseudopregnant (PsEND) and pregnant (pEND) gilts were utilised as negative ligands (0.78-25 microg/ligand). Positive control ligands competed with (125)I-hCG for binding by cCLRc, cMYORc and cENDRc (18-61%/B(0) for hCG and 27-57%/B(0) for LH). Negative ligands (cEND, PsEND and pEND) did not show cRc bindings. This is the first RRA report indicating that in vitro produced porcine TRF/TRD proteins (+PAG) competed (P< or =0.05) with (125)I-hCG for binding by cCLRc, cMYORc and cENDRc in a concentration- and pregnancy stage-dependent manner. The highest competition with (125)I-hCG (up to P< or =0.001) was found for ultra-fractionated TRF/TRD proteins (>10 kDa) during early pregnancy (<22 dpc). The greatest competition (P< or =0.05) of precipitated porcine TRD proteins (>30 dpc) was detected for fractions obtained by saturation with use of 20% of (NH(4))(2)SO(4). Bovine CT proteins revealed lower competition of (125)I-hCG for bovine cCLRc (during 45 dpc only) that was more efficient with CT (up to 71%) than with non-labelled hCG (82%). The PAG proteins may play a role as potential "signal molecules", because they were able to interact with gonadotropin receptors of luteal-phase animals. It seems that the pPAG proteins may be luteoprotective chorionic-origin signals during implantation and placentation, according to binding-effectiveness of the chorionic ligands that was comparable to LH/hCG ligands with gonadal and extragonadal receptors of cyclic animals.

Radiocompetition of secretory pregnancy-associated glycoproteins as chorionic ligands with luteal and uterine gonadotrophin receptors of pregnant pigs

Porcine pregnancy-associated glycoprotein (pPAG) family is very promiscuous and its role(s) remains unknown. The objective of this study was to identify whether secretory placental proteins (including pPAGs), produced in vitro by porcine chorionic explants, may interact with other proteins/targets, i.e. luteal and uterine binding sites of pregnant pigs. Trophoblast (TRF) and trophectoderm (TRD) were harvested during peri-implantation and placentation periods (14-61 dpc-day post coitum). In vitro-produced TRF/TRD proteins were isolated from media by ultrafractionation (>10 kDa MWCO) or precipitation with 20-75% saturation of (NH(4))(2)SO(4) and pPAG proteins were monitored by Western blotting. Secretory TRF/TRD ligands (including PAGs) were serially diluted (0.78-25 microg/ligand) and examined by radioreceptor assay (RRA). Luteal and uterine membrane receptors of pregnant pigs (pRc) were isolated from corpora lutea (pCLRc), myometrium (pMYORc) and endometrium (pENDRc). The three pRc types were harvested during three periods of pregnancy: 14 dpc (14 Rc), 21-26 dpc (21-26 Rc) and 31 dpc (31 Rc). The RRA competitions of individual TRF or TRD ligands were performed with (125)I-hCG as tracer and different pRc types. The RRA results of TRF/TRD were compared to hCG/pLH ligands--as positive controls (0.39-50 ng/ml), and endometrial (END) proteins (0.78-25 microg/ml) produced in vitro by END explants of cyclic, pseudopregnant and pregnant gilts (cEND, PsEND and pEND, respectively)--as negative control ligands. Results indicated that secretory TRF/TRD proteins (+pPAGs) were able to compete with (125)I-hCG for binding with other proteins/targets, i.e. luteal and uterine receptors of pregnant pigs (pCLRc, pMYORc and pENDRc) in a concentration- and pregnancy stage-dependent manner. This study indicated that porcine secretory 14-15 dpc TRF (pPAG; 30-73 kDa) ligands, effectively displaced (125)I-hCG tracer from pCL14Rc (up to P< or =0.01), corresponding to displacement by hCG and porcine LH. During the early stage of pregnancy, some competition tendency (P< or =0.01) was also detected for TRF ligands (14-15 dpc) with pEND14Rc. As pregnancy advanced, significant (125)I-hCG competition (at least P< or =0.05) with secretory semi-purified TRD ligands (30-42 dpc) was determined for all types of examined receptors pCL31Rc, pMYO31Rc and pEND31Rc, mainly with TRD fractions precipitated by 20% saturation of (NH(4))(2)SO(4). It seems that chorionic pPAG family can be involved in luteoprotective mechanism during implantation and placentation, according to the binding-interaction with luteal and uterine gonadotropin receptors of pregnant pigs.

Chorionic mRNA expression and N-glycodiversity of pregnancy-associated glycoprotein family (PAG) of the European bison (Bison bonasus)

Placental PAG mRNA expression and N-glycodiversity of multiple PAG proteins secreted in vitro by trophectoderm (chorion epithelium) of wild pecoran Bovidae taxons was not examined previously. The study on European bison (Eb) aimed: (1) to determine placental PAG mRNA expression by in situ hybridisation; (2) to identify a profile of pecoran PAG protein family secreted in vitro by cotyledonary (CT) explants; (3) to examine N-glycodiversity of the PAG proteins in this wild taxon. In addition, we compared (4) a profile and N-glycodiversity of the PAG protein family secreted in vitro by CT and interCT-trophectoderm (intCT-TRD) explants of domestic ruminants. Cotyledonary sections of the Eb were used for in situ hybridisation (ISH) with (35)S-labelled probes produced with porcine PAG cDNA as templates. Various CT and intCT-TRD explants were long-term cultured in vitro. Chorionic proteins were isolated from media, ultra-filtrated (>10 kDa MWCO) and analysed by PAGE-Western blotting with various polyclonal anti-PAG sera. Protein samples with or without enzymatic deglycosylation were examined after different times of explant cultures. Released chorionic proteins were deglycosylated by N-glycanase F (PNGase F+) and compared to glycosylated forms (PNGase F-). This is the first paper demonstrating the PAG-like mRNA transcript expression (by ISH) and N-glycodiversity of immuno-reactive PAG-like proteins (produced in vitro by chorionic explants) of European bison. Various PAG proteins of Eb (EbPAG) were secreted by CT explants during long-term in vitro studies. Major approximately 78, approximately 67 and approximately 65 kDa EbPAG-like proteins were reduced by enzymatic deglycosylation (at least by 10 kDa). Considerably smaller amounts of approximately 45 kDa EbPAG-like proteins were also observed. In addition, we have found that various PAG proteins (30-73 kDa) were secreted by bovine CT explants, during long-term in vitro cultures. Corresponding amounts of PAG proteins, similar in M(r), were also secreted by intCT-TRD explants, whose tissues were not utilised for PAG protein extraction during other scientists' previous studies. It seems that the M(r)-heterogeneity and N-glycodiversity of the PAG protein family can play very important role during feto-placental interactions in Bovidae species.