Structure of an interferon-alpha 2 gene expressed in the bovine conceptus early in gestation

Transcriptional control of IFNT expression

Once interferon-tau (IFNT) had been identified as a type I IFN in sheep and cattle and its functions were characterized, numerous studies were conducted to elucidate the transcriptional regulation of this gene family. Transfection studies performed largely with human choriocarcinoma cell lines identified regulatory regions of the IFNT gene that appeared responsible for trophoblast-specific expression. The key finding was the recognition that the transcription factor ETS2 bound to a proximal region within the 5'UTR of a bovine IFNT and acted as a strong transactivator. Soon after other transcription factors were identified as cooperative partners. The ETS2-binding site and the nearby AP1 site enable response to intracellular signaling from maternal uterine factors. The AP1 site also serves as a GATA-binding site in one of the bovine IFNT genes. The homeobox-containing transcription factor, DLX3, augments IFNT expression combinatorially with ETS2. CDX2 has also been identified as transactivator that binds to a separate site upstream of the main ETS2 enhancer site. CDX2 participates in IFNT epigenetic regulation by modifying histone acetylation status of the gene. The IFNT downregulation at the time of the conceptus attachment to the uterine endometrium appears correlated with the increased EOMES expression and the loss of other transcription coactivators. Altogether, the studies of transcriptional control of IFNT have provided mechanistic evidence of the regulatory framework of trophoblast-specific expression and critical expression pattern for maternal recognition of pregnancy.

IFN-τ acts in a dose-dependent manner on prostaglandin production by buffalo endometrial stromal cells cultured in vitro

Interferon-τ (IFN-τ) has been recognized as the primary embryonic signal responsible for maternal recognition of pregnancy. Uterine endometrium produces both prostaglandin F2α (PGF2α ) and prostaglandin E2 (PGE2 ). PGF2α is responsible for the luteolysis; however, PGE2 favours establishment of pregnancy by its luteoprotective action. In this study, the dose-response effect of recombinant bovine IFN-τ (rbIFN-τ) on prostaglandin (PG) production by buffalo endometrial stromal cells cultured in vitro was studied. Buffalo endometrial stromal cells were isolated by double enzymatic digestion, initially with trypsin III followed by a cocktail of trypsin III, collagenase type II and DNase I and subsequently cultured till confluence. Further, cells were treated with different doses of rbIFN-τ (0.001, 0.01, 0.1, 1.0 and 10 μg/ml) and keeping a separate set of control. Culture supernatant was collected after 6, 12 and 24 h of treatment. PG levels in the culture supernatant were measured by enzyme immune assay (EIA) and total cellular protein estimated by Bradford method. Results indicated that buffalo endometrial stromal cells following rbIFN-τ treatment enhanced the secretion of both PGE2 and PGF2α , and also its ratio in a strict dose-dependent manner with a significant increase (p < 0.01) in PGE2 production at 1 μg/ml dose of rbIFN-τ and maximal stimulation for both PG was observed at 10 μg/ml. Further, both PG production and its ratio were increased significantly (p < 0.01) in a time-dependent fashion in all the groups at 6, 12 and 24 h post-treatment with highest level achieved at 24 h as compared with control. Absolute levels of PGE2 remained higher than PGF2α indicating PGE2 as the major PG produced by endometrial stromal cells. The dose-dependent response of rbIFN-τ signifies the importance of optimum concentration of IFN-τ for the embryonic development especially during the critical period to establish successful pregnancy.

Expression of Cyclooxygenase-2 and Granulocyte-Macrophage Colony-Stimulating Factor in the Endometrial Epithelium of the Cow Is Up-Regulated During Early Pregnancy and in Response to Intrauterine Infusions of Interferon-τ1

On the basis of results obtained in vitro, we previously proposed a model in which signals from the conceptus, namely interferon-tau (IFN-tau) and prostaglandin E2, increase the expression of cyclooxygenase (COX)-2 or granulocyte-macrophage colony-stimulating factor (GM-CSF) in immune and nonimmune cells of the bovine endometrium. Two experiments were conducted to verify the validity of this hypothesis in vivo. In experiment 1, the in vivo expression of COX-2 and GM-CSF during early pregnancy was monitored. Uteri from heifers were collected at different days (d) of the estrous cycle and pregnancy (P). In experiment 2, the effects of intrauterine infusions of IFN-tau on the expression of COX-2 and GM-CSF were analyzed. Immunohistochemistry was performed on uterine sections, and image analysis was used to evaluate the staining intensity in the conceptus, the luminal epithelium (LE), and the subepithelial stroma. In experiment 1, staining for COX-2 was maximal between d18P and d24P, both in the LE and in the conceptus, whereas staining for GM-CSF reached a plateau between d18P and d30P in the LE. In experiment 2, in response to IFN-tau, COX-2 was up-regulated in the LE of the ipsilateral horn, whereas GM-CSF was enhanced in both uterine horns. The current report supports the view that the conceptus, through its secretion of IFN-tau, stimulates maternal epithelial expression of COX-2 and GM-CSF during the peri-attachment period in the cow.

Increased messenger RNA for allograft inflammatory factor-1, LERK-5, and a novel gene in 17.5-day relative to 15.5-day bovine embryos

Considerable embryonic loss occurs between Gestation Days 15 and 18 in cattle when critical cellular and molecular events occur, including maternal recognition of pregnancy. To gain insight into these events, mRNA differential display analysis was used to identify eight unique cDNA fragments present in greater abundance in 17.5-day than in 15.5-day bovine embryos. Four cDNA fragments, confirmed to be upregulated in 17.5-day embryos using Northern analysis, were cloned and sequenced. Three cDNA fragments shared sequence identities with known homologs: human allograft inflammatory factor-1 (AIF-1), human LERK-5, and bovine interferon-tau. One novel cDNA fragment did not share sequence identity to previously reported genes, except for a similar DNA sequence in the human genome. AIF-1 mRNA was present in developing placenta through Gestation Day 36, and abundant levels were observed in adult bovine spleen and lung. The novel gene, which we have named periattachment factor (PAF), was not detected in adult tissues using Northern analysis or in conceptuses between Days 30 and 36 of pregnancy. Additional sequence information for bPAF was obtained from a cDNA library constructed from a 25-day bovine embryo. The protein corresponding to the open reading frame has four protein kinase C phosphorylation sites, two casein kinase II phosphorylation sites, a nuclear targeting sequence, but no obvious DNA or RNA binding motifs. Abundant expression of this gene during a narrow but critical window of embryonic development makes it worthy of further study.

Polymorphic forms of expressed bovine interferon-tau genes: relative transcript abundance during early placental development, promoter sequences of genes and biological activity of protein products

Multiple interferon (IFN)-tau genes exist in cattle, but it has remained unclear how many are expressed, the extent of their variation, and whether different genes exhibit similar patterns of expression and code for proteins with similar biological activities. A total of 118 complementary DNA (cDNA) were bi-directionally sequenced from reverse-transcribed bovine (bo) conceptus RNA over the period from blastocyst formation until day 25 of pregnancy. Fourteen different cDNAs, encoding eight different IFN-tau, were confirmed unique. All showed high sequence conservation (>98% nucleotide identity; >96% amino acid identity). The cDNA fell into three, recently evolved, phylogenetic groups (tau1, 2, and 3). Mean concentrations of IFN-tau messenger RNA were greater at day 17 and day 19 than at day 14 and day 25, with different genes showing comparable expression patterns, although there appeared to be a major bias in expression of two genes (for boIFN-tau1c and tau3a) in blastocysts. Genes representing members of the three boIFN-tau groups were cloned. Their promoter regions were conserved over regions considered important for transcriptional activation. Recombinant protein generated in Escherichia coli from representative genes in the three groups had similar but not identical antiviral activities. In summary, many IFN-tau genes, which are probably under similar transcriptional control, are expressed in bovine trophoblast during the peri-implantation period of development.

A classification for the interferon-tau

An attempt has been made to provide a rational organization for the many interferon-tau (IFN-tau) sequences entered in GenBank based on phylogenetic analysis and common amino acid substitutions, which might form the basis for a universal nomenclature scheme. Over the 13 years since these genes were first discovered, large numbers of cDNA and gene sequences have been reported, and there is reason to suspect that representatives of all the major ovine and bovine forms have now been described. The data are consistent with the presence of many genes and also allelic variants in sheep and cattle analogous to what has been observed for the IFN-alpha in the human. Future variants should be easily accommodated into the scheme outlined here. A flexible system of nomenclature, based on that used for HuIFN, is needed to provide a common base for comparison between research done in different laboratories and to assign relative biologic potencies to these molecules.

Antiviral and antiluteolytic activity of recombinant bovine IFN-omega1 obtained from Pichia pastoris

The gene coding for bovine interferon-omega1 (BoIFN-omega1) was recently cloned and expressed at high levels in the yeast Pichia pastoris. The recombinant BoIFN-omega1 protein shows antiviral activity in different cell lines and has an antiluteolytic effect in cyclic ewes. In this article, we describe a method for purification of BoIFN-omega1 expressed in the methylotrophic yeast P. pastoris and characterization of its activity in vivo. The recombinant protein secreted to the culture medium had low activity because of self-aggregation. BoIFN-omega1 was solubilized using urea and desalting and finally purified by ion exchange chromatography on Q-Sepharose Fast Flow. The yield of purified product was approximately 300 mg/L of fermentation culture, with a specific antiviral activity of 10(8) IU/mg. Its purity was at least 80%. The biologic characterization of purified BoIFN-omega1 was determined by induction of an antiviral state on ewes challenged with 100 lethal doses (LD) of Aujeszky virus and by the extension of the corpus luteum life span and interestrous interval in cyclic cows. Ewes treated with 2 x 106 IU/kg BoIFN-omega1 were protected from Aujeszky virus infection. In cows receiving an intrauterine infusion of 1 mg BoIFN-omega1, equally distributed between the two uterine horns, twice daily from day 14 to day 22 of the experimental estrous cycle, the lifespan of the corpus luteum (25 vs. 19 days) and the interestrous intervals (26 vs. 21 days) were extended when compared with a control group (p < 0.05). We show that recombinant BoIFN-omega1 purified from P. pastoris has high antiviral activity and is an effective antiluteolytic agent in cattle.

Interferon-tau stimulates granulocyte-macrophage colony-stimulating factor gene expression in bovine lymphocytes and endometrial stromal cells

Interferon-tau (IFN-tau), the antiluteolytic signal produced by the trophoblast prior to implantation in ruminants, exhibits immunomodulatory properties. It stimulates the production of prostaglandin (PG) E(2) in bovine endometrial cells via the induction of cyclooxygenase-2 (COX-2). We previously demonstrated that preconditioning lymphocytes with PGE(2) increases the expression of granulocyte-macrophage colony-stimulating factor (GM-CSF), a cytokine that promotes conceptus growth and survival. Our goal in the present study was to evaluate the impact of IFN-tau on the expression of GM-CSF in bovine peripheral blood lymphocytes (PBL) and endometrial epithelial and stromal cells. Changes in PGE(2) production and mRNA levels of COX-2 were also studied in PBL in response to IFN-tau. Gene expression was estimated by semiquantitative reverse transcription-polymerase chain reaction and Northern analysis. The expression of GM-CSF in PBL was stimulated by treatment with IFN-tau. Furthermore, GM-CSF mRNA levels were increased after preconditioning PBL for 3 days with IFN-tau, followed by a 12-h restimulation without IFN-tau. Inhibition rather than stimulation of PGE(2) production and COX-2 expression in PBL during treatment with IFN-tau suggests a direct effect on GM-CSF expression. Moreover, GM-CSF expression was stimulated in uterine stromal cells in response to IFN-tau. This study provides the first evidence for stimulation of GM-CSF expression by IFN-tau in both leukocytes and endometrial stromal cells. In view of the role of GM-CSF on fetal growth and survival, these results support the hypothesis that the conceptus mediates accommodation mechanisms in the uterus during early pregnancy by modulating the expression of beneficial cytokines at the fetomaternal interface.

Cytokines in implantation

Implantation is a complex process which involves the 'invasion' of the maternal endometrium by the trophoblast surrounding the developing blastocyst. In response to this interaction there is a cellular reaction within the endometrium which has some features analogous to invasion by a tumour and some which are more characteristic of an inflammatory response. In addition, and also in common with cancer and inflammation, there is a release of biologically active molecules, including cytokines, at and around the implantation site. The information on cytokines is complex and often contradictory but it is recognised that they play an important role in the successful establishment of pregnancy. The evidence for this role is examined in this review.

Control of interferon-tau gene expression by Ets-2

Expression of the multiple interferon-tau (IFN-tau) genes is restricted to embryonic trophectoderm of ruminant ungulate species for a few days in early pregnancy. The promoter regions of these genes are highly conserved. A proximal (bp -91 to -69) sequence has been implicated in controlling trophoblast-specific expression. Here it was used as a target for yeast one-hybrid screening of a day 13 conceptus cDNA library. Two transcription factors of the Ets family, Ets-2 and GABPalpha, were identified, consistent with the observation that active ovine IFN-tau genes contain a single 10-bp Ets motif (core: GGAA) in the proximal segment, whereas three known inactive ovine genes contain a mutated core motif (TGAA). Cotransfection of a promoter- (-126 to +50) luciferase reporter construct from an active gene (bovineIFN-tau1; boIFNT1) and an Ets-2 expression plasmid in human JAr cells provided up to a 30-fold increase in reporter expression, whereas promoters from inactive genes were not transactivated. GABPalpha alone was ineffective and had only a approximately 2-fold positive effect when coexpressed with its partner GABPbeta. Other Ets-related transcription factors, which were not detected in the genetic screen, also provided a range of lesser transactivation effects. Coexpression of Ets-2 and activated Ras failed to transactivate the IFNT promoter greater than Ets-2 alone in JAr cells. The presence of Ets-2 in nuclei of embryonic trophectoderm was confirmed immunocytochemically. Together, these data suggest that Ets-2 plays a role in the transient expression of the nonvirally inducible IFNT genes.

In vivo immunosuppressive effects of recombinant ovine interferon-tau (trophoblastin): r.oTP (r.oIFN-tau) inhibits local GVH reaction in mice (PLN assay), prevents fetal resorptions, and favors embryo survival and implantation in the CBA/J x DBA/2 mice combination

PROBLEM

Ovine trophoblastin protein, be it natural or recombinant (oTP,r.oTP), a member of the tau interferon family (r.oIFN-tau), has been shown to possess immunosuppressive properties in vitro. It acts as a cytostatic agent across species. Indeed, it was immunosuppressive when tested on human and murine lymphocytes in a variety of in vitro immune assays, as it is also on syngenic (ovine) lymphocytes.

METHODS

In the present paper, we first verified that this property to act across species also occurred in vivo assays; r.oTP was able to down regulate a local GVH reaction assay (PLN assay) in mice. We then took advantage of these properties of r.oTP to investigate its in vivo effects during murine pregnancy as there is no ovine equivalent of the murine CBA/J x DBA/2 resorption prone mating combination.

RESULTS

When given in the postimplantation period, r.oTP drastically boosted resorptions in the CBA/J x DBA/2 matings, as did murine recombinant gamma interferon. However, the same r.oTP treatment in the peri-implantation period resulted in a reduction in resorptions in this spontaneous abortion system.

CONCLUSION

The data suggested that r.oTP might have acted more by favouring implantation and embryo survival than by preventing the resorption process itself. The mechanisms possibly underlying these effects, as well as the putative uses of r.oTP evolving from these data, are discussed.

Regulation of trophoblast interferon gene expression

The trophoblast of the developing ruminant conceptus secretes large quantities (up to 100 micrograms, or 10(7) IU, per 24 h) of a number of characteristic Type I interferons. Secretion (gene expression) commences at Day 8 or 9 (in the sheep; Day 10 in cattle) and ends at about Day 22 (Day 25). The function of this material is in the inhibition of uterine prostaglandin secretion, and hence in the maintenance of the corpus luteum (the 'maternal recognition of pregnancy'). Such rapid onset and cessation of gene transcription begs questions about the function of trophoblast interferon gene promoters, and a limited number of studies have now been carried out with reporter gene constructs, with inconclusive results. It seems unlikely, however, that viral responsiveness accounts for the phenomenon, as in adult interferon genes, although the trophoblast interferons are highly active antiviral agents.

Cloning and structural analysis of four genes encoding interferon-omega in rabbit

By using an ovine interferon-tau (IFN-tau) cDNA probe, four recombinant phages were isolated from a rabbit genomic library and sequenced from nucleotides -450 to 1,300 relative to the CAP site. Each of the four rabbit genes contains an open reading frame of 595 nucleotides and code for proteins that exhibit structural characteristics of the interferon-omega (IFN-omega) family. They display more than 98% identity in their coding regions. The deduced amino acid sequences share > 96% sequence similarity. In contrast, the 5' and 3' noncoding regions have diverged considerably (approximately 50% identity). Amino acid comparisons of rabbit IFN-omega with IFN-omega of other species reveal the highest degree of identity with human (72%), followed by porcine (68%) IFN-omega. Rabbit IFN-omega displays only 57% sequence similarity with ovine IFN-tau. The coding regions of the four genes subcloned in a cytomegalovirus eukaryotic expression vector and transfected in monkey COS-7 cells direct the production of proteins that protect bovine and rabbit cells against vesicular stomatitis virus infection, thus demonstrating that these genes encode fully active IFN proteins. The expression of these genes was studied in Sendai-induced rabbit leukocytes. A single band of poly(A)+RNA hybridized with a rabbit IFN-omega probe under stringent conditions, whereas no IFN-omega transcript was detected with RNA isolated from uninduced leukocytes. Southern blot analysis suggest the existence of at least eight IFN-omega genes or pseudogenes in the rabbit genome.

Type I interferon genes in cattle: restriction fragment length polymorphisms, gene numbers and physical organization on bovine chromosome 8

Multiple, superimposed Type I interferon (IFN) restriction fragments were resolved following 72-92 h of horizontal electrophoresis. Restriction fragment length polymorphisms (RFLPs) for alpha IFN (IFNA), beta IFN (IFNB), omega IFN (IFNW) and trophoblast IFN (IFNT) genes were identified in HindIII, EcoRI and TaqI digestions from 313 cattle. RFLPs with codominant segregation in cattle pedigrees were considered alleles, and 19 distinct polymorphic Type I IFN loci (5 IFNA, 4 IFNB, 8 IFNW and 2 IFNT) were identified. Allele frequencies and observed heterozygosity values were calculated for each locus and several loci were considered highly informative for linkage analysis. Bovine IFN gene numbers (10 IFNA, 6 IFNB, 20 IFNW and 6 IFNT) were estimated from the number of polymorphic loci plus additional monomorphic hybridizing bands present in EcoRI and HindIII digestions. Physical linkage of the Type I IFN gene families on bovine chromosome 8 was demonstrated by pulsed field gel electrophoresis (PFGE). Hybridization of two or more IFN probes to similarly sized PFGE fragments suggested the tentative gene family order: IFNA/IFNW-IFNT-IFNB. These studies provide a basis for the development of more detailed genetic and physical maps of the bovine Type I IFNs.

Genes for the trophoblast interferons in sheep, goat, and musk ox and distribution of related genes among mammals

The trophoblast interferons (IFNs) are a family of Type 1 IFN found in domestic ruminants that are most closely related to the little-studied 172-amino-acid IFN-omega. They are produced in massive amounts by the preimplantation conceptus at a time coincident with maternal recognition of pregnancy, and are implicated in playing an important role in this process. Here we report the characterization of four distinct members of the ovine trophoblast IFN (oTP-1) gene family, and demonstrate that they, along with previously characterized bovine trophoblast (bTP-1) genes, possess distinctive promoter sequences when compared to ovine and bovine IFN-omega genes. Genomic Southern blot analysis of numerous mammalian species (zoo blots) indicate that, whereas the IFN-omega are widely distributed among mammals, genes for the trophoblast IFN appear to be limited to ruminant species within the Artiodactyla order. Further polymerase chain reaction (PCR) analysis of trophoblast IFN genes in these ruminant species has permitted isolation of genes for goat and musk ox trophoblast IFN. These data suggest that the trophoblast IFNs are a distinct family of IFN with a limited distribution among mammals.

Syntenic mapping and chromosomal localization of bovine alpha and beta interferon genes

The previous assignment of bovine alpha-(IFNA) and beta-(IFNB) interferon gene families to syntenic group U18 was confirmed with additional cDNA probes and a bovine-rodent hybrid somatic cell panel representing all 29 bovine autosomal syntenic groups. Fluorescent in situ hybridization (FISH) localized these genes to bovine Chromosome (Chr) 8 band 15 and demonstrates that with biotinylated plasmids, as few as five tandemly arrayed sequences can be detected by conventional fluorescent microscopy. This technique can be applied to physical mapping of other multicopy genes in domestic animals.

Expression of a biologically active ovine trophoblastic interferon using a baculovirus expression system

Ovine trophoblast protein (oTP) an embryonic interferon, which plays a key role in maternal recognition of pregnancy, has been expressed in insect cells using a baculovirus expression system. A cDNA coding for oTP was inserted downstream of the strong polyhedrin promoter. Cells infected with recombinant virus produced biologically active oTP and greater than 90% was secreted into the culture medium during infection. High amount of antiviral activity were produced (up to 5 x 10(5) IU per ml of culture medium). Recombinant oTP (roTP) was purified by immunoaffinity chromatography and found to be identical to authentic oTP with respect to molecular mass and N-terminal amino acid sequence.

Induction of trophoblastic interferon expression in ovine blastocysts after treatment with double-stranded RNA

Ovine trophoblast protein-1 (oTP-1) is an interferon (IFN) related to the IFN-omega. The objectives of this research were: (i) to attempt to induce oTP-1 mRNA in day-11 ovine conceptuses with polyinosinic-polycytidylic acid (poly(I).poly(C], and (ii) to determine if IFN-omega mRNA is also produced on day 11 of gestation. In experiment I, conceptuses were cultured in presence of 100 micrograms/ml poly(I).poly(C) (n = 5) or medium alone (control, n = 3) for up to 8 h. In situ hybridization was used to assess effects of treatment on mRNA concentrations for oTP-1 and actin (positive hybridization control). Poly(I).poly(C) increased oTP-1 mRNA concentrations approximately 2.5-fold (p less than 0.01), but had no effect on actin mRNA. In experiment II, the presence of mRNA for oTP-1 and ovine IFN-omega was determined by using reverse transcription-polymerase chain reaction (RT-PCR) analysis of conceptus total RNA coupled with Southern blot hybridization of the PCR reaction products with specific cDNA probes. oTP-1 mRNA was detectable in all poly(I).poly(C)-treated (n = 7) and control (n = 6) conceptuses, whereas IFN-omega mRNA was detected in only three of seven poly(I).poly(C)-treated conceptuses and not in any controls. Together these results demonstrate that expression of oTP-1 mRNA can be enhanced by treatment with poly(I).poly(C) and that oTP-1 is the primary but not the only type I-IFN inducible in conceptuses on day 11 of gestation.

Constitutive and trophoblast-specific expression of a class of bovine interferon genes

The early conceptus in sheep and cattle secretes a low molecular weight protein called ovine and bovine trophoblast protein 1 (TP-1) that is critical for establishment of pregnancy. TP-1 is a type I interferon (IFN) and is most related to IFN-omega. Here we have determined if TP-1 genes are regulated similarly to other type I IFNs. Single day 18 bovine conceptuses secrete approximately 10(5) units of IFN antiviral activity per hour in culture, amounts approximately 300 times higher than those produced by Sendai virus-induced leukocytes. Although conceptuses express mRNA for IFN-alpha, IFN-omega, and TP-1, TP-1 constitutes greater than 99% of the IFN produced. In contrast, leukocytes produced predominantly IFN-alpha, although TP-1 mRNA is inducible by Sendai virus to very low levels. TP-1 mRNA is detectable by Northern analysis in conceptuses from early pregnancy but is absent in late gestation placenta and several adult tissues. Transfected bovine TP-1 genes are expressed in human choriocarcinoma (JAR) cells in the absence of any specific stimulus, whereas these cells do not secrete antiviral activity constitutively or after transfection with a bovine IFN-omega gene. The transfected TP-1 gene is not expressed in nontrophoblast cells (mouse L929 and hamster Chinese hamster ovary), however. The 5' promoter region of the TP-1 gene is sufficient to direct trophoblast-specific expression onto a human growth hormone reporter gene in JAR cells. Deletion of the promoter from -450 to -126 results in a 4- to 5-fold decrease in expression. Together these data demonstrate that the genes for TP-1 are inducible by virus but are expressed preferentially in trophoblast cells and are functionally distinct from IFN-omega genes.

Cloning and structural analysis of two distinct families of ovine interferon-alpha genes encoding functional class II and trophoblast (oTP) alpha-interferons

Ovine trophoblast protein (oTP) is a polypeptide secreted by ovine trophectoderm from day 11 to 21, which plays a key role in maternal recognition of pregnancy. Structural analyses established that oTP shares extensive homology with class II alpha-interferon (IFN-alpha II) subfamily. Previous screening of an ovine genomic DNA library probed with an oTP cDNA incidently resulted in the isolation of a functional IFN-alpha II gene and two relevant pseudogenes, as shown by sequence analysis and study of expression in eukaryotic COS cells. The expected oTP gene together with a cognate pseudogene was successfully isolated from the series of clones selected from another genomic library probed with the oTP cDNA, using two specific oligonucleotides, each one complementary to a region of oTP cDNA with little homology with the IFN-alpha II gene and related pseudogenes. Southern blotting of ovine genomic DNA indicated the existence of at least five trophoblast IFN-alpha genes or pseudogenes. Nucleotide sequence comparisons showed that the oTP gene exhibits a higher homology (90%) with bovine trophoblast IFN gene (Stewart et al. (1990) J. Mol. Endocrinol. 4, 275-282) than with oIFN-alpha II gene (70%), thus providing evidence that embryonic IFNs constitute a distinct subfamily of IFN-alpha s.

A role for interferons in early pregnancy

In order to survive, the developing conceptus must interrupt the normal ovarian cycle of the mother and extend the production of progesterone by the corpus luteum. An unusual Type 1 interferon (IFN), related structurally to the IFN-alpha molecule and produced in massive amounts for only a few days by the first epithelium (trophectoderm) of the preimplantation conceptus, has been implicated as the antiluteolytic agent in sheep and cattle. IFN-alpha therapy during this critical period can also improve pregnancy success in sheep. It remains unclear, however, whether the trophoblast IFN have specialized biological properties or whether they are unique merely in the timing, magnitude and site of their expression.

Ovine trophoblast protein-one: evidence for possible glycosylation

1. The polymerase chain reaction has been used to amplify specifically the cDNA coding for the secreted form of ovine trophoblast protein-one from a preparation of total cellular RNA extracted from sheep embryos removed from ewes 16 days after mating. 2. Cloning and sequencing of the amplified cDNA revealed two new sequence variants: SPW49 having 93% similarity with deduced amino acid sequences from published cDNA data, and SPW27 a variant coding for a deleted form of ovine trophoblast protein-one. 3. The gene for ovine trophoblast protein-one is intronless. 4. This study provides further evidence for the existence of an ovine trophoblast protein-one gene family. 5. Both variants contain a potential N-glycosylation site not apparent in published sequences for ovine trophoblast protein-one.

Unique features of the trophoblast interferons

The trophoblast interferons (IFN) are Type I IFN with about 50% amino acid sequence identity to the leukocyte IFN (IFN-alpha). They are the major secretory products of the trophoblast of ruminant ungulate species during pregnancy in the period immediately preceding attachment and implantation when they have been implicated in the phenomenon known as maternal recognition of pregnancy. The trophoblast IFN have antiviral and antiproliferative activities typical of other Type I IFN, but unlike IFN-alpha, -beta and -omega are poorly responsive to viral induction and have a highly restricted pattern of expression. Nevertheless, a recombinant bovine IFN-alpha can mimic many of the properties of the trophoblast IFN and has been used pharmacologically to improve pregnancy success in sheep. It still remains unclear, however, whether the trophoblast IFN have unique biological properties or whether they are unusual merely by virtue of the location, magnitude and temporal nature of their expression at a critical time during pregnancy.