maternal recognition of pregnancy

Successful growth and development of the post-hatching blastocyst and pregnancy establishment are results of the interaction between a competent embryo and a receptive uterine environment. There are certain marker gene transcripts identified which contribute and regulate the bidirectional channel of communication during the pregnancy period in farm animals. The changes in temporal gene expression in the endometrium are similar in pregnant and cyclic animals up to the time of maternal recognition of pregnancy (MRP) when conceptus derived factors affect expression of a large number of genes in pregnant animals. In this review we have discussed a set of candidate genes expressed or induced for MRP. There are certain genes 
playing important role in MRP in farm animals, of which interferon-tau (IFNT), Ubiquitin Cross Reative Protein (UCRP), Ghrelin, Aldoketoreductase-1B5 (AKR1B5), SERPINA14 are having esteemed role in farm animals. These genes appear to have role in successful establishment of pregnancy and expression of the cascade of signalling molecules. However, IFNT was recognized as one of the earliest expressing gene specifically required for maintenance of pregnancy.


Introduction
A transcriptome analysis in the cattle endometrium revealed that Ubiquitin Cross Reative Protein Successful embryo development and survival (UCRP) is one of the differentially expressed genes includes formation of blastocyst, implantation into the which up-regulates in response to conceptus derived uterus, formation of placenta and development of the IFNT.UCRP is an ubiquitin homolog that is expressed heart and vascularisation of both embryo and fetus to transiently in the uterus during early pregnancy in assist nutrient deliverance [1].Among these developseveral species including cattle [5], sheep [6], pigs [7] mental events, implantation of embryo is a crucial step and horse [8].The UCRP has an important role in the and its success mostly dependent on the efficiency with degradation of the cytosolic uterine proteins (e.g. which the MRP is established [2].The MRP includes receptors, enzymes and transcription factors of reguseries of events that are synchronized by the endocrine lating genes) that are detrimental for fetal/embryo interaction between the dam and the embryo.Survivability survival.It ligates and alters the proteosomal degradaand development of the embryo is influenced directly tion of cytosolic uterine proteins that are involved in and indirectly by exogenous and endogenous factors.uterine PGF2α release [9].Consequently, it is postulated Out of these factors, candidate genes influence that the expression of the UCRP is a conserved uterine molecular interactions involved in maintenance of response to the embryo and are hypothesized to play pregnancy through reciprocal interactions between the important biological roles uterine receptivity and conceptus and endometrium.
conceptus implantation [10].However Uterine serpins The majority of studies examining the molecular (SERPINA 14) is secreted from the uterine endometrium mechanisms of conceptus-endometrial interactions mainly under the influence of progesterone in many were carried out during the peri-implantation period of ungulate animal species including cattle [11], sheep pregnancy and described changes in the transcriptome [12], goat [13] and pig [14].The SERPINA14 protein of the endometrium [3,4].Recent studies [4] indicated performs diverse biological functions which include that the major factor affecting gene expression in the endometrium is day of the estrous cycle/early pregnancy.
direct nutrition to the conceptus, growth control, In other words, irrespective of pregnancy status, the inhibition of proteolytic activities and suppression of temporal changes in gene expression in the endothe local maternal immune system for sustaining metrium are similar in pregnant and cyclic animals up pregnancy.to the time of maternal recognition of pregnancy when The opportunity of successful development of an conceptus-derived factors, such as Interferon tau embryo depends on genetic factors of both the embryo (IFNT), induces or further amplifies expression of a and the mother's endometrium.A number of genes have large number of genes in pregnant animals.
been identified that become active after appearance and towards implantation of the embryo in the uterus also called as ubiquitin cross-reactive protein.viz.IFNT, UCRP, Ghrelin, Ghrelin (AKR1B5), SERPINA14.These candidate genes regulate Ghrelin is a novel motilin related endogenous the endometrial environment to establish pregnancy in ligand for growth hormone secretagouge receptor.It farm animals.In this review we summarize the current involves in various biological functions including information on the biology of above genes for estabregulation of female reproduction, but the presence of lishment and maintenance of pregnancy, particularly ghrelin and its role in reproductive functions in goat is on farm animals.not known.It acts as an endogenous ligand for growth

Interferon tau (IFNT)
hormone secretagouge (GHS) receptor, involved in IFNT, a member of the type I interferon family, is several biological functions including the GH releasing secreted by the trophectoderm of the elongating activity [28] and carbohydrate metabolism [29].In blastocyst and acts as a primary signal for MRP.IFNT addition, ghrelin has also been implicated as a crucial is encoded by a cluster of genes [15,16] which have factor affecting female reproduction [30].Ghrelin has been evolved from an ancestral IFN-omega gene that been shown to regulate several reproductive functions acquired a trophectoderm-specific promoter shortly including embryo implantation [31] and modulating after divergence of pecoran ruminants (cattle, sheep, reproductive hormone secretion [32][33][34].Ghrelin is goats, musk oxen, gazelles, giraffes and deer) from other expressed in different parts of reproductive tract artiodactyls [17].Although non-ruminant mammals do including the uterus, placenta, ovary and testis [35][36][37].not produce an IFN that controls maternal recognition Expression of ghrelin mRNA has been found to be of pregnancy, IFNs are expressed by placental tissues increased in early pregnant endometrial tissue compared in various mammals.In ruminant ungulates, such as to proliferative or secretary phase of endometrial tissue cattle, sheep and goats, IFNT is essential for the in human [31].Uterine endometrial tissue is the maintenance of pregnancy [18].IFNT acts on the maternal interface of fetal-maternal interaction and endometrium to abrogate the endometrial luteolytic various locally produced factors regulate the embryo mechanism by either inhibiting the transcription of receptivity of endometrium [38].It has been demonestrogens and/ or oxytocin receptors [19].
strated the involvement of ghrelin in remodeling or It is expressed constitutively by the trophecto-decidualization of human uterine endometrium [35].derm from the period of blastocyst formation until Low level of ghrelin expression in human endometrial attachment of the elongated conceptus to the uterine tissues is associated with decreased fertility [39].wall [16].IFNT is the initial requisite signal for Amongst several factors secreted by the endometrium, pregnancy recognition in ruminants [20].Systemic or ghrelin has been established as one of the factors intrauterine treatment with either native or recombi-influencing fertility in recent studies [39,40].However, nant ovine or bovine IFN-induces a brief pseudo there is no report about the presence of ghrelin and its pregnant condition that lasts from a few days to several expression in reproductive organs of goat and buffalo.weeks in sheep, cattle and goats [21][22][23].

Aldoketoreductase -1B5 (AKR1B5)
Till now, several polymorphic/allelic variants of AKR1B5 a member of Aldoketoreductse (AKR) IFN have been reported in ovine, bovine, bubaline and family, with prostaglandin F synthase (PGFS) activity, different breeds of caprine from livestock species.
is associated with prostaglandins (PGs) biosynthesis.However, possibility of existence of the additional PGs are important regulators of female reproductive allelic variants in the caprine and bubaline genome and functions viz., ovulation, uterine receptivity, implantation their functional role is yet to be explored.
and parturition [41].Among the different classes of

Ubiquitin cross reative protein (UCRP)
PGs, PGF2α-one of main prostanoids produced by UCRP is a member of ubiquitin-like (UBL) protein bovine endometrium [42].In ruminants, it regulates super family, plays an important role for foetal or ovarian cycle by initiating the regression (luteolysis) of embryo survival through establishment and maintencorpus luteum and functions as a major luteolytic agent ance of pregnancy in ruminant ungulates.It functions [43]. in response to conceptus derived IFNT by the PGs are synthesized from arachidonic acid and proteasomal degradation of cytosolic uterine proteins converted to PGH2 by either of two isoforms of PGH that are involved in uterine PGF2 release.synthase (PGHS), the constitutive cyclooxygenase The UCRP gene has been implicated as one of the (COX)-1 or the inducible COX-2.PGH2 is the common key players in determining the reproductive efficiency precursor of all PGs generated by specific terminal in farm animal species.IFNT up-regulates many synthases such as PGF synthase (PGFS) for PGF2α and interferon stimulated genes (ISGs) viz., interferon-PGE2 [44].PGF2α is a bioactive lipid belonging to the stimulated gene-17 (ISG17) in bovine [24] and ovine eicosanoid family.Its biosynthesis occurs via species [25] and its homologs ISG15 in human and reduction of PGH2 by a 9,11-endoperoxyde reductase.murine [26,27].The ISG15/17 gene shares limited Till now several PGFS have been identified, from cow (~30%) amino acid sequence identity with a tandem [45,46], human [47], sheep [48], Trypanosoma brucei ubiquitin repeat [24,26] Thus, both these proteins are [49] and porcine endometrium [50].All mammalian

Aldoketoreductase -1B5
PGFS belong to Aldoketoreductase 1 C (AKR1C) [31] and modulating reproductive hormone secretion family, with hydroxylsteroid dehydrogenase (HSD) [32,33].Besides Ghrelin and AKR1B5 which regulates activity.However, none of known functional PGFS endometrial function, the SERPINA14 protein from AKR1C family was detected in bovine performs diverse biological functions which included endometrium, while the expression of PGF2α was very direct nutrition to the conceptus, growth control, high [42].So.It was hypothesized that AKR1B5, inhibition of proteolytic activities and suppression of recently renamed as Bos taurus AKR1B1 was the the local maternal immune system for sustaining factor, responsible for the release of huge amount of pregnancy.The functional role of these genes for PGF2α in bovine endometrium [42].Due to its 20α establishment of pregnancy is yet to be explored in HSD activity, AKR1B5 (share 86% homology with different domestic species.Further, studies on these AKR1B1 in human) is responsible for the release of genes can improve the reproductive efficiency, PGF2α and inactivate progesterone to regulate establishment and maintenance of pregnancy in farm endometrial function in bovine endometrium [51,52].
animals.Apart from above, these gene can also be established as a competent marker to improve breed also responsible for the proper functioning of UCRP.