Major histocompatibility antigen expression on the bovine placenta: its relationship to abnormal pregnancies and retained placenta

Global gene expression analysis of bovine blastocysts produced by multiple methods

Reproductive efficiency using somatic cell nuclear transfer (SCNT) technology remains suboptimal. Of the various efforts to improve the efficiency, chromatin transfer (CT) and clone-clone aggregation (NTagg) have been reported to produce live cloned animals. To better understand the molecular mechanisms of somatic cell reprogramming during SCNT and assess the various SCNT methods on the molecular level, we performed gene expression analysis on bovine blastocysts produced via standard nuclear transfer (NT), CT, NTagg, in vitro fertilization (IVF), and artificial insemination (AI), as well as on somatic donor cells, using bovine genome arrays. The expression profiles of SCNT (NT, CT, NTagg) embryos were compared with IVF and AI embryos as well as donor cells. NT and CT embryos have indistinguishable gene expression patterns. In comparison to IVF or AI embryos, the number of differentially expressed genes in NTagg embryos is significantly higher than in NT and CT embryos. Genes that were differentially expressed between all the SCNT embryos and IVF or AI embryos are identified. Compared to AI embryos, more than half of the genes found deregulated between SCNT and AI embryos appear to be the result of in vitro culture alone. The results indicate that although SCNT methods have altered differentiated somatic nuclei gene expression to more closely resemble that of embryonic nuclei, combination of insufficient reprogramming and in vitro culture condition compromise the developmental potential of SCNT embryos. This is the first set of comprehensive data for analyzing the molecular impact of various nuclear transfer methods on bovine pre-implantation embryos.

Progesterone During Pregnancy: Endocrine?Immune Cross Talk in Mammalian Species and the Role of Stress

Progesterone is critical for the establishment and the maintenance of pregnancy, both by its endocrine and immunological effects. The genomic actions of progesterone are mediated by the intracellular progesterone receptors; A and B. A protein called P-induced blocking factor (PIBF), by inducing a T(H2) dominant cytokine production, mediates the immunological effects of progesterone. Progesterone plays a role in uterine homing of NK cells and up-regulates HLA-G gene expression, the ligand for various NK inhibitory receptors. At high concentrations progesterone is a potent inducer of Th2-type cytokines as well as of LIF and M-CSF production by T cells. Though a key role for progesterone in creating local immunosuppression has been conserved during the evolution of an epitheliochorial placenta, there has been some divergence in the pattern of endocrine-immunological cross talk in Bovidae. In sheep, uterine serpin, a progesterone-induced endometrial protein, mediates the immunosuppressive effects of progesterone. Epidemiological studies suggest the role of stress in premature pregnancy termination and exposure to stress induces abortion in mice via a significant reduction in progesterone levels, accompanied by reduced serum levels of PIBF. These effects are corrected by progesterone supplementation. These findings indicate the significance of a progesterone-dependent immuno-modulation in maternal tolerance of the fetus, which is discussed in this review.

Placentation in cloned cattle: Structure and microvascular architecture

To elucidate the morphological differences between placentas from normal and cloned cattle pregnancies reaching term, the umbilical cord, placentomes and interplacentomal region of the fetal membranes were examined macroscopically as well as by light and scanning electron microscopy. In pregnancies established by somatic nucleus transfer (NT), the umbilical cord and fetal membranes were edematous. Placentomal fusion was common, resulting in increased size and a decreased number of placentomes. Extensive areas of the chorioallantoic membrane were devoid of placentomes. An increased number of functional or accessory microcotyledons (<1 cm) were present at the maternally oriented surface of fetal membranes. Extensive areas of extravasated maternal blood were present within the placentomes and in the interplacentomal region. The crypts on the caruncular surface were dilated and accommodated complexes of more than one primary villus, as opposed to a single villus in non-cloned placentae. Scanning electron microscopy of blood vessel casts revealed that there was also more than one stem artery per villous tree and that the ramification of the vessels failed to form dense complexes of capillary loops and sinusoidal dilations as in normal pregnancies. At the materno-fetal interface, however, the trophoblast and uterine epithelium had normal histology. In conclusion, the NT placentas had a range of pathomorphological changes; this was likely associated with the poor clinical outcome of NT pregnancies.

Why is the fetal allograft not rejected?1

In viviparous species, the conceptus must be protected from a potentially hostile maternal immune system. The major histocompatibility complex (MHC) is a genetic region that encodes MHC class I and class II proteins, which present peptide antigens to T lymphocytes and induce graft rejection. The MHC, class II proteins are only expressed on professional, antigen-presenting cells. However, classical, MHC class I proteins are expressed on all nucleated somatic cells. Protection of the conceptus from immune-mediated rejection involves downregulation of classical MHC class I antigen expression on trophoblast cells, which form the external epithelial layer of the placenta, and maintenance of an immunologically favorable immunosuppressive environment in the uterus. Normally, bovine trophoblast cells do not express MHC class I antigens before d 120 of pregnancy. However, during the last third of gestation, trophoblast cells in the inter-placentomal and arcade regions of the placenta express classical, MHC class I proteins, which could potentially induce fetal rejection, as well as nonclassical, MHC class I proteins. A human, nonclassical, MHC class I antigen, human leukocyte antigen G, is an important immunoregulatory factor required for the maintenance of pregnancy. In cattle, MHC class I expression during the last third of pregnancy has no adverse effects and probably contributes to placental separation at parturition. However, somatic cell nuclear transfer (SCNT) conceptuses, the majority of which are aborted between d 30 and 90 of pregnancy, had trophoblast cell expression of MHC class I antigens before d 34 of pregnancy. In conjunction with increased trophoblast MHC class I expression, SCNT pregnancies exhibited a marked increase in the number of stromal lymphocytes in the uteri of surrogate dams. A retrospective study found that SCNT pregnancies established using MHC class I-homozygous cell lines, in which the immunological barrier is greatly reduced, had significantly improved fetal survival from d 28 to term (51% survival for MHC-homozygous and 5% for MHC-heterozygous SCNT fetuses). Consequently, it appears that the high rate of fetal mortality in SCNT pregnancies is due, at least in part, to inappropriate expression of trophoblast, MHC class I antigens resulting in immune-mediated placental rejection. This suggests that appropriate regulation of MHC class I genes is critical for immunological acceptance of an allogeneic conceptus.

Evaluation of intrauterine antibiotic treatment of clinical metritis and retained fetal membranes in dairy cows

Retained fetal membranes (RFM) and clinical metritis (CM) are frequently diagnosed disease conditions in dairy cows and considered of major economic impact due to negative effect on reproduction and milk production. The objective of this study was to evaluate the efficacy of i.u. tetracycline for the treatment of RFM and CM in dairy cows. Affected cows were randomly assigned to two groups; treatment group animals received i.u. 5g chlortetracycline twice weekly for 2 wks, and no treatment group. A total of 1416 cows and 804 heifers in 5 herds calved during the study period. CM was diagnosed in 18.6% (inter farm range; 15.2-23.5%) and 30% (19.4-42.3%) of cows and heifers, respectively. RFM was diagnosed in 13.1% (9.4-18.1%) and 9.2% (3.6-13.8%) of cows and heifers, respectively. Conception rates after first insemination were 38.3%, 42.5% and 18% in normal, treated and non-treated CM cows, respectively. Numbers of days open were 140.5, 136.2 and 165.5 in normal, treated and non-treated CM cows, respectively. Based on 305-d corrected milk yield, cows and heifers affected by RFM and CM produced 300-500kg less milk compared with their normal herd mates. Cows treated for CM produced 654kg more milk per 305-d corrected lactation compared to non-treated control cows. Treatment of RFM had no effect on reproductive performance or milk production. In conclusion, i.u. chlortetracycline treatment was proven to prevent the detrimental effect of CM on reproductive performance in heifers and cows and on milk production in cows only.

The E5 oncoprotein of BPV-4 does not interfere with the biosynthetic pathway of non-classical MHC class I

The major histocompatibility complex (MHC) class I region in mammals contains both classical and non-classical MHC class I genes. Classical MHC class I molecules present antigenic peptides to cytotoxic T lymphocytes, whereas non-classical MHC class I molecules have a variety of functions. Both classical and non-classical MHC molecules interact with natural killer cell receptors and may under some circumstances prevent cell death by natural killer cytotoxicity. The E5 oncoprotein of BPV-4 down-regulates the expression of classical MHC class I on the cell surface and retains the complex in the Golgi apparatus. The inhibition of classical MHC class I to the cell surface results from both the impaired acidification of the Golgi, due to the interaction of E5 with subunit c of the H+ V-ATPase, and to the physical binding of E5 to the heavy chain of MHC class I. Despite the profound effect of E5 on classical MHC class I, E5 does not retain a non-classical MHC class I in the Golgi, does not inhibit its transport to the cell surface and does not bind its heavy chain. We conclude that, as is the case for HPV-16 E5, BPV-4 E5 does not down-regulate certain non-classical MHC class I, potentially providing a mechanism for the escape of the infected cell from attack by both cytotoxic T lymphocytes and NK cells.

Aberrant profile of gene expression in cloned mouse embryos derived from donor cumulus nuclei

Somatic cell nuclear transfer has successfully been used to clone several mammalian species including the mouse, albeit with extremely low efficiency. This study investigated gene expression in cloned mouse embryos derived from cumulus cell donor nuclei, in comparison with in vivo fertilized mouse embryos, at progressive developmental stages. Enucleation was carried out by the conventional puncture method rather than by the piezo-actuated technique, whereas nuclear transfer was achieved by direct cumulus nuclear injection. Embryonic development was monitored from chemically induced activation on day 0 until the blastocyst stage on day 4. Poor developmental competence of cloned embryos was observed, which was confirmed by lower cell counts in cloned blastocysts, compared with the in vivo fertilized controls. Subsequently, real-time polymerase chain reaction was used to analyze and compare embryonic gene expression at the 2-cell, 4-cell, and blastocyst stages, between the experimental and control groups. The results showed reduced expression of the candidate genes in cloned 2-cell stage embryos, as manifested by poor developmental competence, compared with expression in the in vivo fertilized controls. Cloned 4-cell embryos and blastocysts, which had overcome the developmental block at the 2-cell stage, also showed up-regulated and down-regulated expression of several genes, strongly suggesting incomplete nuclear reprogramming. We have therefore demonstrated that aberrant embryonic gene expression is associated with low developmental competence of cloned mouse embryos. To improve the efficiency of somatic cell nuclear transfer, strategies to rectify aberrant gene expression in cloned embryos should be investigated.

Effects of cow age and pregnancy on Bartonella infection in a herd of dairy cattle

Bartonella spp. are small hemotropic bacteria infecting mammals. Four Bartonella species have been recently described in cattle and wild ruminants. To date, the biology and possible pathogenic role of Bartonella species isolated from ruminants are poorly understood. Therefore, a dairy herd of 448 cows and heifers was surveyed in order to establish the prevalence of Bartonella bovis and B. chomelii infections, the level of bacteremia, and the relationship between bacteremia and age or pregnancy status. The putative impact of Bartonella infection on production performance (individual milk cell count, milk yield) and reproductive status (success of artificial insemination [AI], placental retention, embryonic death, and abortion) was also assessed. The overall mean prevalence of B. bovis bacteremia was 59%, with the highest prevalence in heifers (92.5%). No B. chomelii was isolated, and 95% (114/120) of the B. bovis strains isolated and tested by PCR-restriction fragment length polymorphism belonged to type I. The level of bacteremia was higher in pregnant cows than in nonpregnant cows (P = 0.05), and the level of bacteremia rose during the last two-thirds of gestation (P < 0.001). There was no correlation between bacteremia and milk yield, individual milk cell count, success of first AI, interval between two calvings, or incidence of abortion and embryonic death. The interval from calving to first AI was shorter and the incidence of placental retention was lower in bacteremic animals than in nonbacteremic ones (P = 0.03 and P = 0.01, respectively).

Evidence for Expression of Both Classical and Non-Classical Major Histocompatibility Complex Class I Genes in Bovine Trophoblast Cells

PROBLEM

During the third trimester of pregnancy bovine trophoblast cells in the interplacentomal and arcade regions of the placenta express major histocompatibility complex class I (MHC-I) antigens. At parturition immunological recognition of MHC-I antigens appears to contribute to normal placental release. Therefore, we hypothesized that during late pregnancy bovine trophoblast cells express polymorphic, classical MHC-I antigens.

METHOD OF STUDY

Cloning, microarray screening and sequencing of cDNA were used to study transcription of MHC-I genes in peripheral blood mononuclear cells (PBMC) and interplacentomal, trophoblast cells. Real-time reverse transcription, polymerase chain reaction (RT-PCR) was used to compare the abundance of MHC-I transcripts in PBMC and trophoblast cells.

RESULTS

Screening of cloned MHC-I cDNA on MHC-I microarrays indicated that in PBMC 90-98% of MHC-I transcripts were encoded by classical MHC-I genes with the remainder encoded by non-classical MHC-I genes. In contrast, 21-66% of MHC-I transcripts from interplacentomal trophoblast cells were from classical genes and 34-79% were from non-classical genes. Transcripts from four non-classical MHC-I loci were identified by sequence analysis. Real-time RT-PCR indicated that the overall levels of MHC-I gene expression in PBMC and trophoblast were similar.

CONCLUSION

Bovine interplacentomal trophoblast cells express both classical and non-classical MHC-I genes, but the relative level of expression varies considerably.

Outbred embryos rescue inbred half-siblings in mixed-paternity broods of live-bearing females

Females commonly mate with more than one male, and polyandry has been shown to increase reproductive success in many species. Insemination by multiple males shifts the arena for sexual selection from the external environment to the female reproductive tract, where sperm competition or female choice of sperm could bias fertilization against sperm from genetically inferior or genetically incompatible males. Evidence that polyandry can be a strategy for avoiding incompatibility comes from studies showing that inbreeding cost is reduced in some egg-laying species by postcopulatory mechanisms that favour fertilization by sperm from unrelated males. In viviparous (live-bearing) species, inbreeding not only reduces offspring genetic quality but might also disrupt feto-maternal interactions that are crucial for normal embryonic development. Here we show that polyandry in viviparous pseudoscorpions reduces inbreeding cost not through paternity-biasing mechanisms favouring outbred offspring, but rather because outbred embryos exert a rescuing effect on inbred half-siblings in mixed-paternity broods. The benefits of polyandry may thus be more complex for live-bearing females than for females that lay eggs.

Errors in development of fetuses and placentas from in vitro-produced bovine embryos

In vitro systems for oocyte maturation, fertilization and embryo culture [in vitro production (IVP)] have the potential for more wide-spread use in creative breeding programs for dairy and beef cattle. However, one negative consequence of both IVP and somatic cell nuclear transfer (SCNT) in cattle and other species is that embryos, fetuses, placentas, and offspring can differ significantly in morphology and developmental competence compared with those from embryos produced in vivo. Fetuses and placentas derived from IVP and SCNT embryos may fall within the normal range of development, may have obvious abnormalities such as increased fetal and placental weights, or may have subtle abnormalities such as aberrant development of fetal skeletal muscle, placental blood vessels, and altered metabolism. Failures in physiologic and/or genetic mechanisms essential for proper fetal growth and survival outside of the uterus contribute significantly to pregnancy and neonatal losses. Oversized fetuses are at increased risk of death during parturition and the adverse consequences of severe dystocia may compromise the dam. Collectively, these abnormalities have been referred to as 'large offspring syndrome' or 'large calf syndrome'. Abnormal phenotypes resulting from IVP and SCNT embryos are stochastic in occurrence and they have not been consistently linked to aberrant expression of single genes or specific pathophysiology. Thus, reliable methods of early diagnosis of the condition are not yet available. The objective of this paper is to examine abnormal development of fetuses and placentas resulting from embryos produced using in vitro systems. The term 'abnormal offspring syndrome (AOS)' is introduced and a classification system of developmental outcomes is proposed to facilitate research efforts on the mechanisms of the various abnormal phenotypes. We also discuss potential genetic and physiologic mechanisms that may contribute to abnormal phenotypes following transfer of IVP and SCNT embryos.

The Development and Application of the Modern Reproductive Technologies to Horse Breeding

Although the horse was probably the first animal to experience and benefit from artificial insemination, it trailed the field somewhat with regard to the application of embryo transfer and other oocyte and embryo-related modern breeding technologies. But with a late run it is now back in mid-field and gaining fast on the other large domestic species in the application of the many technological advances of the past 20 years to sound breeding practice. Improvements in extenders and cryoprotectants have resulted in a veritable upsurge in the transport and insemination of cooled and frozen stallion semen, and parallel improvements in ovulation induction and synchrony, exogenous gonadotrophic stimulation of multiple fertile ovulations and simplified, more efficient methods for non-surgical transfer of embryos to recipient mares, coupled with relaxation of breed society registration restrictions, have together contributed to a similar upsurge in the application of embryo transfer to all breeds and athletic types of horses worldwide, with the continuing and notable exception of the Thoroughbred. Although conventional in vitro fertilization remains something of an unjumped fence in equids, other modern breeding technologies like hysteroscopic low-dose insemination, fluorescence-activated sex sorting of stallion spermatozoa, between-species embryo transfer, embryo freezing and bisection, transvaginal ultrasound-guided oocyte collection, intracytoplasmic sperm injection for fertilization (ICSI), gamete intrafallopian transfer (GIFT) and now nuclear transfer (cloning), have all been applied to equids with encouraging success. Cloning, especially, holds enormous promise for the Sporthorse industry to re-create champion geldings in stallion form for breeding purposes.