Removal of Qa-2 antigen alters the Ped gene phenotype of preimplantation mouse embryos

New Insights Into the Role of Qa-2 and HLA-G Non-classical MHC-I Complexes in Malignancy

It is well established that the immune system can identify and destroy neoplastic transformed cells in a process known as immunosurveillance. Most studies have focused on the classical major histocompatibility complex (MHC) class Ia molecules, which are known to play an important role on the presentation of tumor antigens to the immune system in order to activate a response against tumor cells. However, a larger family of non-classical MHC class Ib-related molecules has received less attention. In this mini-review, we discuss the role of class Ib murine Qa-2 and its proposed human HLA-G homolog on immunosurveillance during embryogenesis and cancer. Whereas, both HLA-G and Qa-2 are involved in immune tolerance in pregnancy, the current evidence suggests that they play opposite roles in cancer. HLA-G appears to promote tumor progression while Qa-2 acts as a tumor suppressor awaking the immune system to reject tumor cells, as suggested by studies on different cancer cell models, such as melanoma, lymphoma, lung carcinoma, and our own results in mammary carcinoma.

Systematic analysis of the factors that adversely affect the rate of cell accumulation in mouse embryos during their culture in vitro

BACKGROUND

Retarded embryo growth is a pervasive effect of culture in vitro.

METHODS

A systematic analysis of the interactions between media design, embryo culture density, oxygen tension, amino acids, trophic ligands and the genetic background of the mouse on embryo growth rates in vitro was performed.

RESULTS

Growth retardation of mouse zygotes was greater in 20% O2 than 5%, a sequential media design was superior to static simple media designs, but the supplementation of simple media with mixed amino acids mitigated this difference. There was a beneficial effect of communal culture in small volumes, and supplementation with a trophic ligand (Paf) further enhanced growth rates. For hybrid strain zygotes (B6CBF1) communal culture in KSOM media supplemented with amino acids, albumin and Paf under 5% O₂ resulted in complete rescue of their rate of accumulation of cells and blastocyst formation. Inbred strain (C57BL6/J) zygotes, however, still showed some retardation of development under these conditions. The additional supplementation of media with another trophic ligand (IGF1) showed a further additive beneficial effect on development of inbred strain embryos but they still showed a growth deficit of ~ 23% cell number. The results show that optimising the interactions between a range of culture conditions and media design can rescue hybrid strain embryos from a retarded rate of cell proliferation caused by culture in vitro, but this was incomplete for the B6 strain.

CONCLUSIONS

The results indicate that the growth requirement of embryos in vitro varies depending upon their genetic background and provide models for the further genetic analysis of embryo growth.

Differential transcript profiles of MHC class Ib(Qa-1, Qa-2, and Qa-10) and Aire genes during the ontogeny of thymus and other tissues

Qa-2 and Qa-1 are murine nonclassical MHC class I molecules involved in the modulation of immune responses by interacting with T CD8(+) and NK cell inhibitory receptors. During thymic education, the Aire gene imposes the expression of thousands of tissue-related antigens in the thymic medulla, permitting the negative selection events. Aiming to characterize the transcriptional profiles of nonclassical MHC class I genes in spatial-temporal association with the Aire expression, we evaluated the gene expression of H2-Q7(Qa-2), H2-T23(Qa-1), H2-Q10(Qa-10), and Aire during fetal and postnatal development of thymus and other tissues. In the thymus, H2-Q7(Qa-2) transcripts were detected at high levels throughout development and were positively correlated with Aire expression during fetal ages. H2-Q7(Qa-2) and H2-T23(Qa-1) showed distinct expression patterns with gradual increasing levels according to age in most tissues analyzed. H2-Q10(Qa-10) was preferentially expressed by the liver. The Aire transcriptional profile showed increased levels during the fetal period and was detectable in postnatal ages in the thymus. Overall, nonclassical MHC class I genes started to be expressed early during the ontogeny. Their levels varied according to age, tissue, and mouse strain analyzed. This differential expression may contribute to the distinct patterns of mouse susceptibility/resistance to infectious and noninfectious disorders.

MHC class I protein is expressed by neurons and neural progenitors in mid-gestation mouse brain

Proteins of the major histocompatibility complex class I (MHCI) are known for their role in the vertebrate adaptive immune response, and are required for normal postnatal brain development and plasticity. However, it remains unknown if MHCI proteins are present in the mammalian brain before birth. Here, we show that MHCI proteins are widely expressed in the developing mouse central nervous system at mid-gestation (E9.5-10.5). MHCI is strongly expressed in several regions of the prenatal brain, including the neuroepithelium and olfactory placode. MHCI is expressed by neural progenitors at these ages, as identified by co-expression in cells positive for neuron-specific class III β-tubulin (Tuj1) or for Pax6, a marker of neural progenitors in the dorsal neuroepithelium. MHCI is also co-expressed with nestin, a marker of neural stem/progenitor cells, in olfactory placode, but the co-localization is less extensive in other regions. MHCI is detected in the small population of post-mitotic neurons that are present at this early stage of brain development, as identified by co-expression in cells positive for neuronal microtubule-associated protein-2 (MAP2). Thus MHCI protein is expressed during the earliest stages of neuronal differentiation in the mammalian brain. MHCI expression in neurons and neural progenitors at mid-gestation, prior to the maturation of the adaptive immune system, is consistent with MHCI performing non-immune functions in prenatal brain development. These results raise the possibility that disruption of the levels and/or patterns of MHCI expression in the prenatal brain could contribute to the pathogenesis of neurodevelopmental disorders.

Early transcription from the maternal genome controlling blastomere integrity in mouse two-cell-stage embryos

Blastomere cytofragmentation in mammalian embryos poses a significant problem in applied and clinical embryology. Mouse two-cell-stage embryos display strain-dependent differences in the rate of cytofragmentation, with a high rate observed in C3H/HeJ embryos and a lower rate observed in C57BL/6 embryos. The maternally inherited genome exerts the strongest effect on the process, with lesser effects mediated by the paternally inherited genome and the ooplasm. The effect of the maternal genome is transcription dependent and independent of the mitochondrial strain of origin. To identify molecular mechanisms that underlie cytofragmentation, we evaluated transcriptional activities of embryos possessing maternal pronuclei (mPN) of different origins. The mPN from C57BL/6 and C3H/HeJ strains directed specific transcription at the two-cell stage of mRNAs corresponding to 935 and 864 Affymetrix probe set IDs, respectively. Comparing transcriptomes of two-cell-stage embryos with different mPN revealed 64 transcribed genes with differential expression (1.4-fold or greater). Some of these genes occupy molecular pathways that may regulate cytofragmentation via a combination of effects related to apoptosis and effects on the cytoskeleton. These results implicate specific molecular mechanisms that may regulate cytofragmentation in early mammalian embryos. The most striking effect of mPN strain of origin on gene expression was on adenylate cyclase 2 (Adcy2). Treatment with dibutyryl cAMP (dbcAMP) elicits a high rate and severe form of cytofragmentation, and the effective dbcAMP concentration varies with maternal genotype. An activator of exchange proteins directly activated by cAMP (EPACs, or RAPGEF 3 and 4) 8-pCPT-2'-O-methyl-cAMP, elicits a high level of fragmentation while the PKA-specific activator N6-benzoyl-cAMP does not. Inhibition of A kinase anchor protein activities with st-Ht31 induces fragmentation. Inhibition of phosphatidylinositol 3-kinase signaling also induces fragmentation. These results reveal novel mechanisms by which maternal genotype affects cytofragmentation, including a system of opposing signaling pathways that most likely operate by controlling cytoskeletal function.

MicroRNA expression in preimplantation mouse embryos from Ped gene positive compared to Ped gene negative mice

PURPOSE

The mouse preimplantation embryo development (Ped) gene product, Qa-2, influences the rate of preimplantation embryonic development and overall reproductive success. Here we investigated the expression pattern of two microRNAs, miR-125a and miR-125b, known to be involved in development in lower organisms, in preimplantation embryos from the two-cell, four-cell, eight-cell, morula, and blastocyst stages of development from the congenic B6.K1 (Ped negative) and B6.K2 (Ped positive) strains of mice.

METHOD

B6.K1 and B6.K2 congenic mice differ only in the absence (B6.K1) or presence (B6.K2) of the genes encoding Qa-2 protein. We analyzed the expression of miR-125a and miR-125b in B6.K1 and B6.K2 preimplantation embryos by using real-time PCR.

RESULT

We found no variability in miR-125b expression at any developmental stage in both strains. However, miR-125a expression increased during development in both strains and was ten times higher in Ped negative (B6.K1) embryos than in Ped positive (B6.K2) embryos by the blastocyst stage of development.

CONCLUSION

Our results show that the absence of the Ped gene profoundly affects the level of a miRNA (miR-125a) known to regulate early development. The implication is that miR-125a is likely involved in the regulation of timing of early development in mice.

Preimplantation embryo development (Ped) gene copy number varies from 0 to 85 in a population of wild mice identified as Mus musculus domesticus

The preimplantation embryo development (Ped) gene regulates the rate of preimplantation embryonic cleavage division and subsequent embryo survival. In the mouse, the Ped gene product is Qa-2 protein, a nonclassical MHC class I molecule encoded by four tandem genes, Q6/Q7/Q8/Q9. Most inbred strains of mice have all four genes on each allelic chromosome, making a total of eight Qa-2 encoding genes, but there are a few strains that are missing all eight genes, defining a null allele. Mouse strains with the presence of the Qa-2 encoding genes express Qa-2 protein and produce embryos with a faster rate of preimplantation embryonic development and a greater chance of embryo survival compared to mouse strains with the null allele. There is extensive evidence that the human homolog of Qa-2 is HLA-G. HLA-G in humans, like Qa-2 in mice, is associated with enhanced reproductive success. The human population is an outbred population. Therefore, for a better comparison to the human population, we undertook an investigation of the presence of the genes encoding Qa-2 in an outbred population of mice. We used Real-Time Quantitative PCR to quantify the number of Qa-2 encoding genes in a population of 32 wild mice identified as Mus musculus domesticus both by morphologic assessment and by PCR analysis of their DNA. We found great variability in the number of Qa-2 encoding genes in the wild mice tested. The wild mouse with the highest number of Qa-2 encoding genes had 85 such genes, whereas we discovered one wild mouse without any Qa-2 encoding genes. Evolutionary implications of a range of Qa-2 encoding gene numbers in the wild mouse population are discussed, as well as the relevance of our findings to humans.

Genetics and imaging to assess oocyte and preimplantation embryo health

Two major criteria are currently used in human assisted reproductive technologies (ART) to evaluate oocyte and preimplantation embryo health: (1) rate of preimplantation embryonic development; and (2) overall morphology. A major gene that regulates the rate of preimplantation development is the preimplantation embryo development (Ped) gene, discovered in our laboratory. In mice, presence of the Ped gene product, Qa-2 protein, results in a fast rate of preimplantation embryonic development, compared with a slow rate of preimplantation embryonic development for embryos that are lacking Qa-2 protein. Moreover, mice that express Qa-2 protein have an overall reproductive advantage that extends beyond the preimplantation period, including higher survival to birth, higher birthweight, and higher survival to weaning. Data are presented that suggest that Qa-2 increases the rate of development of early embryos by acting as a cell-signalling molecule and that phosphatidylinositol-32 kinase is involved in the cell-signalling pathway. The most likely human homologue of Qa-2 has recently been identified as human leukocyte antigen (HLA)-G. Data are presented which show that HLA-G, like Qa-2, is located in lipid rafts, implying that HLA-G also acts as a signalling molecule. In order to better evaluate the second criterion used in ART (i.e. overall morphology), a unique and innovative imaging microscope has been constructed, the Keck 3-D fusion microscope (Keck 3DFM). The Keck 3DFM combines five different microscopic modes into a single platform, allowing multi-modal imaging of the specimen. One of the modes, the quadrature tomographic microscope (QTM), creates digital images of non-stained transparent cells by measuring changes in the index of refraction. Quadrature tomographic microscope images of oocytes and preimplantation mouse embryos are presented for the first time. The digital information from the QTM images should allow the number of cells in a preimplantation embryo to be counted non-invasively. The Keck 3DFM is also being used to assess mitochondrial distribution in mouse oocytes and embryos by using the k-means clustering algorithm. Both the number of cells in preimplantation embryos and mitochondrial distribution are related to oocyte and embryo health. New imaging data obtained from the Keck 3DFM, combined with genetic and biochemical approaches, have the promise of being able to distinguish healthy from unhealthy oocytes and embryos in a non-invasive manner. The goal is to apply the information from our mouse model system to the clinic in order to identify one and only one healthy embryo for transfer back to the mother undergoing an ART procedure. This approach has the potential to increase the success rate of ART and to decrease the high, and undesirable, multiple birth rate presently associated with ART.

HLA-G is found in lipid rafts and can act as a signaling molecule

HLA-G protein is the functional homolog of Qa-2, the product of the mouse preimplantation embryo development (Ped) gene. Embryos expressing Qa-2 on the cell surface exhibit a faster rate of preimplantation cleavage and preferential survival in utero compared with Qa-2-negative embryos. Qa-2 is glycosylphosphatidylinositol (GPI) linked in the cell membrane. As a result, Qa-2 proteins cluster in cholesterol- and sphingolipid-rich lipid raft microdomains in the cell membrane and can signal via raft-associated intracellular signaling molecules. Using T cells as a model system, cross-linking of Qa-2 on the cell membrane has been shown to induce proliferation of resting cells. HLA-G, like Qa-2, lacks a cytoplasmic domain capable of transducing signals from the cell surface to the nucleus, but unlike Qa-2, HLA-G has a short six-amino acid cytoplasmic tail rather than a GPI anchor. To test whether HLA-G, like Qa-2, is located in lipid rafts and can act as a signaling molecule, we used an HLA-G transgenic mouse system. T cells were isolated and tested for HLA-G expression by immunofluorescence and for localization of HLA-G in lipid rafts by immunofluorescence and Western blotting. Next, the T cells were cross-linked with anti-HLA-G antibody to test for induction of proliferation. Our novel results show that HLA-G, like GPI-linked Qa-2, is present in lipid rafts in the cell membrane and can act as a signaling molecule to induce proliferation of resting T cells.

Influence of the preimplantation embryo development (Ped) gene on embryonic platelet-activating factor (PAF) levels

PURPOSE

A major gene responsible for the control of preimplantation cleavage rate is the Ped gene, the product of which is the Qa-2 protein. Fast, but not slow developing mouse embryos express the Qa-2 protein. Platelet-activating factor (PAF) is a novel and potent signaling phospholipid that has unique pleiotropic properties in addition to platelet activation. PAF plays a significant role in virtually every reproductive event, including ovulation, fertilization, implantation, and parturition. The role of the Ped gene in PAF production by preimplantation embryos is yet to be established. The presence of this gene provides embryos with a reproductive advantage over those that are Ped negative, and may also serve as a regulator of PAF synthesis. The study hypothesis is that the amount of PAF produced is dependent upon the presence or absence of the Ped gene.

METHODS

B6.K1 (Ped negative) and B6.K2 (Ped positive) mouse embryo-conditioned culture media were assayed for PAF content by a PAF-specific radioimmunoassay.

RESULTS

There was a significant (p < 0.001) difference in blastocyst development rates between the Ped+ B6.K2 (61.0%) and the Ped- B6.K1 (25.3%) embryo culture groups. There was a significant difference (p < 0.05) in PAF production between the Ped+ B6.K2 (4.70+/-0.46 pmol per embryo) embryo culture group and the Ped- B6.K1 (10.02+/-3.49 pmol per embryo) embryo group. The B6.K1 (Ped-) embryo group produced >2x more PAF than did the B6.K2 (Ped+) group.

CONCLUSIONS

The Ped gene plays a role in PAF production and release in preimplantation stage embryos. The use of two mouse identical strains, except for the Ped gene, show that its presence is associated with an increase in developmental potential. Embryos where the Ped gene was absent produced significantly higher levels of PAF, which may aid in their survival.

The influence of mouse Ped gene expression on postnatal development

The Ped (preimplantation embryo development) gene, whose product is Qa-2 protein, is correlated with a faster rate of preimplantation development (Ped fast phenotype) in mice that express Qa-2 protein compared with mice with an absence of Qa-2 protein (Ped slow phenotype). In the current study, we have used two congenic mouse strains differentially expressing the Ped gene, strain B6.K1 (Ped slow; Qa-2 negative) and strain B6.K2 (Ped fast; Qa-2 positive), to investigate the effects of Ped gene expression on postnatal growth profiles, systolic blood pressure and adult organ allometry. At birth, B6.K1 mice were moderately lighter than B6.K2 mice. B6.K1 mice became heavier during postnatal life (P < 0.05) and had elevated systolic blood pressure at 21 weeks of age when compared with B6.K2 mice (P = 0.006). B6.K1 mice also demonstrated elevated serum angiotensin-converting enzyme (ACE) activity, a known regulator of blood pressure (P = 0.037). Altered organ:body weight ratios were also observed, with the B6.K1 females having a higher ratio for lungs than B6. K2 females (P = 0.014). These data provide evidence of an association between the rate of preimplantation embryo development, postnatal growth and later cardiovascular function.

Search for the Bovine Homolog of the Murine Ped Gene and Characterization of Its Messenger RNA Expression During Bovine Preimplantation Development1

In mice, a gene (Ped: preimplantation embryo development) that regulates preimplantation embryonic growth, including cleavage rate and embryo survivability, has been described. The objective of the current study was to identify the bovine homolog of the Ped gene and to characterize the mRNA expression pattern of this gene during bovine preimplantation embryo development. The NCBI GenBank/EBI expressed sequence tags (EST) databases were searched for bovine ESTs that were homologous to the murine Ped gene, and the resulting ESTs were aligned and assembled into a contiguous sequence. The homology of the sequence to the murine Ped gene was confirmed. Primers were designed for the sequence, and the mRNA expression pattern was characterized during bovine preimplantation embryo development in vivo and in vitro. In vitro-produced bovine zygotes were cultured either in vitro, in synthetic oviduct fluid, or in vivo in the ewe oviduct for 1-7 days and processed for quantitative real-time polymerase chain reaction (PCR). Transcript abundance increased at each stage of development. However, the expression levels were consistently higher in in vivo-cultured embryos at all stages, with in vivo-cultured embryos showing a 9-fold increase in relative transcript abundance during culture from the zygote to the blastocyst stage in contrast to just under a 4-fold increase during the same culture period in vitro. The mRNA expression pattern of the gene was investigated in early- and late-cleaving two-cell embryos collected at 25, 28, 32, and >or=36 h postinsemination (pi). Transcript relative abundance was highest in those embryos that had cleaved by 28 hpi and decreased almost 3-fold thereafter. In conclusion, we have identified a potential bovine homolog of the murine Ped gene. We have characterized the mRNA expression pattern of this gene during preimplantation embryo development in cattle and shown that a greater relative abundance of the gene transcript is associated with embryos of higher quality (in vivo cultured) and greater developmental potential (early cleaving).

Expression of nonclassical MHC class Ib genes: comparison of regulatory elements

Peptide binding proteins of the major histocompatibility complex consist of the "classical" class Ia and "nonclassical" class Ib genes. The gene organization and structure/function relationship of the various exons comprising class I proteins are very similar among the class Ia and class Ib genes. Although the tissue-specific patterns of expression of these two gene families are overlapping, many class Ib genes are distinguished by relative low abundance and/or limited tissue distribution. Further, many of the class Ib genes serve specialized roles in immune responses. Given that the coding sequences of the class Ia and class Ib genes are highly homologous we sought to examine the promoter regions of the various class Ib genes by comparison to the well characterized promoter elements regulating expression of the class Ia genes. This analysis revealed a surprising complexity of promoter structures among all class I genes and few instances of conservation of class Ia promoter regulatory elements among the class Ib genes.

Genetic regulation of preimplantation embryo survival

Mammalian embryonic death is the most common outcome of fertilization. This review focuses on the recent advances concerning genetic regulation of preimplantation embryo survival. The predominant role of the Ped(preimplantation embryo development) gene, which regulates fast or slow cleavage of preimplantation mouse embryos, and its implication on embryo survival are discussed. Recent morphological and biochemical observations suggested that programmed cell death was an essential mechanism in preimplantation embryo fragmentation and survival, thus leading to original investigations on apoptosis and apoptosis-related genes. Other genes, transcripts, or proteins seem to be involved in embryo development and control of survival. In particular, the role of heat shock proteins (HSP), telomerase activity (human telomerase catalytic subunit hTCS), and the developmental significance of regulatory protein polarization (leptin, STAT 3) in preimplantation embryos are discussed.

Identification of two major histocompatibility complex class Ib genes, Q7 and Q9, as the Ped gene in the mouse

The Ped (preimplantation embryonic development) gene influences the rate of preimplantation embryonic development and subsequent embryonic survival. The protein product of the Ped gene, the Qa-2 protein, is a major histocompatibility complex (MHC) class Ib protein. There are two alleles of the Ped gene, fast (Qa-2 [+]) and slow (Qa-2 [-]). Qa-2 is encoded by four very similar MHC class Ib genes: Q6, Q7, Q8, and Q9. Recent research in our laboratory has shown that the Ped phenotype is potentially encoded by the Q7 and/or Q9 gene because the Q7 and Q9 genes, but not the Q6 or Q8 gene, are expressed during preimplantation mouse embryonic development. In this study we utilized microinjection of transgenes to assess the functional roles of both the Q7 and Q9 genes in control of the rate of preimplantation development. The Q7 gene, the Q9 gene, and a combination of the Q7 and Q9 genes were microinjected into Ped slow zygotes, and the Ped phenotype and cell surface expression of Qa-2 protein were assayed after a 72-h or 96-h incubation period. We found that the microinjected individual Q7 and Q9 genes increased the rate of preimplantation development. Simultaneous injection of the Q7 and Q9 genes did not have a synergistic effect on the Ped phenotype. Microinjection of the Q7 and/or Q9 genes resulted in protein expression in 10-25% of the microinjected embryos. These results show that both the Q7 and Q9 genes encode the mouse Ped phenotype.

Mechanisms of action of major-histocompatibility-complex-linked genes affecting reproduction

PROBLEM

To provide insight into the mechanisms of action of the major-histocompatibility-complex (MHC)-linked genes affecting reproduction.

METHOD OF STUDY

The data were obtained using a variety of cellular and molecular techniques in experimental animals and from population genetic studies in humans.

RESULTS

In the mouse, the preimplantation embryonic development (Ped) locus, whose functional gene is Q9, regulates fast and slow cleavage of the early embryo. There is also evidence for a growth and reproduction complex (Grc)-like region from serologic, molecular, and cytogenetic studies. In the human, the human leukocyte antigen (HLA)-G gene has been associated with an increased rate of embryonic cleavage in those embryos that express the HLA-G antigen. Sharing of HLA antigens in couples has been associated with recurrent spontaneous abortions, gestational trophoblastic tumors, and unexplained infertility. Detailed mapping studies showed that the genes responsible are not the HLA genes themselves, but genes closely linked to the HLA-DR-DQ-B genes. The HLA region genes can interact epistatically with the C3 allele of transferrin to increase the incidence of fetal loss. In the rat, the Grc region, which is closely linked to the MHC, has been associated with embryonic loss, growth defects, and susceptibility to chemical carcinogens. The Grc can interact epistatically with the tail anomaly lethal (Tal) gene or the hood restriction (Hre) gene to enhance these effects.

CONCLUSIONS

There are two basic mechanisms for the effects of MHC-linked genes on reproduction and development: individual gene effects (Ped [Q9], HLA-G) and extended genetic effects (MHC-linked genes in the rat [Grc] and in the human). The nature of these genetic effects, particularly the MHC-linked effects, can also provide some insight into the different theories of human origins: These effects are most consistent with the monogenic theory.

Major histocompatibility complex (MHC) class I KbDb -/- deficient mice possess functional CD8+ T cells and natural killer cells

We obtained mice deficient for major histocompatibility complex (MHC) molecules encoded by the H-2K and H-2D genes. H-2 KbDb -/- mice express no detectable classical MHC class I-region associated (Ia) heavy chains, although beta2-microglobulin and the nonclassical class Ib proteins examined are expressed normally. KbDb -/- mice have greatly reduced numbers of mature CD8+ T cells, indicating that selection of the vast majority (>90%) of CD8+ T cells cannot be compensated for by beta2-microglobulin-associated molecules other than classical H-2K and D locus products. In accord with the greatly reduced number of CD8+ T cells, spleen cells from KbDb -/- mice do not generate cytotoxic responses in primary mixed-lymphocyte cultures against MHC-disparate (allogeneic) cells. However, in vivo priming of KbDb -/- mice with allogeneic cells resulted in strong CD8+ MHC class Ia-specific allogeneic responses. Thus, a minor population of functionally competent peripheral CD8+ T cells capable of strong cytotoxic activity arises in the complete absence of classical MHC class Ia molecules. KbDb -/- animals also have natural killer cells that retain their cytotoxic potential.

Differential expression of Ped gene candidates in preimplantation mouse embryos

The Ped (preimplantation embryonic development) gene influences the rate of mouse preimplantation embryonic development and subsequent survival. Four similar tandem genes in the Q region of the major histocompatibility complex-Q6, Q7, Q8, and Q9-were identified as Ped gene candidates. In this study, expression of these genes during preimplantation development was examined and quantitated by reverse transcription-polymerase chain reaction and single nucleotide primer extension assays in order to investigate their contribution to the Ped gene phenotype. The Q7/Q9 gene pair was found to be transcribed in preimplantation mouse embryos, whereas transcription of the Q6/Q8 gene pair was undetectable. Both Q7 and Q9 are expressed in embryos from one Ped fast strain, C57BL/6, while only the Q9 gene is expressed in another Ped fast strain, B6.K2. These results suggest that both the Q7 and Q9 genes can function as the Ped gene in the mouse. Interestingly, the expression pattern of the Q7 and Q9 genes in preimplantation embryos is the same as in splenic lymphocytes. However, the Q6 and Q8 genes are expressed in splenic lymphocytes but not in preimplantation embryos. Treatment of mouse preimplantation embryos with interferon gamma (gamma-IFN) did not induce expression of the Q6/Q8 genes but enhanced expression of the Q7/Q9 genes. The mechanism of this differential transcription pattern is currently under investigation.

Role of the Ped gene and apoptosis genes in control of preimplantation development

PURPOSE

The properties of the mouse Ped gene and the genes that mediate apoptosis in mediating preimplantation embryonic survival were reviewed.

METHODS

Preimplantation mouse oocytes and embryos were evaluated microscopically and biochemically for rate of development, degree of fragmentation, and gene expression to correlate these characteristics with embryo mortality, Biochemical assays included PCR for DNA analysis, RT-PCR for mRNA analysis, immuno-PCR for protein analysis, and TUNEL assay for assessment of apoptosis.

RESULTS

Using the mouse as a model system we have identified a gene that controls the rate of development, the Ped gene. The Ped gene product is a class Ib major histocompatibility complex protein called the Qa-2 antigen. Research to understand the molecular mechanisms of Ped gene action and to identify the human homologue of the Ped gene is under way. We have also shown using the mouse model, that fragmented embryos show the morphological and biochemical characteristics of apoptosis. Genes in the two major gene families that regulate apoptosis, the caspase and Bcl-2 families, are expressed in mouse oocytes and preimplantation embryos.

CONCLUSIONS

Preimplantation embryonic survival depends on two major morphological parameters: rate of development and degree of fragmentation. A fast rate of development and a low degree of fragmentation lead to a better chance of producing live offspring. Both rate of development and degree of fragmentation are genetically controlled, the former by the Ped gene and the latter most likely by genes that mediate apoptosis. It seems probable that regulation of apoptosis will prove to be a major mechanism that mediates oocyte and preimplantation embryonic survival.

PCR identification of class I major histocompatibility complex genes transcribed in mouse blastocyst and placenta

We used an RT-PCR based strategy to amplify, clone and sequence MHC class I genes transcribed in the blastocyst and placenta of BALB/c mice. The PCR primers used were capable of amplifying many novel class I sequences from genomic DNA. By comparing the resulting sequence data with known class I sequences, we identified a number of different class I genes transcribed in these tissues. These include H2-K, -D, -L and a novel sequence in blastocysts, and H2-K, -D, -L, -D2, -T9, -T13, -T17, -T18, -M2 and three additional novel sequences in placenta. We postulate that some members of this spectrum of blastocyst and placentally-expressed MHC class Ib genes may act together at the maternal-fetal interface in ways that are important for a successful pregnancy.

The effect of melatonin on cleavage rate of C57BL/6 and CBA/Ca preimplantation embryos cultured in vitro

There is growing interest in using melatonin as a therapeutic agent for the treatment of a variety of medical conditions, including cancer, heart disease, glaucoma, stress, jet lag, and sleep disorders. In addition, melatonin is being evaluated in a clinical trial to test its efficacy as an oral contraceptive. In order to test any possible adverse effects of melatonin on preimplantation embryos, we used the mouse as a model system. Two strains of mice, a Ped fast, melatonin-deficient strain, C57BL/6, and a Ped slow strain previously found to have detectable melatonin levels at nighttime, CBA/Ca, were studied. Two cell embryos were incubated with melatonin concentrations from 10(-5) M to 10(-13) M for 48 or 72 hours and the number of cells per embryo assessed quantitatively at the end of the incubation period. We used sufficiently high levels of melatonin to mimic the pharmacological concentration used in the oral contraceptive. It was found that there was no effect of melatonin on embryos from either mouse strain at any of the concentrations tested. Our results suggest that if conception occurs while melatonin is being administered to treat a range of conditions, it would not adversely affect the embryo.

A knock-out model of paroxysmal nocturnal hemoglobinuria: Pig-a(-) hematopoiesis is reconstituted following intercellular transfer of GPI-anchored proteins

We created a "knockout" embryonic stem cell via targeted disruption of the phosphatidylinositol glycan class A (Pig-a) gene, resulting in loss of expression of cell surface glycosyl phosphatidylinositol-anchored proteins and reproducing the mutant phenotype of the human disease paroxysmal nocturnal hemoglobinuria. Morphogenesis of Pig-a- embryoid bodies (EB) in vitro was grossly aberrant and, unlike EB derived from normal embryonic stem cells, Pig-A EB produced no secondary hematopoietic colonies. Chimeric EB composed of control plus Pig-A- cells, however, appeared normal, and hematopoiesis from knock-out cells was reconstituted. Transfer in situ of glycosyl phosphatidylinositol-anchored proteins from normal to knock-out cells was demonstrated by two-color fluorescent analysis, suggesting a possible mechanism for these functional effects. Hematopoietic cells with mutated PIG-A genes in humans with paroxysmal nocturnal hemoglobinuria may be subject to comparable pathophysiologic processes and amenable to similar therapeutic protein transfer.

Influence of genetic background and media components on the development of mouse embryos in vitro

One-cell embryos from some inbred and random-bred mice, but not those derived from certain F1 hybrids, suffer from a block during in vitro development known as the two-cell block. This two-cell block can be overcome by removing glucose or inorganic phosphate from the culture system or by altering the ratio of other medium components such as sodium, potassium, or bicarbonate. This issue is made more complex by the fact that the rate of development is different for each strain of mouse and this rate of development is invariably slowed under in vitro culture conditions. This study investigated the role of glucose and inorganic phosphate, individually or in combination, in relation to the two-cell block, and rate of development in vitro of two random-bred strains (CF-1 and CD-1) and an F2 hybrid derived from a nonblocking F1 hybrid cross (C57Bl/6NCr x C3H/HeNCr). Results were compared with in vivo data for each strain, and between media. There was a significant difference in the rate of preimplantation development in vivo of the three strains chosen, which was mirrored in vitro, regardless of the medium. The two random-bred strains suffered from a glucose-related two-cell block which was primarily mediated by inorganic phosphate. Inorganic phosphate was detrimental to embryo development regardless of strain or the presence of glucose. Although glucose, in the absence of inorganic phosphate, resulted in some blocking in development in the inbred strains initially, its presence in media was associated with increased rates of development at later stages in embryos that did not block. Glucose, but not inorganic phosphate, was beneficial but not essential to the development of the F2 embryos. The results of this study demonstrated that mouse embryos from different strains have differential rates of development in vivo and in vitro, and different sensitivities to glucose and inorganic phosphate. The two-cell block was primarily induced in the combined presence of glucose and inorganic phosphate. Glucose was beneficial in the absence of inorganic phosphate, and inorganic phosphate was detrimental to the rate of in vitro development.

HLA-G expression during preimplantation human embryo development

HLA-G is a nonclassical class I major histocompatibility complex molecule with a restricted pattern of expression that includes the placental extravillus cytotrophoblast cells in direct contact with maternal tissues. Circumstantial evidence suggests that HLA-G may play a role in protection of the semiallogeneic human fetus. We examined whether HLA-G is expressed during the critical period of preimplantation human development and whether expression of this molecule could be correlated with the cleavage rate of embryos. Using reverse transcription PCR on surplus human embryos and unfertilized oocytes from patients undergoing in vitro fertilization we detected HLA-G heavy chain mRNA in 40% of 148 of blastocysts tested. The presence of HLA-G mRNA was also detected in unfertilized oocytes and in early embryos, but not in control cumulus oophorus cells. beta 2-Microglobulin mRNA was also found in those embryos expressing HLA-G. In concordance with our mRNA data, a similar proportion of embryos stained positive for HLA-G utilizing a specific monoclonal antibody. Interestingly, expression of HLA-G mRNA was associated with an increased cleavage rate, as compared to embryos lacking HLA-G transcript. Thus, HLA-G could be a functional homologue of the mouse Qa-2 antigen, which has been implicated in differences in the rate of preimplantation embryo development. To our knowledge, the presence of HLA-G mRNA and protein in human preimplantation embryos and oocytes has not been reported previously. The correlation of HLA-G mRNA expression with cleavage rate suggests that this molecule may play an important role in human pre-embryo development.

Induction of embryonic major histocompatibility complex antigen expression by gamma-IFN

Preimplantation mouse embryos were incubated in vitro with mouse recombinant gamma-interferon (IFN). The effect of the gamma-IFN on major histocompatibility complex (MHC) class I antigen expression was tested using an ELISA procedure. It was found that there is a doubling of Db antigens and a tripling of Qa-2 antigens on C57BL/6 mouse embryos cultured from the 8-cell stage for 24 h in the presence of 10(5) units/ml gamma-IFN. The effect of gamma-IFN on the rate of preimplantation embryonic development was tested by culturing 2-cell embryos for 48 h and 8-cell embryos for 24 h in the presence of varying concentrations of gamma-IFN up to 10(6) units/ml. Two methods were used to assess the cell number per embryo after the culture period: incorporation of [3H]thymidine into DNA, and direct counting of nuclei in fixed and stained embryos. Both methods showed that treatment with gamma-IFN increases the rate of development of preimplantation mouse embryos. Since rate of preimplantation embryonic development is genetically controlled by the Ped gene, it is suggested that gamma-IFN has a direct effect on the Ped gene phenotype of preimplantation mouse embryos.

Preimplantation mouse embryos express Mhc class I genes before the first cleavage division

We have used oligonucleotide primers complementary for polymorphic regions of the mouse H-2D gene in a highly sensitive polymerase chain reaction (PCR) assay to detect the transcription of maternal and paternal class I mRNAs in gametes and preimplantation embryos. Using congenic strains of mice differing only at the major histocompatibility loci, class I (H-2D) mRNA of both the maternal and paternal haplotypes was demonstrated in embryos from the one-cell zygote to the late blastocyst stage of development but could not be detected in vas deferens or in vitro capacitated sperm or in ovulated secondary oocytes. These data clearly show that both paternally and maternally inherited Major histocompatibility complex (Mhc) class I genes are transcribed from the earliest stages of embryonic development, and suggest that developmental regulation of expression of their protein products is principally at the post-transcriptional level.