Genetic differences in glucose phosphate isomerase activity among mouse embryos

We have compared mouse embryos of three heterozygous, congenic genotypes (with high, medium and low levels of oocyte-coded glucose phosphate isomerase (GPI-1) activity respectively) to test whether 1) the survival time of oocyte-coded GPI-1 activity in the early embryo is affected by its activity level in the oocyte and 2) whether embryo-coded GPI-1 is detected earlier in embryos that inherit low levels of oocyte-coded GPI-1. The oocyte-coded GPI-1 was entirely GPI-1A allozyme in the high and medium groups but was the less stable GPI-1C allozyme in the low group. We determined total GPI-1 activity and the ratio of different GPI-1 allozymes in early embryos and calculated the activity of oocyte-coded and embryo-coded GPI-1. In all three groups, the oocyte-coded enzyme activity remained at a more or less constant level for the first 21 1/2 days. Some oocyte-coded GPI-1 remained in 4 1/2 day embryos from the high and medium groups but was gone by 5 1/2 days. Very little remained in 4 1/2 day embryos that inherited low levels of a less stable form of the enzyme (GPI-1C allozyme). Despite a 4- to 5-fold difference in initial oocyte-coded GPI-1 activity, no differences were seen among the three genotypically distinct groups of embryos in the time of activation of the embryonic Gpi-1s genes. The embryo-coded GPI-1 was first detectable in 3 1/2 day compacted morulae in all three groups. The level of oocyte-coded GPI-1, in the high group, when embryo-coded GPI-1 was first detected was higher than the level in the low group at any stage prior to detection of embryo-coded GPI-1.(ABSTRACT TRUNCATED AT 250 WORDS)     

Expression of glucose phosphate isomerase in interspecific hybrid (Mus musculus x Mus caroli) mouse embryos.

Hybrid Mus musculus x Mus caroli embryos were produced by inseminating M. musculus (C57BL/OlaWs) females with M. caroli sperm. Control M. caroli embryos developed more rapidly than did control M. musculus embryos and implanted approximately 1 day earlier. At 1 1/2 days, both the hybrid embryos and those of the maternal species (M. musculus) had cleaved to the 2-cell stage. By 2 1/2 days some of the hybrids were retarded compared to M. musculus, and by 3 1/2 days most were lagging behind. This is consistent with the idea that the rate of development of hybrid embryos declines once it becomes dependent on embryo-coded gene products. We have used this difference in rate of preimplantation development, between hybrid and M. musculus embryos, to try to determine whether the activation of embryonic Gpi-1s genes, that encode glucose phosphate isomerase (GPI-1), is age-related or stage-related. In control M. musculus embryos (both mated and Al groups), the GPI-1AB and GPI-1A allozyme, indicative of paternal gene expression, were detected in 7 of 9 samples of 3 1/2-day compacted morula stage embryos and were seen in all 19 samples of 3 1/2-day blastocysts. In hybrid embryos, these allozymes were detected 1 day later. They were not detected in any 3 1/2-day samples (12 samples of compacted morulae) but were consistently detected at 4 1/2 days (4 samples of blastocysts and 2 samples of uncompacted morulae). Our interpretation of the results is that gene activation in hybrid embryos is stage-specific, rather than age-specific, and probably begins around the 8-cell stage, with detectable levels of enzyme accumulating later. Analysis of GPI-1 electrophoresis indicated that both the paternal (M. caroli) and maternal (M. musculus) Gpi-1s alleles were equally expressed in hybrid embryos and that the paternally derived allele was not activated before the maternally derived allele.     

High activity of an unstable form of glucose phosphate isomerase in the mouse

Quantitative electrophoretic studies of the three allozymes of glucose phosphate isomerase (GPI-1) produced byGpi-1s ^a/Gpi-1s^c heterozygous mice revealed two opposing influences on GPI-1 activity. First, the GPI-1 AC heterodimer is less stable than GPI-1 AA but more stable than the GPI-1 CC homodimer. Second, a genetic determinant that maps close to or within theGpi-1s structural gene causes elevated activity of GPI-1 AC and probably also GPI-1 CC dimers. The relative lability of these allozymes masks this elevated activity in some tissues but the effect is probably ubiquitous. The significance of these observations is discussed.This study was begun while JDW was at the MRC Radiobiology Unit and continued at the Department of Obstetrics and Gynaecology of the University of Edinburgh, where it was supported, in part, by a grant from the Moray Endowment Fund.     

Immunochemical differentiation of glucose phosphate isomerase (GPI) allozymes of the mouse

Polyclonal xenoantisera against mouse GPI-1B and GPI-1C were produced in rabbits and analyzed for their ability to recognize allozyme-specific determinants. These studies showed a high degree of serological similarity among the three allozymes of mouse glucose phosphate isomerase (GPI). However, GPI-1B and GPI-1C could be differentiated from GPI-1A as well as GPI-1A and GPI-1B from GPI-1C using quantitative solid-phase immunobinding assays. In addition, polyclonal and monoclonal alloantibodies specific for GPI-1C were produced in BALB/c (Gpi-1a/Gpi-1a) mice. As indicated by immunoblotting data, the allozyme specificity of rabbit antisera and monoclonal alloantibodies against GPI-1C is dependent on the native structure of that allozyme.     

A fine analysis of glucose-phosphate-isomerase patterns in single preimplantation mouse embryos

Mouse embryos were derived from eggs heterozygous for alleles of the dimeric enzyme glucose phosphate isomerase (Gpi-1a/Gpi-1b) that had been fertilized with sperm carrying a third allele (Gpi-1c). This particular combination makes it possible to study the activity of the paternally derived as well as the maternally derived genes, the persistence of oocyte-coded enzyme throughout early development and the possible simultaneous expression of both the paternally derived allele and the maternal message. The different isozymes present in single embryos were separated by electrophoresis. The results show that the oocyte-coded glucose phosphate isomerase is gradually replaced by embryo-coded enzyme. Expression of the paternally derived allele was first detected at the morula stage, during which the translation of the maternally derived message seemed to be either exhausted or below the detection limit of our system. Some oocyte-coded enzyme persisted until after implantation.     

Expression of paternal glucose phosphate isomerase-1 (Gpi-1) in preimplantation stages of mouse embryos

Electrophoretic variants of glucose phosphate isomerase have been used to study the time of paternal gene activation during early embryogenesis of the mouse. Hybrid embryos obtained from matings of GPI-1A ♀ X GPI-1B ♂ were examined electrophoretically, and assayed for GPI activity during preimplantation stages. The heteropolymeric GPI-1AB band was detected in late blastocysts and all three bands of the hybrid pattern were discernible in samples of expanded blastocysts, day 6. These findings indicate that the Gpi-1 paternal locus is expressed by day 5. Activity levels of GPI were comparable to values reported for G6PD. The activity of GPI was constant for days 1, 2, and 3; however, a marked decrease in activity occurred by day 4. A slight decrease in activity was observed in embryos from days 5 and 6. Our results demonstrate the value of using electrophoretic variants to pinpoint synthesis of new enzyme which may not be reflected in changes in levels of activity.     

Onset of paternal and maternal Gpi-1 expression in preimplantation mouse embryos

The initial activation of the glucose phosphate isomerase gene, Gpi-1, was studied in mouse embryos produced by transplanting pronuclei between two strains of mice differing in alleles for this enzyme. Protein isozymes encoded by the embryonic cell nuclei were first detected on Day 4 of embryogenesis, and the maternal and paternal genes are seen to be activated simultaneously. Comparison of isozymes produced by these nuclear-transfer embryos and by F1 embryos from these two strains suggests the absence of oocyte mRNA for GPI-1 at the time when these genes are first activated. Thus, the GPI-1 present is derived from newly transcribed mRNA contributed by both maternal and paternal genes. The relative proportion of maternal cytoplasmic GPI-1 enzyme declines from Day 3 to Day 6, such that on Day 6, almost no oocyte GPI-1 is detected.     

Developmental profile of glucose phosphate isomerase allozymes in parthenogenetic and tetraploid mouse embryos.

Glucose phosphate isomerase (GPI) allozymes were compared in eggs and embryos of the mouse strains C57BL/6-JHan (GPI-1BB) and 129/Sv (GPI-1AA) under different experimental conditions. The quantitative differences in eggs of the two strains disappeared by the blastocyst stage at day 4 to 5, both in fertilized and diploid parthenogenetic embryos. The degree of degradation of oocyte-coded enzyme molecules and the activation of the embryonic genome for GPI appeared to be equivalent in parthenogenetic embryos from heterozygous females when only one or other maternal allele type remained in the egg after meiosis. Also in tetraploid embryos, generated by electrofusion of homozygous fertilized eggs from the two strains, both genomes seemed to be activated at the same time at day 4; here, however, the GPI-1BB allozyme remained predominant up to day 6.     

Non-additive inheritance of glucose phosphate isomerase activity in mice heterozygous at the Gpi-1s structural locus

The activity of blood glucose phosphate isomerase (GPI-1) in mice heterozygous for various alleles at the Gpi-1s structural locus (heterozygotes a/b, a/c and b/c) was significantly higher than expected, on the basis of additive inheritance, from the levels in parental homozygotes. Moreover, the GPI-1 activity was higher in a/b heterozygotes than in either parent (heterosis). Studies of heat stability with kidney homogenates revealed that the relative stabilities of GPI-1 dimers was AA greater than AB greater than BB greater than AC greater than or equal to BC greater than CC. Differences in dimer stabilities in vivo would affect the total GPI-1 levels in heterozygotes and could account for non-additive inheritance but would be insufficient to explain heterosis for GPI-1 activity. Other possible contributing factors include unequal production or stability of monomers, or higher catalytic activity of heterodimers. Monomers could also associate non-randomly but this would not be sufficient to explain heterosis. It is clear that non-additive inheritance patterns may be produced by variants of either structural or regulatory genes.     

A glucosephosphate isomerase (GPI) null mutation in Mus musculus: evidence that anaerobic glycolysis is the predominant energy delivering pathway in early post-implantation embryos.

1. A heterozygous mouse mutant exhibiting approximately 50% of wild-type glucose-6-phosphate isomerase (GPI) activity in blood was recovered in mutagenicity experiments after combined treatment of spermatogonia with triethylenemelamine and irradiation. 2. Biochemical and immunological studies revealed no differences in physicochemical, kinetic and immunological properties between the erythrocytic enzyme of heterozygous and wild-type animals. This suggests that the mutation generates a null allele at the Gpi-1s structural locus, producing neither enzyme activity nor immunologically detectable material. 3. In accordance with the presence of only one functional Gpi-1s gene per haploid genome in the mouse, the 50% deficiency in heterozygotes is expressed in plasma and all tissues studied. 4. The genetic and physiological analyses provided no indications for further altered traits in heterozygous animals including fertility, viability and several other traits. 5. Homozygous mutants died at an early post-implantation stage of embryogenesis. 6. These findings support the hypothesis that a mutation resulting in a total loss of catalytic activity of a glycolytic enzyme leads to lethality of homozygous carriers at an early post-implantation stage of embryonic development due to a block of glycolysis and the resulting inability to utilize glucose as a source of metabolic energy. Furthermore, they indicate that anaerobic glycolysis primarily supplies the metabolic energy used by early post-implantation mouse embryos.     

Expression of glucose phosphate isomerase in interspecific hybrid (Mus musculus × Mus caroli)

Hybrid Mus musculus × Mus caroli embryos were produced by inseminating M. musculus (C57BL/Ola Ws) females with M. caroli sperm. Control M. caroli embryos developed more rapidly than did control M. musculus embryos and implanted approximately 1 day earlier. At 1 1/2 days, both the hybrid embryos and those of the maternal species (M. musculus) had cleaved to the 2-cell stage. By 2 1/2 days some of the hybrids were retarded compared to M. musculus, and by 3½ days most were lagging behind. This is consistent with the idea that the rate of development of hybrid embryos declines once it becomes dependent on embryo-coded gene products. We have used this difference in rate of preim-plantation development, between hybrid and M. musculus embryos, to try to determine whether the activation of embryonic Gpi-1s genes, that encode glucose phosphate isomerase (GPI-1), is age-related or stage-related. In control M. musculus embryos (both mated and Al groups), the GPI-1AB and GPI-1A allozyme, indicative of paternal gene expression, were detected in 7 of 9 samples of 3 1/2-day compacted morula stage embryos and were seen in all 19 samples of 31/2-day blastocysts. In hybrid embryos, these allozymes were detected 1 day later. They were not detected in any 31/2-day samples (12 samples of compacted morulae) but were consistently detected at 4½ days (4 samples of blastocysts and 2 samples of uncompacted morulae). Our interpretation of the results is that gene activation in hybrid embryos is stage-specific, rather than age-specific, and probably begins around the 8-cell stage, with detectable levels of enzyme accumulating later. Analysis of GPI-1 elec-trophoresis indicated that both the paternal (M. caroli) and maternal (M. musculus) Gpi-1s alleles were equally expressed in hybrid embryos and that the paternally derived allele was not activated before the maternally derived allele. © 1992 Wiley-Liss, Inc.     

Glucosephosphate isomerase (GPI-1) expression in mouse ova: cis regulation of monomer realization

A survey of the glucosephosphate isomerase (GPI-1) activity expressed in mature mouse ova has revealed multiple interstrain differences. Genetic variation at a site either linked to (less than 1.1 cM) or directly associated with Gpi-1 affects the realization of GPI-1 monomers during the later stages of oocyte maturation.     

Assignment of the gene for lactic dehydrogenase A to mouse chromosome 7 using mouse-human hybrids

We have studied somatic cell hybrids between either mouse peritoneal macrophages or spleen cells and HT-1080-6TG human fibrosarcoma cells for the expression of mouse lactic dehydrogenase A (LDH-A). The hybrids were also studied for the expression of mouse glucose phosphate isomerase (GPI-1), the gene for which has been assigned to chromosome 7. Concordant segregation of the expression of mouse GPI-1 and LDH-1 was observed in 61 independent hybrid clones. These results indicate that the gene coding for LDH-A is located on mouse chromosome 7.     

Pluripotency of mouse embryonic cells on germline at 3.5–8.5 and 11.5 days post-coitum after aggregation with precompacted embryos

Albino mouse embryonic cells (Gpi-la/a) at 3.5–8.5 and 11.5 days were aggregated with zona cut 8–16 cell stage embryos from F₁ females (Gpi-1 b/b), respectively. The aggregated embryos were transferred to pseudopregnant female mice. The recipients were allowed to go to term or were dissected at mid-gestation to assess the donor contribution in the conceptuses using glucose phosphate isomerase (GPI) analysis. The donor cells, which were previously labeled with fluorescent latex microparticles, were aggregated with embryos, and the allocation of the donor cells at the compacted morula and blastocyst stages were observed under a fluorescence microscope. When 3.5 and 45 day old inner-cell-mass (ICM) cells were used, fertile chimeric mice were obtained (50 and 19%, respectively), and when 5.5 days old primitive ectoderm cells were aggregated, they did not form chimeras but contributed to the fetuses, placenta and membrane after 13.5 days of pregnancy. However, cells from further stages never contributed to the conceptuses even though they were analyzed after 10.5 days of pregnancy. The labeled donor cells at these stages were not positively incorporated in the interior part of the compacted morula and the ICM of the blastocyst stage unlike the ICM at 3.5 days post-coitum after overnight culture.     

A comparative investigation on the potency of cells from the inner cell mass and trophectoderm of mouse blastocysts to produce chimeras

The ability of trophectoderm (TE) cells to produce chimeric mice (pluripotency) was compared with that of inner cell mass (ICM) cells. TE and ICM cells of blastocysts and hatching or hatched blastocysts derived from albino mice (CD-1, Gpi-1a/a) were aggregated with zona cut 8- to 16-cell stage embryos or injected into the blastocoele from non-albino mice (C57BL/6 x C3H/He, Gpi-1b/b). After transfer to pseudopregnant female mice, the contribution of the donor cells was examined by glucose phosphate isomerase (GPI) analysis of embryos, membrane and placenta at mid-gestation (Day 10.5 and 12.5) or by the coat color of newborn mice. In contrast to ICM cells, there was no contribution of TE cells in the conceptuses and no coat color chimeric young were obtained. After pre-labeling of TE cells with fluorescent latex microparticles, they were aggregated with embryos and the allocation of TE cells at the compacted morula and blastocyst stages was observed under a fluorescent microscope. Although the TE cells were observed attached onto the surface of the embryos at morula and blastocyst stages, unlike the ICM cells, they were not positively incorporated into the embryos. Thus, the pluripotency of TE cells from mouse blastocysts was not induced by the aggregation and injection methods.     

Unusual glucose phosphate isomerase isozyme patterns in lymphocytes from two C57BL/6J in equilibrium A/J allophenic mice

Analysis of C57BL/6J in equilibrium A/J allophenic mice for their lymphocyte composition, using H-2 antigens as external markers, and glucose phosphate isomerase (GPI) isozymes as internal markers, has led to the discovery of two unusual mice. Both mice showed heterodimers of GPI isozymes upon electrophoresis of the lymphocyte lysate. Specific anti-H-2 antisera confirmed that the cells of the mice were of C57BL/6J and A/J origin, as expected, but that the "A/J" cells seemed to behave as F1 hybrids containing the Gpi-1a and Gpi-1b alleles. Possible origins of the Gpi-1b allele in the "A/J" cells are discussed.     

Expression of specific genes in early mouse embryos blocked by cytochalasin

Summary Mouse embryos at the two cell stage derived from C57BL/6 × C3H/Aa F₁-females heterozygous at the X-linked phosphoglycerate kinase locus (Pgk-1) were cultured continuously in the presence of cytochalasin B or D. Further cleavage of the two cell embryos was thus prevented and the embryos became polyploid during culture. The onset of expression of the maternally inherited Pgk-1 gene and of the paternally inherited glucosephosphate isomerase (Gpi-1) gene was determined in these polyploid embryos by cellulose acetate gel electrophoresis of single embryos. In contrast to euploid preimplantation embryos developing normally in utero or in culture without cytochalasins, expression of maternal Pgk-1 was never observed at days 4 and 5 of gestation in polyploid two cell embryos, showing that the Pgk-1 allele on the maternally inherited X chromosome is not activated independently of cytokinesis and morphogenesis. Expression of paternally derived Gpi-1, however, occurred in cleavage blocked embryos von day 5 of development. This may indicate that the activation of two genes which are both expressed during preimplantation development and which both code for glycolytic enzymes, is initiated by different signals.     

Quantitative analysis of mid-gestation mouse aggregation chimaeras: non-random composition of the placenta

Mouse chimaeras were produced by aggregating eight-cell embryos from two different F₂ matings, abbreviated to AF₂ and BF₂ respectively: (C57BL/ OIa.AKR-Gpi-1s ^a, c/Ws female × BALB/c male)F₂ and (C57BL/Ws female × CBA/Ca male)F₂. Quantitative electrophoresis of glucose phosphate isomerase (GPI-1) was used to estimate the proportions of the two cell populations in different tissues of the 12 day chimàeric conceptuses, with the % GPI-1A indicating the percentage of cells derived from the AF₂ embryos. The % GPI-1A was found to be highly positively correlated within the primitive ectoderm lineage (between the fetus, amnion and yolk sac mesoderm) and within the primitive endoderm lineage (between the yolk sac endoderm and the parietal endoderm) but no correlation (either positive or negative) was seen between the two lineages. This confirms the results of a previous,study of chimaeras made between partially congenic strains and suggests the original conclusions have general validity. The % GPI-1A in the placenta was corrected for the expected contribution of maternal GPI-1, based on control experiments involving transfer of homozygous Gpi-1s ^b /Gpi-1s ^b embryos to the uteri of Gpi-1s ^a /Gpi-1s ^a pseudopregnant females. The corrected % GPI- lA in the placenta was positively correlated with that in each of the three primitive ectoderm derivatives. This suggests either (1) exchange of cells between the polar trophectoderm and the underlying part of the inner cell mass that forms the primitive ectoderm or (2) cells are incompletely mixed in the chimaeric blastocyst and patches of AF₂ and BF₂ cells straddle the boundary between the polar trophectoderm and the underlying primitive ectoderm. The second explanation does not imply the existence of shared developmental lineages between trophectoderm and primitive ectoderm in non-chimaeric embryos. Unlike that of any other tissue, the distribution of placental GPI-1A was U-shaped; in 17/28 placenta samples the proportion of the minor component was 10% or less. This suggests that the placental trophoblast is derived from a small number of coherenct clones of polar trophectoderm cells (either a small number of polar trophectoderm cells or a larger number if the two cell populations are not finely intermingled). Thus, although as a population the placentas of chimaeric conceptuses are balanced with respect to the % GPI-1A (mean close to 50%), individually most placentas are extremely unbalanced in their chimaeric composition (< 10% or > 90% GPI-IA). This non-random composition of the chimaeric placentas is in contrast to the widely held assumption that the distribution of cells in chimaeric conceptuses is normally random. Correspondence to: J.D. West