Reactivation of chicken erythrocyte nuclei in heterokaryons results in expression of adult chicken globin genes

The Epimmunity Theory: The Single Cell Defenses against Infectious and Genetic Diseases

Single cell defense against diseases defines “epimmunity.” Epimmunity is complementary to the immune system and can neither be substituted by innate nor by acquired immunity. Epimmunity, the proposed new branch of immunity, is further explored and analyzed for enucleated mature mammalian erythrocytes and nucleated erythrocytes of non-mammalian vertebrates leading to the development of “The Epimmunity Theory.” Enucleation of mammalian erythroblast and inactivation of nuclei in erythrocytes of non-mammalian vertebrates are major contributors to the collective immunity: epimmunity, innate, and acquired. The fact that diseases of mature erythrocytes (MEs) are rare supports the notion that a single cell can resist microbial and genetic diseases; MEs are refractory to malaria and cancer. Nucleated cells, such as B-cells, T-cells, hepatocytes, and cell developmental stages are susceptible to genetic and specific microbial diseases depending on their nuclear activities and the receptors they express; such cells show lower epimmunity relative to MEs. Epimmunity is important as a disease insulator that prevents the spread of diseases from an infected tissue to the majority of other tissues. Breakdown of epimmunity may lead to disease development.

Use of somatic cell fusion to reprogram globin genes

The developmental phenomenon of hemoglobin switching occurs in all classes of vertebrates and is due to differential regulation of divergent globin genes which are arranged in chromosomally clustered families. By fusing erythroid cells of different developmental programs, it has been shown that erythroid nuclei of either early or late developmental stage can be reprogrammed, i.e. the gene switch can be reversed in adult erythroid nuclei and/or prematurely-induced in fetal/embryonic erythroid nuclei. Experiments with heterokaryons demonstrate that the reprogramming is due to trans-acting factors that are developmental-stage-specific. These results suggest the feasibility of using fusisome-carried sets of nuclear factors to reprogram somatic cells.

Nuclear envelope removal/maintenance determines the structural and functional remodelling of embryonic red blood cell nuclei in activated mouse oocytes

Nuclei of embryonic red blood cells (e-RBC) from 12-day mouse fetuses are arrested in G0 phase of the cell cycle and have low transcriptional activity. These nuclei were transferred with help of polyethylene glycol (PEG)-mediated fusion to parthenogenetically activated mouse oocytes and heterokaryons were analysed for nuclear structure and transcriptional activity. If fusion proceeded 25-45 min after oocyte activation, e-RBC nuclei were induced to nuclear envelope breakdown and partial chromatin condensation, followed by formation of nuclei structurally identical with pronuclei. These 'pronuclei', similar to egg (female) pronuclei, remained transcriptionally silent over several hours of in vitro culture. If fusion was performed 1 h or later (up to 7 h) after activation, the nuclear envelope of e-RBC nuclei remained intact and nuclear remodelling was less spectacular (slight chromatin decondensation, formation of nucleolus precursor bodies). These nuclei, however, reinforced polymerase-II-dependent transcription within a few hours of in vitro culture. Our present experiments, together with our previous work, demonstrate that nuclear envelope breakdown/maintenance are critical events for nuclear remodelling in activated mouse oocytes and that somatic dormant nuclei can be stimulated to renew transcription at a time when the female pronucleus remains transcriptionally silent.

Hemoglobin switching in Rana/Xenopus erythroid heterokaryons: factors mediating the metamorphic hemoglobin switch are conserved

Hemoglobin switching, which occurs in all classes of vertebrates as well as in certain invertebrates, is due to developmental regulation of different globin genes which are typically arranged in clustered families. By fusing erythroid cells of different developmental programs, trans-acting factors that regulate this switch in gene expression have been detected [Ramseyer et al. (1989): Dev Biol 133:262-271]. Adult erythroid cells of one anuran species, Xenopus laevis, were fused with tadpole erythroid cells of another frog, Rana catesbeiana, creating developmental erythroid heterokaryons that synthesize adult Rana globin mRNA and hemoglobins. The results show that factors from adult Xenopus erythroid cells are capable of inducing adult Rana globin gene expression in the Rana tadpole erythroid cell nucleus. We have used the cross-induction of adult Rana hemoglobin synthesis in these adult Xenopus/Rana tadpole erythroid heterokaryons to address two practical questions, answers to which may be helpful in isolating developmental stage-specific globin gene regulatory proteins: 1) Are erythroblasts which are actively expressing globin mRNAs and hemoglobins richer in specific globin-inducing activities than other stages of erythroid cellular differentiation? 2) Do mature, circulating erythrocytes still have the activities necessary to mediate the cross-induction of Hb synthesis? The results reported here show that the answers to both questions are affirmative and show that quiescent, fully differentiated adult erythroid cells are still capable of expressing the trans-activator(s). These findings show that factors which mediate the metamorphic hemoglobin switch are conserved between these two genera of frogs.

Interspecific genetic complementation analysis of human and sheep fibroblasts with beta-galactosidase deficiency

Interspecific somatic cell hybrids were analyzed by genetic complementation to determine if a lysosomal storage disease in sheep associated with deficiencies of beta-galactosidase and alpha-neuraminidase was homologous with any of four beta-galactosidase-deficient human diseases. Fibroblasts from beta-galactosidase-deficient sheep, cats, and human patients were fused and assayed histochemically for beta-galactosidase, with 5-bromo-4-chloro-3-indolyl beta-D-galactoside. We observed complementation in heterokaryons consisting of fibroblasts from beta-galactosidase-deficient sheep and fibroblasts from patients with galactosialidosis or mucolipidosis type II, but no complementation in heterokaryons consisting of fibroblasts from beta-galactosidase-deficient sheep and fibroblasts from human or feline GM1 gangliosidosis (type I) or from human mucopolysaccharidosis type IVB fibroblasts. We conclude that the ovine disease is due to a mutation at the genetic locus homologous with that of GM1 gangliosidosis and mucopolysaccharidosis type IVB, suggesting that the primary defect in the ovine disease is a mutation of the beta-galactosidase structural gene.

Biochemical genetics of the Lapland dog model of glycogen storage disease type II (acid alpha-glucosidase deficiency)

A recently described canine model (Lapland dog) of glycogen storage disease type II (GSD II, Pompe disease, acid alpha-glucosidase deficiency) was identified with several biochemical genetic methods. Complementation studies in which fibroblasts from a GSD II dog were fused with fibroblasts derived from control dogs and from human patients with different clinical forms of the disease did not lead to restoration of acid alpha-glucosidase activity in the heterokaryon cell populations. These results indicate that acid alpha-glucosidase deficiency is the primary defect in canine GSD II and that there is a close genetic parallelism with human GSD II. Immunotitration analysis of the residual acid alpha-glucosidase activity in the canine GSD II fibroblasts and liver demonstrated that this residual activity was not due to acid alpha-glucosidase enzyme, in which respect canine GSD II was similar to the infantile form of the human disease. Double immunodiffusion studies showed the presence of catalytically inactive acid alpha-glucosidase enzyme protein in canine GSD II. This is consistent with a structural gene mutation. It is concluded that canine GSD II in the Lapland dog is a homologous model of the infantile form of human GSD II, a conclusion in concordance with clinical and pathological studies.

Changes in nuclear antigens during reactivation of chick erythrocyte nuclei in heterokaryons

Reactivation of dormant chick erythrocyte (CE) nuclei was studied by fusing chick red cells with rat myoblasts, HeLa cells, and chick fibroblasts. Heterokaryons representing different stages of nuclear reactivation were fixed and examined for nuclear antigens using polyclonal patient autoantisera reacting with mammalian (human, mouse, and rat) nuclear envelope, nucleoplasm, and chromatin (DNA) antigens. Reactivation of CE nuclei was associated with marked changes in nuclear antigenicity. In rat myoblast and HeLa heterokaryons the CE nuclei acquired mammalian nucleoplasmic and nuclear envelope antigens in the corresponding nuclear subcompartments. Drastic changes in nuclear antigenicity were noted also in heterokaryons stained with DNA antisera. The compact chromatin of nuclei in mature chick erythrocytes showed little binding of DNA antibodies. Isolated nuclei on the other hand gave a strong immunofluorescence. CE nuclei in heterokaryons were strongly positive during the early stages of nuclear reactivation but then exhibited decreased reactivity. An unexpected finding was a marked reduction in the capacity of mammalian nuclei in heterokaryons to bind DNA-antibodies. This observation is discussed in relation to the previous finding that in CE-heterokaryons these nuclei often show reduced transcription and replication. The present results indicate that in heterokaryons both types of nuclei exchange macromolecules of regulatory importance via the common cytoplasm.

Nuclear matrix DNA from chicken erythrocytes contains beta-globin gene sequences

Nuclear matrices containing residual DNA were isolated from chicken erythrocytes after extraction of purified nuclei with buffered 2 M NaCl. After further purification of this residual DNA, it was found to contain high concentrations of beta-globin gene sequences as assayed by dot hybridization with 32P-labeled nick-translated pHB1001. Electron microscopy of a random sample of this residual DNA fraction shows the DNA to be intimately associated with protein at various intervals. A hypothesis for enrichment of active genes in residual DNA from purified chromatin or in nuclear matrix DNA is also discussed.

Analysis of muscle protein expression in polyethylene glycol-induced chicken: rat myoblast heterokaryons

Heterokaryons derived from polyethylene glycol-mediated fusion of myoblasts at different stages of development were used to investigate the transition of cells in the skeletal muscle lineage from the determined to the differentiated state. Heterokaryons were analyzed by immunofluorescence, using rabbit antibodies against the skeletal muscle isoforms of chicken creatine kinase and myosin, and a mouse monoclonal antibody that cross-reacts with chicken and rat skeletal muscle myosin. When cytochalasin B-treated rat L8(E63) myocytes (Konieczny S.F., J. McKay, and J. R. Coleman, 1982, Dev. Biol., 91:11-26) served as the differentiated parental component and chicken limb myoblasts from stage 23-26 or 10-12-d embryos were used as the determined, undifferentiated parental cell, heterokaryons exhibited a progressive extinction of rat skeletal muscle myosin during a 4-6-d culture period, and no precocious expression of chicken differentiated gene products was detected. In the reciprocal experiment, 85-97% of rat myoblast X chicken myocyte heterokaryons ceased expression of chicken skeletal muscle myosin and the M subunit of chicken creatine kinase within 7 d of culture. Extinction was not observed in heterokaryons produced by fusion of differentiated chicken and differentiated rat myocytes and thus is not due to species incompatibility or to the polyethylene glycol treatment itself. The results suggest that, when confronted in a common cytoplasm, the regulatory factors that maintain myoblasts in a proliferating, undifferentiated state are dominant over those that govern expression of differentiated gene products.

Pattern of chick gene activation in chick erythrocyte heterokaryons

The reactivation of chicken erythrocyte nuclei in chick-mammalian heterokaryons resulted in the activation of chick globin gene expression. However, the level of chick globin synthesis was dependent on the mammalian parental cell type. The level of globin synthesis was high in chick erythrocyte-rat L6 myoblast heterokaryons but was 10-fold lower in chick erythrocyte-mouse A9 cell heterokaryons. Heterokaryons between chick erythrocytes and a hybrid cell line between L6 and A9 expressed chick globin at a level similar to that of A9 heterokaryons. Erythrocyte nuclei reactivated in murine NA neuroblastoma, 3T3, BHK and NRK cells, or in chicken fibroblasts expressed less than 5% chick globin compared with the chick erythrocyte-L6 myoblast heterokaryons. The amount of globin expressed in heterokaryons correlated with globin mRNA levels. Hemin increased beta globin synthesis two- to threefold in chick erythrocyte-NA neuroblastoma heterokaryons; however, total globin synthesis was still less than 10% that of L6 heterokaryons. Distinct from the variability in globin expression, chick erythrocyte heterokaryons synthesized chick constitutive polypeptides in similar amounts independent of the mammalian parental cell type. Approximately 40 constitutive chick polypeptides were detected in heterokaryons after immunopurification and two-dimensional gel electrophoresis. The pattern of synthesis of these polypeptides was similar in heterokaryons formed by fusing chicken erythrocytes with rat L6 myoblasts, hamster BHK cells, or mouse neuroblastoma cells. Three polypeptides synthesized by non-erythroid chicken cells but less so by embryonic erythrocytes were conspicuous in heterokaryons. Two abundant erythrocyte polypeptides were insignificant in non-erythroid chicken cells and in heterokaryons.

Transcription of chick genes by mammalian RNA polymerase II in chick erythrocyte-mammalian cell heterokaryons

The introduction of chick erythrocyte nuclei into mammalian cell cytoplasms results in their reactivation as evidenced by the de novo transcription of chick genes and the synthesis of both globin and constitutive proteins. In the present study, chick erythrocytes have been fused to L6 rat myoblasts and to alpha-amanitin-resistant variants of L6 to determine whether the chick or the mammalian RNA polymerase II was responsible for transcription of chick genes. Heterokaryons formed by fusing chick erythrocytes with alpha-amanitin-resistant L6 myoblasts synthesize both chick globin and chick constitutive proteins in the continued presence of 5 micrograms/ml alpha amanitin ten days postfusion. Both the synthesis of globin and other chick polypeptides occurs at levels comparable to those observed for untreated heterokaryons. Synthesis occurs under conditions in which insignificant chick RNA polymerase II activity can be detected in wild-type heterokaryons by autoradiography. These results demonstrate that RNA polymerase II is one of the mammalian proteins that is selectively taken up by the chick nucleus during reactivation in the presence of alpha amanitin. Furthermore, the mammalian RNA polymerase II alone can account for the transcription of both differentiation specific and constitutive genes in the chick nucleus.

Restricted nucleocytoplasmic relationship in activation of T and B lymphocytes

Nuclei of murine T lymphocytes or B lymphocytes were purified and transferred into lethally irradiated whole spleen cells or B or T lymphocytes by means of polyethyleneglycol-mediated cell fusion. Transfer of lymphocyte nuclei could save the irradiated cells from cell death, and such reconstituted cells could respond to mitogens. The present study showed that nuclei of T cells could be activated in the concanavalin A-stimulated T cell cytoplasms but not in the lipopolysaccharide-stimulated B cell cytoplasms. On the other hand, nuclei of B cells were activated in the lipopolysaccharide-stimulated B cells but not in the concanavalin A-stimulated T cell cytoplasms. These data suggested that a specific interaction between cytoplasm and nucleus might exist in the activation of nuclei of each lymphocyte subset.