Electrophoretic variation for x-chromosome-linked phosphoglycerate kinase (pgk-1) in the mouse

The single active X in human cells: evolutionary tinkering personified

All mammals compensate for sex differences in numbers of X chromosomes by transcribing only a single X chromosome in cells of both sexes; however, they differ from one another in the details of the compensatory mechanisms. These species variations result from chance mutations, species differences in the staging of developmental events, and interactions between events that occur concurrently. Such variations, which have only recently been appreciated, do not interfere with the strategy of establishing a single active X, but they influence how it is carried out. In an overview of X dosage compensation in human cells, I point out the evolutionary variations. I also argue that it is the single active X that is chosen, rather than inactive ones. Further, I suggest that the initial events in the process-those that precede silencing of future inactive X chromosomes-include randomly choosing the future active X, most likely by repressing its XIST locus.

X-inactivation analysis of embryonic lethality in Ocrl wt/-; Inpp5b-/- mice

Mutations in the human OCRL gene, which encodes a phosphatidylinositol(4,5)bisphosphate 5-phosphatase, result in the X-linked oculocerebrorenal syndrome of Lowe. Mice with a targeted disruption of Ocrl have no phenotypic abnormalities. Targeted disruption of its closest paralog, Inpp5b, causes male infertility in the 129S6 background. Mice with disruptions of both genes are lost in utero prior to 9.5-10.5 dpc, indicating that there is a functional overlap between the two paralogs early in development. We analyzed the pattern of X-inactivation in four tissues of distinct embryonic origin from Ocrl (wt/-);Inpp5b (-/-) females to explore the timing and tissue distribution of the functional overlap. X-inactivation was strongly skewed against the disrupted Ocrl (-) allele being on the active X chromosome in all four tissues tested, indicating that there is early selection against cell lineages lacking both Ocrl and Inpp5b. Extraembryonic tissue was also involved in the lethality because there were never any live-born Ocrl (wt/-);Inpp5b (-/-) females when the functional Ocrl (wt ) allele was on the paternal X chromosome, which is preferentially inactivated in trophoblast-derived extraembryonic tissues. Live-born Ocrl (wt/-);Inpp5b (-/-) females were found when the functional Ocrl (wt) allele was maternal, although in fewer numbers than expected. The importance of the extraembryonic tissues in the early embryonic lethality of embryos lacking both Ocrl and Inpp5b is reinforced by the successful isolation of a viable 40,XX Ocrl (-/-);Inpp5b (-/-) embryonic stem cell from the inner cell mass of a 3.5-dpc blastocyst prior to implantation. These results indicate a functional overlap of Ocrl and Inpp5b in most cell lineages, especially in extraembryonic tissues.

Genetic polymorphism of adenosine deaminase and mannose phosphate isomerase in blood of arctic foxes, Alopex lagopus

Blood samples of 70 foxes, including 10 families, have been investigated by horizontal starch gel electrophoresis for the enzymes adenosine deaminase (ADA) and mannose phosphate isomerase (MPI). The observed variation of the enzymes could be explained as a result of one locus with two codominant alleles and one with three respectively. The segregation in the families of the alleles assumed for the two loci is in accordance with this genetic model. The frequency of the two alleles at the Ada locus is about the same and the slowest anodic migrating allele at the Mpi locus is the most frequent.

X chromosome effect on maternal recombination and meiotic drive in the mouse

We observed that maternal meiotic drive favoring the inheritance of DDK alleles at the Om locus on mouse chromosome 11 was correlated with the X chromosome inactivation phenotype of (C57BL/6-Pgk1(a) x DDK)F(1) mothers. The basis for this unexpected observation appears to lie in the well-documented effect of recombination on meiotic drive that results from nonrandom segregation of chromosomes. Our analysis of genome-wide levels of meiotic recombination in females that vary in their X-inactivation phenotype indicates that an allelic difference at an X-linked locus is responsible for modulating levels of recombination in oocytes.

Genetic and developmental analysis of X-inactivation in interspecific hybrid mice suggests a role for the Y chromosome in placental dysplasia

It has been shown previously that abnormal placental growth, i.e., hyper- and hypoplasia, occurs in crosses and backcrosses between different mouse (Mus) species. A locus that contributes to this abnormal development has been mapped to the X chromosome. Unexpectedly, an influence of fetal sex on placental development has been observed, in that placentas attached to male fetuses tended to exhibit a more pronounced phenotype than placentas attached to females. Here, we have analyzed this sex dependence in more detail. Our results show that differences between male and female placental weights are characteristic of interspecific matings and are not observed in intraspecific Mus musculus matings. The effect is retained in congenic lines that contain differing lengths of M. spretus-derived X chromosome. Expression of the X-linked gene Pgk1 from the maternal allele only and lack of overall activity of two paternally inherited X-linked transgenes indicate that reactivation or lack of inactivation of the paternal X chromosome in trophoblasts of interspecific hybrids is not a frequent occurrence. Thus, the difference between male and female placentas seems not to be caused by faulty preferential X-inactivation. Therefore, these data suggest that the sex difference of placental weights in interspecific hybrids is caused by interactions with the Y chromosome.

Menkes disease: recent advances and new aspects

Images

Mosaic methylation of Xist gene before chromosome inactivation in undifferentiated female mouse embryonic stem and embryonic germ cells

Epigenetic modification is implicated in the choice of the X chromosome to be inactivated in the mouse. In order to gain more insight into the nature of such modification, we carried out a series of experiments using undifferentiated mouse cell lines as a model system. Not only the paternally derived X (XP) chromosome, but the maternally derived one (XM) was inactivated in the outer layer of the balloon-like cystic embryoid body probably corresponding to the yolk sac endoderm of the post-implantation embryo in which XP is preferentially inactivated. Hence, it is likely that the imprint responsible for the nonrandom XP inactivation in early mouse development has been erased or masked in female ES cells. CpG sites in the 5' region of the Xist gene were partially methylated in female ES and EG and parthenogenetic ES cell lines as in the female somatic cell in which the silent Xist allele on the active X is fully methylated, whereas the expressed allele on the inactive X is completely unmethylated. In the case of undifferentiated ES cells, however, methylation was not differential between two Xist alleles. This observation was supported by the demonstration that single-cell clones derived from female ES cell lines were not characterized by either allele specific Xist methylation or nonrandom X inactivation upon cell differentiation. Apparently these findings are at variance with the view that Xist expression and X inactivation are controlled by preemptive methylation in undifferentiated ES cells and probably in epiblast.

A novel Tth111I restriction fragment length polymorphism (RFLP) allows tracing of X-chromosome inactivation in the (Xid) heterozygote

The X-linked immunodeficiency (Xid) in CBA/N mice serves as a model for the X-linked agammaglobulinemia (XLA) syndrome in man. X-chromosome inactivation in F1 heterozygotes derived from CBA/N (Xxid/Xxid) and B6.Pgk-1a (X+/Y) was investigated by monitoring the methylation status of the individual Pgk-1 alleles, Pgk-1b and Pgk-1a, respectively, using a novel Tth111I RFLP. Results indicate that in circulating B lymphocytes of female heterozygotes, only the X chromosomes carrying the normal alleles (X+) are active (nonrandom inactivation of the X chromosome), whereas in non-B cells both the X chromosomes (X+ and Xxid) are active (random inactivation of the X chromosome). These results were further confirmed by direct evaluation of transcription of the Btk gene, the gene mutated both in Xid and in XLA.

Xist is expressed in female embryonal carcinoma cells with two active X chromosomes

The Xist gene resides on the X chromosome and is expressed in female but not male somatic cells. In female cells, only the Xist allele on the inactive X chromosome is transcribed. We investigated the expression of Xist in diploid P10 female embryonal carcinoma cells that have two active X chromosomes. Xist RNA was present in these P10 cells. The X chromosomes in P10 cells carry different Xist alleles whose transcripts can be distinguished by restriction digestion of their cDNAs. Both alleles were expressed. Clones of P10 cells that had lost an X chromosome did not express Xist from the remaining allele. Thus Xist is expressed in cultured cells developmentally arrested prior to X chromosome inactivation, indicating that the Xist transcript is not always derived from an inactive X chromosome. Therefore, Xist expression per se cannot be a sufficient signal to inactivate an X chromosome.

Mutations in the murine homologue of the Menkes gene in dappled and blotchy mice

The murine homologue of the Menkes disease gene (MNK) was isolated from cDNA libraries, using human cDNA clones as probes, and by PCR. The predicted amino acid sequence shows a high level of identity (89.9%) with the human protein, and the predicted functional domains in the human protein are present. Using probes to the mouse Mnk gene, we found that the mottled dappled mutation was caused by alteration in the Mnk locus and lack of expression of Mnk RNA. Tissues of the blotchy mouse contained two larger sizes of MNK mRNA demonstrating a likely defect in RNA splicing. Thus, the mottled locus is homologous to the human MNK locus and dappled and blotchy are allelic mutations in this gene.

Clonal origin of skin and bone tumors produced by repeated beta-irradiation in mosaic cell mice

Clonal origin of skin and bone tumors produced by repeated beta-irradiation was determined by using mice with cellular mosaicism created by random X-chromosome inactivation, on the basis of phosphoglycerate kinase-1 (PGK). The backs of female C3H/He (Pgk-1a/Pgk-1b) mice were exposed to beta rays from 90Sr-90Y at a dose of 3 Gy per exposure 3 times weekly until tumors appeared. The cumulative tumor incidence reached 100% 500 days after the beginning of irradiation, as determined by the Kaplan-Meier method. All 8 tumors examined were of a single PGK phenotype: 5 squamous cell carcinomas and 2 osteosarcomas of A-type, and 1 squamous cell carcinoma of B-type. The absence of double PGK phenotype (AB-type) tumors indicated the monoclonal origin of the tumors produced by repeated irradiation.

Characterization of two electrophoretic lactate dehydrogenase-A mutants in Mus musculus

Two lactate dehydrogenase (LDH) mutations were recovered independently among offspring of ethylnitrosourea-treated male mice by screening for alterations of isoelectric focusing pattern in liver homogenates. Investigations of physicochemical and kinetic properties of the mutant enzymes indicated that the mutant traits resulted from point mutations at the Ldh-1 structural locus. Therefore, the new alleles were designated Ldh-1a-m5Neu and Ldh-1a-m6Neu, respectively. Both mutant alleles code for proteins which exhibit an altered stability to heat, in addition to changes in isoelectric focusing pattern and a reduction in anodal electrophoretic mobility. While LDH-Aa-m5Neu proteins are markedly less heat stable, LDH-Aa-m6Neu proteins are more heat stable than the wild-type enzyme. Furthermore, a small elevation of Km for pyruvate, a slightly reduced inhibition by high pyruvate concentrations, and a slight acidic shift of the pH activity profile distinguish LDH-Aa-m6Neu from both wild-type and LDH-Aa-m5Neu enzymes. Significant alterations of LDH activity were detected in some tissues from LDH-Aa-m5Neu individuals but not in those from LDH-Aa-m6Neu animals. Erythrocytes and blood of LDH-Aa-m5Neu mutants revealed activity levels which were reduced by approximately 6 and 13% compared with those of wild types in heterozygous and homozygous individuals, respectively. In addition, an elevation of approximately 6% in LDH activity was found in skeletal muscle in homozygous mutants. Consistent with the unaltered or only slightly altered LDH activity in tissues, the genetic as well as the physiological characterization yielded no easily detectable effects from either mutation on metabolism or fitness of the affected individuals.

Further evidence for the importance of parental source of the Xce allele in X chromosome inactivation

Using mice that were mosaics for both Xce and phosphoglycerate kinase (Pgk-1) alleles, we present further evidence that the parental source of the X chromosome may affect the probability of that X chromosome remaining active. The reciprocal cross differences in PGK-1 activity described here are intermediate between those published previously for other alleles of Xce.

Localization of the translocation breakpoint in a female with Menkes syndrome to Xq13.2-q13.3 proximal to PGK-1

Menkes syndrome is a rare X-linked recessive disorder characterized by an inability to metabolize copper. A female patient with both this disease and an X; autosome translocation with karyotype 46,X,t(X;2)(q13;q32.2) has previously been described. The translocation breakpoint in Xq13 coincides with a previous assignment of the Menkes gene at Xq13 by linkage data in humans and by analogy to the mottled mutations which are models for Menkes disease in the mouse. Therefore, this translocation probably interrupts the gene for Menkes syndrome in band Xq13. We describe here experiments to precisely map the translocation breakpoint within this chromosomal band. We have established a lymphoblastoid cell line from this patient and have used it to isolate the der(2) translocation chromosome (2pter----2q32::Xq13----Xqter) in human/hamster somatic cell hybrids. Southern blot analyses using a number of probes specific for chromosomes X and 2 have been studied to define precisely the location of the translocation breakpoint. Our results show that the breakpoint in this patient--and, therefore, likely the Menkes gene--maps to a small subregion of band Xq13.2-q13.3 proximal to the PGK1 locus and distal to all other Xq13 loci tested.

Polymorphisms in the coding and noncoding regions of murine Pgk-1 alleles

The mouse X-linked Pgk-1 gene encodes phosphoglycerate kinase. When transfected into human cells, the Pgk-1b allele causes the appearance of mouse PGK-1b enzyme activity. We describe here cloning of mouse Pgk-1a, an allele of Pgk-1 which encodes an enzyme, PGK-1a, with distinct electrophoretic mobility. We constructed recombinants between the DNA encoding Pgk-1b and Pgk-1a and transfected these constructs into human cells to assess the electrophoretic characteristics of each recombinant. In this way the charge variation between the two proteins was localized to exons 4 or 5. Sequencing of these exons revealed a single base-pair difference between the two alleles at codon 155, which predicts the amino acids lysine and threonine in PGK-1b and PGK-1a, respectively. A number of other DNA sequence polymorphisms exist between Pgk-1b and Pgk-1a including part of an L1 repeated element unique to Pgk-1a.

Efficient linkage of 10 loci in the proximal region of the mouse X chromosome

Interspecific Mus species crosses were used to construct a multilocus genetic map of the mouse X chromosome that extends for more than 50 cM. In these studies, we established the segregation of eight loci in more than 200 backcross progeny from crosses of M. musculus and M. spretus with a common inbred strain (C57BL/6JRos). Genetic divergence at the level of the nucleotide sequences makes these crosses a useful cumulative genetic resource for mapping additional genes defined by genomic or cDNA probes in a highly efficient manner. We have therefore devised a mapping strategy that uses a subset of these backcrosses that are recombinant between successive anchor loci to both localize and order an additional set of six genes without necessarily resorting to an analysis of the entire backcross series. Using this approach, we have defined the linkage of cytochrome b245 beta-chain (Cybb), synapsin (Syn-1), and two members of the X-linked lymphocyte-regulated gene family (Xlr-1, Xlr-2), as well as DXSmh141 and DXSmh172, two loci defined by random genomic probes. All six loci have been localized to the proximal portion of the mouse X chromosome and their order has been defined as Cybb, Otc, Syn-1/Timp, DXSmh141/Xlr-1, DXSmh172, Hprt, Xlr-2, Cf-9. Gene order was established by minimizing multiple recombination events across the region spanning an estimated 20 cM of the proximal X chromosome. The possible significance of the Xlr loci is discussed with respect to other X-chromosome loci that regulate the immune response.

Comparative and genetic studies of isozymes in resynthesized and cultivated Brassica napus L., B. campestris L. and B. alboglabra Bailey

Enzyme electrophoresis was used to compare newly resynthesized Brassica napus with its actual parental diploid species, B. campestris and B. alboglabra. Comparisons were also made with cultivated B. napus. Of the eight enzyme systems assayed, four were monomorphic (hexokinase, malate dehydrogenase, mannose phosphate isomerase and peroxidase), whereas the remaining four were polymorphic (glucosephosphate isomerase, leucine aminopeptidase, phosphoglucomutase and shikimate dehydrogenase), when comparisons were made within or between species. The polymorphic enzyme patterns observed in the newly resynthesized B. napus disclosed that the homoeologous loci contributed by the parental species were expressed in the amphiploid. Analysis of the glucosephosphate isomerase enzyme in a breeding line (Sv 02372) of B. napus indicated that, in this case, the gene originating from B. campestris was switched off whereas that of B. oleracea was expressed. Duplicated enzyme loci were observed in B. campestris and B. alboglabra, thus providing additional evidence to support the hypothesis that these species are actually secondary polyploids derived from an unknown archetype of x=6.

Allelic variation linked to adenine phosphoribosyltransferase locus in mouse teratocarcinoma cell line and feral-derived mouse strains

Southern blot analysis reveals two distinct adenine phosphoribosyltransferase (APRT) alleles in the P-19 mouse teratocarcinoma cell line. One allele is identical to that observed in common laboratory mouse strains (Mus musculus domesticus). The restriction enzyme site variations between the two alleles occur in sequences located both upstream and downstream of the APRT gene, but not within it. Although the P-19 cell line was established from a C3H strain embryo (Mus musculus domesticus), a sixth generation ancestor of this embryo was a feral mouse (Mus musculus musculus). The restriction pattern of the variant APRT allele in P-19 is identical to that of a feral-derived Mus musculus musculus animal, establishing the origin of this allele in the P-19 cell line. A third, distinct APRT allele was found in a Mus spretus feral-derived mouse. Exploiting the differences between the two APRT alleles in the P-19 cell line, we have demonstrated their sequential loss in APRT-deficient clones.

Prolonged survival of mice with myeloid leukemia by subcutaneous injection of recombinant human G-CSF

We studied the effect of recombinant human granulocyte colony-stimulating factor (rhG-CSF) on leukemia development and survival of mice with leukemia by using a radiation-induced myeloid leukemia cell line (C2M) with A-type phosphoglycerate kinase (PGK) as marker isoenzyme. C3H/He mice with B-type PGK were inoculated with 2 x 10(6) C2M cells through the tail vein. From the next day, they received a daily subcutaneous injection of 1 microgram rhG-CSF or control solution. The survival of rhG-CSF-treated recipients of C2M was significantly longer than control-solution-treated recipients. In rhG-CSF-treated recipients, not only spleen weight but also the number of blasts in hemopoietic organs was less than those in control recipients. While there was a remarkable decrease in bone marrow content of CFU-GM in control recipients, the content in rhG-CSF-treated recipients was comparable to that in normal mice. A reduced bone marrow and spleen content of leukemic colony-forming cells (L-CFU) was observed in rhG-CSF-treated recipients in comparison with control recipients. The electrophoretic analysis of PGK phenotypes of hemopoietic organs indicated the delayed appearance of A-type PGK from C2M cells in rhG-CSF-treated recipients. From these findings, we concluded that the injection of rhG-CSF delayed the onset of leukemia and improved the survival and several hematological parameters by suppressing C2M cells in recipient mice.

Multilocus molecular mapping of the mouse X chromosome

Using restriction fragment length polymorphisms (RFLPs) and enzymatic variants between distantly related mouse species, we have assigned three genes to the mouse X chromosome and concurrently mapped a total of eight genes spanning an estimated 50 cM of the chromosome. Segregation of RFLPs in over 200 male progeny from interspecies backcrosses between the inbred strain C57BL/6JRos and either wild-derived Mus musculus or Mus spretus was followed for the murine genes Timp (tissue inhibitor of metalloproteinases), Cf-8 (coagulation factor VIII), and Rsvp (red-sensitive visual pigment) and the known X-linked markers Otc, Hprt, Cf-9, G6pd, and Ags. From the centromere, the gene order was defined as Otc, Timp, Hprt, Cf-9, (Cf-8/Rsvp/G6pd), Ags, by minimizing the number of multiple recombinational events. No significant differences in map order or frequency of recombination were observed between the two backcross series studied. The use of Southern analysis has allowed us to add new genes to the map in a cumulative manner, and as probes become available, additional markers can be mapped, using the same set of mice, by utilizing existing blots or resampling the DNAs. The use of probes for functional genes has allowed us to directly compare the X chromosomes of mouse and man and has provided insight into chromosomal rearrangements which have occurred during the evolutionary divergence of these species, as well as to define the extent of linkage homologies.

Clonal nature of murine hemopoietic blast cell colonies

Murine hemopoietic blast cell colonies obtained from spleen cells of 5-fluorouracil (5-FU)-treated mice give rise to many multilineage colonies including granulocyte - erythrocyte - macrophage - megakaryocyte (GEMM) colonies in secondary cultures. Progenitor cells for blast cell colonies are considered to be more primitive than colony forming units (CFU)-GEMM. To determine whether they are clonal, we examined the phosphoglycerate kinase-1 (PGK-1) isozyme type of colonies originally grown from spleen cells of 5-FU-treated mice which had PGK-1 isozyme mosaicism. PGK assays of whole secondary colonies derived from one blast cell colony showed that they were either of type A or type B but not both. These results suggest that murine hemopoietic blast cell colonies are clonal.

A new cell line of murine myeloid leukemia with A-type phosphoglycerate kinase as marker isoenzyme

A new murine myeloid leukemia cell line (C2M) with A-type phosphoglycerate kinase (PGK) as marker isoenzyme was established from myeloid leukemia which arose in a female C3H/He strain mouse of the genotype Pgk-1a/Pgk-1b 1 yr after a whole body X-irradiation of 3 Gy. Cytochemical stainings indicated that C2M cells had myelomonocytic characteristics. Chromosomal analysis showed the partial deletion of No. 2 chromosome. Intravenous injection of C2M cells resulted in the development of myeloid leukemia in syngeneic mice owing to the growth of C2M cells. When C2M cells were transplanted to C3H/He mice with B-type PGK, PGK of spleen expressed two bands on electrophoresis; A-type PGK from transplanted C2M cells and B-type PGK from recipient mice, and the density of A-type PGK became prominent as the disease progressed. When granulocyte/macrophage progenitor cells of bone marrow cells from leukemic mice were cultured, two types of colonies were observed. By determining PGK types of the colonies, leukemic colonies could be differentiated from normal granulocyte/macrophage colonies. Since C2M cell line has an advantage of processing A-type PGK which can be readily distinguished by the electrophoresis from normal cells, it will serve as a useful tool to study the interaction between leukemic cells and normal hematopoietic cells.

X-linked genetic homologies between mouse and man

X-linked genes are conserved among all mammalian species, but the organization of genes on the X chromosome varies from one species to another. This review summarizes the evidence for established gene homologies between mice and human beings. It also describes genes that are possible homologies because of their locations in the human and murine X chromosomes and similarities in the phenotypes they produce. Based on current knowledge of homologous gene location, the human and murine X chromosomes appear to contain four highly conserved segments and differ in organization by only three to four simple chromosomal rearrangements.

Myeloproliferative disorder due to abnormal production of hematopoietic stimulators

A new kind of myeloproliferative disorder (L-8313) has been discovered. It was transplantable into syngeneic mice with spleen cells. The mice showed hepato-splenomegaly with a marked leukocytosis and anemia 3 weeks after transplantation of L-8313 cells. The number of GM-CFU and CFU-S per spleen increased to more than 40 times normal. The results of chromosomal and PGK analysis demonstrated that these increased stem cells were of host origin. Both the culture medium of the spleen cells and the serum from L-8313 bearing mice showed high levels of IL-3, BPA and CSF. Consequently, hematopoietic cells of the host mice underwent remarkable proliferation in response to these stimulating factors when L-8313 cells were transplanted. We also have been successful in establishing an in-vitro cell line and have maintained it for over one year. The phenotype of L-8313 cells was Thy 1.2 positive. Some L-8313 cells showed a positive acid phosphatase reaction but the cytochemical character of myeloid lineage was not observed. Therefore, L-8313 is considered to be a T-cell derived hematopoietic regulatory cell neoplasm with the ability to produce several hematopoietic stimulating factors.

Dosage of the Sts gene in the mouse

In this study we compared steroid sulfatase levels in XO, XX, and XY mice and carried out a clonal analysis in fibroblast cell cultures from mice heterozygous for the steroid sulfatase deficiency gene and heterozygous at the X-linked electrophoretic phosphoglycerate kinase locus. The combined results indicate that the murine steroid sulfatase locus is not dosage compensated and is not subject to X-inactivation. With respect to X-inactivation, it behaves in a somewhat different way from the closely linked sex-reversed gene and the human steroid sulfatase locus.

Expression of X-linked phosphoglycerate kinase in early mouse embryos homozygous at the Xce locus

The expression of maternally derived X-chromosomal Pgk-1 alleles was investigated in oocytes and early embryos of mice carrying different alleles (Xcea, Xcec) of the X-chromosome controlling element (Xce) locus. Pgk-1 allelic expression was determined by measuring their gene products using Cellogel electrophoresis and a sensitive fluorimetric enzyme assay. In addition to the already existing mouse strain of the genotypes Pgk-1a Xcec and Pgk-1b Xcea, a new line was bred carrying the combination Pgk-1b Xcec. The X chromosomes carrying the combinations Pgk-1a Xcec and Pgk-1b Xcec were of feral origin, whereas Pgk-1b Xcea was derived from a laboratory line. Our results using Xcec homozygous females confirm that maternal Pgk-1 is already expressed on day 4 of embryogenesis, thus substantiating data previously obtained using Xcea/Xcec heterozygous females. This finding also demonstrates that the timing of reactivation of maternal Pgk-1 is not influenced by the Xce locus. Furthermore, we found that oocytes from Xcec homozygous females have a balanced PGK-1 A/PGK-1 B allozyme ratio (50:50), whereas in oocytes obtained from Xcea/Xcec heterozygotes, the PGK-1 allozyme ratio is about 60:40. In tissues of adult Xce homozygous females, the PGK-1 allozymes are also balanced, whereas in Xcea/Xcec heterozygous females, the ratio is about 35:65. In addition to the relative activity of the PGK-1 allozymes, we also measured the absolute activity of PGK-1 in oocytes obtained from three types of Xce homozygous females.(ABSTRACT TRUNCATED AT 250 WORDS)

In situ identification of host derived infiltrating cells in chemically induced fibrosarcomas of interspecific chimeric mice

Chimeric mice have been used to investigate the cellular origin of chemically induced tumors. Interspecific chimeras were formed between the Ha/ICR strain of Mus musculus and Mus caroli. The normal tissues of the chimeric mice were composed of a mixture of cells which originated from each of the 2 species. The species of origin of the cells was determined both histologically with in situ hybridization using a DNA probe which recognizes M. musculus satellite DNA and by electrophoretic analysis of phosphoglycerate kinase-1 (PGK-1) isozyme expression. The 2 parental species, M. musculus and M. caroli, had comparable levels of inducible cytochrome P-450-dependent mixed function oxidase activity. Subcutaneous fibrosarcomas were induced with 3-methylcholanthrene. Electrophoretic analysis of many samples from the tumors revealed that some demonstrated both isozymes of PGK-1. However, extensive sectioning with subsequent in situ hybridization revealed that the only cells of mixed genotype were small, infiltrating inflammatory cells. These results confirmed PGK-1 analysis of the tissue culture cell lines derived from the tumors. This is the first report of direct visualization of the lineage origin of various cellular components in chemically induced tumors in a mosaic system and supports the contention that, while the neoplastic cells are clonal in origin, the tumors also contain non-neoplastic "host" cells which are derived from both sets of parents.

Differential expression of alpha-fetoprotein genes on the inactive X chromosome in extraembryonic and somatic tissues of a transgenic mouse line

During development of the female mouse embryo, one of the two X chromosomes is inactivated in a random manner in most cell lineages. However, in the extraembryonic trophectoderm and primary endoderm lineages there is preferential inactivation of the paternally derived X chromosome. The inactivated X chromosomes of the extraembryonic and somatic tissues appear equally inactive at the level of the expression of X-linked genes. However, there are differences in the timing of their replication and the extent of DNA modification as determined by gene transfer. The identification of transgenic animals carrying X-linked modified alpha-fetoprotein (AFP) genes allowed us to examine whether the inactivation process extends to an autosomal gene which is normally expressed at high levels in specific extraembryonic and somatic cells, and if so, whether the inactivation process is different in these two tissues. Our results demonstrate that the X-linked AFP genes were expressed on the inactive X chromosome in the visceral endoderm of the yolk sac but not in fetal liver. Thus, the transcriptional activity of the AFP minigene on the inactive X chromosome is dependent on the tissue in which it resides, and most probably reflects differences in the nature of the maintenance of the inactive state of the extraembryonic and embryonic X chromosomes.

Sex ratio and testis size in mice carrying Sxr and T(X;16)16H

Mice heterozygous for the T(X;16)16H translocation and carrying Sxr on their normal (inactive) X chromosome (ie, T16H/X Sxr individuals) may develop as males, females, or hermaphrodites. The proportion of males varied from 22% to 65% depending on the source of the normal X chromosome. A model is proposed, according to which relatively small variations in the spreading of inactivation from the X chromosome into the attached Sxr fragment produce large changes in the proportion of males. Testis weight in T16H/X Sxr males was found to be significantly smaller than in X/X Sxr males, irrespective of the source of the normal X chromosome.

Physiopathological studies on granulocyte-macrophage colony stimulating factor and multi colony stimulating factor producing leukemia, L8313, induced by irradiation of C3H mice

Radiation-induced L8313 leukemia bearing mice (L8313 mice) had marked granulocytosis with splenomegaly. Hemopoietic stem cells and progenitors increased in the spleen but not in the bone marrow. Spleen conditioned-medium and serum from L8313 mice induced the formation of granulocyte-macrophage colonies (CFU-GM), erythroid bursts (BFU-E) and mixed colonies (CFU-Mix). Bone marrow conditioned medium did not show such activity. A cell line (STIL-3) was established from the spleen cells of L8313 mice. Surface marker analysis showed that the established cells were suppressor T cell. The cells produced IL-3 and GM-CSF in vitro, and induce essentially the same "leukemic" response in recipient mice. Inoculation of STIL-3 in diffusion chamber also induced leukemoid reaction, i.e. a marked granulocytosis with splenomegaly. Therefore, L8313 leukemia may be linked to an abnormality of growth and production of hemopoietic factors in hemopoietic regulatory cells.

Test of recurrence after experimental radiation therapy of chemically induced autochthonous tumors in mosaic mice

True recurrence was distinguished from induction of new second tumors after experimental radiation therapy using monoclonal tumors produced in the mosaic cell background of mice. The mice were C3H/He females heterozygous at the X-chromosome-linked locus of phosphoglycerate kinase (PGK) and consisted of two types (A and B) of somatic cells by inactivation of one of X-chromosomes. Sarcomas and carcinomas with a single PGK phenotype were produced by subcutaneous injection of 3-methylcholanthrene (MCA) into the groin of the mice, and locally and singly irradiated with 4-6.5 Krad of X rays generated by a 6 Mev linear accelerator, when they were 8-10 mm in diameter. Of 69 mice irradiated, 17 were available for comparison of the PGK and histological types of primary and recurrent tumors. Of these, 10 recurrent tumors with A-type PGK and 3 with B-type PGK exhibited the same PGK type as that of primary tumors, while one was distinguishable histologically. Only one recurrent tumor was of the opposite PGK and a different histological type from the primary tumor. Considering the probability of new tumor formation among A----A recurrent tumors, it was calculated that 79% (11/14) of the tumors that reappeared in the irradiated area were actually true recurrent tumors. Autochthonous tumors may be important in testing therapeutic methods.

Rapid changes in specificity within single clones of cytolytic effector cells

We find rapid changes in the specificity of the cytolytic effector cells in a mixed lymphocyte culture. The lysis patterns produced by cytolytic effector cells generated near limiting dilution in murine mixed lymphocyte reactions of three types, F1 anti-parent (F1(A X B) anti-A), allogeneic (C anti-F1(A X B)), and F1 antimodified parent (F1(A X B) anti-A-TNP), were investigated. Cultures were characterized by their ability or inability to lyse a panel of target cells (e.g., A, B, F1). When individual cultures were tested at two different times, changes in lytic pattern were routinely seen, with some patterns reproducibly increasing in frequency and others reproducibly decreasing (e.g., patterns involving lysis of F1 decreased in an F1 anti-A response but increased in a C anti-F1 response). X-linked isoenzyme analysis showed that changes can occur within a single clone of effector cells. These results imply that the T cell specificity repertoire continues to evolve during an ongoing immune response, a conclusion incompatible with clonal selection theory.

Cell proliferation and DNA repair in the liver during early stages of chemical carcinogenesis

X-chromosomal phosphoglycerate kinase mocaicisms in organ samples of female heterozygous mice provided a means to prove, because of a selective expression of one of the two allozymes, the clonal origin of carcinogen-induced preneoplastic hepatocellular populations (see also ref. 61). The occurrence of these clonal preneoplastic foci was used in rats to determine cell cycle dependent differences of transformation sensitivity and DNA repair. The highest transformation rate was found after carcinogen exposure in late G1/early S phase of the cell cycle. Experimental disturbance of DNA precursor pools by continuous thymidine infusion during carcinogen exposure results in an increased formation of preneoplastic clones. This is a further argument in favor of an essential role of base-mispairing during initiation. Cell cycle dependent fluctuations of O6-methylguanine DNA transferase with an increasing enzyme activity in late G1 and a maximum in early S phase indicate that cells possess an increased potential for eliminating promutagenic O6-methylguanine during the most transformation sensitive parts of the cell cycle to prevent base-mispairing during DNA replication or transcription. However, this putatively protective effect is limited because the enzyme is rapidly expended in the reaction and drops again in later stages of the cell cycle.

X-linked allozymes of phosphoglycerate kinase as tools in experimental carcinogenesis in the mouse

Experimental conditions are discussed that are necessary for a useful application of genetically marked laboratory animals to distinguish between clonal and nonclonal origin of induced tumors: quantitative discrimination of biochemical markers, definition of the "patch" sizes, evaluation of possible admixture of "contaminating" cells and the approach to congenicity of parental animal strains.

Feline glucose-6-phosphate dehydrogenase cellular mosaicism. Application to the study of retrovirus-induced pure red cell aplasia

Neoplasms result from the uncontrolled proliferation of abnormal or transformed cells. The early stages of this process are difficult to study because of the lack of sensitive and specific markers of clonal evolution in an experimental system. We have developed a cat model using cellular mosaicism for glucose-6-phosphate dehydrogenase (G-6-PD). Our findings confirm that the structural locus for feline G-6-PD is on the X-chromosome and demonstrate that it is randomly inactivated in somatic cells. Heterozygous cats have balanced ratios of G-6-PD enzyme types in peripheral blood cells and hematopoietic progenitors that remain stable over time. In our initial studies, we used the model to analyze the events surrounding marrow failure experimentally induced by selected strains of feline leukemia virus (FeLV). Two G-6-PD heterozygous cats, one F1 male hybrid and one domestic cat were infected with FeLV (C or KT) and developed pure red cell aplasia (PRCA). Colonies arising from the more mature erythroid colony-forming cell were not detected in marrow culture of anemic animals although erythroid bursts persisted, suggesting that the differentiation of early erythroid progenitors (BFU-E) was inhibited in vivo. The ratio of G-6-PD types in hematopoietic progenitors and peripheral blood cells from the heterozygous cats did not change when the animals developed PRCA. Thus, the anemia did not result from the clonal expansion of a transformed myeloid stem cell. With this experimental approach, one may prospectively assess clonal evolution and cellular interactions in other FeLV-induced diseases.