Poor response of Wv/Wx mice to a grafted neutrophilia-inducing, colony-stimulating-factor-producing tumor

Although mice possessing two mutant genes at the W locus have a defect in multipotential hematopoietic stem cells that form macroscopic colonies in the spleen of irradiated mice, the number of neutrophils in the blood of these mutant mice is normal or nearly normal. We investigated neutrophil production using the NFSA fibrosarcoma of C3H mouse origin, which induces neutrophilia accompanied by production of a neutrophil-macrophage colony-stimulating factor by the tumor. When the NFSA tumor was transplanted to (C57BL/6 X C3H/He)F1-Wv/Wx or to congenic +/+ mice, neutrophilia developed in mice of both genotypes. However, there was a significant difference between the degree of neutrophilia that developed in them; there was a 107-fold increase in the +/+ mice, but only a 28-fold increase in the Wv/Wx mice four weeks after tumor transplantation. This result is consistent with the concept that doubly heterozygous W mice have multipotential stem cells with diminished ability to respond to stimulation. The unperturbed condition may not provide a sufficient stimulus to demonstrate the defect in neutrophil production in doubly heterozygous W mutant mice.     

Mutant gene-induced disorders of structure, function and thyroglobulin synthesis in congenital goitre (cog/cog) in mice.

We have investigated thyroid structure and function in mice homozygous for the chromosome 15 mutation, congenital goitre (cog). Abnormal thyroidal hypertrophy and reduced iodine uptake in cog/cog mice were observed as early as day 18 of gestation, corresponding to the onset of thyroid function. Growth continued unabated in mutants throughout the 10-month period of observation. By 2 months of age, thyroid cell hypertrophy obliterated nearly all follicular lumina in cog/cog glands and by 10 months mean mutant thyroid mass exceeded that of age-matched littermates. Twenty-fold serum concentrations of thyrotrophin were significantly increased at all ages examined. While wild type (+/+) and heterozygote (+/cog) mice are indistinguishable from each other, thyroids of homozygote mutants (cog/cog) and the +/cog type are easily discernible from thyroids of the +/+ type by microscopic and thyroglobulin (Tg) analyses. Thyrofollicular cells of both cog/cog and +/cog genotypes contain large vesicles of accumulated, nonglycosylated proteinaceous material not observed in cells from +/+ mice. Autoradiography showed 125I was incorporated only into Tg within recognizable follicular lumina of thyroids from +/cog mice. Serum concentrations of tri-iodothyronine are depressed during development in cog/cog mice. Serum concentrations of thyroxine are depressed during postnatal development but increase progressively to normal concentrations by 10 months of age. Our analyses indicate that full size Tg is produced in thyroid cells from cog/cog mice, though in a greatly reduced quantity, and that Tgs which are several sizes smaller than normal are also produced in both homozygote and heterozygote thyroids.(ABSTRACT TRUNCATED AT 250 WORDS)     

Structural analysis of chromosomal rearrangements associated with the developmental mutations Ph, W19H, and Rw on mouse chromosome 5.

We are studying the chromosomal structure of three developmental mutations, dominant spotting (W), patch (Ph), and rump white (Rw) on mouse chromosome 5. These mutations are clustered in a region containing three genes encoding tyrosine kinase receptors (Kit, Pdgfra, and Flk1). Using probes for these genes and for a closely linked locus, D5Mn125, we established a high-resolution physical map covering approximately 2.8 Mb. The entire chromosomal segment mapped in this study is deleted in the W19H mutation. The map indicates the position of the Ph deletion, which encompasses not more than 400 kb around and including the Pdgfra gene. The map also places the distal breakpoint of the Rw inversion to a limited chromosomal segment between Kit and Pdgfra. In light of the structure of the Ph-W-Rw region, we interpret the previously published complementation analyses as indicating that the pigmentation defect in Rw/+ heterozygotes could be due to the disruption of Kit and/or Pdgfra regulatory sequences, whereas the gene(s) responsible for the recessive lethality of Rw/Rw embryos is not closely linked to the Ph and W loci and maps proximally to the W19H deletion. The structural analysis of chromosomal rearrangements associated with W19H, Ph, and Rw combined with the high-resolution physical mapping points the way toward the definition of these mutations in molecular terms and isolation of homologous genes on human chromosome 4.     

Abnormal plasma glucose and insulin responses in heterozygous lean (ob/+) mice

Summary To investigate the effect of the ob gene in the heterozygous condition, plasma glucose and insulin responses of adult heterozygous lean (ob/+) mice were compared with mice of the homozygous lean (+/+) and homozygous obese (ob/ob) genotypes. The ob/+ mice consumed 24% more food than +/+ mice although body weights were similar. Plasma glucose and insulin concentrations were respectively 16% and 176% higher in ob/+ mice than +/+ mice in the freely fed state, and 44% and 88% higher during glucose tolerance tests. In 24 hour fasted ob/+ mice, plasma glucose concentrations were 23% higher than +/+ mice but plasma insulin concentrations were not significantly different. Arginine produced a greater insulin response (172%) and a greater fall in glycaemia (200%) in ob/ + mice. A significant difference in the hypoglycaemic effect of insulin in ob/+ and +/+ mice was not observed. These results demonstrate an effect of the ob gene on glucose homeostasis in heterozygous lean (ob/+) mice. The abnormalities were qualitatively similar but considerably less severe than those in ob/ob mice, suggesting that ob/+ mice might prove useful to study factors predisposing to inappropriate hyperglycaemia.     

Plasma clearance of transferrin in control and hypotransferrinaemic mice: implications for regulation of transferrin turnover

Summary. Kinetic studies were performed to determine the clearance of iodinated transferrin in hypotransferrinaemic mice, as compared to normal animals. Clearance of i.v. (and i.p.) administered radiolabelled protein in homozygous (hpx/hpx) mice was significantly faster than in heterozygous (hpx/+) and wild-type control (+/+) groups. A comparable t_1/2 value for transferrin clearance in hpx/hpx mice was derived from a study in which immunoassay was performed on serum samples obtained at various times post-injection with normal mouse serum, indicating that the clearance of ¹²⁵I reflected true clearance of transferrin protein. The clearance rate in the hpx/+ group was significantly slower than in +/+ mice. Calculation of transferring synthesis rates in these two groups suggested that transferrin levels do not regulate transferrin synthesis rates, but may affect degradation; this observation is consistent with the fact that transferrin levels in hpx/+ mice are > 50% of the values in +/+ mice, and indicates a partial compensation for reduced synthesis. The rapid clearance in hpx/hpx mice is an additional factor in determining the low levels of circulating transferrin in these synthesis-impaired mutants.     

Stromal cells (CFU-F) in normal and genetically anemic mouse strains

Mice of the Sl/Sld genotype have an approximately 3-fold higher number of fibroblastoid progenitors (CFU-F) in their spleens than their normal +/+ littermates. Experiments were performed to determine whether the elevated Sl/Sld splenic CFU-F numbers were due to compensatory mechanisms acting in the presence of a functionally abnormal CFU-F population or to a nonspecific response to chronic anemia. Comparison of the functional ability of Sl/Sld splenic fibroblasts to produce granulocyte/macrophage colony-stimulating activity with +/+ splenic fibroblasts demonstrated that there was no difference. Similar results were obtained for Sl/Sld and +/+ femoral fibroblasts. Analysis of CFU-F in W/Wv mice revealed an approximately 3-fold higher number of splenic CFU-F than in either +/+ or heterozygous (W/+ and Wv/+) littermates. Since the anemia in W/Wv mice is attributed to a hemopoietic stem cell defect and that of the Sl/Sld mice is attributed to a microenvironmental defect, we suggest that the increased splenic CFU-F number in Sl/Sld mice is not specifically due to the microenvironmental defect, but is part of a general response to hemopoietic stress.     

Mast cell number in the skin of heterozygotes reflects the molecular nature of c-kit mutation

The W locus of mice encodes the c-kit receptor tyrosine kinase. Heterozygous WJic/+ and Wn/+ mice and homozygous Wf/Wf mice were similar in appearance; all of them have large depigmented areas lacking any well-defined pattern. The WJic, Wn, and Wf mutant alleles were characterized and their molecular nature was correlated with the mast cell differentiation in the skin and the biologic features of cultured mast cell (CMC). All WJic, Wn, and Wf were point mutations at the tyrosine kinase domain, and c-kit mRNA was normally transcribed from all of them. The mature 145-Kd form of the c-kit protein was produced from the WJic and Wf alleles, but not from the Wn allele. c-kit proteins produced by the WJic or Wf allele were expressed on the surface of CMCs, but those of the Wn allele were not. When double heterozygous mice were produced between W and WJic and between W and Wn, both W/WJic and W/Wn mice lacked skin mast cells. W/WJic CMCs and W/Wn CMCs did not survive in the coculture with fibroblasts. W/WJic CMCs normally attached to fibroblasts, but W/Wn CMCs did not. The defect of W/Wn CMCs in the attachment was attributed to the deficient extracellular expression of the c-kit protein. The number of skin mast cells was compared among WJic/+, Wn/+, Wf/+, and Wf/Wf mice. Mast cells decreased in WJic/+ and Wf/Wf mice, but not in Wn/+ and Wf/+ mice. Although the Wn was a point mutation at the kinase domain, the biologic effect of the Wn was comparable with that of the W mutant allele, which produces truncated c-kit protein without the transmembrane domain. The weak phenotype of Wn/+ mice may be explained by the deficient extracellular expression of c-kit proteins produced by the Wn allele. When WJic/WJic, Wn/Wn, and Wf/Wf CMCs were stimulated by the recombinant c-kit ligand, autophosphorylation activity was observed only in Wf/Wf CMCs. This result was consistent with the weak biologic effect of the Wf mutant allele.     

Histochemical characteristics of soleus muscle in angiotensin-converting enzyme gene knockout mice.

We examined the histochemical characteristics of soleus muscle in the angiotensin-converting enzyme (ACE) gene (Ace in mice, ACE in humans) knockout mice. Serial sections of soleus muscle of wild-type (Ace+/+, n=20) and heterozygous mutant (Ace+/-, n=24) mice were stained for myosin adenosine triphosphatase activity to identify different muscle fiber types. Capillaries were visualized by amylase-periodic acid-Schiff staining. ACE activity in the serum and gastrocnemius muscle was higher in male mice than in female mice. Female and male Ace+/- mice had markedly lower ACE activity in the serum and the gastrocnemius muscle than did female and male Ace+/+ mice, respectively. In both male and female mice, the composition of fiber types (type I and IIa) did not differ significantly between Ace+/+ and Ace+/- mice. There was no significant gender difference in capillary density. Ace+/- mice had significantly more capillaries around type IIa fibers (5.44 +/- 0.18 vs. 5.01 +/- 0.13, p<0.05) than Ace+/+ mice. The differences in the number of capillaries around type I fibers and in the number of capillaries around per fiber (capillary:fiber ratio) between Ace+/- and Ace+/+ mice were not significant (p<0.1). There was no significant difference in the mean cross-sectional area occupied by one capillary and the number of capillaries per fiber area between Ace+/+ and Ace+/- mice. In conclusion, knockout of the Ace gene in mice increased capillary density, as expressed by the mean number of capillaries around type IIa fibers. This finding suggests a possible mechanism for the cardioprotective effects of ACE inhibitors.     

Co-inheritance of alpha- and beta-thalassaemia in mice ameliorates thalassaemic phenotype

Beta-thalassaemia is an inherited disease caused by defective synthesis of the beta-globin chain of haemoglobin, leading to an imbalance in globin chains. Excess alpha-globin chains precipitate in erythroid progenitor cells resulting in cell death, ineffective erythropoiesis and severe anaemia. Decreased alpha-globin synthesis leads to milder symptoms, exemplified by individuals who co-inherit alpha-thalassaemia and beta-thalassaemia. In this study, we set out to investigate whether co-inheritance of alpha- and beta-thalassaemia in mice leads to reduced anaemia. Heterozygous murine beta-globin knockout (KO) mice (beta+/-) which display severe anaemia were mated with heterozygous alpha-globin KO mice (alpha++/--). The resulting progeny were genotyped and classed as wild-type WT (alpha++/++;beta+/+), heterozygous alpha-KO (alpha++/--;beta+/+), heterozygous beta-KO (alpha++/++;beta+/-) or double heterozygous (DH) alpha-KO/beta-KO (alpha++/--;beta+/-). Mice were bled and full blood examinations (FBE) performed. FBE results for heterozygous beta-KO mice (beta+/-) showed marked reductions in haemoglobin and haematocrit levels and significant increases in red cell distribution widths and reticulocyte counts compared to WT mice. In contrast, FBE results for DH alpha-KO/beta-KO mice showed near normal red blood cell indices. These results indicate that reduction of alpha-globin expression leads to correction of the globin chain imbalance in beta-thalassaemic mice and therefore an improved phenotype. The analysis of DH alpha-KO/beta-KO mice leads to the following conclusions: (1) co-inheritance of alpha- and beta-thalassaemia in mice improves the thalassaemic phenotype, identical to the situation in humans; (2) the heterozygous murine beta-globin KO mouse model is a suitable in vivo model to test for therapeutic knockdown of alpha-globin.     

Impact of antithrombin deficiency in thrombogenesis: lipopolysaccharide and stress-induced thrombus formation in heterozygous antithrombin-deficient mice

Antithrombin (AT) deficiency is an autosomal disorder associated with venous thromboembolism. However, a diagnosis of homozygous AT deficiency is seldom made. Most patients are heterozygous and have approximately 50% AT activities, and they are at higher risk for the development of thromboembolism. Through gene targeting we generated AT-deficient mice and previously reported that completely AT-deficient mice could not survive the prenatal period because of extensive thrombosis in the myocardium and liver sinusoids. In contrast, heterozygous AT-deficient mice with 50% AT activities have not shown spontaneous thromboembolic episodes. To demonstrate a thrombotic tendency in heterozygous AT deficiency, we challenged heterozygous AT-deficient mice (AT+/- mice) with the administration of lipopolysaccharide (LPS) or with restraint stress by immobilization. LPS injection markedly induced fibrin deposition in the kidney glomeruli, myocardium, and liver sinusoids in AT+/- mice compared with wild-type mice (AT+/+ mice). Restraint stress tests were performed by placing mice in 50-mL conical centrifuge tubes for 20 hours. Fibrin deposition was observed in the kidney of AT+/+ and AT+/- mice, but AT+/- mice exhibited more extensive fibrin deposition than AT+/+ mice. After prophylactic administration of human AT concentrates to increase plasma AT activities of AT+/- mice, LPS-induced fibrin deposition was effectively prevented. These results suggest that heterozygous AT deficiency is significantly associated with a tendency toward thrombosis formation in the kidney. The AT+/- mouse thus is a useful model for studying the effect of environmental or genetic risk factors on thrombogenesis.     

大鼠γ谷氨酰半胱氨酸合成酶催化亚单位基因5''端调控序列初步分析

目的分析大鼠γ谷氨酰半胱氨酸合成酶(γ-GCS)催化亚单位(GCLC)基因5'端调控区域和相应转录因子的特性.方法克隆1 760 bp大鼠GCLC上游调控基因并构建含荧光素酶基因的报道载体GCLC-Luc(GCLC/pGL-3),利用外切核酸酶Ⅲ将大鼠GCLC基因的5'端序列单向切成不同长度的缺失体,将所构建的GCLC-Luc及其11个缺失体转染大鼠肺泡上皮细胞,通过测量转染后细胞的荧光素酶活性确定该基因的调控区域,并通过转录因子分析软件分析出可能与这些调控区域结合的转录因子,最后通过电泳迁移率改变实验(EMSA)以明确该调控区的顺式元件和转录因子.结果实验成功地克隆出大鼠GCLC上游调控基因及其报道载体GCLC-Luc及GCLC-Luc的11个缺失体.将GCLC-Luc及其缺失体转染肺泡上皮细胞并分析荧光素酶活性GCLC-Luc(-1 758/+2-Luc),缺失体1(-1 231/+2-Luc),缺失体2(-1 108/+2-Luc),缺失体3(-1 087/+2-Luc),缺失体4(-876/+2-Luc),缺失体5(-745/+2-Luc),缺失体6(-705/+2-Luc),缺失体8(-613/+2-Luc),缺失体9(-595/+2-Luc),缺失体10(-403/+2-Luc)和缺失体11(-111/+2-Luc)的荧光素酶值分别为(90 012±2 445)、(77 652±840)、(149 927±4 915)、(71 588±1 108)、(99 283±2 612)、(75 443±1 438)、(282 772±7 046)、(96 891±2 275)、(148 917±5 966)、(258 991±5 015)和(895±49)U.EMSA证实核因子1(NF-1)、CCAAT/增强子结合蛋白(C/EBP)能与-705～-613 bp区段的序列结合,活化蛋白1(AP-1)、核因子κB(NF-κB)能与-403～-111 bp区段的序列结合,上游刺激因子(USF)能与-745～-705 bp区段的序列结合.结论 GCLC基因的-403～-111 bp和-705～-613 bp区段属正调控区域,NF-1、C/EBP、AP-1、NF-κB等转录因子能与这些正调控区域结合并可能参与GCLC基因的表达调控;-745～-705 bp属负调控区域,USF能与该负调控区域的E-box元件结合,提示E-box与USF相互作用可能抑制GCLC基因的表达.     

Leptin administration prevents spontaneous gestational diabetes in heterozygous Lepr(db/+) mice: effects on placental leptin and fetal growth.

Gestational diabetes mellitus (GDM) results from an interaction between susceptibility genes and the diabetogenic effects of pregnancy. During pregnancy, mice heterozygous for the lepin receptor (db/+) gain more weight, are glucose intolerant, and produce macrosomic fetuses compared with wild-type (+/+) mothers, suggesting that an alteration in leptin action may play a role in GDM and fetal overgrowth. To investigate whether leptin administration or pair-feeding can reduce adiposity and thereby prevent GDM and neonatal overgrowth, we examined energy balance, glucose and insulin tolerance, and fetal growth in pregnant db/+ and +/+ mice treated with recombinant human leptin-IgG during late pregnancy. Leptin reduced food intake and adiposity in pregnant db/+ mice to levels similar to pregnant +/+ mice and significantly reduced maternal weight gain. Maternal glucose levels were markedly lower during glucose and insulin challenge tests in leptin-treated db/+ mice relative to db/+ and pair-fed controls. Despite reduced energy intake and improved glucose tolerance, leptin administration did not reduce fetal overgrowth in offspring from db/+ mothers. Fetal and placental leptin levels were 1.3- to 1.5-fold higher in offspring from db/+ mothers and remained unchanged with leptin administration, whereas leptin treatment in +/+ mothers or pair-feeding decreased placental leptin concentration and reduced fetal birth weight. Our results provide evidence that leptin administration during late gestation can reduce adiposity and improve glucose tolerance in the db/+ mouse model of spontaneous GDM. However, fetal and placenta leptin levels are higher in db/+ mothers and are subject to reduced negative feedback in response to leptin treatment. These data suggest that alterations in placenta leptin may contribute to the regulation of fetal growth independently of maternal glucose levels.     

Promotion of murine hepatocarcinogenesis by testosterone is androgen receptor-dependent but not cell autonomous.

Tfm (testicular feminization) mutant mice lack functional androgen receptors. By studying liver tumor development in Tfm mice, we have shown that the greater susceptibility of male mice relative to female mice for liver tumor induction by N,N-diethylnitrosamine is androgen receptor-dependent. C57BL/6J normal and Tfm mutant mice were injected at 12 days of age with N,N-diethylnitrosamine (0.2 mumol/g, i.p.), and liver tumors were enumerated in 50-week-old animals. Normal males averaged 20 liver tumors per animal; Tfm males, 0.7; normal females, 0.6; and Tfm/+ heterozygous females, 1.5. The androgen receptor gene and the Tfm mutation are X chromosome linked. Because of random X chromosome inactivation, hepatocytes from Tfm/+ heterozygous female mice are mosaic with respect to the expression of mutant or wild-type receptors. To determine if testosterone acts directly as a liver tumor promoter, through the androgen receptor in preneoplastic hepatocytes, or by an indirect mechanism, we chronically treated these mosaic female mice with testosterone and measured the androgen receptor content of the resulting tumors. B6C3F1 Tfm/+ mosaic and +/+ wild-type female mice were injected i.p. at 12 days of age with N,N-diethylnitrosamine (0.1 mumol/g) and ovariectomized at 8 weeks of age. Half of the mice of each group subsequently received biweekly s.c. injections of testosterone (0.15 mg per mouse) for 30 weeks. Tumor multiplicity was the same for wild-type and Tfm/+ mosaic females treated with testosterone (31-32 tumors per animal at 38 weeks of age) and was increased relative to females not treated with testosterone (13-17 tumors per animal at 50 weeks of age). Testosterone treatment did not significantly increase the percentage of androgen receptor-positive tumors in Tfm/+ mosaic females: 58% of the tumors from Tfm/+ mosaic females treated with testosterone were receptor positive compared to 48% in Tfm/+ females not treated with testosterone and 92% in wild-type females treated with testosterone. Finally, the number of androgen receptors in the majority of liver tumors examined was greatly decreased relative to the surrounding normal liver tissue. We conclude that liver tumor promotion by testosterone requires a functional androgen receptor in the intact animal. However, this promotion is not cell autonomous; that is, the response of the preneoplastic hepatocyte is not dependent on the expression of functional receptor in the target cell.     

Double leptin and melanocortin-4 receptor gene mutations have an additive effect on fat mass and are associated with reduced effects of leptin on weight loss and food intake

Melanocortin-4 receptors (MC4Rs) are involved in the regulation of food intake, sympathetic nervous activity, and adrenal and thyroid function by leptin. The role of MC4Rs in regulating energy balance by leptin was investigated using double heterozygote or homozygous leptin (Lep(ob)) and Mc4r gene mutant mice. Double heterozygous or homozygous mutants were generated by crossing MC4R knockout (Mc4r-/-) mice, backcrossed onto C57BL/6J, with B6.V-Lep(ob) mice. Energy expenditure was measured using indirect calorimetry. The effect of leptin on food intake, weight loss, insulin, and corticosterone was compared for Lep(ob)/Lep(ob)Mc4r-/- mice and Lep(ob)/Lep(ob) mice. Double heterozygous and homozygous mutants exhibited an additive effect on fat mass. The 2-fold increase in body weight associated with severe obesity of Lep(ob)/Lep(ob) mice was associated with a significantly higher 24 h total and resting energy expenditure. The effect of obesity on energy expenditure was attenuated by 50% in Lep(ob)/Lep(ob) Mc4r+/- and Lep(ob)/Lep(ob) Mc4r-/- mice. Loss of MC4Rs did not affect basal food intake of Lep(ob)/Lep(ob) mice but was associated with partial leptin resistance in terms of food intake and weight loss. Leptin suppression of insulin and corticosterone in Lep(ob)/Lep(ob) mice were not significantly affected by Mc4r genotype. These results suggest a complex interaction between the Lep and Mc4r genes in energy homeostasis and suggest that MC4Rs retain significant anti-obesity function in the obese leptin-deficient state. Increased adiposity with double mutations may involve a reduction in energy expenditure. MC4Rs might have a modest role in the regulation of energy balance by exogenously administered leptin, primarily effecting food intake.     

ApcMin, a mutation in the murine Apc gene, predisposes to mammary carcinomas and focal alveolar hyperplasias.

ApcMin (Min, multiple intestinal neoplasia) is a point mutation in the murine homolog of the APC gene. Min/+ mice develop multiple intestinal adenomas, as do humans carrying germ-line mutations in APC. Female mice carrying Min are also prone to develop mammary tumors. Min/+ mammary glands are more sensitive to chemical carcinogenesis than are +/+ mammary glands. Transplantation of mammary cells from Min/+ or +/+ donors into +/+ hosts demonstrates that the propensity to develop mammary tumors is intrinsic to the Min/+ mammary cells. Long-term grafts of Min/+ mammary glands also gave rise to focal alveolar hyperplasias, indicating that the presence of the Min mutation also has a role in the development of these lesions.     

Establishment of permanent chimerism in a lactate dehydrogenase-deficient mouse mutant with hemolytic anemia

Pluripotent hemopoietic stem cell function was investigated in the homozygous muscle type lactate dehydrogenase (LDH-A) mutant mouse using bone marrow transplantation experiments. Hemopoietic tissues of LDH-A mutants showed a marked decreased in enzyme activity that was associated with severe hemolytic anemia. This condition proved to be transplantable into wild type mice (+/+) through total body irradiation (TBI) at a lethal dose of 8.0 Gy followed by engraftment of mutant bone marrow cells. Since the mutants are extremely radiosensitive (lethal dose50/30 4.4 Gy vs 7.3 Gy in +/+ mice), 8.0-Gy TBI followed by injection of even high numbers of normal bone marrow cells did not prevent death within 5-6 days. After a nonlethal dose of 4.0 Gy and grafting of normal bone marrow cells, a transient chimerism showing peripheral blood characteristics of the wild type was produced that returned to the mutant condition within 12 weeks. The transfusion of wild type red blood cells prior to and following 8.0-Gy TBI and reconstitution with wild type bone marrow cells prevented the early death of the mutants and permanent chimerism was achieved. The chimeras showed all hematological parameters of wild type mice, and radiosensitivity returned to normal. It is concluded that the mutant pluripotent stem cells are functionally comparable to normal stem cells, emphasizing the significance of this mouse model for studies of stem cell regulation.     

Engraftment of bone marrow transplants in W anemic mice measured by electronic determination of the red blood cell size profile.

Defective stem cells of WBB6F1-W/Wv mice produce macrocytic red blood cells (RBCs); stem cells of WBB6F1-+/+ mice produce normocytic RBCs. Utilization of the Coulter counter channelyzer permitted good dissociation between the size distribution of populations of +/+ and W/Wv RBCs. Peaks (mean cell volumes) for +/+ and W/Wv RBCs have been determined to be between the 30th and 40th channel and 50th and 60th channel, respectively. Variability of profiles for individual mice of both genotypes did not exceed the variability of separate determinations of the same cell suspension from a single mouse. Admixture (approximately 15%) of either type of erythrocytes could be quantitatively detected by this method. One week after transplant of 10(7) +/+ marrow cells into W/Wv recipients, 25% of donor type erythrocytes were detected. Eighteen days post-graft, concentration of +/- normocytes exceeded the concentration of macrocytes in the W/Wv recipients' circulation. Approximately 45 days post-transplant, the proportion of macrocytes decreased below the 10% detectable level. Calculation of the daily RBC production rate during repopulation and estimation of the number of RBCs produced by a single hematopoietic colony were determined. The RBC size profile was found to be a convenient method for studying the effect of implantation of W/Wv marrow into lethally irradiated +/+ mice. This method proved suitable for repetitive determination of the size population in individual transplanted mice.     

Characterization of Conduction in the Ventricles of Normal and Heterozygous Cx43 Knockout Mice Using Optical Mapping

INTRODUCTION: Gap junction channels are important determinants of conduction in the heart and may play a central role in the development of lethal cardiac arrhythmias. The recent development of a Cx43-deficient mouse has raised fundamental questions about the role of specific connexin isoforms in intercellular communication in the heart. Although a homozygous null mutation of the Cx43 gene (Cx43-/-) is lethal, the heterozygous (Cx43+/-) animals survive to adulthood. Reports on the cardiac electrophysiologic phenotype of the Cx43+/- mice are contradictory. Thus, the effects of a null mutation of a single Cx43 allele require reevaluation. METHODS AND RESULTS: High-resolution video mapping techniques were used to study propagation in hearts from Cx43+/- and littermate control (Cx43+/+) mice. Local conduction velocities (CVs) and conduction patterns were quantitatively measured by determining conduction vectors. We undertook the characterization of ECG parameters and epicardial CVs of normal and Cx43+/- mouse hearts. ECG measurements obtained from 12 Cx43+/+ and 6 Cx43+/- age matched mice did not show differences in any parameter, including QRS duration (14.5 +/- 0.9 and 15.7 +/- 2.3 msec for Cx43+/+ and Cx43+/-, respectively). In addition, using a sensitive method of detecting changes in local CV, video images of epicardial wave propagation revealed similar activation patterns and velocities in both groups of mice. CONCLUSION: A sensitive method that accurately measures local CVs throughout the ventricles revealed no changes in Cx43+/- mice, which is consistent with the demonstration that ECG parameter values in the heterozygous mice are the same as those in wild-type mice.     

Studies on the Defective Haematopoietic Microenvironment of Sl/Sld Mice

S ummary . Femurs and spleens of both Sl/Sl^d and +/+ origin were implanted into both Sl/Sl^d and +/+ hosts. Eight weeks later the +/+ grafts incorporated more radioactive iron than did the Sl/Sl^d ones. The number of colony forming units (CFU) in the marrow of +/+ femur grafts and in +/+ spleen grafts was several fold greater than that in Sl/Sl^d grafts. X-irradiation of femur and spleen donors with 950 R reduced the number of CFU in the grafts to 40–60%, whereas grafts from donors exposed to 2500 R supported no CFU growth at all. The haematopoietic cells in the grafts after 6 weeks were almost entirely of host origin.
These studies suggest that Sl/Sl^d mice have a congenital defect in some stromal elements of their haematopoietic tissues which are essential for the normal growth of CFU. These stromal factors are likely to be cellular, are less radiosensitive than are the CFU, and support the growth of CFU rather than actually differentiate into these cells. These stromal factors are present in both spleens and femurs of mice. The model described here appears to be a useful one for further characterizing stromal factors essential for supporting haematopoiesis.