Prenatal expression of a lethal genetic defect in carbohydrate metabolism in mice.

Mouse fetuses homozygous for the lethal cab (cardiac abnormal) mutation are characterized by pleiotropic effects that lead to immediate postnatal death. Mutant fetuses have only 4% of the normal amount of hepatic glycogen and 39% of the normal cardiac glycogen reserve, coupled with lower specific activities of glycogen synthase and phosphorylase. Analysis with the periodic acid-Schiff reagent histochemical stain demonstrated that cab homozygotes also have reduced amounts of structural polysaccharides. One of the most distinctive mutant phenotypic traits is severe prenatal hypoglycemia, with average (+/-SEM) plasma glucose concentrations of 0.35 +/- 0.14 mM in late fetuses compared to 3.47 +/- 0.69 mM in normal littermates. Compromise of glucose transport from dam to fetus or altered cellular glucose utilization was considered as a possible basis for the low extracellular and intracellular (hepatic) levels of glucose in mutants. Transport of the glucose analogue alpha-methyl[14C]glucoside by the placenta of cab homozygotes is normal. However, metabolism of [14C]glucose by mutant cells yields only 20% of the normal amount of 14CO2. This reduced efficiency of glucose metabolism is correlated with lower ATP concentrations in mutant organs. Aberrant glucose utilization may account for the pleiotropic features of the cab syndrome.     

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.     

Cerebral cortical astroglia from the trisomy 16 mouse, a model for Down syndrome, produce neuronal cholinergic deficits in cell culture

Trisomy 21 (Down syndrome) is associated with a high incidence of Alzheimer disease and with deficits in cholinergic function in humans. We used the trisomy 16 (Ts16) mouse model for Down syndrome to identify the cellular basis for the cholinergic dysfunction. Cholinergic neurons and cerebral cortical astroglia, obtained separately from Ts16 mouse fetuses and their euploid littermates, were cultured in various combinations. Choline acetyltransferase activity and cholinergic neuron number were both depressed in cultures in which both neurons and glia were derived from Ts16 fetuses. Cholinergic function of normal neurons was significantly down-regulated by coculture with Ts16 glia. Conversely, neurons from Ts16 animals could express normal cholinergic function when grown with normal glia. These observations indicate that astroglia may contribute strongly to the abnormal cholinergic function in the mouse Ts16 model for Down syndrome. The Ts16 glia could lack a cholinergic supporting factor present in normal glia or contain a factor that down-regulates cholinergic function.     

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.     

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.     

Murine amebiasis: the role of the macrophage in host defense

The congenitally athymic nude (nu/nu) mouse was studied as a model for amebic liver disease, using Entamoeba histolytica. Despite intrahepatic inoculation of massive numbers of amebae, we could not produce sustained infections in nu/nu mice. We also failed to induce hepatic amebiasis in thymus-intact nu/+ and +/+ littermates, or in nu/+ mice pretreated with rabbit antimouse thymocyte globulin. Humoral response was measured in both the nu/nu and nu/+ mice. Nu/+ but not nu/nu animals developed a specific IgG response after challenge with E. histolytica. There were no significant IgM responses. Pretreatment with silica increased susceptibility of both nu/nu and nu/+ mice to development of liver abscesses. These studies suggest that host resistance in murine amebiasis is critically dependent upon the macrophage, but not upon T cell-mediated defenses.     

Nerve growth factor corrects developmental impairments of basal forebrain cholinergic neurons in the trisomy 16 mouse.

The trisomy 16 (Ts16) mouse, which shares genetic and phenotypic homologies with Down syndrome, exhibits impaired development of the basal forebrain cholinergic system. Basal forebrains obtained from Ts16 and euploid littermate fetuses at 15 days of gestation were dissociated and cultured in completely defined medium, with cholinergic neurons identified by choline acetyltransferase (ChAT) immunoreactivity. The Ts16 cultures exhibited fewer ChAT-immunoreactive neurons, which were smaller and emitted shorter, smoother, and more simplified neurites than those from euploid littermates. Whereas the addition of beta-nerve growth factor (100 ng/ml) augmented the specific activity of ChAT and neuritic extension for both Ts16 and euploid cholinergic neurons, only Ts16 cultures exhibited an increase in the number and size of ChAT-immunoreactive neurons. Furthermore, Ts16 ChAT-immunoreactive neurites formed varicosities only in the presence of beta-nerve growth factor.     

Osteopenia in mice with genetic diabetes

Bone mass and growth were studied in mice with genetic diabetes (db/db) characterized by obesity, hyperinsulinemia and hyperglycemia, in their lean litter mates (db/+) and in non-diabetic mice of the same strain (+/+). No significant difference was observed between db/+ and +/+ mice. The length, bone mass, bone mineral mass, bone mineral density and content of moisture of the tibia of the db/db mice were significantly decreased compared with the db/+ and +/+ mice. Microradiographs of the distal femur diaphysis of the db/db mice showed a significant reduction of the spongious bone area and of the number and thickness of bone trabeculae with a normal mineralization. The amount of osteoid was significantly increased in the db/db mice. The area of cortical bone of the tibia epiphysis of the db/db mice was significantly decreased compared with the db/+ and +/+ mice. The data suggest the occurrence of osteopenia due to decreased mineralization in mice with genetic diabetes.     

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)     

The gene triplet Rw W Ph controls murine haematopoiesis

Having shown a haematopoietic role for Patch (Ph), especially when doubly heterozygous with the mutant Wct (Loutit & Cattanach, 1983) we have similarly examined the Rw locus, the third member of the triplet. Mature Rw/+mice have a just detectable macrocytic anaemia. When doubly heterozygous with Wct and Wv the mild anaemia of these W mutants is exaggerated but with W19H (not anaemic as single heterozygote) red cell factors are as for Rw/+. Rw/+mice are strikingly more sensitive to the lethal effects of X-irradiation (MLD 6.66 +/- 0.10 Gy) on haematopoiesis than comparable +/+ mice (MLD 8 Gy). Those mice that do recover after X-irradiation do not exhibit the delay in recovery of erythropoiesis that is evident with characteristic W mutants in both single and double dose. Furthermore the double heterozygote Wct+/+Rw has a significantly lower MLD (5.19 +/- 0.17 Gy) for X-radiation than Wct/+ (MLD 6.48 +/- 0.24 Gy). We argue that all three loci W, Ph and Rw, influence haematopoietic stem cells, leading to increased radiosensitivity when deletions or mutant genes are present.     

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.     

The copper transporter CTR1 provides an essential function in mammalian embryonic development

Copper serves as an essential cofactor for a variety of proteins in all living organisms. Previously, we described a human gene (CTR1;SLC31A1) that encodes a high-affinity copper-uptake protein and hypothesized that this protein is required for copper delivery to mammalian cells. Here, we test this hypothesis by inactivating the Ctr1 gene in mice by targeted mutagenesis. We observe early embryonic lethality in homozygous mutant embryos and a deficiency in copper uptake in the brains of heterozygous animals. Ctr1(-/-) embryos can be recovered at E8.5 but are severely developmentally retarded and morphologically abnormal. Histological analysis reveals discontinuities and variable thickness in the basement membrane of the embryonic region and an imperfect Reichert's membrane, features that are likely due to lack of activity in the collagen cross-linking cupro-enzyme lysyl oxidase. A collapsed embryonic cavity, the absence of an allantois, retarded mesodermal migration, and increased cell death are also apparent. In the brains of heterozygous adult mice, which at 16 months are phenotypically normal, copper is reduced to approximately half compared with control littermates, implicating CTR1 as the required port for copper entry into at least this organ. A study of the spatial and temporal expression pattern of Ctr1 during mouse development and adulthood further shows that CTR1 is ubiquitously transcribed with highest expression observed in the specialized epithelia of the choroid plexus and renal tubules and in connective tissues of the eye, ovary, and testes. We conclude that CTR1 is the primary avenue for copper uptake in mammalian cells.     

Hereditary emphysema in the tight-skin mouse. Evaluation of pathogenesis

The tight-skin (Tsk/+) mouse is a genetically determined model characterized by alveolar enlargement and physiologic evidence of emphysema. Morphologic evaluation of the lungs of these animals demonstrated increased numbers of potential protease-secreting cells (alveolar macrophages and neutrophils) in the lower respiratory tract prior to development of the emphysematous lesions. Quantitation of the neutrophils in the lungs of these animals was carried out by bronchoalveolar lavage. In the Tsk/+ mice, neutrophils constituted 3.5 +/- 2% of all inflammatory and immune effector cells present compared with 0.4 +/- 0.1% in control (+/+) mice (p less than 0.01). The Tsk/+ animals had no evidence of infection to explain the presence of the neutrophils and had normal proportions of lung T- and B-lymphocytes, suggesting that their lungs were immunologically normal. There was no evidence that the Tsk/+ mice have an antiprotease deficit; the capacity of serum of Tsk/+ mice to inhibit neutrophil elastase was no different from that of control +/+ animals. However, the fact that these animals have a persistent low level macrophage-neutrophil alveolitis prior to the development of the emphysematous lesion implies that the lung destruction may be associated, in part, with a chronic protease-antiprotease imbalance, similar to that hypothesized for human emphysema.     

Expression of connexin 43 (Cx43) is critical for normal hematopoiesis

Gap junctions are intercellular channels, formed by individual structural units known as connexins (Cx), that allow the intercellular exchange of various messenger molecules. The finding that numbers of Cx43-type gap junctions in bone marrow are elevated during establishment and regeneration of the hematopoietic system has led to the hypothesis that expression of Cx43 is critical during the initiation of blood cell formation. To test this hypothesis, lymphoid and myeloid development were examined in mice with a targeted disruption of the gene encoding Cx43. Because Cx43-/- mice die perinatally, initial analyses were performed on Cx43-/-, Cx43+/-, and Cx43+/+ embryos and newborns. The data indicate that lack of Cx43 expression during embryogenesis compromises the terminal stages of primary T and B lymphopoiesis. Cx43-/- embryos and neonates had a reduced frequency of CD4(+) and T-cell receptor-expressing thymocytes and surface IgM(+) cells compared to their Cx43+/+ littermates. Surprisingly, Cx43+/- embryos/neonates also showed defects in B- and T-cell development similar to those observed in Cx43-/- littermates, but their hematopoietic system was normal at 4 weeks of age. However, the regeneration of lymphoid and myeloid cells was severely impaired in the Cx43+/- mice after cytoablative treatment. Taken together, these data indicate that loss of a single Cx43 allele can affect blood cell formation. Finally, the results of reciprocal bone marrow transplants between Cx43+/+ and Cx43+/- mice and examination of hematopoietic progenitors and stromal cells in vitro indicates that the primary effects of Cx43 are mediated through its expression in the hematopoietic microenvironment.     

Caspase inhibition reduces tubular apoptosis and proliferation and slows disease progression in polycystic kidney disease

We have previously demonstrated an increase in proapoptotic caspase-3 in the kidney of Han:SPRD rats with polycystic kidney disease (PKD). The aim of the present study was to determine the effect of caspase inhibition on tubular cell apoptosis and proliferation, cyst formation, and renal failure in the Han:SPRD rat model of PKD. Heterozygous (Cy/+) and littermate control (+/+) male rats were weaned at 3 weeks of age and then treated with the caspase inhibitor IDN-8050 (10 mg/kg per day) by means of an Alzet (Palo Alto, CA) minipump or vehicle [polyethylene glycol (PEG 300)] for 5 weeks. The two-kidney/total body weight ratio more than doubled in Cy/+ rats compared with +/+ rats. IDN-8050 significantly reduced the kidney enlargement by 44% and the cyst volume density by 29% in Cy/+ rats. Cy/+ rats with PKD have kidney failure as indicated by a significant increase in blood urea nitrogen. IDN-8050 significantly reduced the increase in blood urea nitrogen in the Cy/+ rats. The number of proliferating cell nuclear antigen-positive tubular cells and apoptotic tubular cells in non-cystic and cystic tubules was significantly reduced in IDN-8050-treated Cy/+ rats compared with vehicle-treated Cy/+ rats. On immunoblot, the active form of caspase-3 (20 kDa) was significantly decreased in IDN-8050-treated Cy/+ rats compared with vehicle-treated Cy/+ rats. In summary, in a rat model of PKD, caspase inhibition with IDN-8050 (i) decreases apoptosis and proliferation in cystic and noncystic tubules; (ii) inhibits renal enlargement and cystogenesis, and (iii) attenuates the loss of kidney function.     

Variability of enzyme activity and urinary orotic acid in ornithine transcarbamylase deficient spf/+ heterozygotic mice

Urinary orotate excretion is used as a clinical parameter to distinguish female carriers of X-linked ornithine transcarbamylase deficiency. The value of this test has been considered doubtful due to a lack of knowledge about the true variability of hepatic enzyme activity and its effect on orotate synthesis. We have used a purebred population of spf/+ heterozygous females (n = 90), with an X-linked structural mutation of ornithine transcarbamylase, to study this variability in comparison with normal +/+ females (n = 19) and hemizygous spf/Y males (n = 20). Our results show that spf/+ heterozygotes have a mean hepatic enzyme activity equal to 64% of the normal group, as compared to 44-56% reported previously. They have a very wide variability (range 28-107 mumol/h/mg protein) which overlap the normal distribution curves of +/+ and spf/Y groups. Similar overlapping is shown in the distribution of urinary orotate excretion. The correlation studies indicate that the urinary orotate level as an index of hepatic enzyme deficiency is of value only in heterozygotes having an activity less than 50% of normal. This parameter cannot, therefore, be used to screen for all heterozygotes. However, it would still be valuable in distinguishing female-children at risk of developing hyperammonemic symptoms.     

Inactivation of the GR in the nervous system affects energy accumulation

The homeostatic regulation of body weight protects the organism from the negative consequences of starvation and obesity. Glucocorticoids (GCs) modulate this regulation, although the underlying mechanisms remain unclear. To address the role of central GRs in the regulation of energy balance, we studied mice in which GRs have selectively been inactivated in the nervous system. Mutant mice display marked growth retardation. During suckling age this is associated with normal fat deposition causing a 60% temporary increase of percent body fat, compared with control littermates. After weaning, fat and protein depositions are reduced so that adults are both smaller and leaner than their controls. Decreased food intake and, after weaning, reduced metabolic efficiency account for these developmental disturbances. Plasma levels of leptin and insulin, two important energy balance regulators, are elevated in young mutants but normal in adults. Leptin/body fat ratio is higher at all ages, suggesting disturbed control of circulating leptin as a consequence of chronically elevated GC levels in mutant animals. Adult mutants display increased hypothalamic CRH and NPY levels, but peptide levels of melanin concentrating hormone and Orexin A and B are unchanged. The increased levels of plasma GCs and hypothalamic CRH may act as catabolic signals most likely leading to persistently reduced energy accumulation.     

Hemonectin mediates adhesion of engrafted murine progenitors to a clonal bone marrow stromal cell line from Sl/Sld mice

Mutant Sl/Sld mice exhibit decreased marrow hematopoiesis. The defect is known to reside in the marrow microenvironment of these animals, which is reproduced in vitro by primary marrow explants as well as by cloned marrow stromal cell lines. Bone marrow progenitor cells are incapable of adhering to primary Sl/Sld stromal cells or cloned stromal cell lines derived from them to form cobblestone-islands and proliferate. The role of hemonectin, a marrow-specific adhesion protein in the defective hematopoiesis of the Sl/Sld mice, was studied. Indirect immunoperoxidase staining of marrow in situ from Sl/Sld mice showed little specific staining while specific staining was seen in a pericellular distribution in marrow from +/+ mice. Hemonectin expression in several cloned stromal cell lines from Sl/Sld mice was compared by immunoblotting with that in cloned stromal cell lines from normal +/+ littermates. Cell line Sld3, which has the least hematopoiesis supportive capacity in vitro, showed no detectable hemonectin by immunoblotting, while Sld1 and Sld2 showed detectable but greatly reduced amounts compared with normal +/+ 2.4, GBI/6, and D2XRII. Confluent cultures incubated with purified hemonectin and engrafted with enriched progenitors showed a significant increase in the cumulative number of cobbleston-islands and day 14 spleen colony-forming units (CFU-s) forming progenitors (39.15 +/- 3.6/dish; 16.3 +/- 3.1/dish, respectively), compared with untreated Sld3 cultures (cobblestone-islands 8.1 +/- 3.6/dish; CFU-s forming progenitors 8.8 +/- 0.05/dish). Hemonectin-mediated progenitor cell binding to the Sld3 stromal cells was specifically inhibited by antihemonectin but not by preimmune serum. These data support the role of hemonectin in early progenitor-stromal cell interactions.     

Role of the GH/IGF-I axis in the growth retardation of weaver mice

IGF-I is a well-established anabolic growth factor essential for growth and development. Although the role of the GH/IGF-I axis is established for normal postnatal growth, its functional state in neurodegenerative diseases is not fully characterized. The weaver mutant mouse is a commonly used model for studying hereditary cerebellar ataxia and provides an opportunity to investigate the function of IGF-I in postnatal growth following neurodegeneration. Previously, we reported that weaver mice are growth retarded and their body weights correlate with a decrease in circulating IGF-I levels. Because weaver mice have the same food intake/body weight ratios as their wild type littermates, our observation suggests that an impairment of the GH/IGF-I axis, rather than poor nutrition, likely contributes to their growth retardation. This study further investigated the etiology of reduced circulating IGF-I levels. We found that GH levels in weaver mice were reduced following acute insulin injection, but the hepatic GH receptor transduction pathway signaled normally as evidenced by increased STAT5b phosphorylation and IGF-I mRNA levels in response to acute GH administration. In addition, 2-week GH treatment induced a significant increase in body weight and circulating IGF-I levels in homozygous weaver mice but not in wild type littermates. In summary, a deficiency in the GH/IGF-I axis may be partially responsible for postnatal growth retardation in weaver mutant mice. This deficiency may occur at the level of the pituitary and/or hypothalamus and can be improved with GH administration.     

Mice severely deficient in growth hormone have normal hematopoiesis

OBJECTIVE: Many studies suggest that growth hormone (GH) is important for hematopoietic stem cell (HSC) function. The objective of this study is to determine if the genetic absence of GH reduces hematopoietic function and recovery, by testing various points in hematopoiesis, from numbers and functional abilities of primitive stem cells to the maintenance of normal numbers of differentiated cells. MATERIALS AND METHODS: Analyses were conducted on blood and bone marrow to compare GH-deficient C57BL/6J-Ghrhr(lit) / Ghrhr(lit) (lit/lit) mice with their normal (lit/+) littermates. Flow cytometric analysis was used to measure numbers of HSC and progenitor cells based on antigenic markers. Spleen colony-forming units (CFU-S) were examined to determine function of common myeloid progenitor (CMP) cells. Competitive repopulation assays were conducted to test whether normally functional HSCs are produced and supported in the lit/lit hematopoietic environment. RESULTS: The lit/lit mutant mice produced HSC and progenitor cells at least as well as their lit/+ control littermates. In CFU-S assays, the CMP from the lit/lit mice functioned as well as those from the lit/+ controls. Marrow cells from lit/lit mice repopulated irradiated recipients long-term better than did marrow cells from C57BL/6J(+/+) controls; thus, HSC produced in the absence of GH can replenish irradiated recipients. When lit/lit mice were used as irradiated recipients, they supported HSC function as well as lit/+ control recipients did; thus, the lit/lit hematopoietic environment can support normal hematopoiesis.