Germ cell development in the XXY mouse: evidence that X chromosome reactivation is independent of sexual differentiation.
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Prior to entry into meiosis, XX germ cells in the fetal ovary undergo X chromosome reactivation. The signal for reactivation is thought to emanate from the genital ridge, but it is unclear whether it is specific to the developing ovary. To determine whether the signals are present in the developing testis as well as the ovary, we examined the expression of X-linked genes in germ cells from XXY male mice. To facilitate this analysis, we generated XXY and XX fetuses carrying X chromosomes that were differentially marked and subject to nonrandom inactivation. This pattern of nonrandom inactivation was maintained in somatic cells but, in XX as well as XXY fetuses, both parental alleles were expressed in germ cell-enriched cell populations. Because testis differentiation is temporally and morphologically normal in the XXY testis and because all germ cells embark upon a male pathway of development, these results provide compelling evidence that X chromosome reactivation in fetal germ cells is independent of the somatic events of sexual differentiation. Proper X chromosome dosage is essential for the normal fertility of male mammals, and abnormalities in germ cell development are apparent in the XXY testis within several days of X reactivation. Studies of exceptional germ cells that survive in the postnatal XXY testis demonstrated that surviving germ cells are exclusively XY and result from rare nondisjunctional events that give rise to clones of XY cells. (+info)
Influence of nitric oxide modulators on cholinergically stimulated hormone release from mouse islets.
(18/15570)
1. We have investigated, with a combined in vitro and in vivo approach, the influence on insulin and glucagon release stimulated by the cholinergic, muscarinic agonist carbachol of different NO modulators, i.e. the nitric oxide synthase (NOS) inhibitors NG-nitro-L-arginine methyl ester (L-NAME), NG-monomethyl-L-arginine (L-NMMA) and 7-nitroindazole as well as the intracellular NO donor hydroxylamine. 2. At basal glucose (7 mM) carbachol dose-dependently stimulated insulin release from isolated islets with a half-maximal response at approximately 1 microM of the agonist. In the presence of 5 mM L-NAME (a concentration that did not influence basal insulin release) the insulin response was markedly increased along the whole dose-response curve and the threshold for carbachol stimulation was significantly lowered. 3. Carbachol-stimulated islets displayed an increased insulin release and a suppressed glucagon release in the presence of L-NAME, L-NMMA or 7-nitroindazole. Significant suppression of glucagon release (except for L-NAME) was achieved at lower concentrations (approximately 0.1-0.5 mM) of the NOS inhibitors than the potentiation of insulin release (1.0-5.0 mM). The intracellular NO donor hydroxylamine dose-dependently inhibited carbachol-induced insulin release but stimulated glucagon release only at a low concentration (3 microM). 4. In islets depolarized with 30 mM K+ in the presence of the KATP channel opener diazoxide, NOS inhibition by 5 mM L-NAME still markedly potentiated carbachol-induced insulin release (although less so than in normal islets) and suppressed glucagon release. 5. In vivo pretreatment of mice with L-NAME was followed by a markedly increased insulin release and a reduced glucagon release in response to an i.v. injection of carbachol. 6. The data suggest that NO is a negative modulator of insulin release but a positive modulator of glucagon release induced by cholinergic muscarinic stimulation. These effects were also evident in K+ depolarized islets and thus NO might exert a major influence on islet hormone secretion independently of membrane depolarization events. (+info)
The role of the sympathetic nervous system in the regulation of leptin synthesis in C57BL/6 mice.
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The objectives of this study were to determine whether leptin synthesis is regulated by the sympathetic nervous system and if so whether beta-adrenergic receptors mediate this effect. We show that sympathetic blockade by reserpine increases leptin mRNA levels in brown but not white adipose tissue, while acute cold-exposure decreases leptin expression 10-fold in brown adipose tissue and 2-fold in white adipose tissue. The cold-induced reduction in leptin mRNA can be prevented by a combination of propranolol and SR 59230A but not by either antagonist alone, indicating that beta3-adrenergic receptors and classical beta1/beta2-adrenergic receptors both mediate responses to sympathetic stimulation. Circulating leptin levels reflect synthesis in white adipose tissue but not in brown adipose tissue. (+info)
Somatostatin induces hyperpolarization in pancreatic islet alpha cells by activating a G protein-gated K+ channel.
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Somatostatin inhibits glucagon-secretion from pancreatic alpha cells but its underlying mechanism is unknown. In mouse alpha cells, we found that somatostatin induced prominent hyperpolarization by activating a K+ channel, which was unaffected by tolbutamide but prevented by pre-treating the cells with pertussis toxin. The K+ channel was activated by intracellular GTP (with somatostatin), GTPgammaS or Gbetagamma subunits. It was thus identified as a G protein-gated K+ (K(G)) channel. RT-PCR and immunohistochemical analyses suggested the K(G) channel to be composed of Kir3.2c and Kir3.4. This study identified a novel ionic mechanism involved in somatostatin-inhibition of glucagon-secretion from pancreatic alpha cells. (+info)
Innate and acquired humoral immunities to influenza virus are mediated by distinct arms of the immune system.
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"Natural" Igs, mainly IgM, comprise part of the innate immune system present in healthy individuals, including antigen-free mice. These Igs are thought to delay pathogenicity of infecting agents until antigen-induced high affinity Igs of all isotypes are produced. Previous studies suggested that the acquired humoral response arises directly from the innate response, i.e., that B cells expressing natural IgM, upon antigen encounter, differentiate to give rise both to cells that secrete high amounts of IgM and to cells that undergo affinity maturation and isotype switching. However, by using a murine model of influenza virus infection, we demonstrate here that the B cells that produce natural antiviral IgM neither increase their IgM production nor undergo isotype switching to IgG2a in response to the infection. These cells are distinct from the B cells that produce the antiviral response after encounter with the pathogen. Our data therefore demonstrate that the innate and the acquired humoral immunities to influenza virus are separate effector arms of the immune system and that antigen exposure per se is not sufficient to increase natural antibody production. (+info)
Norepinephrine, released from sympathetic neurons, and epinephrine, released from the adrenal medulla, participate in a number of physiological processes including those that facilitate adaptation to stressful conditions. The thymus, spleen, and lymph nodes are richly innervated by the sympathetic nervous system, and catecholamines are thought to modulate the immune response. However, the importance of this modulatory role in vivo remains uncertain. We addressed this question genetically by using mice that lack dopamine beta-hydroxylase (dbh-/- mice). dbh-/- mice cannot produce norepinephrine or epinephrine, but produce dopamine instead. When housed in specific pathogen-free conditions, dbh-/- mice had normal numbers of blood leukocytes, and normal T and B cell development and in vitro function. However, when challenged in vivo by infection with the intracellular pathogens Listeria monocytogenes or Mycobacterium tuberculosis, dbh-/- mice were more susceptible to infection, exhibited extreme thymic involution, and had impaired T cell function, including Th1 cytokine production. When immunized with trinitrophenyl-keyhole limpet hemocyanin, dbh-/- mice produced less Th1 cytokine-dependent-IgG2a antitrinitrophenyl antibody. These results indicate that physiological catecholamine production is not required for normal development of the immune system, but plays an important role in the modulation of T cell-mediated immunity to infection and immunization. (+info)
Genetic control of cytolytic T-lymphocyte responses. I. Ir gene control of the specificity of cytolytic T-lymphocyte responses to trinitrophenyl-modified syngeneic cells.
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The ability of cytotoxic T lymphocytes (CTL) induced in vitro to trinitrophenyl (TNP)-modified syngeneic cells to cross-reactively lyse a TNP allogeneic spleen target varies among inbred mouse strains. The cross-reactive CTL phenotype was found to be histocompatibility 2 (H-2) linked and to be dominant in F1 hybrid mice. All strains investigated demonstrated cross-reactivity except for some strains bearing portions of the H-2k haplotype. The gene(s) controlling this response maps to the K and/or I-A region of the H-2 complex. We have termed the immune response (Ir) gene responsible for controlling the specificity of CTL induced to TNP-modified syngeneic cells Ir-X-TNP. (+info)
Genetic control of cytolytic t-lymphocyte responses. II. The role of the host genotype in parental leads to F1 radiation chimeras in the control of the specificity of cytolytic T-lymphocyte responses to trinitrophenyl-modified syngeneic cells.
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Bone marrow cells from C3H (H-2k) mice, a strain that does not exhibit cross-reactive lysis of trinitrophenyl (TNP)-modified allogeneic targets, were allowed to mature in heavily irradiated (B6 times C3H)F1 (H-2b/k) recipients, an F1 hybrid that does demonstrate cross-reactive lysis. Spleen cells from these chimeric mice were removed after 3-4 mo and by H-2 typing shown to be of C3H origin. These cells were found to be tolerant to B6 alloantigens by mixed lymphocyte reaction and cell-mediated cytotoxicity and, when stimulated in vitro with TNP-modified syngeneic cells, now cross-reactively lysed TNP-modified allogeneic targets. These studies demonstrate that the host environment where T cells differentiate influences the specificity of the primary cytolytic T-lymphocyte (CTL) response to TNP-modified syngeneic antigens. (+info)