Biomedical subjects

G Levi

Publications and source records attributed to G Levi.

At least 19 recordsLinked to original sources

PubMed1999

Expression and translocation of protein kinase C isoforms in rat microglial and astroglial cultures.

Cellular distribution and activation by phorbol myristate acetate (PMA) of classical (alpha, betaI, betaII,gamma), novel (delta, epsilon, theta, eta), and atypical (zeta, iota) protein kinase C (PKC) isoforms were studied in cultured rat neonatal microglial and astroglial cells by Western blot analysis. Among the classical isoforms, only betaII was expressed in microglia and astrocytes in the same abundance. The expression of betaI in microglia was less abundant, while PKCalpha was not detectable in this cell type. PKCgamma was absent in both cell populations. A different pattern of expression was also found for novel and atypical isoenzymes: Both cell types expressed delta, theta, eta, zeta, and iota isoforms, but PKCepsilon was absent in microglia and the expression of PKCzeta and PKCiota in these cells was low compared to astrocytes. The pattern of PKC distribution in cytosolic and particulate fractions as well as activation by short (10 min) and prolonged (4 hr) PMA treatment in both cell types were similar. On the whole, in comparison with astrocytes, PKC in microglial cells was less expressed, both in terms of number of isoforms and level of expression. The microglial profile of PKC isoforms differed from that of rat peritoneal macrophages, which did express PKCalpha. Preliminary evidence suggests that the ability of PMA to enhance cyclic AMP responses in astrocytes, but not in microglia, is related to the different pattern of expression of PKCalpha and PKCepsilon in the two cell types.

Animals↗

PubMed1999

Opposite effects of interferon-gamma and prostaglandin E2 on tumor necrosis factor and interleukin-10 production in microglia: a regulatory loop controlling microglia pro- and anti-inflammatory activities.

Following brain injury, microglial cells produce pro- and anti-inflammatory cytokines, such as tumor necrosis factor (TNF) and interleukin-10 (IL-10). IL-10 provides an efficient autocrine mechanism for controlling microglia activation. To elucidate the mechanisms that regulate the cytokine profile of microglia, we examined the effects of several immunomodulators on IL-10 and TNF production by cultured mouse microglia. Lipopolysaccharide (LPS) was the only inducer of IL-10 and TNF gene expression and secretion. The T helper 1-type cytokine interferon-gamma (IFN-gamma) induced TNF transcripts, but not TNF secretion, and suppressed LPS-induced IL-10 mRNA and secretion by microglia. Opposite to IFN-gamma, the lipid mediator prostaglandin E2 (PGE2) enhanced the LPS-induced production of IL-10 and inhibited that of TNF. The effects of PGE2 on cytokine gene expression and secretion were antagonized by IFN-gamma. Agents that increase cAMP levels mimicked the action of PGE2 on cytokine secretion, indicating the involvement of cAMP-coupled prostaglandin receptors. In conclusion, IFN-gamma and PGE2, two mediators released at inflammatory sites, differentially regulate the production of a proinflammatory and an anti-inflammatory cytokine in microglia. We suggest that the activity and role of microglia in the damaged CNS could be finely tuned by the local concentration ratio of these mediators.

Animals↗

PubMed1999

Gene transfer in astrocytes: comparison between different delivering methods and expression of the HIV-1 protein Nef.

To identify a good system to introduce foreign genes into normal and tumoral astrocytes, we studied the efficiency of two chemical methods, calcium phosphate precipitation and lipofection, and of a viral-mediated transfer by a vector derived from the highly attenuated modified vaccinia virus Ankara (MVA). Using the beta-galactosidase (beta-gal) gene (lacZ) as reporter, we searched for optimal experimental conditions to obtain an efficient gene transfer into human embryonic and neonatal rat astrocytes and into a human astrocytoma cell line (U373 MG). The beta-gal protein production was evaluated by cytochemical staining and enzymatic activity assay. Among chemical methods, lipofection was the most efficient system to transfect astrocytes in providing up to 60% of beta-gal-positive cells in all the cell types analyzed. MVA infection also proved to be an efficient system to introduce heterologous genes into human embryonic astrocytes that appeared 80-100% positive 48-96 hr after an infection at a multiplicity of 1-10. In contrast, only a limited infection was observed with rat astrocytes, human astrocytoma cells, and human leptomeningeal cells. A recombinant MVA vector expressing the human immunodeficiency virus-1 (HIV-1) regulatory protein Nef was used to transfect human embryonic astrocytes, and the resulting Nef expression was compared with that detected after lipofection in the same cells. By Western blot analysis, Nef expression was observed in human astrocytes 24-96 hr after infection and was similar to that present in stably HIV-1-infected astrocytoma cells. Lipofection resulted in lower Nef expression. In spite of these promising results, the negative effects of MVA infection on cell viability and the possibility that a productive infection occurs in human embryonic astrocytes limit the use of this vector for gene delivery in developmentally immature human glial cells.

Animals↗

PubMed1999

Localization and expression of integrin subunits in the embryoid bodies of F9 teratocarcinoma cells.

F9 embryonal carcinoma cells can differentiate in vitro into either parietal (PE) or visceral (VE) endoderm, depending upon specific retinoic acid (RA) treatment and growth conditions. In differentiated aggregates of F9 cells (EB), the VE is a polarized monolayer surrounding a core of undifferentiated cells. Within 7 days of treatment the cells organize their cytoskeleton and synthesize large amounts of extracellular matrix proteins to form a basal lamina under the newly formed epithelium. All these changes are likely to involve integrin expression and organization. In this study we have analyzed the spatio-temporal changes in the pattern and level of expression of beta1, beta4, alpha5, alpha6A, and alpha6B integrin subunits. We found that the organization of the VE monolayer in F9 aggregates involves both qualitative and quantitative changes in integrin expression. beta1 is downregulated and accumulates in the forming epithelium. The same occurs for alpha5, although its location on the surface of the aggregate appears to be transient as in fully differentiated EB its distribution is uniform. beta4 and alpha6A are also mainly localized in the VE but they are undetectable in undifferentiated aggregates and their expression is induced by RA treatment. An important exception is represented by alpha6B whose distribution and expression remain almost unchanged throughout treatment.

Animals↗

PubMed1999

Thyroid hormone effects on Krox-24 transcription in the post-natal mouse brain are developmentally regulated but are not correlated with mitosis.

Krox-24 (NGFI-A, Egr-1) is an immediate-early gene encoding a zinc finger transcription factor. As Krox-24 is expressed in brain areas showing post-natal neurogenesis during a thyroid hormone (T3)-sensitive period, we followed T3 effects on Krox-24 expression in newborn mice. We analysed whether regulation was associated with changes in mitotic activity in the subventricular zone and the cerebellum. In vivo T3-dependent Krox-24 transcription was studied by polyethylenimine-based gene transfer. T3 increased transcription from the Krox-24 promoter in both areas studied at post-natal day 2, but was without effect at day 6. An intact thyroid hormone response element (TRE) in the Krox-24 promoter was necessary for these inductions. These stage-dependent effects were also seen in endogenous Krox-24 mRNA levels: activation at day 2 and no effect at day 6. Moreover, similar results were obtained by examining beta-galactosidase expression in heterozygous mice in which one allele of the Krox-24 gene was disrupted with an inframe Lac-Z insertion. However, bromodeoxyuridine incorporation showed mitosis to continue through to day 6. We conclude first, that T3 activates Krox-24 transcription during early post-natal mitosis but that this effect is extinguished as development proceeds and second, loss of T3-dependent Krox-24 expression is not correlated with loss of mitotic activity.

Animals↗

PubMed1999

Down-regulation of microglial cyclo-oxygenase-2 and inducible nitric oxide synthase expression by lipocortin 1.

1. Activated microglial cells are believed to play an active role in most brain pathologies, during which they can contribute to host defence and repair but also to the establishment of tissue damage. These actions are largely mediated by microglial secretory products, among which are prostaglandins (PGs) and nitric oxide (NO). 2. The anti-inflammatory protein, lipocortin 1 (LC1) was reported to have neuroprotective action and to be induced by glucocorticoids in several brain structures, with a preferential expression in microglia. In this paper we tested whether the neuroprotective effect of LC1 could be explained by an inhibitory effect on microglial activation. 3. We have previously shown that bacterial endotoxin (LPS) strongly stimulates PGE2 and NO production in rat primary microglial cultures, by inducing the expression of the key enzymes cyclo-oxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS), respectively. 4. Dexamethasone (DEX, 1-100 nM) and LC1-derived N-terminus peptide (peptide Ac2-26, 1-100 microg ml(-1)) dose-dependently inhibited the production of both PGE2 and NO from LPS-stimulated microglia. The inhibitory effects of DEX on NO and of the peptide on NO and PGE2 synthesis were partially abrogated by a specific antiserum, raised against the N-terminus of human LC1. The peptide Ac2-26 did not affect arachidonic acid release from control and LPS-stimulated microglial cultures. 5. Western blot experiments showed that the LPS-induced expression of COX-2 and iNOS was effectively down-regulated by DEX (100 nM) and peptide Ac2-26 (100 microg ml(-1)). 6. In conclusion, our findings support the hypothesis that LC1 may foster neuroprotection by limiting microglial activation, through autocrine and paracrine mechanisms.

Animals↗

PubMed1999

[Preparation and amplification of cDNAs from a single cell].

OBJECTIVE: To set up the technique by which gene expression analysis could be done from a few cells so as to resolve the challenging problem between increasingly needs of cellular gene expression pattern analysis and the difficulty of obtaining homogeneous cell materials in some cases. METHODS: Pick up a single cell to do reverse transcription directly, and then amplify cDNA in sequence-independent manner by using a single primer containing oligo (dT) and test the representation of cDNA. RESULTS: Representatively amplified cDNAs from a single HL-60 cell. CONCLUSION: Producing whole cellular cDNAs probe from samples as small as a single cell could provide an ideal way to analyze differential gene expression in heterogeneous highly differentiating system and to establish cell type/tissue type specific gene expression profiles.

DNA, Complementary↗

PubMed1998

Inhibition of cancer cell growth by all-trans retinoic acid and its analog N-(4-hydroxyphenyl) retinamide: a possible mechanism of action via regulation of retinoid receptors expression.

In order to better understand the mechanisms that underlie the antiproliferative effect of retinoids, we have examined the response of human carcinoma cell lines to all-trans retinoic acid (RA) and N-(4-hydroxyphenyl) retinamide (4HPR) in terms of cell growth, apoptosis and regulation of retinoic acid receptors (RARs) and retinoid X receptors (RXRs) mRNA. GLC82 (lung adenocarcinoma), BGC823 (stomach adenocarcinoma) and EC109 (esophageal squamous carcinoma) cells were treated with 10 microM of RA or 4HPR for various length of time and analyzed. The results show that growth inhibition by RA and 4HPR in GLC82 and BGC823 cells correlates with the induction of RARbeta2 gene, whereas RA resistance in EC109 cells parallels loss of RARbeta2 induction. Exogenous RARbeta2 expression did not restore RA responsiveness in EC109 cells, but potentiated 4HPR-induced growth inhibition, suggesting that 4HPR acts at least in part via the RARbeta receptor. We speculate that the loss of RARbeta2 inducibility in EC109 cells may be due to an unknown repressor.

Adenocarcinoma↗

PubMed1998

Interferon gamma gene expression in rat central nervous system glial cells.

The expression of interferon gamma (TFN-gamma) mRNA in purified cultures of glial cells and leptomeningeal fibroblasts from the neonatal rat brain was analysed using semi-quantitative reverse transcriptase-polymerase chain reaction. IFN-gamma specific transcripts were clearly detected in rat astrocytes and were upregulated after treatment with IFN-gamma itself or cycloheximide. In microglial cells, IFN-gamma transcripts were barely detectable in basal conditions and were upregulated by lipopolysaccharide and, to a lesser extent, by IFN-gamma or cycloheximide. IFN-gamma mRNA was neither detected not inducible in oligodendrocytes and leptomeningeal cells. The demonstration that IFN-gamma is expressed in astrocytes and microglia widens the putative role of these cells in local immunoregulation and antiviral responses.

Animals↗

PubMed1998

Virological and molecular parameters of HIV-1 infection of human embryonic astrocytes.

Two different strains of HIV-1, the lymphotropic HIV-IIIB and the monocytotropic HIV-Ba-L, were able to infect tertiary cultures of astrocytes established from the human embryonic brain. The infection did not require contact with infected cells, as astrocytes were exposed to infectious cell-free supernatants. Except for an early transient peak of p24 consistently observed after infection with HIV-Ba-L, the infection of astrocytes appeared to be nonproductive. However, viral production was always observed when infected astrocytes were cocultured with permissive cells (CEM-SS or monocytes). To exclude the possibility that undetectable levels of virus are chronically produced by astrocytes, we exposed permissive cells to p24 negative supernatants taken from infected cultures. In such conditions permissive cells were never infected. Infection of astrocytes by HIV-1 was further supported by the finding that provirus persisted in these cells. Indeed, by a nested PCR, we detected HIV-1 DNA even one month after infection. Moreover, at the transcriptional level we observed expression of the multiply spliced RNA (tat and nef primers). Noteworthy, this pattern of HIV-1 expression did not change appreciably when astrocytes were pretreated and cultivated in the presence of IL-1 beta. Altogether, our data support the concept that astrocytes may play a role in the spread of HIV-1 infection within the brain and in the pathogenesis of neuro-AIDS.

Astrocytes↗

PubMed1998

Regulation of prostanoid synthesis in microglial cells and effects of prostaglandin E2 on microglial functions.

Brain prostanoid levels are normally low but can increase after ischemia and during inflammatory and infectious diseases. High prostanoid levels can affect brain function in several ways. In particular, prostaglandin E2 (PGE2) might exert both immunodepressive and proinflammatory actions. The present short review focuses on the regulation of prostanoid synthesis in microglial cultures and on the possible role of PGE2 in the down-regulation of microglial activation induced by lipopolysaccharide (LPS). Our studies were carried out using purified mouse or rat microglial cultures. LPS induced a dose-dependent expression of the inducible isoform of cyclooxygenase (COX-2), both in neonatal and adult microglial cultures. In the latter, the inducibility of COX-2 increased with time in culture, paralleling the acquisition of a more 'activated' microglial phenotype, and appeared to account for the time-dependent increase in the PGE2/TXB2 production ratio. The LPS-induced COX-2 expression and prostanoid production were down-regulated by potentially neurotoxic agents, such as nitric oxide (NO), the proinflammatory cytokine IFN-gamma (which acted both directly and indirectly, through its NO-inducing activity) and the HIV regulatory protein tat. On the other hand, COX-2 expression was up-regulated by the macrophage-deactivating cytokine TGF-beta 1, by exogenous PGE2 itself, which acted through EP2 receptors linked to cyclic AMP generation, and by non steroidal anti-inflammatory drugs. Interestingly, PGE2 utilized the same EP2 receptor-mediated signal transduction mechanism to down-regulate the expression of the inducible NO synthase and the production of NO. Largely, but not exclusively, through its effect on cyclic AMP, PGE2 can also: i) depress the expression of major histocompatibility complex class II antigens and of the costimulatory molecule B7-2; ii) down-regulate TNF and up-regulate IL-10 microglial production; iii) inhibit microglial IL-12 secretion. These observations, together with literature data on in vivo models of central nervous system (CNS) diseases, suggest a neuroprotective role of PGE2 in pathological conditions.

Animals↗

PubMed1998

Microglia as effector cells in brain damage and repair: focus on prostanoids and nitric oxide.

Microglial cells are believed to play an active role in brain inflammatory, immune and degenerative processes. Depending on the magnitude of microglial reaction, on the type of stimulus and on the concurrence of other local factors, microglia can contribute to host defence and repair, or to the establishment and maintenance of brain damage. Many of the effects of microglial cells can be ascribed to the numerous substances that these cells can synthesize and release in response to a variety of stimuli (cytokines, pro-inflammatory substances, neurotransmitters, toxins, etc.). The present article deals with two classes of compounds that activated microglial cells can produce in large amounts: prostanoids (that derive from arachidonic acid through the cyclooxygenase pathway), and nitric oxide (that is synthesized from arginine by nitric oxide synthase). Prostanoids and nitric oxide have a number of common targets, on which they may exert similar or opposite actions, and have a crucial role in the regulation of inflammation, immune responses and cell viability. Their synthesis can massively increase when the inducible isoforms of cyclooxygenase and nitric oxide synthase are expressed. The metabolic pathways of prostanoids and nitric oxide are finely tuned by the respective end-products, by cyclic AMP and by a number of exogenous factors, such as cytokines, glucocorticoids, lipocortin-1 and others. Some of these factors (e.g. transforming growth factor-beta 1, interleukin-10, lipocortin-1) may be secreted by microglial cells themselves, and act in an autocrine-paracrine way. In view of the neuroprotective role attributed to some prostaglandins and to the cytotoxicity of excessive levels of nitric oxide or its derivatives, the balance between prostanoid and nitric oxide levels may be crucial for orienting microglial reactions towards neuroprotection or neurotoxicity.

Animals↗

PubMed1998

Size, diffusibility and transfection performance of linear PEI/DNA complexes in the mouse central nervous system.

Currently in vivo gene delivery by synthetic vectors is hindered by the limited diffusibility of complexes in extra-cellular fluids and matrices. Here we show that certain formulations of plasmid DNA with linear polyethylenimine (22 kDa PEI, ExGene 500) can produce complexes that are sufficiently small and stable in physiological fluids so as to provide high diffusibility. When plasmid DNA was formulated with 22 kDa PEI in 5% glucose, it produced a homogeneous population of complexes with mean diameters ranging from 30 to 100 nm according to the amount of PEI used. In contrast, formulation in physiological saline produced complexes an order of magnitude greater (> or = 1 micron). Intraventricular injection of complexes formulated in glu-cose showed the complexes to be highly diffusible in the cerebrospinal fluid of newborn and adult mice, diffusing from a single site of injection throughout the entire brain ventricular spaces. Transfection efficiency was followed by histochemistry of beta-galactosidase activity and double immunocytochemistry was used to identify the cells transfected. Transgene expression was found in both neurons and glia adjacent to ventricular spaces. Thus, this method of formulation is promising for in vivo work and may well be adaptable to other vectors and physiological models.

Animals↗

PubMed1998

Polyethylenimine-based intravenous delivery of transgenes to mouse lung.

Generally, cationic vector-based intravenous delivery of DNA is hindered by interactions of positively charged complexes with serum proteins. However, if optimally formulated, cationic vectors can provide reasonable levels of transfection in the lung either by intravenous or intrapulmonary routes. We investigated the in vivo transfection capacity of a cationic polymer: linear, 22 kDa polyethylenimine. PEI/DNA complexes were formulated in 5% glucose and delivered into adult mice through the tail vein. Two marker genes were used, beta-galactosidase and luciferase. High levels of luciferase expression (10(7) RLU/mg protein) were found in the lung when DNA was complexed with PEI at a ratio of 4 nitrogen equivalents per DNA phosphate. Lower levels of transfection were found in the heart, spleen, liver and kidney. Expression was dose- and time-dependent in all tissues examined. In the lung, beta-galactosidase staining showed transgene expression in clusters of 10 or more pulmonary cells including the alveolar endothelium, squamous and great alveolar epithelial cells (type I and II pneumocytes) and septal cells. These findings indicate that the complexes pass the capillary barrier in the lung. Although the delivery mechanism requires elucidation, linear PEI has promise as a vector for intravenous transfer of therapeutic genes.

Animals↗

PubMed1998

Follicular bisection in hair transplantation surgery: an in vitro model.

The aim of this study was to evaluate, in an in vitro model, the survival and growth rates of transversely sectioned human hair follicles to assess experimentally the soundness of this approach as a future possible method for "duplicating" available donor hair grafts in hair transplantation procedures. A total of 300 human anagen hair follicles was obtained from 10 healthy male patients. Follicles were thus randomly assigned to one of the following groups: group A (control; n = 100 follicles), cultured intact as dissected, and group B (experimental; n = 200 follicles), transversely transected, parallel to the epidermal surface and immediately below the bulge area, to obtain 200 lower-half follicles and 200 upper-half follicles. Isolated hair follicles from both groups were maintained in culture for 10 days. The length of each follicle was measured immediately following isolation and at the end of the 10-day culture period. No statistically significant differences were found between the growth rate of intact follicles (mean 10-day growth rate = 2.71 mm) and of lower-half follicles (mean 10-day growth-rate = 2.64 mm), whereas a statistically significant difference was found between the growth rate of follicles from the two above-mentioned groups and the growth rate of the "upper-half" follicles (mean 10-day growth rate = 1.07 mm). Histologic analysis demonstrated that both intact and lower-half follicles maintained a normal histologic appearance, whereas in upper-half follicle sections we invariably detected a region of intense cell proliferation, reminiscent of a regenerated follicular papilla, surrounding the lowermost part of the follicle. In our opinion, the reported in vitro survival rate of transected human hair follicles might represent an interesting starting point in striving to augment the number of donor hairs available during a hair transplantation procedure.

Adult↗

PubMed1998

Synergistic stimulation of MHC class I and IRF-1 gene expression by IFN-gamma and TNF-alpha in oligodendrocytes.

In order to understand the molecular basis of the synergistic action of interferon gamma (IFN-gamma) and tumour necrosis factor alpha (TNF-alpha) on rat oligodendrocyte development, we studied some aspects of the signalling pathways involved in the regulation of the major histocompatibility complex (MHC) class I and the interferon regulatory factor 1 (IRF-1) gene expression. Two well-defined inducible enhancers of the MHC class I gene promoter, the MHC class I regulatory element (MHC-CRE) and the interferon consensus sequence (ICS), were analysed. Neither IFN-gamma nor TNF-alpha was capable of inducing MHC-CRE binding activity when administrated alone. Following the exposure of oligodendrocytes to IFN-gamma, TNF-R1 expression was transcriptionally induced by the binding of signal transducer and activator of transcription (STAT-1) homodimers to the IFN-gamma activated site (GAS) present in the gene promoter. The upregulation of TNF-R1 allowed TNF-alpha to induce the binding of nuclear factor-kappaB (NF-kappaB) to the MHC-CRE site. With respect to ICS element, IFN-gamma induced IRF-1 binding, that was further enhanced upon co-treatment with TNF-alpha. The existence of a synergism between IFN-gamma and TNF-alpha in stimulating IRF-1 expression at the transcriptional level was supported by IRF-1 promoter analysis: IFN-gamma directly induced the binding of STAT-1 homodimers to the GAS element, while NF-kappaB binding to the kappaB sequence was activated by TNF-alpha only after IFN-gamma treatment. This transcriptional regulation of IRF-1 gene by IFN-gamma and TNF-alpha was confirmed at the mRNA level. The synergism demonstrated in the present study highlights the importance of cytokine interactions in magnifying their biological effects during brain injury and inflammation.

Animals↗

PubMed1998

Retinoic acid receptor gamma1 (RARgamma1) levels control RARbeta2 expression in SK-N-BE2(c) neuroblastoma cells and regulate a differentiation-apoptosis switch.

Vitamin A and its derivatives (retinoids) have profound effects on the proliferation and differentiation of many cell types and are involved in a diverse array of developmental and physiological regulatory processes, including those responsible for the development of the mature nervous system. Retinoid signals are mediated by retinoic acid (RA) receptors (RARs) and retinoid X receptors (RXRs), which show distinct spatio-temporal patterns of expression during development and in adult tissues. We have used SK-N-BE2(c) neuroblastoma cells to study the effects of reciprocal regulation of expression of various RARs. We show that in these cells RARgamma1 acts as a repressor of RARbeta2 transcription in the absence of an agonist. In the presence of RA, the expression of RARgamma1 is reduced and that of RARbeta2 is induced. Overexpression of RARgamma1 neutralizes the effects of RA on RARbeta induction. Expression of an RARgamma1-specific antisense construct leads to the constitutive expression of RARbeta2. Although both overexpression of RARgamma1 and its reduction of expression can result in inhibition of cell proliferation, they induce different morphological changes. Reduction of RARgamma1 (and induction of RARbeta) leads to increased apoptosis, whereas RARgamma1 overexpression leads to differentiation in the absence of apoptosis. Thus, RARgamma1 appears to control a differentiation-apoptosis switch in SK-N-BE2(c) neuroblastoma cells.

Apoptosis↗

PubMed1998

Multiple pituitary and ovarian defects in Krox-24 (NGFI-A, Egr-1)-targeted mice.

The zinc finger transcription factor Krox-24 (NGFI-A, Egr-1) is encoded by an immediate-early serum response gene expressed in various physiological situations and tissues. To investigate its function, we have created a null allele. Mice homozygous for the mutation have a reduced body size, and both males and females are sterile. These phenotypes were related to defects in the anterior pituitary of both sexes and in the ovary. In the pituitary, two cell lineages expressing Krox-24 are differentially affected by the mutation: somatotropes present abnormal cytological features and are reduced in number, consistent with the decreased GH content observed in these animals; in contrast gonadotropes are normal in number, but specifically fail to synthesize the beta-subunit of LH. In the ovary, LH receptor expression is prevented, indicating an involvement of Krox-24 at two levels at least of the pituitary-gonadal axis. Our data, together with the results of a previous report describing another Krox-24 mutant allele, suggest that Krox-24 may have two distinct molecular functions in the anterior pituitary: transcriptional activation of the LHbeta gene in gonadotropes and control of cell proliferation and/or survival in somatotropes by unknown mechanisms.

Animals↗