c-fos proto-oncogene expression in the nervous system during mouse development

c-Fos downregulation positively regulates EphA5 expression in a congenital hypothyroidism rat model

The EphA5 receptor is well established as an axon guidance molecule during neural system development and plays an important role in dendritic spine formation and synaptogenesis. Our previous study has showed that EphA5 is decreased in the developing brain of congenital hypothyroidism (CH) and the EphA5 promoter methylation modification participates in its decrease. c-Fos, a well-kown transcription factor, has been considered in association with brain development. Bioinformatics analysis showed that the EphA5 promoter region contained five putative c-fos binding sites. The chromatin immunoprecipitation (ChIP) assays were used to assess the direct binding of c-fos to the EphA5 promoter. Furthermore, dual-luciferase assays showed that these three c-fos protein binding sites were positive regulatory elements for EphA5 expression in PC12 cells. Moreover, We verified c-fos positively regulation for EphA5 expression in CH model. Q-PCR and Western blot showed that c-fos overexpression could upregulate EphA5 expression in hippocampal neurons of rats with CH. Our results suggest that c-fos positively regulates EphA5 expression in CH rat model.

Brain development is impaired in c-fos -/- mice

c-Fos is a proto-oncogene involved in diverse cellular functions. Its deregulation has been associated to abnormal development and oncogenic progression. c-fos−/− mice are viable but present a reduction in their body weight and brain size. We examined the importance of c-Fos during neocortex development at 13.5, 14.5 and 16.5 days of gestation. At E14.5, neocortex thickness, apoptosis, mitosis and expression of markers along the different stages of Neural Stem Progenitor Cells (NSPCs) differentiation in c-fos−/− and wild-type mice were analyzed. A ∼15% reduction in the neocortex thickness of c-fos−/− embryos was observed which correlates with a decrease in the number of differentiated cells and an increase in apoptosis at the ventricular zone. No difference in mitosis rate was observed, although the mitotic angle was predominantly vertical in c-fos−/− embryos, suggesting a reduced trend of NSPCs to differentiate. At E13.5, changes in differentiation markers start to be apparent and are still clearly observed at E16.5. A tendency of more AP-1/DNA complexes present in nuclear extracts of cerebral cortex from c-fos−/− embryos with no differences in the lipid synthesis activity was found. These results suggest that c-Fos is involved in the normal development of NSPCs by means of its AP-1 activity.

Redox control in mammalian embryo development

The development of an embryo constitutes a complex choreography of regulatory events that underlies precise temporal and spatial control. Throughout this process the embryo encounters ever changing environments, which challenge its metabolism. Oxygen is required for embryogenesis but it also poses a potential hazard via formation of reactive oxygen and reactive nitrogen species (ROS/RNS). These metabolites are capable of modifying macromolecules (lipids, proteins, nucleic acids) and altering their biological functions. On one hand, such modifications may have deleterious consequences and must be counteracted by antioxidant defense systems. On the other hand, ROS/RNS function as essential signal transducers regulating the cellular phenotype. In this context the combined maternal/embryonic redox homeostasis is of major importance and dysregulations in the equilibrium of pro- and antioxidative processes retard embryo development, leading to organ malformation and embryo lethality. Silencing the in vivo expression of pro- and antioxidative enzymes provided deeper insights into the role of the embryonic redox equilibrium. Moreover, novel mechanisms linking the cellular redox homeostasis to gene expression regulation have recently been discovered (oxygen sensing DNA demethylases and protein phosphatases, redox-sensitive microRNAs and transcription factors, moonlighting enzymes of the cellular redox homeostasis) and their contribution to embryo development is critically reviewed.

A novel mouse c-fos intronic promoter that responds to CREB and AP-1 is developmentally regulated in vivo

Background

The c-fos proto-oncogene is an archetype for rapid and integrative transcriptional activation. Innumerable studies have focused on the canonical promoter, located upstream from the transcriptional start site. However, several regulatory sequences have been found in the first intron.

Methodology/Principal Findings

Here we describe an extremely conserved region in c-fos first intron that contains a putative TATA box, and functional TRE and CRE sites. This fragment drives reporter gene activation in fibroblasts, which is enhanced by increasing intracellular calcium and cAMP and by cotransfection of CREB or c-Fos/c-Jun expression vectors. We produced transgenic mice expressing a lacZ reporter controlled by the intronic promoter. Lac Z expression of this promoter is restricted to the developing central nervous system (CNS) and the mesenchyme of developing mammary buds in embryos 12.5 days post-conception, and to brain tissue in adults. RT-QPCR analysis of tissue mRNA, including the anlage of the mammary gland and the CNS, confirms the existence of a novel, nested mRNA initiated in the first intron.

Conclusions/Significance

Our results provide evidence for a novel, developmentally regulated promoter in the first intron of the c-fos gene.

Differential activation of c-fos immunoreactivity after hypophysectomy in developing and adult rats

The aim of the present study is to compare c-fos expression in identified hypothalamic vasopressin (AVP) and oxytocin (OT) neurons in developing (PN7 and PN14) and adult rats following hypophysectomy using dual-labeled immunostaining. Our results showed that hypophysectomy induced c-fos expression in supraoptic (SON) and paraventricular (PVN) nuclei in both the developing and adult rats. Few or no positive cells were observed in the same nuclei in sham-operated animals. Quantitative analysis for c-fos and either of the above named neuropeptides revealed that almost all AVP and OT neurons in the adult and PN14 groups expressed c-fos in response to hypophysectomy. In PN7, hypophysectomy also induced all AVP neurons to express c-fos in SON and PVN. However, few OT neurons in the SON and PVN produced c-fos after hypophysectomy. In addition, the time course of c-fos expression was different in the developing and adult rats after hypophysectomy. The c-fos expression in the developing rats exhibited a more prolonged induction in which staining for c-fos persisted for at least 3 days after hypophysectomy compared with that in the adult in which c-fos immunoreactivity disappeared within 24 hr post-lesion. This study demonstrates that c-fos expression after hypophysectomy is regulated differently during development.

Spatio-temporal expression of immediate early genes in the central nervous system of SJL/J mice

Gene products of immediate early genes (IEGs) interact with specific binding sites in promoter regions of inducible and constitutively expressed genes. Thereby, they control transcription of down-stream targets, like pro- and anti-apoptotic genes and matrix-metalloproteinases (MMPs), known to play an important role in development, plasticity, response to injury and repair of the central nervous system (CNS). A real-time quantitative RT-PCR and immunohistochemical investigation was performed to study mRNA expression levels and protein distribution patterns of IEGs in cerebrum, cerebellum, and spinal cord of SJL/J mice between postnatal weeks 1 and 40. A down-regulation of c-jun, NF-kappaB1, Max, Ets-1, and p53 mRNA, and an up-regulation of c-fos mRNA was noticed. Down-regulations of Ets-1 and p53 were most prominent between week 1 and 3. The prominent role in CNS development for c-jun, Ets-1 and Max was supported by immunohistochemistry. One-week-old mice were strongly positive for all three proteins in cerebral cortex, medulla oblongata, and gray matter of the spinal cord. A high staining intensity was detected in the developing granule cell layer of the cerebellum for c-jun and Ets-1, and in the Purkinje cell layer of the cerebellum for Max. In addition to the general down-regulation of most mRNAs, minor up-regulations of all IEG proteins could be detected in restricted parts of the CNS indicating regional variations and differential expression and translation during development. Apoptosis was demonstrated using immunohistochemistry for active caspase-3. The expression patterns of IEGs might represent the key to understand the balance of proteolytic activities by MMPs, myelination, and the induction of apoptosis during the development of the CNS.

Hippocampal expression of c-fos is not essential for spatial learning

The formation of long-term memory is thought to involve underlying changes in synaptic strength. Many studies have focused on the mechanisms of spatial learning behavior in mammals that is critically dependent on the proper function of the hippocampus. Because of the enduring nature of long-term memory, it is thought that gene expression is involved in this process. The immediate early gene (IEG) c-fos encodes a transcription factor. The c-Fos proteins form heterodimeric proteins with the c-Jun family proteins and the resulting AP-1 transcription complex plays a key role in coupling short-term events elicited by stimuli received at the cell membrane to long-term neuroplastic changes by regulating gene expression. c-fos is induced in the hippocampus after spatial learning. Despite this knowledge, the precise role of c-fos in memory formation and the underlying mechanisms remain unknown. To start investigating the role of c-fos in learning and memory and underlying mechanisms, we evaluated spatial learning capabilities using mice carrying a hippocampal region-specific mutation of c-fos. We found that the c-fos mutant mice exhibit normal spatial learning behaviors in both the Morris water maze and the Barnes maze tests compared to control mice. Our results suggest that hippocampal c-fos expression is not essential for spatial learning.

CROC-4: a novel brain specific transcriptional activator of c-fos expressed from proliferation through to maturation of multiple neuronal cell types

A novel, brain-specific cDNA, denoted CROC-4, was cloned from human brain by a contingent replication of cDNA procedure capable of detecting transcriptional activators of the human c-fos proto-oncogene promoter. CROC-4 encoded an 18-kDa serine/threonine-rich polypeptide containing a P-loop motif and an SH3-binding region with phosphorylation sites for a variety of protein kinases (cdc2, CDK2, MAPK, CDK5, protein kinase C, Ca(2+)/calmodulin protein kinase 2, casein kinase 2) involved in cell proliferation and differentiation. Immunohistochemistry revealed that during early development, expression was associated with proliferating and migrating cells throughout the rodent brain, initially appearing in the proliferative ventricular zones. During late development and in adult human brain, CROC-4 was expressed in diverse brain regions including the thalamus, subthalamic nucleus, corpus callosum, substantia nigra, caudate nucleus, amygdala, and hippocampus. The association of CROC-4 expression with proliferating regions of developing brain and retention in regions of the adult brain, as well as the punctate nuclear location, suggest that CROC-4 participates in brain-specific c-fos signaling pathways involved in cellular remodeling of brain architecture.

c-Fos basal immunoreactivity decreases in rat spinal cord during normal ageing

The pattern of distribution in rat spinal cord and changing pattern during normal ageing of c-Fos expression were investigated by immunohistochemical staining in male Sprague-Dawley rats at the age of 1 week, 5 months and 2 years. c-Fos immunoreactivity was observed diffusely in gray matters in neonatal rats, preferentially located in deep dorsal horn and around central canal. Compared with those of neonatal rats, these cells decreased prominently in adult rats. In aged rats, immunoreactive cells were not seen in any segments. c-Fos immunoreactivity in spinal cord may be related to stress response, functional differentiation, and in part, neuronal death with target dependence. In conclusion, we demonstrated for the first time that c-Fos expression patterns change during normal ageing.

Inducible and constitutive transcription factors in the mammalian nervous system: control of gene expression by Jun, Fos and Krox, and CREB/ATF proteins

This article reviews findings up to the end of 1997 about the inducible transcription factors (ITFs) c-Jun, JunB, JunD, c-Fos, FosB, Fra-1, Fra-2, Krox-20 (Egr-2) and Krox-24 (NGFI-A, Egr-1, Zif268); and the constitutive transcription factors (CTFs) CREB, CREM, ATF-2 and SRF as they pertain to gene expression in the mammalian nervous system. In the first part we consider basic facts about the expression and activity of these transcription factors: the organization of the encoding genes and their promoters, the second messenger cascades converging on their regulatory promoter sites, the control of their transcription, the binding to dimeric partners and to specific DNA sequences, their trans-activation potential, and their posttranslational modifications. In the second part we describe the expression and possible roles of these transcription factors in neural tissue: in the quiescent brain, during pre- and postnatal development, following sensory stimulation, nerve transection (axotomy), neurodegeneration and apoptosis, hypoxia-ischemia, generalized and limbic seizures, long-term potentiation and learning, drug dependence and withdrawal, and following stimulation by neurotransmitters, hormones and neurotrophins. We also describe their expression and possible roles in glial cells. Finally, we discuss the relevance of their expression for nervous system functioning under normal and patho-physiological conditions.

Aberrant expression of c-Fos accompanies photoreceptor cell death in the rd mouse

Selective degeneration of rod photoreceptor cells in the retinal degenerative (rd) mouse prior to their complete maturation is thought to result from elevated cyclic guanosine monophosphate (cGMP) levels owing to the inherited defect in cGMP-phosphodiesterase. To investigate potential signaling pathways which might lead to apoptotic death of photoreceptors in the rd retina, the expression of immediate-early genes (IEG) of the activating protein-1 transcription factor (AP-1) family was examined. Increasing numbers of apoptotic photoreceptor nuclei were observed in the outer nuclear layer of the rd mouse beginning at postnatal day (P) 10. The peak incidence of apoptotic cells was observed at P13; by P16, almost the entire population of photoreceptors had been lost. Although c-Fos-like immunoreactivity was absent in photoreceptors of normal retinas, we observed that commencing at around P10, increasing numbers of rod photoreceptors in the rd retina exhibited nuclear staining for c-Fos protein. While no change in the distribution patterns of other members of the AP-1 family (c-Jun, JunB, and JunD) was observed in photoreceptors, Müller cell nuclei were transiently immunoreactive for c-Jun on P11. The incidence of c-Fos-positive photoreceptors peaked sharply at P12, 1 day earlier than the peak in apoptosis. Furthermore, the population of c-Fos-positive photoreceptors was distinct from apoptotic photoreceptors exhibiting chromatin condensation. The aberrant expression of c-Fos protein in rod photoreceptors immediately prior to their death in the rd mouse raises the possibility that c-Fos may be directly or indirectly involved in triggering the apoptotic cascade. Furthermore, the additional finding of c-Jun induction in Müller glia suggests that the IEG response to photoreceptor degeneration involves both intra- and intercellular signal transduction pathways.

Expression of the c-fos transcription factor in the rat auditory pathway following postnatal auditory deprivation

As an animal model for inborn hearing loss rat pups were reared in a sound-proof chamber from birth until age 21 days. In addition, pinnae were bilaterally sutured closed to reduce any influence of ambient sound. At the end of the sound deprivation, outer ear channels were reopened. Since previous studies failed to show any difference in the number or morphology of neurons in the auditory pathway in bilaterally sound-deprived animals, expression of c-fos protein was used as a functional marker to map trans-synaptic information transfer in the auditory pathway with cellular resolution. At day 21 sound-deprived rats and untreated controls were stimulated with pure tones of 8kHz for 5min at different sound pressure levels. Acoustic stimulation induced c-fos in both parts of the cochlear nucleus, superior olivary complex and inferior colliculus. Compared to untreated rats, deprivation reduced the number of c-fos labeled neurons in the dorsal and ventral part of the cochlear nucleus and inferior colliculus by 58% and 30%, respectively, following low sound pressure levels (90dB). In contrast, high sound pressure levels (120dB) increased the number of c-fos labeled neurons in these areas and evoked only minor differences in the number of labeled neurons in both untreated and sound deprived rats.

Dopaminergic control of gene transcription during striatal ontogeny: c-fos induction by D1 receptor activation in the developing striosomes

During striatal development, dopamine afferents initially reach the striosomal compartment, and this early dopamine innervation is thought to influence, through the D1 receptors first expressed in the developing patches, the phenotype of target striatal cells. Dopaminergic control of gene expression during ontogeny could be mediated by transcription factors such as c-fos, whose expression is regulated by synaptic signals. However, in the striatum of intact adult animals, D1 dopamine agonists fail to induce c-fos expression. The c-fos response to D1 receptor activation in adults requires a previous sensitization of dopaminergic receptors by chronic treatment with reserpine or by lesion of the nigro-striatal pathway. In this work, we investigated through in situ hybridization the ability of striatal cells to express c-fos messenger RNA (mRNA) in response to the D1 agonist SKF 38393 (4 to 8 mg/kg) in developing mice. During a transient postnatal period, c-fos expression in a patchy distribution was induced by D1 receptor activation: only a faint response was detected on postnatal day 1, but islands of strong hybridization signals for c-fos mRNA in response to the D1 agonist were observed at postnatal day 3, with a progressive decrease in intensity from day 6 to day 15. The distribution of this transient c-fos response corresponded to the early striosomal compartment since it matched with the regions of intense mu-opioid and dopamine-D1 receptor binding, as assessed by autoradiography performed on adjacent sections. By day 21, as in adult animals, no more c-fos response to D1 agonists was observed, except in the most caudal division of the striatum. Strong expression, which persisted into adulthood, was detected in this region from the third postnatal day. This induction of striatal c-fos expression by D1 agonists during early postnatal development is indicative of an enhanced sensitivity of D1 receptors or of D1-associated transduction pathways compared to the adult pattern, and suggests a possible role for dopamine-controlled c-fos gene expression in the development of target striatal neurons during this critical period.

Developmental expression of APEX nuclease, a multifunctional DNA repair enzyme, in mouse brains

Expression of the mammalian major apurinic/apyrimidinic (AP) endonuclease (designated as APEX nuclease, or HAP1, APE or Ref-1 gene product) during mouse brain development was investigated by in situ and northern blot hybridizations. The enzyme is known to be a redox factor (Ref-1) stimulating DNA binding activity of AP-1 binding proteins such as Fos and Jun as well as a multifunctional DNA repair enzyme having 5' AP endonuclease, DNA 3' repair diesterase, 3'-5' exonuclease and DNA 3'-phosphatase activities. In the embryonic and postnatal development, APEX mRNA was expressed at high levels in the proliferative zone of various brain regions, with showing temporal and spatial changes. Its expression decreased in association with brain development to the basal expression level which was observed even in adulthood, with the exception of its expression in the hippocampal formation. The growth-dependent expression of APEX gene suggests that it has some roles on cell proliferation and/or differentiation in developmental brain. Its expression on the hippocampal formation became significant from postnatal day 7 and then increased. The pyramidal and granule cell layers expressed it at a higher level than most other brain regions at postnatal day 21. The developmental change of APEX gene expression was not necessarily associated with the changes of expression of c-fos and c-jun genes measured by northern blot hybridization. However, the present results suggested that APEX/Ref-1 gene product can interact with AP-1 binding proteins in brain, especially in the hippocampal formation, to regulate some brain functions by redox-activation.

Fos protein immunoreactivity in the developing olfactory bulbs of normal and naris-occluded rats

Immediate early genes such as c-fos may be a route through which extracellular events affect genomic expression. Expression of immediate early genes is important in the transcriptional regulation necessary for the normal development of the nervous system. Developmental patterns of Fos protein (the product of c-fos immediate early gene expression) were studied in the main olfactory bulb of the rat using immunocytochemistry. Embryonic Day 21 (E21, the last prenatal day), as well as Postnatal Day 0 (P0), P1, P5, P10, P15, P20 and P30 subjects were examined. Although staining was absent in the E21 bulb, there was a rapid onset of Fos synthesis within hours after birth. Distribution of Fos-immunoreactive (Fos-ir) nuclei corresponded to the sequence of bulb maturation: numerous mitral/tufted and granule cells were labeled on P0, followed by the appearance of Fos-ir in the nuclei of periglomerular cells and an increase in the number of stained granule cells with development. Surgical closure of an external naris on P1 resulted in a 70% reduction in the number of Fos-ir granule cell nuclei as early as 2 h after the manipulation. During the next 30 days, levels of Fos staining further diminished in experimental bulbs when compared to their contralateral controls. Nevertheless, electrical stimulation of the contralateral bulb in P20 pups resulted in a robust increase of Fos labeling in most main and accessory olfactory bulb mitral cells and in many granule and periglomerular neurons, suggesting that the experimental bulbs remain competent to express Fos protein.

Central mechanism of neural activation with cold acclimation of rats using Fos immunohistochemistry

The expression of Fos protein in the rat diencephalon, brain stem, cerebellum, and spinal cord was investigated using immunohistochemistry during chronic cold exposure, in order to clarify the neural regions involved in the thermoregulatory responses and the central mechanism of neural activation with cold acclimation. Numerous Fos-positive cells were observed in many brain regions after cold exposure and changes in the number of Fos-positive cells were analyzed quantitatively. Fos-positive regions were classified into three groups on the basis of the expression period of Fos protein. The first group was where a significant number of Fos-positive cells were seen 3 h and 24 h after cold exposure, but not observed 14 days after exposure; the regions included the lateral septal nucleus (LS), parvocellular paraventricular hypothalamic nucleus (pPVN), posterior hypothalamic area (PH), supramammillary nucleus (SuM), locus coeruleus (LC), dorsal tegmental nucleus (DTg), vestibular nucleus (Ves), and nucleus of solitary tract (Sol). The second group was where a significant number of Fos-positive cells were found 3 h, 24 h and 14 days after cold exposure; the regions included the preoptic hypothalamic area (POA), paraventricular thalamic nucleus (PV), lateral preoptic area (LPO), zona incerta (ZI), subparafascicular thalamic nucleus (SPF), lateral dorsal central grey (CGLD), lateral ventral central grey (CGLV), microcellular tegmental nucleus (MiTg), lateral lemniscus nucleus (LL), dorsal parabrachial nucleus (DPB), and the cerebellum. The third group was where Fos-positive cells were more numerous 14 days after cold exposure than they were after 3 h and 24 h of exposure; these regions included the ventromedial hypothalamic nucleus (VMH) and the spinal cord. These results demonstrate that the numbers and regions of Fos-positive cells in the rat brains changed during chronic cold exposure, and such changes may reveal the cellular adaptation of the thermogenic responsive neurons in the rat brain to cold acclimation.

Expression and regulation of kainate and AMPA receptors in uncommitted and committed neural progenitors

Here we review experimental evidence of non-NMDA glutamate receptor expression in the embryonic central nervous system. AMPA- and kainate-preferring glutamate receptor subunit mRNA transcripts are detected in embryonic neurons, glia and neural progenitors. Functional assays demonstrate that in some cell subpopulations ionotropic glutamate receptors are expressed by progenitors before synapse formation and terminal differentiation, and may be present before lineage determination is specified. The activation of these receptors triggers induction of immediate early gene transcription in progenitor cells. The cloning and transcriptional analysis of upstream regulatory regions of glutamate receptor genes governing their temporal and tissue-specific expression are also discussed.

Postnatal age defines specificity of immediate early gene induction by cocaine in developing rat brain

Clinical and animal data suggest that exposure of developing brain to cocaine has adverse consequences. One candidate mechanism for such effects is drug regulation of gene expression. In adult rats, cocaine induces expression of nuclear immediate early genes with specific spatial and temporal patterns. The products of such genes (e.g., c-Fos, c-Jun, and Zif/268) subserve the coupling of cell surface receptor stimulation to transcriptional regulation. Thus, activation of immediate early gene expression in developing brain by cocaine could alter programs of neural gene expression and, thereby, neuronal phenotype and function. We report that, during rat brain development, cocaine produced brain region-specific and developmental age-specific induction of c-fos, c-jun, and zif/268 mRNAs. At each age studied (P8, P15, P28, and adults), we found that acute cocaine administration resulted in a unique cell-specific pattern of c-fos mRNA induction and c-Fos protein expression in striatum. We also observed cocaine-induced activation of AP-1 DNA binding activity in striatal extracts prepared at these different ages, suggesting that the observed induction of c-fos and c-jun may have biological consequences for the developing brain. These findings suggest a mechanism by which cocaine could alter patterns of gene expression during critical developmental periods with differential regional, temporal, and cellular vulnerabilities and, therefore, consequences for developing brain.

Temporal changes of c-fos expression in oxytocinergic magnocellular neuroendocrine cells of the rat hypothalamus with restraint stress

The present experiments were undertaken to examine c-fos expression in magnocellular neuroendocrine cells (MNCs) of the rat hypothalamus with restraint stress using dual immunohistochemistry for c-fos and oxytocin. Restraint stress induced c-fos expression in oxytocinergic MNCs in the supraoptic nucleus (SON) and paraventricular nucleus (PVN). Quantitative immunohistochemical analysis revealed that percentages of c-fos-positive cells to oxytocin-immunoreactive MNCs in the SON and PVN maximally increased at 2 h after restraint stress had started, and began to decline in spite of the fact that the restraint of animals were continued. Similar results were obtained from time course of c-fos expression in parvocellular neurons of the PVN. When animals were released to move freely in their home cages following the 3-h restraint, the plasma levels of oxytocin declined to reach basal levels within 30 min and c-fos immunoreactivity in the hypothalamic MNCs and parvocellular neurons disappeared faster than those of the continually restrained. These results demonstrate that restraint stress induces c-fos expression in oxytocinergic MNCs in the SON and PVN, and that time course of c-fos expression is transient even in the continuation of restraint stress.

Upregulation of c-fos protooncogene expression in pagetic osteoclasts

Using in situ hybridization we show that expression of the c-fos oncogene, a gene normally associated with osteosarcomas, is greatly elevated in osteoclasts of patients with Paget's disease. Immunohistochemical staining with c-fos antibodies also shows increased protein in pagetic osteoclasts. In light of transgenic mouse experiments showing a key role for c-fos in bone resorption, we propose that elevated c-fos gene expression in pagetic osteoclasts is an important component in producing the pagetic phenotype. Levels of c-fos gene and protein expression in pagetic osteoblasts are lower than those detected in osteoclasts but still higher than in nonpagetic osteoblasts. This may provide an explanation for the increased incidence of osteosarcomas in patients with Paget's disease because overexpression of c-fos in osteoblasts of transgenic mice induces osteosarcoma formation.

Expression of c-fos immunoreactivity in the hypothalamic magnocellular neurons during chronic osmotic stimulations

The immunoreactivity of c-fos protein was transiently detected in magnocellular neurons of the supraoptic nucleus (SON) and paraventricular nucleus (PVN) of the rat hypothalamus after intraperitoneal injection of hypertonic NaCl solution. In contrast, c-fos-positive magnocellular neurons were persistently observed in the SON and PVN of the rats which were chronically stimulated by the drinking of hypertonic NaCl solution instead of water or by water deprivation. c-fos immunoreactivity was eliminated in the animals which were allowed to drink tap water for 24 h following the chronic osmotic stimulations. These results suggest that persistent expression of c-fos protein is closely associated with the neural plasticity of the hypothalamic magnocellular neuron.

Transcription factor expression is induced by axonal stimulation and glutamate in the glia of the developing optic nerve

Recent experiments have demonstrated that stimulation of the developing optic nerve affects several glial cell characteristics, such as ionic fluxes and cell proliferation. This investigation asked if transcription factor expression may be another stimulation-dependent process in the glia of the developing optic nerve. In unstimulated optic nerves, an antibody to c-fos-related antigens demonstrated positive cell body staining at postnatal days (P) 2, 7, 14, and 60. This nuclear staining was most prominent at early postnatal ages, although young adult (P60) optic nerves showed occasional positive cells. To demonstrate the inducibility of transcription factor antigens, optic nerves from P7 animals received intermittent 15-20 Hz electrical stimulation for 5-15 min. Two hours after this stimulation, an increased number of immunoreactive cells for c-fos-related antigens, c-jun, and NGFI-A was demonstrated. Additionally, optic nerves were exposed for 5-30 min to a solution of 300 microM glutamate, latter maintained in a glutamate-free solution for 2 h, and then quickly frozen. Glutamate-treated nerves showed an increased expression of c-fos-related antigens compared to control nerves. No c-fos increase was seen in the absence of calcium. Expression of c-fos or NGFI-A occurred in cells that were S-100 positive, and most likely represented type 1 astrocytes. These studies indicate that developing (P7) optic nerves show a baseline expression of c-fos-related antigens, c-jun and NGFI-A. Stimulation through electrical nerve stimulation or glutamate results in an increased expression of these transcription factors.

Developmental regulation of Fos and Fos-related antigens in cerebral cortex, striatum, hippocampus, and cerebellum of the rat

Previous work has associated the proto-oncogene c-fos with such events as neuronal excitation and cell growth and differentiation. This study specifically examined the expression of the Fos protein as well as other Fos-related antigens (Fras) during postnatal development of rat brain. Ages P1 through P15 as well as adult animals (P60) were examined. Particular focus was placed on developing cerebral cortex, striatum, hippocampus, and cerebellum. We used both the Alu antiserum, which recognizes the Fos protein specifically, and the M5 antiserum, which recognizes both Fos and a family of Fos-related antigens. Fos and Fras were developmentally regulated in a region- and cell-specific manner. Differential nuclear and cytoplasmic labeling appeared age dependent. Transient Fos expression was generally followed by a more protracted time course of Fra expression. Fos and a delayed or an extended expression of Fras were observed in subplate neurons between P1 and P15, in striatal striosome and matrix neurons between P1 and P9, and in hippocampal pyramidal neurons between P1 and P9. Fras alone were expressed in cerebral cortex pyramidal neurons and other cortical neurons between ages P1 and P15. Fos and Fras were concomitantly expressed in piriform and entorhinal cortical neurons between P1 and P9 and in cerebellar Purkinje cells between ages P5 and P10. Constitutive levels of Fos and Fras remained detectable in adult animals in a subset of cerebral cortical neurons and cerebellar Purkinje neurons.

Induction and suppression of immediate early genes in specific rat brain regions by the non-competitive N-methyl-D-aspartate receptor antagonist MK-801

The expression pattern of six different immediate early gene-encoded proteins was examined in the rat forebrain after intraperitoneal administration of MK-801, a non-competitive N-methyl-D-aspartate receptor antagonist, at doses of 3 mg/kg and 0.3 mg/kg, respectively. Following MK-801 treatment, the presence of c-FOS, FOS B, KROX-24, c-JUN, JUN B, and JUN D were investigated by immunocytochemistry with specific antisera at different time intervals up to 48 h. Selective induction of all six immediate early genes was found in layer III neurons of the posterior cingulate and retrosplenial cortex. More complex effects were observed in the neocortex: MK-801 did not influence constitutive expression of different FOS and JUN proteins, but caused marked induction of c-FOS, FOS B, JUN B and JUN D, mainly in layer IV, but also in layers V and VI. In contrast, strong neocortical constitutive expression of KROX-24 was almost abolished by MK-801 administration, and replaced by an expression pattern similar to that of FOS and JUN proteins. Subcortical areas such as the hypothalamus and thalamus demonstrated an induction of a subset of immediate early genes (c-fos, fos B, Krox-24, jun B). Injection of MK-801 caused the same distributional pattern of immediate early gene expression irrespective of the dose given, but the extent of changes was stronger after 3 mg/kg, and altered levels of immunoreactivity persisted longer. In many experimental paradigms, immediate early genes are induced by N-methyl-D-aspartate receptor-mediated mechanisms. This induction can readily be blocked by N-methyl-D-aspartate receptor antagonists like MK-801. Our data, however, indicate that MK-801 itself causes immediate early gene expression in specific neuronal populations. In the present study MK-801-elicited expression of immediate early gene-encoded proteins seems to identify reversibly injured neurons, mainly in layer III of the posterior cingulate and retrosplenial cortex. These neurons have previously been shown to be the principal target of N-methyl-D-aspartate receptor antagonist toxicity. Since immediate early gene induction precedes heat-shock protein expression as well as pathomorphological changes, and is induced in additional cortical cell populations, it seems to be a more rapid and more sensitive indicator of non-lethal neuronal injury.

Pleiotropic effects of a null mutation in the c-fos proto-oncogene

The c-fos proto-oncogene has been implicated as a central regulatory component of the nuclear response to mitogens and other extracellular stimuli. Embryonic stem cells targeted at the c-fos locus have been used to generate chimeric mice that have transmitted the mutated allele through the germline. Homozygous mutants show reduced placental and fetal weights and significant loss of viability at birth. Approximately 40% of the homozygous mutants survive and grow at normal rates until severe osteopetrosis, characterized by foreshortening of the long bones, ossification of the marrow space, and absence of tooth eruption, begins to develop at approximately 11 days. Among other abnormalities, these mice show delayed or absent gametogenesis, lymphopenia, and altered behavior. Despite these defects, many live as long as their wild-type or heterozygous littermates (currently 7 months). These data indicate that c-fos is not required for the growth of most cell types but is involved in the development and function of several distinct tissues.

Induction of FOS and JUN proteins after focal ischemia in the rat: differential effect of the N-methyl-D-aspartate receptor antagonist MK-801

FOS and JUN proteins are transcription factors thought to be involved in coupling neuronal excitation to target gene expression. Cortical infarction of consistent size and location was produced by irradiating the rat brain with Xenon light through the intact skull for 20 min following systemic injection of the photo-sensitizing dye, rose bengal. To investigate the time course and distribution pattern of five cellular immediate early gene (IEG)-encoded proteins after focal ischemia, the expression of c-FOS, FOS B, c-JUN, JUN B and JUN D was studied immunocytochemically in sham-operated control animals and at different postischemic time intervals up to 24 h. A separate group of animals was pretreated with the non-competitive N-methyl-D-aspartate (NMDA) antagonist MK-801. Photochemically induced focal ischemia caused a rapid induction of FOS and JUN proteins in the entire ipsilateral cortex apart from the ischemic focus. Immunoreactivity in the ipsilateral subcortical gray and white matter and in the entire contralateral hemisphere was indistinguishable from control animals. Individual IEG-encoded proteins were sequentially induced with increased levels of immunoreactivity persisting for different time periods up to 24 h. c-FOS, FOS B, c-JUN and JUN B exhibited a characteristic distribution pattern as reflected by different staining intensities in individual cortical layers. The rapid IEG induction in the entire ipsilateral sensorimotor and limbic structure-associated cortices after photochemically induced infarction most likely reflects spreading depression caused by ischemia and mediated by NMDA receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

The mas proto-oncogene is developmentally regulated in the rat central nervous system

The mas proto-oncogene encodes a protein with a predicted structure similar to members of the family of seven transmembrane domain spanning receptors. These receptors are thought to transduce extracellular signals to G-proteins. Angiotensin II and III have been reported to be the functional ligands for the mas oncogene-encoded receptor (Jackson et al., 1988). We show here using in situ hybridization histochemistry and RNase protection assays that mas mRNA is expressed in a subpopulation of neurons in both the adult and developing rat CNS. In the adult CNS, mas mRNA is most abundant in hippocampal pyramidal neurons and dentate granule cells; mas transcripts are also present at low levels in the cortex and thalamus. mas is first expressed in the developing rat CNS at postnatal day 1 (P1). Even at this early stage in CNS development the pattern of mas expression is similar to that seen in the adult. Although at P1 most neurons of the dentate gyrus are not yet generated and cells of the hippocampal CA fields are undergoing migration and synaptogenesis (Bayer 1980; Altman and Bayer, 1990a, 1990b, 1990c), mas is specifically expressed in these cell populations. This extremely restricted pattern of expression suggests that mas may function in determining the morphology and connections of specific cell types in the hippocampus. This function may in part be carried out by the ability of mas to link external cues to intracellular processes.

krox 20 messenger RNA and protein expression in the adult central nervous system

krox 20 is an inducible immediate early response gene. To determine if krox 20 has a physiological role in the adult central nervous system (CNS), this study sought to demonstrate the presence of krox 20 in adult rat brain. RNA analysis showed the presence of krox 20 transcripts in the CNS, including the cortex. Polyclonal antibodies to a Krox 20 fusion protein demonstrated 79 and 55 kDa antigens in nuclear CNS homogenates. Neither RNA nor protein analysis was able to demonstrate an induction of krox 20 by a seizure at times when other immediate early response genes are known to be induced. Immunohistochemical analysis revealed staining at several levels throughout the nervous system. This staining was predominantly nuclear, consistent with the role of krox 20 as a transcription factor. These data show that krox 20 is present in the adult CNS, yet differs in response to stimuli as compared to other related transcription factors with a zinc finger motif, such as NGFI-A and NGFI-C.

Induction of immediate early gene encoded proteins in the rat hippocampus after bicuculline-induced seizures: differential expression of KROX-24, FOS and JUN proteins

Immunocytochemistry with specific antisera was used to assess regional levels of six immediate early gene encoded proteins (KROX-24, c-FOS, FOS B, c-JUN, JUN B and JUN D) in the rat hippocampus after 15 min of bicuculline-induced seizures. Serial sections of the dorsal hippocampus were examined at various postictal recovery periods up to 24 h. The results demonstrate a complex temporal and spatial pattern of immediate early gene synthesis and accumulation. Three major categories of immediate early gene products could best be distinguished in the dentate gyrus: KROX-24 and c-FOS showed a concurrent rapid rise with peak levels at 2 h and a return to baseline levels within 8 h after seizure termination. FOS B, c-JUN and JUN B levels increased more gradually with peak intensities in the dentate gyrus reached at 4 h. These immediate early gene products showed above normal levels in various hippocampal subpopulations up to 24 h. JUN D exhibited the most delayed onset combined with a prolonged increase of seizure-induced immunoreactivity. Irrespective of this differential temporal expression profile of individual transcription factors, the sequence of induction in the hippocampal subpopulations was identical for all immediate early gene-encoded proteins examined: first in the dentate gyrus granule cells followed by CA1 and CA3 neurons, respectively. Our data indicate an asynchronous synthesis of several immediate early gene-encoded proteins in the brain after status epilepticus. FOS and JUN proteins act via homo- or heterodimer complexes at the AP-1 and other DNA binding sites. The different time-courses for individual immediate early gene products strongly suggest, that at different time-points after status epilepticus, different AP-1 complexes are effective. In vitro studies have shown that different AP-1 complexes possess different DNA binding affinities as well as different transcriptional regulatory effects. Our results suggest that these molecular mechanisms are also effective in vivo.

Changes in immediate early gene expression during postnatal development of cat cortex and cerebellum

Postnatal brain development involves interactions between extracellular signals and preprogrammed genetic events. Immediate early genes (IEGs) are a group of genes that are induced by extracellular signals and their protein products alter transcription by binding regulatory elements in other genes. Using Northern and slot blot analysis of total RNA isolated from visual cortex, frontal cortex, and cerebellum of cats, we have determined the postnatal development patterns of mRNA expression for 5 of these genes, c-fos, erg-1, c-jun, jun-B, and c-myc. Each gene had a distinct developmental pattern of mRNA expression, and for a given gene, these patterns were often different in different brain structures. These results suggest that temporal changes in the combinatorial interaction of different IEGs during early postnatal life are important for normal brain development.

Expression of the proto-oncogene c-fos in three-dimensional fetal brain cell cultures and the lack of correlation with maturation-inducing stimuli

Previous work has shown that aggregating fetal brain cell cultures are able to attain a highly differentiated state, and that their development is greatly enhanced by growth and/or differentiation factors such as epidermal growth factor (EGF), basic fibroblast growth factor (bFGF), and the protein kinase C-activating tumor promoter mezerein. The present study shows that in these 3-dimensional cultures the peptide growth factors EGF and bFGF as well as mezerein are able to induce the expression of the proto-oncogene c-fos. This induction was rapid and transient, in good agreement with observations reported from a wide variety of cell types in vitro. The maximal levels of c-fos mRNA found after stimulation were low in immature cultures and increased greatly as maturation progressed. Of the three factors tested, mezerein was the most potent inducer of c-fos. In contrast to the peptide growth factors EGF and bFGF which were found to induce c-fos only in glial cells, mezerein was stimulatory in glial cells as well as in neurons. A similar cell type specificity has been observed previously for the maturation-enhancing response in immature aggregate cultures. However, in the present study no correlation was found between the degree of c-fos induction and the extent of the maturation-enhancing stimulation. Immature cultures known to be most sensitive and responsive to these maturation-enhancing agents required relatively high doses of peptide growth factors for the induction of c-fos, and the maximal levels of c-fos mRNA elicited were much lower than those in differentiated cultures which did not show any long-term response to these stimuli.(ABSTRACT TRUNCATED AT 250 WORDS)

Transient expression of c-fos during the development of the rat cerebral cortex

The present study has explored with immunocytochemical methods the expression of the proto-oncogene c-fos during the pre- and postnatal development of the cerebral cortex of the rat. The immunostaining of the Fos protein follows a strikingly precise spatiotemporal pattern: it occurs uniquely within layer VIb of the developing cerebral cortex, and is transient, lasting only from embryonic day 20 until postnatal day 1. The expression of c-fos in layer VIb may be related to the dynamic changes that occur at this level during development.

Stage and tissue-specific expression of fosB during mouse development

The product of the fos-related fosB gene shares many properties with c-Fos such as inducibility by growth factors, complex formation with members of the Jun family and cooperative binding with Jun to the TPA response element (TRE). To investigate whether in contrast to these functional similarities, the two genes might be differentially regulated, we have analysed the expression of fosB during mouse development by in situ hybridization. A spatially restricted accumulation of fosB mRNA in the visceral yolk sac and the nervous system was observed during late gestation. The highest levels of fosB mRNA were found in the cortex and the dorsal columns of the spinal cord. Moreover, stage-specific expression was seen in sensory organs such as retina and vibrissae, where the levels of fosB RNA either increased (retina) or decreased (vibrissae) between days 15 and 18. Our results suggest that fosB may have a specific function in the development of ectoderm-derived tissues. Expression of fosB during prenatal development differs markedly from the known expression pattern of c-fos, pointing to different tissue-specific functions for c-fos and fosB.

Expression of c-myc and c-fos oncogenes in different rat brain regions during postnatal development

We have studied the expression of c-myc and c-fos proto-oncogenes in various areas of the central nervous system during postnatal development. c-myc mRNA levels increased during the first 5 days and then decreased over the next 15 days in all nervous regions studied. c-fos mRNA levels changed in a different way in four brain areas. While in cerebral cortex and cerebellum there was a sharp decrease during the first 10 days, in white matter and hypothalamus c-fos transcript levels remained high during the same period, decreasing at a later stage. Changes in oncogenes mRNA levels are related to various developmental events, such as neurite growth, myelination and cell proliferation. The dissimilar patterns of c-myc and c-fos expression suggests that they play different functions in CNS maturation. c-myc mRNA levels are temporally related to active neurite growth and to cell proliferation. Changes in c-fos mRNA correlate in time with early developmental processes and also with those occurring at later stages, such as myelination.

Oncogenes, antioncogenes, and the regulation of cell growth

A variety of proto-oncogenes are present in normal cells, and many of these genes are expressed in different cell types in a tissue-specific and developmentally specific fashion. Although proto-oncogenes have normal functions, apparently related to cell proliferation and differentiation, these genes are able to cause cancer when they are expressed inappropriately (usually as a result of a mutation). Most oncogene mutations promote tumor growth by inducing autonomous activity of proteins, which normally transmit growth signals that are triggered by extracellular factors. Studies of oncogenes and suppressor genes (antioncogenes) have greatly contributed to our understanding of the regulation of normal cell growth by focusing on the molecular mechanisms by which the signals for cell proliferation exert their effects.

Mitogenically uncoupled insulin and IGF-I receptors of differentiated human neuroblastoma cells are functional and mediate ligand-induced signals

The SH-SY5Y human neuroblastoma cell line is differentiated in vitro with nanomolar concentrations of 12-O-tetradecanoyl-phorbol-13-acetate (TPA). Untreated cells express insulin receptors, and both type I and type II insulin-like growth factor (IGF) receptors, as has been shown by agonist binding and immunoprecipitation studies. Via interaction with its own receptor and the IGF-I receptor, insulin induced a mitogenic response in these cells. IGF-I and IGF-II are also mitogens for SH-SY5Y cells, as shown by a transient increase of the c-fos mRNA level, ornithin decarboxylase activity, thymidine incorporation, and, finally, cell division. TPA-differentiated cells do not respond mitogenically to any of these factors, although insulin and IGF-I receptors are still present on the cell surface and remain functional, as demonstrated by ligand-stimulated autophosphorylation, actin reorganization, and c-fos induction. However, other prereplicative responses, i.e., increased ornithin decarboxylase activity and c-myc mRNA levels, cannot be induced. These phenomena, may be part of a receptor uncoupling mechanism(s). The findings are discussed in terms of differentiation stage-dependent signaling of growth factor receptors. We suggest that these receptors switch from controlling cell division in replicative neuronal cells to mediating externally controlled functions related to the differentiated neuronal phenotype.