Deficits across multiple behavioral domains align with susceptibility to stress in 129S1/SvImJ mice

Acute physical or psychological stress can elicit adaptive behaviors that allow an organism maintain homeostasis. However, intense and/or prolonged stressors often have the opposite effect, resulting in maladaptive behaviors and curbing goal-directed action; in the extreme, this may contribute to the development of psychiatric conditions like generalized anxiety disorder, major depressive disorder, or post-traumatic stress disorder. While treatment of these disorders generally focuses on reducing reactivity to potentially threatening stimuli, there are in fact impairments across multiple domains including valence, arousal, and cognition. Here, we use the genetically stress-susceptible 129S1 mouse strain to explore the effects of stress across multiple domains. We find that 129S1 mice exhibit a potentiated neuroendocrine response across many environments and paradigms, and that this is associated with reduced exploration, neophobia, decreased novelty- and reward-seeking, and spatial learning and memory impairments. Taken together, our results suggest that the 129S1 strain may provide a useful model for elucidating mechanisms underlying myriad aspects of stress-linked psychiatric disorders as well as potential treatments that may ameliorate symptoms.

Deletion of corticotropin-releasing factor binding protein selectively impairs maternal, but not intermale aggression

Corticotropin-releasing factor (CRF) binding protein (CRF-BP) is a secreted protein that acts to bind and limit the activity of the neuropeptides, CRF and urocortin (Ucn) 1. We previously selected for high maternal defense (protection of offspring) in mice and found CRF-BP to be elevated in the CNS of selected mice. We also previously determined that both CRF and Ucn 1 are potent inhibitors of offspring protection when administered centrally. Thus, elevated CRF-BP could promote defense by limiting endogenous actions of CRF or Ucn 1. To test this hypothesis, we crossed the deletion for CRF-BP into the mice selected for high maternal defense and evaluated offspring protection and other maternal behaviors. CRF-BP knockout (KO) mice exhibited significant deficits in maternal aggression relative to wild-type (WT) mice in three different measures. Other maternal features were almost identical between groups, including dam and pup weight, litter size, nursing time, and pup retrieval. Both groups performed similarly in a forced swim stress test and aggression in both groups was reduced following the swim test. Virgin KO female mice exhibited higher levels of anxiety-like behavior in terms of decreased time in the light portion of the light/dark box test. For males, no differences in light/dark box or swim test were found. However, increased anxiety-like behavior in male KO mice was identified in terms of contact and approach to a novel object both with and without previous exposure to the swim test. No differences in isolation induced resident intruder male aggression were found between groups. Together, these results indicate that loss of CRF-BP selectively impairs maternal, but not intermale aggression and that loss of the gene induces anxiety-like behavior in males and females, but there are sex differences in terms of how that anxiety is revealed.

Decreased locomotor activity in mice expressing tTA under control of the CaMKII alpha promoter

Transgenic mice in which the tetracycline transactivator (tTA) is driven by the forebrain-specific calcium-calmodulin-dependent kinase II alpha promoter (CaMKII alpha-tTA mice) are used to study the molecular genetics of many behaviors. These mice can be crossed with other transgenic mice carrying a transgene of interest coupled to the tetracycline-responsive promoter element to produce mice with forebrain-specific expression of the transgene under investigation. The value of using CaMKII alpha-tTA mice to study behavior, however, is dependent on the CaMKII alpha-tTA mice themselves lacking a behavioral phenotype with respect to the behaviors being studied. Here we present data that suggest CaMKII alpha-tTA mice have a behavioral phenotype distinct from that of their wild-type (WT) littermates. Most strikingly, we find that CaMKII alpha-tTA mice, both those with a C57BL/6NTac genetic background (B6-tTA) and those with a 129S6B6F1/Tac hybrid genetic background (F1-tTA), exhibit decreased locomotor activity compared with WT littermates that could be misinterpreted as altered anxiety-like behavior. Despite this impairment, neither B6-tTA nor F1-tTA mice perform differently than their WT littermates in two commonly used learning and memory paradigms - Pavlovian fear conditioning and Morris water maze. Additionally, we find data regarding motor coordination and balance to be mixed: B6-tTA mice, but not F1-tTA mice, exhibit impaired performance on the accelerating rotarod and both perform as well as their WT littermates on the balance beam.

Skeletal dysplasia and male infertility locus on mouse chromosome 9

In mice and humans, growth insufficiency and male infertility are common disorders that are genetically and phenotypically complex. We describe a spontaneously arising mouse mutant, chagun, that is affected by both dwarfism and male infertility. Dwarfism disproportionately affects long bones and is characterized by a defect in the proliferative zone of chondrocytes in the growth plate. Gonads of mutant males are small, with apparent germ cell loss and no evidence of mature sperm. The locus responsible for chagun is recessive and maps to distal chromosome 9, in a region homologous to human chromosome 3. This location is consistent with chagun defining a novel locus. Identification of the mutant gene will uncover the basis for another type of skeletal dysplasia and male infertility.

Corticotropin-releasing hormone-binding protein: biochemistry and function from fishes to mammals

Corticotropin-releasing hormone (CRH) plays multiple roles in vertebrate species. In mammals, it is the major hypothalamic releasing factor for pituitary adrenocorticotropin secretion, and is a neurotransmitter or neuromodulator at other sites in the central nervous system. In non-mammalian vertebrates, CRH not only acts as a neurotransmitter and hypophysiotropin, it also acts as a potent thyrotropin-releasing factor, allowing CRH to regulate both the adrenal and thyroid axes, especially in development. The recent discovery of a family of CRH-like peptides suggests that multiple CRH-like ligands may play important roles in these functions. The biological effects of CRH and the other CRH-like ligands are mediated and modulated not only by CRH receptors, but also via a highly conserved CRH-binding protein (CRH-BP). The CRH-BP has been identified not only in mammals, but also in non-mammalian vertebrates including fishes, amphibians, and birds, suggesting that it is a phylogenetically ancient protein with extensive structural and functional conservation. In this review, we discuss the biochemical properties of the characterized CRH-BPs and the functional roles of the CRH-BP. While much of the in vitro and in vivo data to date support an 'inhibitory' role for the CRH-BP in which it binds CRH and other CRH-like ligands and prevents the activation of CRH receptors, the possibility that the CRH-BP may also exhibit diverse extra- and intracellular roles in a cell-specific fashion and at specific times in development is also discussed.

Mouse models of altered CRH-binding protein expression

CRH is the key physiological mediator of the endocrine, autonomic, and behavioral responses to stress. The recent characterization of urocortin, a new mammalian CRH-like ligand, adds to the complexity of the CRH system. Both CRH and urocortin mediate their endocrine and/or synaptic effects via two classes of CRH receptors. Similarly, both CRH and urocortin bind to the CRH-binding protein (CRH-BP). This secreted binding protein is smaller than the CRH receptors, but binds CRH and urocortin with an affinity equal to or greater than that of the receptors, and blocks CRH-mediated ACTH release in vitro. Several regions of CRH-BP expression colocalize with sites of CRH synthesis or release, suggesting that this binding protein may have a profound impact on the biological activity of CRH (or urocortin). While in vitro and in vivo studies have characterized the biochemical properties and regulation of the CRH-BP, animal models of altered CRH-BP expression can provide additional information on the in vivo role of this important modulatory protein. This review focuses on three mouse models of CRH-BP overexpression or deficiency. These animal models show numerous physiological changes in the HPA axis and in energy balance, with additional alterations in anxiogenic behavior. These changes are consistent with the hypothesis that CRH-BP plays an important in vivo modulatory role by regulating levels of "free" CRH and other CRH-like peptides in the pituitary and central nervous system.

Hypothalamo-pituitary-adrenocortical dysregulation in aging F344/Brown-Norway F1 hybrid rats

Hypothalamo-pituitary-adrenocortical (HPA) axis aging was studied in young (3 mo), middle aged (15 mo) and aged (30 mo) F344/Brown Norway hybrid rats. This strain was selected to obviate HPA-relevant pathologies found in other aging models. Aged, unstressed rats showed enhanced central HPA drive, marked by elevated ACTH release and decreased pituitary proopiomelanocortin and corticotropin-releasing factor receptor 1 (CRH-R1) mRNAs. Acute corticosterone responses to spatial novelty were exacerbated in aged rats; however, responses to restraint or hypoxia were not affected. Chronic stress exposure also differentially increased HPA drive in aged animals, marked by elevated paraventricular nucleus CRH peptide levels and pituitary proopiomelanocortin mRNA. Plasma ACTH and pituitary POMC and CRH-R1 mRNA expression in middle-aged rats were intermediate those of young and aged animals. Middle-aged animals responded to chronic stress with disproportionate increases in CRH mRNA levels, and increased corticosterone secretion following hypoxia but not novelty. The results suggest a gradual increase in HPA tone across the aging process, culminating in marked hyperresponsivity to both acute and chronic stress in senescence.

Biochemical characterization and expression analysis of the Xenopus laevis corticotropin-releasing hormone binding protein

Corticotropin-releasing hormone (CRH) plays a key role in the regulation of responses to stress. The presence of a high affinity binding protein for CRH (CRH-BP) has been reported in mammals. We have characterized the biochemical properties and expression of CRH-BP in the South African clawed frog, Xenopus laevis. Apparent inhibition constants (K(i[app])) for different ligands were determined by competitive binding assay. Xenopus CRH-BP (xCRH-BP) exhibited a high affinity for xCRH (K(i[app])=1.08 nM) and sauvagine (1.36 nM). Similar to rodent and human CRH-BPs, the frog protein binds urotensin I and urocortin with high affinity, and ovine CRH with low affinity. RT-PCR analysis showed that xCRH-BP is expressed in brain, pituitary, liver, tail, and intestine. Brain xCRH-BP mRNA is expressed at a relatively constant level throughout metamorphosis and increases slightly in the metamorphic frog. By contrast, the gene is strongly upregulated in the tail at metamorphic climax. Thus, regulation of xCRH-BP gene expression is tissue specific. Because xCRH-BP binds CRH-like peptides with high affinity the protein may regulated, the bioavailability of CRH in amphibia as it does in mammals.

Cre-mediated recombination in the pituitary gland

Organ-specific expression of a cre recombinase transgene allows for the analysis of gene function in a particular tissue or cell type. Using a 4.6 kb promoter from the mouse glycoprotein hormone alpha-subunit (alphaGSU or Cga) gene, we have generated and characterized a line of transgenic mice that express cre recombinase in the anterior and intermediate lobes of the pituitary gland. Utilizing a cre-responsive reporter transgene, alphaGSU-cre transgene expression was detected in the pituitary primordium and in all five cell types of the adult anterior pituitary. alphaGSU-cre transgene activity was also detected in the cardiac and skeletal muscle. Little or no activity was evident in the gonads, adrenal glands, brain, ventromedial hypothalamus, or kidneys. The alphaGSU-cre transgenic mice characterized here will be a valuable tool for examining gene function in the pituitary gland.

Regulation of corticotropin-releasing factor-binding protein expression in amygdalar neuronal cultures

Corticotropin-releasing factor-binding protein (CRF-BP) is known to regulate the bioavailability of CRF and may also play a role in stress behaviours. CRF-BP has been localized in the pituitary as well as central nervous system (CNS) limbic and cortical areas, including the amygdala. The signal transduction pathways which regulate amygdalar CRF-BP are not well understood. In this report, we have examined the effect of protein kinase A and C activators, CRF, dexamethasone and interleukin-6 (IL6) on CRF-BP mRNA and protein expression in dissociated fetal amygdalar cultures. CRF-BP mRNA levels were determined by Northern analysis following 12 h treatment with the following agents: forskolin (1-30 microM), CRF (1-1000 nM), phorbol-12-myristate-13-acetate (TPA; 1-50 nM), dexamethasone (1-100 nM) and IL6 (10-500 pM). Significant increases in CRF-BP mRNA were observed in response to forskolin (30 mM), CRF (100, 1000 nM), IL6 (100, 500 pM), TPA (50 nM) and dexamethasone (100 nM; P<0.05 for all; n=3-6 for all). We extended our observations of CRF-BP expression to the protein level by performing semiquantitative Western analysis of total cellular protein after treatment with the same agents. Twenty-four hour treatment with 30 microM forskolin, 1000 nM CRF, 50 nM TPA, 100 pM IL6 or 100 nM dexamethasone significantly increased CRF-BP expression (P<0.05, n=3 for each treatment). The primary cultures were then transfected with a rat CRF-BP-reporter construct containing 3500 base pairs of CRF-BP 5' flanking DNA. Treatment with all five agents produced statistically significant increases above control (P<0.05; n=3 for each). The results suggest that CRF-BP in the amygdala is stimulated by numerous pathways which may play a significant role in promoting behavioural changes.

Altered anxiety and weight gain in corticotropin-releasing hormone-binding protein-deficient mice

Corticotropin-releasing hormone (CRH) is widely recognized as the primary mediator of the neuroendocrine and behavioral responses to stress, including stress-induced anxiety. The biological activity of CRH and other mammalian CRH-like peptides, such as urocortin, may be modulated by CRH-binding protein (CRH-BP). To assess directly the CRH-BP function, we created a mouse model of CRH-BP deficiency by gene targeting. Basal adrenocorticotropic hormone and corticosterone levels are unchanged in the CRH-BP-deficient mice, and the animals demonstrate a normal increase in adrenocorticotropic hormone and corticosterone after restraint stress. In contrast, adult male CRH-BP-deficient mice show significantly reduced body weight when compared with wild-type controls. CRH-BP-deficient mice also exhibit a significant increase in anxiogenic-like behavior as assessed by the elevated plus maze and defensive withdrawal tests. The increased anorectic and anxiogenic-like behavior most likely is caused by increased "free" CRH and/or urocortin levels in the brain of CRH-BP-deficient animals, suggesting an important role for CRH-BP in maintaining appropriate levels of these peptides in the central nervous system.

Transcriptional regulation of corticotropin-releasing hormone-binding protein gene expression in astrocyte cultures

The molecular mechanisms involved in regulation of CRH-binding protein (CRH-BP) gene expression were examined using primary rat astrocyte cultures. The cells were treated with various regulators, and CRH-BP messenger RNA (mRNA) levels were determined using ribonuclease protection assays. Forskolin (Fsk, 10 microM) or 12-O-tetradecanoyl-phorbol 13-acetate (TPA, 100 nM) increases CRH-BP mRNA levels up to 30 times control level, and together they act synergistically to increase CRH-BP gene expression up to 100 times control levels. CRH can also positively regulate CRH-BP gene expression to 6.1 times control levels. All of these increases in steady-state CRH-BP mRNA levels can be repressed by dexamethasone, a synthetic glucocorticoid. To determine whether these changes in steady-state CRH-BP mRNA levels are caused by altered transcription or RNA stability, heteronuclear (hn) CRH-BP species were examined using ribonuclease protection assays. CRH-BP hnRNA transcripts can be detected transiently after the addition of Fsk or TPA, and dexamethasone can repress Fsk- or TPA-induced CRH-BP hnRNA levels in this assay. These results demonstrate that CRH, glucocorticoids, and the protein kinase A and protein kinase C signaling pathways are involved in regulation of CRH-BP gene expression in astrocyte cultures, and that this regulation is caused, at least in part, by altered transcription of the gene.

Nitric oxide/cyclic guanosine monophosphate pathway in the peripheral and central auditory system of the rat

The neuronal isoform of nitric oxide synthase (nNOS) and soluble guanylate cyclase (sGC) were localized in the cochlea, the cochlear nucleus (CN), and the superior olivary complex (SOC) of Fisher 344 rats. In the cochlea, nNOS was identified in spiral ganglion cells by using nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase histochemistry and in situ hybridization. NADPH-diaphorase staining also was detected in blood vessels of the modiolus. By using immunohistochemistry against cyclic guanosine monophosphate, cochlear sGC activity was localized to pericytes in the spiral ligament as well as nerve fibers innervating outer hair cells. In the lower auditory brainstem, nNOS was localized to principal cells of the medial nucleus of the trapezoid body (MNTB) with NADPH-diaphorase histochemistry and in situ hybridization. NADPH-diaphorase activity also was observed in the lateral and medial superior olive (LSO and MSO, respectively), the superior periolivary nucleus (SPN), the ventral and lateral nuclei of the trapezoid body (VNTB and LNTB, respectively), and the ventral cochlear nucleus (VCN). Transcripts of the beta-subunit of sGC were localized in rat brainstem by using in situ hybridization. mRNA for sGC was expressed in neurons within the SPN, LSO, MSO, LNTB, MNTB, VNTB, and VCN. Highest levels of sGC expression were seen in the SPN. These results suggest that the NO/cGMP pathway is involved in both the ascending and descending pathways of the auditory brainstem.

Regulation of pituitary corticotropin-releasing hormone-binding protein messenger ribonucleic acid levels by restraint stress and adrenalectomy

CRH is the primary hypothalamic regulator of the stress response in higher organisms, where it acts as the key mediator of ACTH release in the hypothalamus-pituitary-adrenal axis. The 37-kDa CRH-binding protein (CRH-BP) is known to bind CRH and antagonize CRH-induced ACTH release in vitro. The expression of this protein in anterior pituitary corticotrophs suggests a role for CRH-BP in modulation of the stress response. To investigate the in vivo role of rat CRH-BP, the regulation of pituitary CRH-BP gene expression by acute restraint stress and/or adrenalectomy was examined using ribonuclease protection assays. After restraint stress, steady-state levels of CRH-BP transcripts increase two to three times over basal level and remain significantly higher than basal levels for 120 min after the start of restraint. Adrenalectomy decreases CRH-BP messenger RNA steady-state levels to 8% of control levels. These results demonstrate that pituitary CRH-BP messenger RNA levels are increased in response to acute restraint stress and that glucocorticoids play a significant role in this positive regulation. These data also suggest that increased CRH-BP levels, in response to stress, may modulate the endocrine stress response by providing an additional feedback mechanism to maintain homeostasis of the hypothalamus-pituitary-adrenal axis.

Excess corticotropin releasing hormone-binding protein in the hypothalamic-pituitary-adrenal axis in transgenic mice

Corticotropin-releasing hormone (CRH) is the primary hypothalamic releasing factor that mediates the mammalian stress response. The CRH-binding protein (CRH-BP) is secreted from corticotropes, the pituitary CRH target cells, suggesting that the CRH-BP may modulate hypothalamic-pituitary-adrenal (HPA) axis activity by preventing CRH receptor stimulation. Transgenic mice were generated that constitutively express elevated levels of CRH-BP in the anterior pituitary gland. RNA and protein analyses confirmed the elevation of pituitary CRH-BP. Basal plasma concentrations of corticosterone and adrenocorticotropin hormone (ACTH) are unchanged, and a normal pattern of increased corticosterone and ACTH was observed after restraint stress. However, CRH and vasopressin (AVP) mRNA levels in the transgenic mice are increased by 82 and 35%, respectively, to compensate for the excess CRH-BP, consistent with the idea that CRH-BP levels are important for homeostasis. The transgenic mice exhibit increased activity in standard behavioral tests, and an altered circadian pattern of food intake which may be due to transgene expression in the brain. Alterations in CRH and AVP in response to elevated pituitary CRH-BP clearly demonstrate that regulation of CRH-BP is important in the function of the HPA axis.

Identification and characterization of GFRalpha-3, a novel Co-receptor belonging to the glial cell line-derived neurotrophic receptor family

A new family of neuronal survival factors comprised of glial cell line-derived neurotrophic factor (GDNF) and neurturin has recently been described (Kotzbauer, P. T., Lampe, P. A., Heuckeroth, R. O., Golden, J. P., Creedon, D. J., Johnson, E. M., Jr., and Milbrandt, J. (1997) Nature 384, 467-470). These molecules, which are related to transforming growth factor-beta, are important in embryogenesis and in the survival of distinct neuronal populations. These molecules signal through a novel receptor system that includes the Ret receptor tyrosine kinase, a ligand (i.e. GDNF or neurturin), and an accessory glycosyl-phosphatidylinositol-linked molecule that is responsible for high affinity binding of the ligand. Two accessory molecules denoted GDNF family receptor 1 and 2 (GFRalpha-1 and GFRalpha-2) have been described that function in GDNF and neurturin signaling complexes. We have identified a novel co-receptor belonging to this family based on similarity to GFRalpha-1, which we have named GFRalpha-3. GFRalpha-3 displays 33% amino acid identity with GFRalpha-1 and 36% identity with GFRalpha-2. Despite the similarity of GFRalpha-3 to GFRalpha-1 and GFRalpha-2, it is unable to activate Ret in conjunction with GDNF, suggesting that there are likely additional undiscovered ligands and/or Ret-like receptors to be identified. GFRalpha-3 is anchored to the cell membrane by a phosphatidylinositol-specific phospholipase C-resistant glycosyl-phosphatidylinositol linkage. GFRalpha-3 is highly expressed by embryonic day 11 but is not appreciably expressed in the adult mouse. In situ hybridization analyses demonstrate that GFRalpha-3 is located in dorsal root ganglia and the superior cervical sympathetic ganglion. Comparison of the expression patterns of GFRalpha-3 and Ret suggests that these molecules could form a receptor pair and interact with GDNF family members to play unique roles in development.

Isolation and characterization of the rat corticotropin-releasing hormone (CRH)-binding protein gene: transcriptional regulation by cyclic adenosine monophosphate and CRH

The CRH-binding protein (CRH-BP) antagonizes the ACTH-releasing activity of the neuropeptide CRH in vitro. However, the function of CRH-BP in vivo and the molecular mechanisms that regulate CRH-BP expression are not well understood. In this study, the rat CRH-BP gene was characterized, and CRH-BP promoter sequences were identified. The rat CRH-BP gene spans almost 12 kilobases and contains 7 exons. Ribonuclease protection experiments indicate that transcription of the CRH-BP gene initiates at multiple sites in rat cerebral cortex. Transfection experiments with CRH-BP-reporter constructs, containing 88-3500 bp 5' flanking and 66 bp 5' untranslated DNA from the rat CRH-BP gene, demonstrate basal promoter activity in multiple cell lines. CRH-BP-reporter constructs also demonstrate positive regulation of promoter activity by cAMP in a variety of cell lines and by CRH in cells expressing the CRH receptor. The DNA sequences between -341 and -88 bp, including the cAMP response element-like sequence at -127 bp, are required for maximal cAMP and CRH regulation of CRH-BP promoter activity. These studies suggest that CRH-BP transcription in vivo may be positively regulated by cAMP and CRH.

Targeted ablation of cells in the pituitary primordia of transgenic mice

The various hormones of the anterior pituitary are expressed in a specific temporal and spatial pattern during organogenesis, which is interpreted as a reflection of a temporal pattern of pituitary cytodifferentiation. The first pituitary transcripts detected are from alpha GSU, which encodes the alpha-subunit common to the gonadotropins (FSH and LH) and TSH. TSH beta-subunit transcripts appear several days later but precede transcription of the GH and FSH beta and LH beta-subunit genes. To determine the lineage relationship between the alpha-subunit-expressing cells and the other hormone-producing cells of the anterior pituitary, we have employed the technique of transgene ablation. Transgenic mice were generated that express either the normal diphtheria toxin A chain or a 30-fold less active attenuated version in pituitary gonadotrope and thyrotrope cells. The absence of detectable transcripts for alpha-subunit, TSH beta-subunit, or LH beta-subunit by in situ hybridization confirmed that ablation was complete. In spite of the absence of gonadotropes and thyrotropes, the GH and ACTH-producing cells developed normally. These results imply that although thyrotropes appear early in pituitary development, they are not obligate intermediates in the developmental pathway. Instead, commitment to individual differentiated pituitary cell fates must occur autonomously or before the expression of currently known differentiation markers.

Glial cell line-derived neurotrophic factor signals through the RET receptor and activates mitogen-activated protein kinase

Glial cell line-derived neurotrophic factor (GDNF), a member of the transforming growth factor-beta family of growth factors, was first identified by its ability to promote the survival of midbrain dopaminergic neurons in culture. We demonstrate that GDNF treatment of several neuroblastoma cell lines leads to dose-dependent tyrosine phosphorylation of the RET receptor and that other transforming growth factor-beta family members are not able to activate the RET receptor. GDNF treatment of neuroblastoma cells also results in increased transcription of an Elk luciferase reporter gene, suggesting that GDNF activates the mitogen-activated protein kinase signal transduction pathway.

Negative glucorticoid regulation of cyclic adenosine 3', 5'-monophosphate-stimulated corticotropin-releasing hormone-reporter expression in AtT-20 cells

The negative glucocorticoid regulation of CRH gene expression is a critical control element in the hypothalamic-pituitary-adrenal axis. In this study, the molecular mechanisms mediating the glucocorticoid repression of cAMP-induced CRH-reporter expression in AtT-20 cells have been examined. In these cells, dexamethasone decreases forskolin-induced expression of CRH-reporter activity in a dose-dependent manner. This repression is mediated by the glucocorticoid receptor (GR) and does not require ongoing protein synthesis. Several binding sites for the GR DNA-binding domain were identified within the CRH 5'-flanking and 5'-untranslated regions utilizing in vitro DNase I protection assays. These sites were independently mutated and/or deleted. Functional studies in transfected cells suggest that none of the protected DNA sequences mediate the glucocorticoid regulation and that the regulatory element(s) mediating negative glucocorticoid regulation is contained within the CRH DNA sequences from -248 to +4 bp relative to the major transcription initiation site. To further localize the DNA sequence(s) responsive to glucocorticoids, DNA fragments containing various amounts of human CRH 5'flanking sequences were inserted 5' to the SV40 promoter. An 18-bp DNA fragment containing the CRH cAMP-responsive element is sufficient to confer both positive cAMP regulation and glucocorticoid repression of cAMP-stimulated expression to the SV40 promoter. These results suggest that glucocorticoid repression of forskolin-activated CRH-reporter expression in AtT-20 cells occurs via interference with the cAMP-mediated activation of gene expression, possibly via direct or indirect interactions between the GR and the cAMP-responsive element-binding proteins.

hVH-5: a protein tyrosine phosphatase abundant in brain that inactivates mitogen-activated protein kinase

A novel protein tyrosine phosphatase [homologue of vaccinia virus H1 phosphatase gene clone 5 (hVH-5)] was cloned; it shared sequence similarity with a subset of protein tyrosine phosphatases that regulate mitogen-activated protein kinase. The catalytic region of hVH-5 was expressed as a fusion protein and was shown to hydrolyze p-nitrophenylphosphate and inactivate mitogen-activated protein kinase, thus proving that hVH-5 possessed phosphatase activity. A unique proline-rich region distinguished hVH-5 from other closely related protein tyrosine phosphatases. Another feature that distinguished hVH-5 from related phosphatases was that hVH-5 was expressed predominantly in the adult brain, heart, and skeletal muscle. In addition, in situ hybridization histochemistry of mouse embryo revealed high levels of expression and a wide distribution in the central and peripheral nervous system. Some specific areas of abundant hVH-5 expression included the olfactory bulb, retina, layers of the cerebral cortex, and cranial and spinal ganglia. hVH-5 was induced in PC12 cells upon nerve growth factor and insulin treatment in a manner characteristic of an immediate-early gene, suggesting a possible role in the signal transduction cascade.

Molecular and biochemical characterization of the mouse brain corticotropin-releasing hormone-binding protein

A 37 kDa corticotropin-releasing hormone-binding protein (CRH-BP), distinct from the CRH receptor, is expressed in rat anterior pituitary corticotrophs and many regions of the brain, suggesting that CRH-BP may modulate the biological activity of CRH. In these studies a mouse brain CRH-BP (mCRH-BP) cDNA has been isolated and characterized. The 1666 nucleotide mCRH-BP cDNA is expressed in brain and pituitary and encodes a 322 amino acid protein that is highly homologous to human and rat CRH-BPs. Recombinant mCRH-BP, expressed in cultured mammalian cells, binds human CRH (Kd(app) = 0.56 nM and Ki(app) = 0.37 nM) and the alpha-helical (9-41) CRH antagonist (Ki(app) = 0.28 nM) with high affinity, but exhibits much weaker affinity for ovine CRH (Ki(app) = 206 nM). Recombinant mCRH-BP also blocks CRH-induced adrenocorticotropin release from AtT-20 cells. Additional biochemical characterization of the binding activity of mCRH-BP indicates that CRH-BP and CRH receptor utilize different molecular interactions to bind CRH.

Differential expression of mRNAs for protein kinase inhibitor isoforms in mouse brain

Many neurotransmitters are known to regulate neuronal cell function by means of activation of cAMP-dependent protein kinase (PKA) and phosphorylation of neuronal substrate proteins, including transcription factors and ion channels. Here, we have characterized the gene expression of two isoforms of a protein kinase inhibitor (PKI) specific for PKA in mouse brain by RNase protection and in situ hybridization histochemistry. The studies demonstrate that the PKI alpha isoform is abundant in many regions of the adult mouse brain but particularly in cerebellum, hypothalamus, hippocampus, and cortex. In contrast, PKI beta is present at much lower levels in most brain regions but is found in significant amounts in the cerebellum, as well as in distinct nuclei within the pons, medulla, and hypothalamus. These results are consistent with a regulatory role of endogenous PKI in PKA-mediated signal transduction in brain and suggest differential functions for the two isoforms of PKI within the central nervous system.

Implementing transgenic and embryonic stem cell technology to study gene expression, cell-cell interactions and gene function

This review highlights the use of transgenic mice and gene targeting in the study of reproduction, pituitary gene expression, and cell lineage. Since 1980 numerous applications of transgenic animal technology have been reported. Altered phenotypes resulting from transgene expression demonstrated that introduced genes can exert profound effects on animal physiology. Transgenic mice have been important for the study of hormonal and developmental control of gene expression because gene expression in whole animals often requires more DNA sequence information than is necessary for expression in cell cultures. This point is illustrated by studies of pituitary glycoprotein hormone alpha- and beta-subunit gene expression (Kendall et al., Mol Endocrinol 1994; in press [1]. Transgenic mice have also been invaluable for producing animal models of cancer and other diseases and testing the efficacy of gene therapy. In addition, cell-cell interactions and cell lineage relationships have been explored by cell-specific expression of toxin genes in transgenic mice. Recent studies suggest that attenuated and inducible toxins hold promise for future transgene ablation experiments. Since 1987, embryonic stem (ES) cell technology has been used to create numerous mouse strains with targeted gene alterations, contributing enormously to our understanding of the functional importance of individual genes. For example, the unexpected development of gonadal tumors in mice with a targeted disruption of the inhibin gene revealed a potential role for inhibin as a tumor suppressor (Matzuk et al., Nature 1992:360: 313-319 [2]. The transgenic and ES cell technologies will undoubtedly continue to expand our understanding and challenge our paradigms in reproductive biology.

Expression of corticotropin-releasing hormone transgenes in neurons of adult and developing mice

The DNA sequences important for cell-specific expression and developmental regulation of corticotropin-releasing hormone (CRH) were analyzed in transgenic mice. A construct containing 0.5 kb of CRH 5' flanking DNA linked to the chloramphenicol acetyltransferase reporter gene was expressed in many brain regions and in several ectopic peripheral sites, suggesting that this portion of the CRH gene contains basal promoter activity but lacks DNA elements necessary for appropriate tissue specificity. Cell specificity of transgene expression was examined with a CRH-beta-galactosidase reporter construct containing the same 0.5-kb CRH promoter fragment, but also including the CRH structural gene and 2 kb of CRH 3' flanking DNA. Transgene expression was observed in inappropriate regions of the brain, but no expression was detected in peripheral tissues, suggesting that these additional CRH sequences suppress inappropriately high levels of peripheral expression. Cell-specific expression improved significantly with the inclusion of 8.7 kb of CRH 5' flanking DNA. Individual transgenic lines exhibited expression in a number of the major CRH neuronal groups including the paraventricular nucleus, medial geniculate nucleus, inferior olivary nucleus, and Barrington's nucleus. Transgene expression was properly activated in Barrington's nucleus during development. This study demonstrates that the regulatory control of cell-specific and developmentally appropriate CRH expression is complex, utilizing multiple DNA sequence elements located upstream and downstream of the CRH transcription start site.

Differential expression of corticotropin-releasing hormone in developing mouse embryos and adult brain

CRH mRNA was detected by in situ hybridization histochemistry in numerous regions of the adult mouse brain, including most prominently the paraventricular nucleus (PVN) of the hypothalamus, the inferior olivary nucleus, and Barrington's nucleus. After adrenalectomy, steady state CRH mRNA levels increased 1.7-fold, specifically in the PVN, consistent with reports of negative glucocorticoid regulation of CRH expression in the rat PVN. Ontogenetic analysis of CRH expression in fetal and neonatal mouse brain demonstrated CRH mRNA in PVN, Barrington's nucleus, olivary complex, and amygdaloid primordia on embryonic day 13.5. In contrast, CRH mRNA was not detectable in the cortex until after birth. CRH expression also exhibited differential regulation in ontogeny. CRH mRNA reached adult levels at markedly different times of development in each brain region, and CRH expression was reduced specifically in the PVN just before birth and the stress hyporesponsive period. High levels of CRH mRNA were present transiently in the developing lung and celiac ganglion. The novel findings of CRH expression in fetal lung during the period of glucocorticoid-induced lung maturation and in celiac ganglion during development of the sympathetic nervous system indicate that CRH may have some important developmental functions in addition to its role in activation of the stress response.

The cAMP-responsive element in the corticotropin-releasing hormone gene mediates transcriptional regulation by depolarization

Membrane depolarization is a critical element of neuronal signaling. In this study, the biochemical and molecular mechanisms involved in transcriptional regulation of the corticotropin-releasing hormone (CRH) gene by depolarization were investigated. In PC-12 cells, potassium-induced membrane depolarization increased expression of a CRH-reporter construct in a cAMP-dependent manner. This synergistic activation was mediated via calcium influx, predominantly via L-type calcium channels, and calmodulin. RNase protection assays demonstrated increased levels of CRH-reporter transcripts in stably transfected cells after treatment with cAMP and potassium, with the induced transcripts initiating at the major transcription initiation site of the human CRH gene. At the genomic level, the CRH cAMP-responsive element conferred both positive cAMP and synergistic cAMP/depolarization regulation to a heterologous promoter. Additionally, DNase I protection assays demonstrated similar nuclear protein/DNA binding profiles across the cAMP-responsive element after treatment of PC-12 cells with potassium or potassium/cAMP. These results support a model in which the protein(s) binding to the cAMP-responsive element integrates signals initiated by multiple pathways (cAMP and calcium) and transmits that integrated signal to the basal transcription machinery, resulting in increased levels of gene expression.

Regulation of the human enkephalin promoter by two isoforms of the catalytic subunit of cyclic adenosine 3',5'-monophosphate-dependent protein kinase

Cyclic AMP regulates a variety of cellular responses through activation of the catalytic subunit of cAMP-dependent protein kinase. The cDNAs for two protein isoforms of the catalytic subunit, C alpha and C beta, were placed into expression vectors, and their ability to stimulate cAMP-dependent transcription of the human enkephalin promoter was examined in transiently transfected CV-1 cells. Expression vectors for C alpha and C beta that were directed by the human cytomegalovirus promoter produced up to 350- and 200-fold increases in chloramphenicol acetyltransferase activity, respectively, when cotransfected with the ENKAT-12 reporter plasmid. Transcriptional activation was shown to be dependent upon functional kinase activity by point mutations in catalytic subunit vectors which eliminated activation. Transcriptional activation by C alpha and C beta was eliminated when the cAMP response elements (CREs) were deleted from the native enkephalin promoter, but activation was recovered when this region was replaced with an oligonucleotide containing two copies of the somatostatin CRE consensus TGACGTCA. C alpha expression vectors were found to produce 2-fold greater transcriptional activation than C beta expression vectors. These results were most likely due to the cellular kinase activity produced by the catalytic subunit expression vectors and did not appear to be dependent on CRE motif or substrate specificity. In vitro mutagenesis indicates that neither C alpha nor C beta requires N-terminal myristylation for transcriptional activation, but threonine-197 is critical to subunit function.

Identification of a cyclic adenosine monophosphate-responsive element in the rat corticotropin-releasing hormone gene

The molecular mechanisms involved in the regulation of expression of the rat CRH gene have been examined in rat pheochromocytoma (PC-12) cells transiently transfected with a chimeric gene containing 1.4 kilobases of rat CRH 5'-flanking DNA fused to the bacterial reporter gene encoding chloramphenicol acetyltransferase. Cyclic AMP analogs and activators of adenylate cyclase positively regulate the expression of this chimeric gene in PC-12 cells, inducing chloramphenicol acetyltransferase activity more than 15-fold. The DNA sequence required for this response to cAMP has been localized to a 59 base pair region located between 238 and 180 base pairs 5' to the putative CRH mRNA cap site. This sequence can confer cAMP-responsiveness on a heterologous promoter in an orientation independent fashion and has homology to cAMP regulatory regions from a number of other eukaryotic genes.

Effect of bacteriophage T4 DNA topoisomerase gene 39 on level of beta chain of ribonucleoside diphosphate reductase in a T4 nrdB mutant

Bacteriophage T4 ribonucleoside diphosphate reductase consists of alpha 2 and beta 2 subunits encoded by genes nrdA and nrdB, respectively, and plays a central role in the T4-induced deoxyribonucleotide synthetase complex. The accompanying paper describes the decreased rate of synthesis of deoxyribonucleotides after infection by the T4 mutant, nrdB93, and the suppression of this defect by a second mutation in gene 39, coding for one of the three protein chains of T4 DNA topoisomerase. In this study we examined these effects at the protein level. On infection by nrdB93 not only was the beta 93 protein chain altered, as shown by its migration relative to the wild type protein in electrophoretic gels and by its temperature sensitivity, but the infected cells showed very low levels of the protein. However, on infection with the double mutant of nrdB93 and 39-01 (gene 39) the concentration of beta 93 chain returned to the values of beta protein found with wild type phage. A double mutant bearing nrdB93 and an amber mutation of gene 39 also suppressed the nrdB93 defect. By contrast, a temperature-sensitive mutant of gene 39, A41, did not show suppression at either 30 or 41 degrees C. Amber mutations in the two other genes coding for T4 DNA topoisomerase, 52 and 60, did not suppress the defect. We propose that the deficiency in the quantity of beta 93 chain and the suppression of this defect occur at the transcriptional or translational expression of the nrdB93 gene and that a specific domain of the gene 39 protein, not acting in the capacity of T4 DNA topoisomerase, inhibits the expression.

The rat corticotropin-releasing hormone gene

In this paper we have described the isolation and characterization of the rat corticotropin releasing hormone gene. Nucleotide sequence comparisons with the human CRH gene have demonstrated several interesting regions of homology and suggest that the gene was highly conserved through evolution. Additionally we have demonstrated the tissue-specific expression of the rat CRH gene. The regional distribution of expression parallels previously documented immunocytochemical demonstrations and supports the hypothesis that CRH peptides have multiple roles in different tissues. In the peripheral tissues that express CRH mRNA it will be very interesting to document the specific cell type of synthesis by using combined immunocytochemical and in situ histochemical techniques. Additionally we have described initial studies using gene transfer techniques to examine the cAMP responsiveness of the rat CRH gene. We are presently constructing other fusion genes (CRHCAT plasmids) in order to more carefully localize the DNA sequence in the rat CRH gene which mediates this effect, and compare it to the previously reported cAMP-responsive "consensus sequence." Similarly, we also plan to utilize the CRHCAT constructs to examine regulation of the rat CRH gene by glucocorticoids and several other hormone-mediated regulatory pathways. Through these CAT fusion studies we hope to gain a better understanding of the role of certain conserved sequences in the 5' flanking DNA for transcriptional control of the rat (and human) CRH genes.

Rat corticotropin-releasing hormone gene: sequence and tissue-specific expression

The rat corticotropin releasing hormone (CRH) gene has been isolated and characterized by DNA sequence analysis. The gene exhibits a structural organization similar to that of the human CRH gene. The nucleotide sequence encoding the entire rat CRH precursor is located on the second exon, while exon I encodes the 5'-untranslated region of the mRNA. Analysis of the nucleotide sequence homology between the human and rat CRH genes reveals several highly conserved regions including the CRH peptide-encoding sequence and the 5'-flanking sequence. RNA blot analysis demonstrates that CRH mRNA can be observed in numerous regions of the rat brain as well as the spinal cord, adrenal gland, pituitary, and testis.

Identification of bacteriophage T4 gene 60 product and a role for this protein in DNA topoisomerase

Bacteriophage T4 DNA topoisomerase has been isolated and shown to contain the proteins coded by the DNA-delay genes 39 and 52 (Liu, L. F., Liu, C.-C., and Alberts, B. M. (1979) Nature (Lond.) 281, 456-461 and Stetler, G. L., King, G. J., and Huang, W. M. (1979) Proc. Natl. Acad. Sci. U. S. A. 76, 3737-3741). From complementation measurements in vitro and from earlier genetic evidence, these workers suggested that the product of gene 60 (p60) was also a component of the DNA topoisomerase complex. This paper now establishes the identity of p60 and unequivocally shows that this protein is a component of the enzyme complex. T4 DNA topoisomerase was purified by a simplified two-column procedure and found to be a stable complex of p39, p52, and a protein with a relative molecular weight of 18,000. The 18,000-dalton chain has been unambiguously shown to be the product of gene 60 through the use of an amber mutant of gene 60 with Sup+ and Sup- hosts and analyses by two-dimensional gel electrophoresis. While p39 and p52 were tightly associated in the wild type enzyme complex, they were readily separated on a hydroxylapatite column from extracts of cells infected by an amber mutant of gene 60. These findings suggest that p60 plays a structural/functional role in the enzyme complex by holding the larger p39 and p52 in juxtaposition.

Identification of some bacteriophage T4 prereplicative proteins on two-dimensional gel proteins

Profiles of bacteriophage T4 early proteins resolved by a two-dimensional nonequilibrium pH gradient electrophoresis system (P. Z. O'Farrell, H. M. Goodman, and P. H. O'Farrell, Cell 12:1133--1142, 1977) are presented. Over 65 phage-induced proteins were resolved. Amber or deletion mutants were used to identify 17 proteins in the gel patterns as the products of specific genes.