Reciprocal limbic-cortical function and negative mood: converging PET findings in depression and normal sadness

OBJECTIVE

Theories of human behavior from Plato to Freud have repeatedly emphasized links between emotion and reason, a relationship now commonly attributed to pathways connecting phylogenetically "old" and "new" brain regions. Expanding on this theory, this study examined functional interactions between specific limbic and neocortical regions accompanying normal and disease-associated shifts in negative mood state.

METHOD

Regions of concordant functional change accompanying provocation of transient sadness in healthy volunteers and resolution of chronic dysphoric symptoms in depressed patients were examined with two positron emission tomography techniques: [15O]water and [18F]fluorodeoxyglucose, respectively.

RESULTS

With sadness, increases in limbic-paralimbic blood flow (subgenual cingulate, anterior insula) and decreases in neocortical regions (right dorsolateral prefrontal, inferior parietal) were identified. With recovery from depression, the reverse pattern, involving the same regions, was seen--limbic metabolic decreases and neocortical increases. A significant inverse correlation between subgenual cingulate and right dorsolateral prefrontal activity was also demonstrated in both conditions.

CONCLUSIONS

Reciprocal changes involving subgenual cingulate and right prefrontal cortex occur with both transient and chronic changes in negative mood. The presence and maintenance of functional reciprocity between these regions with shifts in mood in either direction suggests that these regional interactions are obligatory and probably mediate the well-recognized relationships between mood and attention seen in both normal and pathological conditions. The bidirectional nature of this limbic-cortical reciprocity provides additional evidence of potential mechanisms mediating cognitive ("top-down"), pharmacological (mixed), and surgical ("bottom-up") treatments of mood disorders such as depression.

Cingulate function in depression: a potential predictor of treatment response

The relationship between pretreatment regional cerebral glucose metabolism and eventual antidepressant drug response was measured using positron emission tomography (PET) in hospitalized patients with unipolar depression. Rostral anterior cingulate metabolism uniquely differentiated eventual treatment responders from non-responders. Hypometabolism characterized non-responders when compared with controls, in contrast to responders who were hypermetabolic. Metabolism in no other region discriminated the two groups, nor did associated demographic, clinical or behavioral measures, including motor speed, cognitive performance, depression severity or illness chronicity. Cingulate hypermetabolism may represent an important adaptive response to depression and failure of this response may underlie poor outcome. A critical role for rostral cingulate area 24a/b in the limbic-cortical network involved in abnormal mood states is proposed.

Use of implicit motor imagery for visual shape discrimination as revealed by PET

Positron emission tomography (PET) can be used to map brain regions that are active when a visual object (for example, a hand) is discriminated from its mirror form. Chronometric studies suggest that viewers 'solve' this visual shape task by mentally modelling it as a reaching task, implicitly moving their left hand into the orientation of any left-hand stimulus (and conversely for a right-hand stimulus). Here we describe an experiment in which visual and somatic processing are dissociated by presenting right hands to the left visual field and vice versa. Frontal (motor), parietal (somatosensory) and cerebellar (sensorimotor) regions similar to those activated by actual and imagined movement are strongly activated, whereas primary somatosensory and motor cortices are not. We conclude that mental imagery is realized at intermediate-to-high order, modality-specific cortical systems, but does not require primary cortex and is not constrained to the perceptual systems of the presented stimuli.

Perception of facial emotion in schizophrenic and right brain-damaged patients

Deficits in the perception of facial emotion have been demonstrated in patients with right-sided brain damage (RBD) and schizophrenia (SZ). Furthermore, recent speculations have implicated right-hemisphere dysfunction in Type II schizophrenics, especially those with a preponderance of "negative symptoms" and flat affect. The performance of SZ, RBD, and normal control subjects was compared on measures assessing facial emotional perception. Both identification and discrimination paradigms were used, with positive/pleasant and negative/unpleasant emotions. To examine the effects of visuospatial and facial processing on facial emotion tasks, the Visual Matrices Test and the Benton Facial Recognition Test were administered. On both facial emotion tests, SZ and RBD patients were significantly impaired relative to normal subjects, but not different from each other. The SZ and RBD patients were also impaired on the matrices and facial recognition tests. When the effects of the matrices and neutral face recognition tests were statistically controlled, significant group differences remained for the identification task but not for the discrimination task. Thus, methodologies are presented for the neuropsychological study of facial emotional perception, and some support is provided for the notion that negative-symptom schizophrenia is associated with right hemisphere dysfunction.

A role for DNA methylation in gastrulation and somite patterning

DNA methylation constitutes an important epigenetic factor in the control of genetic information. In this study, we analyzed expression of the DNA methyltransferase gene and examined DNA methylation patterns during early development of the zebrafish. Maternal transcripts of the zebrafish DNA methyltransferase gene (MTase) are ubiquitously present at high levels in early embryos with overall levels decreasing after the blastula stage. At 24 h, methyltransferase mRNA is predominantly found in the brain, neural tube, eyes, and differentiating somites. Expression of MTase in the somites is highest in the anterior cells of the somites. Despite the high levels of MTase mRNA in blastula-stage embryos, we observe DNA hypomethylation at the blastula and gastrula stages compared to sperm or older embryos. Zebrafish embryos treated with 5-azacytidine (5-azaC) and 5-aza-2-deoxycytidine (5-azadC), nucleotide analogs known to induce cellular differentiation and DNA hypomethylation in mammalian cells, exhibit DNA hypomethylation and developmental perturbations. These defects are specifically observed in embryos treated at the beginning of the blastula period, just prior to midblastula transition. The most common phenotype is the loss of tail and abnormal patterning of somites. Head development is also affected in some embryos. Histological and in situ hybridization analyses reveal whole or partial loss of a differentiated notochord and midline muscle in treated embryos. When examined during gastrulation, 5-azaC-treated embryos have a shortened and thickened axial mesoderm. We propose that DNA methylation is required for normal gastrulation and subsequent patterning of the dorsal mesoderm.

Identification and characterization of a human cDNA and gene encoding a ubiquitously expressed glucose-6-phosphatase catalytic subunit-related protein

Glucose-6-phosphatase (G6Pase) catalyzes the final step in the gluconeogenic and glycogenolytic pathways, the hydrolysis of glucose-6-phosphate (G6P) to glucose and phosphate. This paper describes the identification and characterization of a human cDNA and gene encoding a ubiquitously expressed G6Pase catalytic subunit-related protein (UGRP). The ORF of this UGRP cDNA encodes a protein (346 amino acids (aa); M(r) 38 709) which shares 36% overall identity to the human G6Pase catalytic subunit (357 aa; M(r) 40 487). UGRP exhibits a similar predicted transmembrane topology and conservation of many of the catalytically important residues with the G6Pase catalytic subunit; however, unlike the G6Pase catalytic subunit, UGRP does not catalyze G6P hydrolysis. UGRP mRNA was detected by RNA blot analysis in every tissue examined with the highest expression in muscle. Database analysis showed that the human UGRP gene is composed of six exons, spans approximately 5.4 kbp of genomic DNA and is located on chromosome 17q21 with the G6Pase catalytic subunit gene. The UGRP gene transcription start sites were mapped by primer extension analysis, and the activity of the UGRP gene promoter was analyzed using luciferase fusion gene constructs. In contrast to the G6Pase catalytic subunit gene promoter, the UGRP promoter was highly active in all cell lines examined.

Specific craniofacial cartilage dysmorphogenesis coincides with a loss of dlx gene expression in retinoic acid-treated zebrafish embryos

Treatments of zebrafish embryos with retinoic acid (RA), a substance known to cause abnormal craniofacial cartilage development in other vertebrates, result in dose- and stage-dependent losses of dlx homeobox gene expression in several regions of the embryo. Dlx expression in neural crest cells migrating from the hindbrain and in the visceral arch primordia is particularly sensitive to RA treatment. The strongest effects are observed when RA is administered prior to or during crest cell migration but effects can also be observed if RA is applied when the cells have entered the primordia of the arches. Losses of dlx expression correlate either with the loss of cartilage elements originating from hindbrain neural crest cells or with abnormal morphology of these elements. Cartilage elements that originate from midbrain neural crest cells, which do not express dlx genes, are less affected. Taken together with the observation that the normal patterns of visceral arch dlx expression just prior to cartilage condensation resemble the morphology of the cartilage elements that are about to differentiate, our results suggest that dlx genes are an important part of a multi-step process in the development of a subset of craniofacial cartilage elements.

Cloning and characterization of the human and rat islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP) genes

Islet-specific glucose-6-phosphatase (G6Pase) catalytic subunit-related protein (IGRP) is a homolog of the catalytic subunit of G6Pase, the enzyme that catalyzes the terminal step of the gluconeogenic pathway. Its catalytic activity, however, has not been defined. Since IGRP gene expression is restricted to islets, this suggests a possible role in the regulation of islet metabolism and, hence, insulin secretion induced by metabolites. We report here a comparative analysis of the human, mouse, and rat IGRP genes. These studies aimed to identify conserved sequences that may be critical for IGRP function and that specify its restricted tissue distribution. The single copy human IGRP gene has five exons of similar length and coding sequence to the mouse IGRP gene and is located on human chromosome 2q28-32 adjacent to the myosin heavy chain 1B gene. In contrast, the rat IGRP gene does not appear to encode a protein as a result of a series of deletions and insertions in the coding sequence. Moreover, rat IGRP mRNA, unlike mouse and human IGRP mRNA, is not expressed in islets or islet-derived cell lines, an observation that was traced by fusion gene analysis to a mutation of the TATA box motif in the mouse/human IGRP promoters to TGTA in the rat sequence. The results provide a framework for the further analysis of the molecular basis for the tissue-restricted expression of the IGRP gene and the identification of key amino acid sequences that determine its biological activity.

Disruption of zebrafish somite development by pharmacologic inhibition of Hsp90

Members of the Hsp90 family of molecular chaperones play important roles in allowing some intracellular signaling molecules and transcription factors to reach and maintain functionally active conformations. In the present study, we have utilized the specific Hsp90-binding agent, geldanamycin, to examine the requirement for Hsp90 during zebrafish development. We show that geldanamycin interacts with both the alpha and the beta-isoforms of zebrafish Hsp90 and that geldanamycin-treated embryos consistently exhibit a number of defects in tissues which express either one of these genes. Within the somites, geldanamycin treatment results in the absence of eng-2-expressing muscle pioneer cells. However, early development of adaxial cells, which give rise to muscle pioneers and which strongly express the hsp90alpha gene shortly before muscle pioneer formation, appeared unaffected. Furthermore, development of the notochord, which provides many of the signals required for proper somite patterning and which does not express detectable levels of either hsp90alpha or hsp90beta mRNA, was similarly unaffected in geldanamycin-treated embryos. The data are consistent with there being a temporal and spatial requirement for Hsp90 function within somitic cells which is necessary for the formation of eng-2-expressing muscle pioneers and possibly other striated muscle fiber types.

Deletion of the gene encoding the islet-specific glucose-6-phosphatase catalytic subunit-related protein autoantigen results in a mild metabolic phenotype

AIMS/HYPOTHESIS

Islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP, now known as glucose-6-phosphatase, catalytic, 2 [G6PC2]) has recently been identified as a major autoantigen in mouse and human type 1 diabetes. Strategies designed to suppress expression of the gene encoding G6PC2 might therefore be useful in delaying or preventing the onset of this disease. However, since the function of G6PC2 is unclear, the concern with such an approach is that a change in G6PC2 expression might itself have deleterious consequences.

METHODS

To address this concern and assess the physiological function of G6PC2, we generated G6pc2-null mice and performed a phenotypic analysis focusing principally on energy metabolism.

RESULTS

No differences in body weight were observed and no gross anatomical or behavioural changes were evident. In 16-week-old animals, following a 6-h fast, a small but significant decrease in blood glucose was observed in both male (-14%) and female (-11%) G6pc2 (-/-) mice, while female G6pc2 (-/-) mice also exhibited a 12% decrease in plasma triacylglycerol. Plasma cholesterol, glycerol, insulin and glucagon concentrations were unchanged.

CONCLUSIONS/INTERPRETATION

These results argue against the possibility of G6PC2 playing a major role in pancreatic islet stimulus secretion coupling or energy homeostasis under physiological conditions imposed by conventional animal housing. This indicates that manipulating the expression of G6PC2 for therapeutic ends may be feasible.

The pharmacokinetics of hyperpolarized xenon: implications for cerebral MRI

In this work, a compartmental model to predict the concentration of hyperpolarized xenon (Xe) in the brain is developed based on the well established kinetics of Xe and estimated T1 values for the compartments. For the gaseous compartments, T1 was set to 12 seconds. For the tissue compartments, T1 was set to 6 seconds. Three gas delivery techniques were modeled: hyperventilation followed by breath-hold, continual breathing, and hyperventilation followed by continual breathing. Based on Xe CT, it is estimated that the maximum concentration of Xe that could be breathed is 80%. Based on this value and the estimated maximum polarization of 50%, the peak gray matter concentration of hyperpolarized Xe is calculated to be .036 mM. This leads to an estimated signal-to-noise ratio (SNR), at 2 T, for hyperpolarized Xe that is a factor of 50 lower than the SNR for proton MRI. The peak concentration of hyperpolarized Xe was also calculated over a wide range of gas and tissue T1 values. This model also predicts that the arterial blood will have a concentration of hyperpolarized Xe that is 10 times greater than the concentration in gray matter. An interactive version of the model can be found on the World Wide Web at http:(/)/ric.uthscsa.edu/staff /charlesmartinphd.html.

Genotype-specific modifiers of transgene methylation and expression in the zebrafish, Danio rerio

Previous reports involving mammalian systems, particularly mice, have demonstrated the existence of cis- and trans-acting modifiers of transgene methylation. These modifiers are thought to be important in dominance modification, genome imprinting and cellular expression mosaicism. Their potential role in the penetrance and severity of many complex human diseases could be of even greater significance. In the present investigation we demonstrate that modifiers that act in a similar fashion to those identified in mice also exist in a non-mammalian vertebrate, the zebrafish Danio rerio. We also provide evidence that the transgene methylation pattern may be influenced by the sex of the individual and environmental modulators such as temperature and sodium butyrate. These data support the theory that this type of dominance modification is mechanistically similar to position effect variegation in Drosophila. Furthermore, these data suggest evolutionary conservation of the modifiers, at least within vertebrates, and imply that they and their actions are important in normal vertebrate development.

DNA methylation and genome imprinting in the zebrafish, Danio rerio: some evolutionary ramifications

Although methylation has been recognized as an important component in a number of developmental processes in mammals, in zebrafish almost nothing is known about this epigenetic modification. This is despite the fact that the zebrafish is becoming increasingly popular as a developmental model system. The little work that has been done on methylation and development in fish concerns genomic imprinting. In mammals, imprinting results in an inability to reproduce parthenogenetically because a genetic contribution from both parents is necessary to successfully complete development. However, this is not true of zebrafish, and a number of the theories that have been presented to explain the evolution of imprinting are not consistent with imprinting in these fish. A new model is presented that discusses some of the potential evolutionary ramifications of methylation and imprinting and that leads to the suggestion that imprinting may actually be a simple genetic mechanism to enhance the efficient evolution of both individual genetic loci and combinations of loci with related functions, without risking the population as a whole. This model can accommodate all of the information known about imprinting, including its broad phylogenetic range, imprinting by both males and females, and the diverse nature of the genes that are known to be imprinted.

Social functioning and facial emotional expression in neurological and psychiatric disorders

This study examined the relationship between facial expression and social functioning in schizophrenic, depressed, right-brain-damaged, Parkinson's disease, and normal adult participants. Raters evaluated general intensity and amount of positive and negative facial emotion while participants were producing monologues regarding pleasant and unpleasant experiences. Social functioning items were derived from three standardized inventories. Overall, patient groups displayed more negative and less positive emotion than normals, and the schizophrenic and right-brain-damaged groups showed less intense expressions than normals. Correlational analyses suggested that the more intense the facial expressions, the better the social functioning, and that the more negative emotion displayed, the poorer the social functioning.

Furrowing surface contraction wave coincident with primary neural induction in amphibian embryos

We predicted, and have now observed, a surface contraction wave in axolotl (Ambystoma mexicanum) embryos that appears to coincide temporally and spatially with primary neural induction and homoiogenetic induction, and with involution of the chordomesoderm. The wave starts from a focus anterior to the dorsal lip of the blastopore and spreads as an ellipse, until part of it encounters the rim of the blastopore and vanishes there. The remaining arc then continues over the dorsal hemisphere until it reforms an ellipse that decreases in size. About 9 to 12 hours after it begins, the wave vanishes at a focus diametrically opposite its point of origin. The wave involves both local contraction and furrowing in the monolayer ectoderm. To a good approximation, the hemispherical portion of the ectoderm traversed by the wave becomes neuroepithelium, while the ectoderm not traversed by the wave becomes epidermis. The wave might provide a mechanism to determine the time and location at which neuroepithelial differentiation occurs.

Stable transfer of zebrafish chromosome segments into mouse cells

Whole-cell fusion between zebrafish fibroblast-like ZF4 cells and mouse B78 melanoma cells resulted in hybrids containing one or a few zebrafish chromosome segments in a murine chromosomal background. Fluorescence in situ hybridization to hybrid cell metaphases with a zebrafish genomic DNA probe revealed that many hybrids contained zebrafish chromosome segments that were either inserted or translocated to a mouse chromosome, whereas other hybrids contained zebrafish chromosomes with no evidence of insertion or translocation. We have assigned hybrids to 17 linkage groups of the genetic map of the zebrafish genome. Our results demonstrate the feasibility of producing somatic cell hybrids between distantly related species. Zebrafish/mouse cell hybrids will provide a useful tool for the physical mapping of the zebrafish genome and for the cloning of genes affected in zebrafish mutants.

Upstream stimulatory factor (USF) and neurogenic differentiation/beta-cell E box transactivator 2 (NeuroD/BETA2) contribute to islet-specific glucose-6-phosphatase catalytic-subunit-related protein (IGRP) gene expression

Islet-specific glucose-6-phosphatase (G6Pase) catalytic-subunit-related protein (IGRP) is a homologue of the catalytic subunit of G6Pase, the enzyme that catalyses the final step of the gluconeogenic pathway. The analysis of IGRP-chloramphenicol acetyltransferase (CAT) fusion-gene expression through transient transfection of islet-derived beta TC-3 cells revealed that multiple promoter regions, located between -306 and -97, are required for maximal IGRP-CAT fusion-gene expression. These regions correlated with trans -acting factor-binding sites in the IGRP promoter that were identified in beta TC-3 cells in situ using the ligation-mediated PCR (LMPCR) footprinting technique. However, the LMPCR data also revealed additional trans -acting factor-binding sites located between -97 and +1 that overlap two E-box motifs, even though this region by itself conferred minimal fusion-gene expression. The data presented here show that these E-box motifs are important for IGRP promoter activity, but that their action is only manifest in the presence of distal promoter elements. Thus mutation of either E-box motif in the context of the -306 to +3 IGRP promoter region reduces fusion-gene expression. These two E-box motifs have distinct sequences and preferentially bind NeuroD/BETA2 (neurogenic differentiation/beta-cell E box transactivator 2) and upstream stimulatory factor (USF) in vitro, consistent with the binding of both factors to the IGRP promoter in situ, as determined using the chromatin-immunoprecipitation (ChIP) assay. Based on experiments using mutated IGRP promoter constructs, we propose a model to explain how the ubiquitously expressed USF could contribute to islet-specific IGRP gene expression.

Quantitative PET with positron emitters that emit prompt gamma rays

The purpose of this work was to determine the feasibility of using positron emitting isotopes that emit prompt gammas to acquire quantitative positron emission tomography (PET) data using standard PET instrumentation. Prompt gammas can contaminate PET data by increasing dead time, converting singles into invalid coincidences, and producing multiple coincidences which can lead to the replacement of valid coincidences by invalid coincidences. The measurements in this work were made by scanning point sources containing F-18, Na-22, and Co-60 and studying the effects of the prompt gammas on the PET data, We found that for the Na-22 point source, the annihilation photon coincidence rate was about 25 times the prompt gamma-annihilation photon coincidence rate in the entire active volume of the scanner. With scatter, the Na-22 prompt gamma-annihilation photon coincidence rate was 1.3 times higher than the F-18 scatter coincidence rate. The most significant effect of the prompt gamma was to increase dead time; the dead time correction factor for Cu-60 was 2.4 times higher than the correction factor for N-13 for the same source activity. We conclude that, in many cases, quantitative PET data can be readily obtained with isotopes that emit prompt gammas, using standard PET 2-D instrumentation. However there are some cases, such as 3-D PET, where prompt gammas could significantly contaminate the PET data.

Characterization of the mouse islet-specific glucose-6-phosphatase catalytic subunit-related protein gene promoter by in situ footprinting: correlation with fusion gene expression in the islet-derived betaTC-3 and hamster insulinoma tumor cell lines

Glucose-6-phosphatase (G6Pase) is a multicomponent system located in the endoplasmic reticulum comprising a catalytic subunit and transporters for glucose-6-phosphate, inorganic phosphate, and glucose. We have recently cloned a novel gene that encodes an islet-specific G6Pase catalytic subunit-related protein (IGRP) (Ebert et al., Diabetes 48:543-551, 1999). To begin to investigate the molecular basis for the islet-specific expression of the IGRP gene, a series of truncated IGRP-chloramphenicol acetyltransferase (CAT) fusion genes were transiently transfected into the islet-derived mouse betaTC-3 and hamster insulinoma tumor cell lines. In both cell lines, basal fusion gene expression decreased upon progressive deletion of the IGRP promoter sequence between -306 and -66, indicating that multiple promoter regions are required for maximal IGRP-CAT expression. The ligation-mediated polymerase chain reaction footprinting technique was then used to compare trans-acting factor binding to the IGRP promoter in situ in betaTC-3 cells, which express the endogenous IGRP gene, and adrenocortical Y1 cells, which do not. Multiple trans-acting factor binding sites were selectively identified in betaTC-3 cells that correlate with regions of the IGRP promoter identified as being required for basal IGRP-CAT fusion gene expression. The data suggest that hepatocyte nuclear factor 3 may be important for basal IGRP gene expression, as it is for glucagon, GLUT2, and Pdx-1 gene expression. In addition, binding sites for several trans-acting factors not previously associated with islet gene expression, as well as binding sites for potentially novel proteins, were identified.

Identification and characterization of a cDNA and the gene encoding the mouse ubiquitously expressed glucose-6-phosphatase catalytic subunit-related protein

Glucose-6-phosphatase (G6Pase) catalyzes the final step in the gluconeogenic and glycogenolytic pathways, the hydrolysis of glucose-6-phosphate (G6P) to glucose and phosphate. This paper describes the identification and characterization of a cDNA and the gene encoding the mouse ubiquitously expressed G6Pase catalytic subunit-related protein (UGRP). The open reading frame of this UGRP cDNA encodes a protein (346 amino acids (aa); Mr 38,755) that shares 36% overall identity (56% similarity) with the mouse G6Pase catalytic subunit (357 aa; Mr 40,454). UGRP exhibits a similar predicted transmembrane topology and conservation of many of the catalytically important residues with the G6Pase catalytic subunit; however, unlike the G6Pase catalytic subunit, UGRP does not catalyze G6P hydrolysis and does not contain a carboxy-terminal di-lysine endoplasmic reticulum retention signal. UGRP mRNA was detected by RNA blot analysis in every mouse tissue examined with the highest expression in heart, brain, testis and kidney. Database analysis showed that the mouse UGRP gene is composed of six exons, spans approximately 4.2 kbp of genomic DNA and is located on chromosome 11 along with the G6Pase catalytic subunit gene. The UGRP gene transcription start sites were mapped by primer extension analysis, and the activity of the mouse UGRP gene promoter was analyzed using luciferase fusion gene constructs. In contrast to the G6Pase catalytic subunit gene promoter, the UGRP promoter was highly active in all cell lines examined.

Selective stimulation of G-6-Pase catalytic subunit but not G-6-P transporter gene expression by glucagon in vivo and cAMP in situ

We recently compared the regulation of glucose-6-phosphatase (G-6-Pase) catalytic subunit and glucose 6-phosphate (G-6-P) transporter gene expression by insulin in conscious dogs in vivo (Hornbuckle LA, Edgerton DS, Ayala JE, Svitek CA, Neal DW, Cardin S, Cherrington AD, and O'Brien RM. Am J Physiol Endocrinol Metab 281: E713-E725, 2001). In pancreatic-clamped, euglycemic conscious dogs, a 5-h period of hypoinsulinemia led to a marked increase in hepatic G-6-Pase catalytic subunit mRNA; however, G-6-P transporter mRNA was unchanged. Here, we demonstrate, again using pancreatic-clamped, conscious dogs, that glucagon is a candidate for the factor responsible for this selective induction. Thus glucagon stimulated G-6-Pase catalytic subunit but not G-6-P transporter gene expression in vivo. Furthermore, cAMP stimulated endogenous G-6-Pase catalytic subunit gene expression in HepG2 cells but had no effect on G-6-P transporter gene expression. The cAMP response element (CRE) that mediates this induction was identified through transient transfection of HepG2 cells with G-6-Pase catalytic subunit-chloramphenicol acetyltransferase fusion genes. Gel retardation assays demonstrate that this CRE binds several transcription factors including CRE-binding protein and CCAAT enhancer-binding protein.

Long-range enhancers are required to maintain expression of the autoantigen islet-specific glucose-6-phosphatase catalytic subunit-related protein in adult mouse islets in vivo

OBJECTIVE

Islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP) is selectively expressed in islet beta-cells and is a major autoantigen in both mouse and human type 1 diabetes. This study describes the use of a combination of transgenic and transfection approaches to characterize the gene regions that confer the islet-specific expression of IGRP.

RESEARCH DESIGN AND METHODS

Transgenic mice were generated containing the IGRP promoter sequence from -306, -911, or -3911 to +3 ligated to a LacZ reporter gene. Transgene expression was monitored by 5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside staining of pancreatic tissue.

RESULTS

In all the transgenic mice, robust LacZ expression was detected in newborn mouse islets, but expression became mosaic as animals aged, suggesting that additional elements are required for the maintenance of IGRP gene expression. VISTA analyses identified two conserved regions in the distal IGRP promoter and one in the third intron. Transfection experiments demonstrated that all three regions confer enhanced luciferase reporter gene expression in beta TC-3 cells when ligated to a minimal IGRP promoter. A transgene containing all three conserved regions was generated by using a bacterial recombination strategy to insert a LacZ cassette into exon 5 of the IGRP gene. Transgenic mice containing a 15-kbp fragment of the IGRP gene were then generated. This transgene conferred LacZ expression in newborn mouse islets; however, expression was still suppressed as animals aged.

CONCLUSIONS

The data suggest that long-range enhancers 5' or 3' of the IGRP gene are required for the maintenance of IGRP gene expression in adult mice.

Foxa2 and MafA regulate islet-specific glucose-6-phosphatase catalytic subunit-related protein gene expression

Islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP/G6PC2) is a major autoantigen in both mouse and human type 1 diabetes. IGRP is selectively expressed in islet beta cells and polymorphisms in the IGRP gene have recently been associated with variations in fasting blood glucose levels and cardiovascular-associated mortality in humans. Chromatin immunoprecipitation (ChIP) assays have shown that the IGRP promoter binds the islet-enriched transcription factors Pax-6 and BETA2. We show here, again using ChIP assays, that the IGRP promoter also binds the islet-enriched transcription factors MafA and Foxa2. Single binding sites for these factors were identified in the proximal IGRP promoter, mutation of which resulted in decreased IGRP fusion gene expression in betaTC-3, Hamster insulinoma tumor (HIT), and Min6 cells. ChiP assays have shown that the islet-enriched transcription factor Pdx-1 also binds the IGRP promoter, but mutational analysis of four Pdx-1 binding sites in the proximal IGRP promoter revealed surprisingly little effect of Pdx-1 binding on IGRP fusion gene expression in betaTC-3 cells. In contrast, in both HIT and Min6 cells mutation of these four Pdx-1 binding sites resulted in a approximately 50% reduction in fusion gene expression. These data suggest that the same group of islet-enriched transcription factors, namely Pdx-1, Pax-6, MafA, BETA2, and Foxa2, directly or indirectly regulate expression of the two major autoantigens in type 1 diabetes.

Differential regulation of islet-specific glucose-6-phosphatase catalytic subunit-related protein gene transcription by Pax-6 and Pdx-1

Islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP) is selectively expressed in islet beta cells and is a major autoantigen in a mouse model of type I diabetes. The analysis of IGRP-chloramphenicol acetyltransferase (CAT) fusion gene expression through transient transfection of islet-derived betaTC-3 cells revealed that a promoter region, located between -273 and -254, is essential for high IGRP-CAT fusion gene expression. The sequence of this promoter region does not match that for any known islet-enriched transcription factor. However, data derived from gel retardation assays, a modified ligation-mediated polymerase chain reaction in situ footprinting technique and a SDS-polyacrylamide separation/renaturation procedure led to the hypothesis that this protein might be Pax-6, a conclusion that was confirmed by gel supershift assays. Additional experiments revealed a second non-consensus Pax-6 binding site in the -306/-274 IGRP promoter region. Pax-6 binding to these elements is unusual in that it appears to require both its homeo and paired domains. Interestingly, loss of Pax-6 binding to the -273/ -246 element is compensated by Pax-6 binding to the -306/-274 element and vice versa. Gel retardation assays revealed that another islet-enriched transcription factor, namely Pdx-1, binds four non-consensus elements in the IGRP promoter. However, mutation of these elements has little effect on IGRP fusion gene expression. Although chromatin immunoprecipitation assays show that both Pax-6 and Pdx-1 bind to the IGRP promoter within intact cells, in contrast to the critical role of these factors in beta cell-specific insulin gene expression, IGRP gene transcription appears to require Pax-6 but not Pdx-1.

Expression of the chaperonin 10 gene during zebrafish development

We have isolated a cDNA encoding chaperonin 10 (cpn10) from the zebrafish. Using northern, western, and in situ hybridization analysis, we observed that the cpn10 gene is expressed uniformly and ubiquitously throughout embryonic development of the zebrafish. Upregulation of cpn10 expression was observed following exposure of zebrafish embryos to a heat shock of 1 hour at 37 degrees C compared to control embryos raised at 27 degrees C. The extracellular form of Cpn10 called early pregnancy factor (EPF), found in the serum of pregnant mammals, was not detected in the serum of either male or female zebrafish. These expression studies suggest that Cpn10 plays a general role in zebrafish development as well as being consistent with the hypothesis that EPF is involved in the embryo implantation process in mammals.