MEF2 responds to multiple calcium-regulated signals in the control of skeletal muscle fiber type

Different patterns of motor nerve activity drive distinctive programs of gene transcription in skeletal muscles, thereby establishing a high degree of metabolic and physiological specialization among myofiber subtypes. Recently, we proposed that the influence of motor nerve activity on skeletal muscle fiber type is transduced to the relevant genes by calcineurin, which controls the functional activity of NFAT (nuclear family of activated T cell) proteins. Here we demonstrate that calcineurin-dependent gene regulation in skeletal myocytes is mediated also by MEF2 transcription factors, and is integrated with additional calcium-regulated signaling inputs, specifically calmodulin-dependent protein kinase activity. In skeletal muscles of transgenic mice, both NFAT and MEF2 binding sites are necessary for properly regulated function of a slow fiber-specific enhancer, and either forced expression of activated calcineurin or motor nerve stimulation up-regulates a MEF2-dependent reporter gene. These results provide new insights into the molecular mechanisms by which specialized characteristics of skeletal myofiber subtypes are established and maintained.

A protein encoded within the Down syndrome critical region is enriched in striated muscles and inhibits calcineurin signaling

Here we describe a small family of proteins, termed MCIP1 and MCIP2 (for myocyte-enriched calcineurin interacting protein), that are expressed most abundantly in striated muscles and that form a physical complex with calcineurin A. MCIP1 is encoded by DSCR1, a gene located in the Down syndrome critical region. Expression of the MCIP family of proteins is up-regulated during muscle differentiation, and their forced overexpression inhibits calcineurin signaling to a muscle-specific target gene in a myocyte cell background. Binding of MCIP1 to calcineurin A requires sequence motifs that resemble calcineurin interacting domains found in NFAT proteins. The inhibitory action of MCIP1 involves a direct association with the catalytic domain of calcineurin, rather than interference with the function of downstream components of the calcineurin signaling pathway. The interaction between MCIP proteins and calcineurin may modulate calcineurin-dependent pathways that control hypertrophic growth and selective programs of gene expression in striated muscles.

Transgenic animals in integrative biology: approaches and interpretations of outcome

Technological innovations in methods for genetic manipulation of laboratory animals and in techniques for assessment of cardiovascular, respiratory, behavioral, and metabolic physiology in mouse models afford unprecedented opportunities for research in integrative biology. We provide here an overview of basic and advanced techniques for generation of transgenic mice and a discussion of how transgenic technology can be most advantageously applied to important physiological questions that can be addressed only within the intact organism.

Strain evolution in coherent Ge/Si islands

Strain evolution of coherent Ge islands on Si(001) is measured using a newly developed transmission electron microscopy technique based on two-beam dark-field strain imaging. The strain measurements show that a metastable Ge island shape is involved in the shape transition between pyramids and domes; this shape is more readily observed for growth at 550 than 600 degrees C because of the slower rate at which islands cross the kinetic barrier between shapes. The strain relaxation changes discontinuously between pyramids and domes, indicating that the underlying shape transition is first order.

Stimulation of slow skeletal muscle fiber gene expression by calcineurin in vivo

Adult skeletal muscle fibers can be categorized into fast and slow twitch subtypes based on specialized contractile and metabolic properties and on distinctive patterns of muscle gene expression. Muscle fiber-type characteristics are dependent on the frequency of motor nerve stimulation and are thought to be controlled by calcium-dependent signaling. The calcium, calmodulin-dependent protein phosphatase, calcineurin, stimulates slow fiber-specific gene promoters in cultured skeletal muscle cells, and the calcineurin inhibitor, cyclosporin A, inhibits slow fiber gene expression in vivo, suggesting a key role of calcineurin in activation of the slow muscle fiber phenotype. Calcineurin has also been shown to induce hypertrophy of cardiac muscle and to mediate the hypertrophic effects of insulin-like growth factor-1 on skeletal myocytes in vitro. To determine whether activated calcineurin was sufficient to induce slow fiber gene expression and hypertrophy in adult skeletal muscle in vivo, we created transgenic mice that expressed activated calcineurin under control of the muscle creatine kinase enhancer. These mice exhibited an increase in slow muscle fibers, but no evidence for skeletal muscle hypertrophy. These results demonstrate that calcineurin activation is sufficient to induce the slow fiber gene regulatory program in vivo and suggest that additional signals are required for skeletal muscle hypertrophy.

Lithium therapy and signal transduction

Lithium is the simplest therapeutic agent available for the treatment of depression and has been used for over 100 years, yet no definitive mechanism for its effect has been established. Among the proposed mechanisms, two lithium-sensitive signal transduction pathways are active in the brain; these are mediated by glycogen synthase kinase 3beta (GSK-3beta) and inositol (1,4,5)-trisphosphate [Ins(1,4,5)P3] signalling. This article describes recent experiments in cell and developmental biology that advance our understanding of how lithium works and it presents new directions for the study of both depression and Alzheimer's disease (AD).

PR48, a novel regulatory subunit of protein phosphatase 2A, interacts with Cdc6 and modulates DNA replication in human cells

Initiation of DNA replication in eukaryotes is dependent on the activity of protein phosphatase 2A (PP2A), but specific phosphoprotein substrates pertinent to this requirement have not been identified. A novel regulatory subunit of PP2A, termed PR48, was identified by a yeast two-hybrid screen of a human placental cDNA library, using human Cdc6, an essential component of prereplicative complexes, as bait. PR48 binds specifically to an amino-terminal segment of Cdc6 and forms functional holoenzyme complexes with A and C subunits of PP2A. PR48 localizes to the nucleus of mammalian cells, and its forced overexpression perturbs cell cycle progression, causing a G(1) arrest. These results suggest that dephosphorylation of Cdc6 by PP2A, mediated by a specific interaction with PR48, is a regulatory event controlling initiation of DNA replication in mammalian cells.

Primer system for single cell detection of double mutation for Tay-Sachs disease

PURPOSE

Nearly 100% of infantile Tay-Sachs disease is produced by two mutations occurring in the alpha chain of the lysosomal enzyme beta-N-acetylhexosaminidase (HEXA) in the Ashkenazi Jewish population. Although others have described primer systems used to amplify both sites simultaneously, few discuss the allele dropout problems inherent in this test. Our goal was to construct a more robust test enabling stronger signal generation for single cell preimplantation genetic diagnosis and to investigate the occurrence of allele dropout.

METHODS

New nested primers were designed to optimize detection of both major Tay-Sachs mutations. Four hundred fifty-seven single cells, including normal cells and those carrying mutations of either the 4bp insertion exon 11 or splice-site intron 12 defects, were used to screen a new primer system.

RESULTS

Based on PCR amplified product analysis, total efficiency of amplification was 85.3%, (390/457). The allele dropout rate for the 4bp insertion mutation in exon 11 and splice-site mutation in intron 12 was 4.8% and 5.8%, respectively.

CONCLUSIONS

Multiple mutation detection and analysis within the Tay-Sachs disease gene (HEXA) is possible using single cells for clinical preimplantation genetic diagnosis. Alternative PCR primers and conditions offer various methods for developing systems compatible to specific program requirements.

Electrical stimulation of neonatal cardiac myocytes activates the NFAT3 and GATA4 pathways and up-regulates the adenylosuccinate synthetase 1 gene

Electrically stimulated pacing of cultured cardiomyocytes serves as an experimentally convenient and physiologically relevant in vitro model of cardiac hypertrophy. Electrical pacing triggers a signaling cascade that results in the activation of the muscle-specific Adss1 gene and the repression of the nonmuscle Adss2 isoform. Activation of the Adss1 gene involves the calcineurin-mediated dephosphorylation of NFAT3, allowing its translocation to the nucleus, where it can directly participate in Adss1 gene activation. Mutational studies show that an NFAT binding site located in the Adss1 5'-flanking region is essential for this activation. Electrical pacing also results in the increased synthesis of GATA4, another critical cardiac transcription factor required for Adss1 gene expression. MEF2C also produces transactivation of the Adss1 gene reporter in control and paced cardiac myocytes. Using the Adss1 gene as a model, these studies are the first to demonstrate that electrical pacing activates the calcineurin/NFAT3 and GATA4 pathways as a means of regulating cardiac gene expression.

The winged-helix/forkhead protein myocyte nuclear factor beta (MNF-beta) forms a co-repressor complex with mammalian sin3B

Winged-helix/forkhead proteins regulate developmental events in both invertebrate and vertebrate organisms, but biochemical functions that establish a mechanism of action have been defined for only a few members of this extensive gene family. Here we demonstrate that MNF (myocyte nuclear factor)-beta, a winged-helix protein expressed selectively and transiently in myogenic precursor cells of the heart and skeletal muscles, collaborates with proteins of the mammalian Sin3 (mSin3) family to repress transcription. Mutated forms of MNF-beta that fail to bind mSin3 are defective in transcriptional repression and in negative growth regulation, an overexpression phenotype revealed in oncogenic transformation assays. These data extend the known repertoire of transcription factors with which mSin3 proteins can function as co-repressors to include members of the winged-helix gene family. Transcriptional repression by MNF-beta-mSin3 complexes may contribute to the co-ordination of cellular proliferation and terminal differentiation of myogenic precursor cells.

Laparoscopic oophoropexy and ovarian function in the treatment of Hodgkin disease

BACKGROUND

Hodgkin disease commonly affects women of reproductive age. Total lymph node irradiation (TNI) typically delivers a dose of 2000-4000 centigray (cGy) to the ovaries, which invariably results in premature ovarian failure (POF) and infertility unless the ovaries are shielded. Transposition of the ovaries at staging laparotomy has had mixed success and may be remote in time from pelvic radiation.

METHODS

A laparoscopic technique has been described that allows transposition of the ovaries just prior to pelvic radiation. This is a report of the outcome of 12 patients who underwent laparoscopic oophoropexy at the University of Florida from 1989 to 1995. Two were excluded from analysis, because one died and the other had a second malignancy for which radiation was aborted.

RESULTS

At follow-up, five patients had evidence of ovarian function, and the four patients of these five who desired children achieved pregnancies. All five had zero to two courses of chemotherapy. Two patients who subsequently had pregnancies had staging laparotomy with oophoropexy 5 and 6 months, respectively, before laparoscopy. In both cases the ovaries had migrated back to their original positions, and their therapy would have resulted in ovarian failure had the repeat procedure not been performed. Five patients had ovarian failure at follow-up. Four of the five had received multiple courses of chemotherapy; the other had pelvic primary disease and received 3500 cGy to the femoral lymph nodes and pelvis, with little central shielding.

CONCLUSIONS

Laparoscopic oophoropexy performed immediately prior to pelvic irradiation is effective in preserving ovarian function in nearly all patients who are to undergo TNI for Hodgkin disease and who receive minimal or no chemotherapy.

An inverse relation between the expression of tumor necrosis factor alpha (TNF-alpha) and TNF-alpha receptor in human endometrium

PROBLEM

To determine whether the expression of tumor necrosis factor (TNF-alpha) correlates with TNF-alpha receptor expression in human endometrium.

METHOD OF STUDY

A multiprimer synthetic cDNA standard template containing complimentary sequences for several cytokines including TNF-alpha and TNF-alpha receptor type 2 was constructed and used in quantitative reverse transcription polymerase chain reaction (Q-RT-PCR).

RESULTS

Endometrium from proliferative phase of the menstrual cycle expresses higher levels of TNF-alpha mRNA (2.35 +/- 0.2 x 10(5) copies/microg of total cellular RNA) than secretory phase ([1.3 +/- 0.08 x 10(5) copies] P < 0.05), with a significant reduction during menses (1.2 +/- 0.1 x 10(4) copies) and postmenopausal period (8.1 +/- 1.6 x 10(4) copies [P < 0.05]). In contrast, TNF-alpha type 1 receptor mRNA expression was higher in endometrium from the secretory phase (6.6 +/- 0.6 x 10(7) copies) compared to the menses (5.1 +/- 0.5 x 10(6) copies), proliferative phase (1.9 +/- 0.1 x 10(6) copies) and postmenopausal period (5.8 +/- 0.7 x 10(4) copies [P < 0.05]). Comparatively, TNF-alpha receptor type 2 is expressed 10 to 100 fold higher in the endometrium than TNF-alpha (P < 0.05).

CONCLUSION

The data confirm that human endometrium expresses TNF-alpha; and provide the first evidence that TNF-alpha expression is inversely related to TNF-alpha type 1 receptor expression during the menstrual cycle. Such an inverse relation between TNF-alpha and TNF-alpha receptor expression may provide a regulatory mechanism necessary to overcome the detrimental effect of high levels of TNF-alpha on various endometrial cell types.

Electronically configurable molecular-based logic gates

Logic gates were fabricated from an array of configurable switches, each consisting of a monolayer of redox-active rotaxanes sandwiched between metal electrodes. The switches were read by monitoring current flow at reducing voltages. In the "closed" state, current flow was dominated by resonant tunneling through the electronic states of the molecules. The switches were irreversibly opened by applying an oxidizing voltage across the device. Several devices were configured together to produce AND and OR logic gates. The high and low current levels of those gates were separated by factors of 15 and 30, respectively, which is a significant enhancement over that expected for wired-logic gates.

Loss of a prolyl oligopeptidase confers resistance to lithium by elevation of inositol (1,4,5) trisphosphate

The therapeutic properties of lithium ions (Li+) are well known; however, the mechanism of their action remains unclear. To investigate this problem, we have isolated Li+-resistant mutants from Dictyostelium. Here, we describe the analysis of one of these mutants. This mutant lacks the Dictyostelium prolyl oligopeptidase gene (dpoA). We have examined the relationship between dpoA and the two major biological targets of lithium: glycogen synthase kinase 3 (GSK-3) and signal transduction via inositol (1,4,5) trisphosphate (IP3). We find no evidence for an interaction with GSK-3, but instead find that loss of dpoA causes an increased concentration of IP3. The same increase in IP3 is induced in wild-type cells by a prolyl oligopeptidase (POase) inhibitor. IP3 concentrations increase via an unconventional mechanism that involves enhanced dephosphorylation of inositol (1,3,4,5,6) pentakisphosphate. Loss of DpoA activity therefore counteracts the reduction in IP3 concentration caused by Li+ treatment. Abnormal POase activity is associated with both unipolar and bipolar depression; however, the function of POase in these conditions is unclear. Our results offer a novel mechanism that links POase activity to IP3 signalling and provides further clues for the action of Li+ in the treatment of depression.

Expression of integrin messenger ribonucleic acid in human endometrium: a quantitative reverse transcription polymerase chain reaction study

OBJECTIVE

To assess the expression of selected integrin subunit's messenger RNA (mRNA) in human endometrium during the menstrual cycle.

DESIGN

A prospective comparative study.

SETTING

Academic research environment.

PATIENT(S)

Premenopausal women with histologically normal endometrium who were undergoing hysterectomy.

INTERVENTION(S)

Endometrial tissues were collected.

RESULT(S)

Human endometrium expresses integrins alpha2, alpha3, alpha4, alpha5, alpha6.1, alpha6.2, alpha v, beta1, beta2, beta3, and beta5, as well as fibronectin mRNA. The levels of endometrial integrins mRNA expression varied significantly, with the lowest levels observed for alpha2, beta3, and fibronectin and the highest for alpha5, beta2, and beta5. The levels of integrins alpha2, alpha3, and alpha5 mRNA expression were significantly higher during the proliferative phase, whereas alpha4, alpha6.2, alpha v, beta1, beta2, beta3, beta5, and fibronectin were higher during the secretory phase of the menstrual cycle. The alpha6.1 mRNA was found to be equally expressed in the endometrium during the menstrual cycle, whereas the most dramatic changes occurred in alpha v and beta3 expression, compared with other integrin subunits.

CONCLUSION(S)

Human endometrium expresses mRNA for several integrins and fibronectin, with up-regulation of alpha4, alpha v, beta1, and beta3 during the secretory phase of the menstrual cycle, suggesting that their differential expression may be regulated in part by ovarian steroids.

Cloning and characterization of a eukaryotic pantothenate kinase gene (panK) from Aspergillus nidulans

Pantothenate kinase (PanK) is the key regulatory enzyme in the CoA biosynthetic pathway. The PanK gene from Escherichia coli (coaA) has been previously cloned and the enzyme biochemically characterized; highly related genes exist in other prokaryotes. We isolated a PanK cDNA clone from the eukaryotic fungus Aspergillus nidulans by functional complementation of a temperature-sensitive E. coli PanK mutant. The cDNA clone allowed the isolation of the genomic clone and the characterization of the A. nidulans gene designated panK. The panK gene is located on chromosome 3 (linkage group III), is interrupted by three small introns, and is expressed constitutively. The amino acid sequence of A. nidulans PanK (aPanK) predicted a subunit size of 46.9 kDa and bore little resemblance to its bacterial counterpart, whereas a highly related protein was detected in the genome of Saccharomyces cerevisiae. In contrast to E. coli PanK (bPanK), which is regulated by CoA and to a lesser extent by its thioesters, aPanK activity was selectively and potently inhibited by acetyl-CoA. Acetyl-CoA inhibition of aPanK was competitive with respect to ATP. Thus, the eukaryotic PanK has a distinct primary structure and unique regulatory properties that clearly distinguish it from its prokaryotic counterpart.

Laparoscopic reoperation following failed antireflux surgery

BACKGROUND

The aim was to determine the feasibility of laparoscopic revision surgery following previous open and laparoscopic antireflux operations.

METHODS

The outcome was determined for 27 patients (14 men, 13 women) who had undergone attempted laparoscopic revision between 3 months and 25 years after a previous antireflux operation. Median follow-up was 12 (range 3-48) months.

RESULTS

Thirteen patients had previously had an open antireflux procedure (Nissen fundoplication, seven; transthoracic anatomical repair, five; Belsey procedure, one) and 14 a laparoscopic procedure (Nissen, 12; anterior partial fundoplication, two). The indications for revision were: recurrent reflux, 15; paraoesophageal hiatus hernia, six; troublesome dysphagia, six. Fifteen procedures comprised construction of a new Nissen fundoplication, six conversion from a Nissen to a partial wrap, three repair of a paraoesophageal hernia and three widening of the oesophageal hiatus. Revision was successfully completed laparoscopically in 12 patients following a previous laparoscopic procedure and in nine following a previous open operation. Median operating time was 105 min after previous open surgery and 80 min after laparoscopic surgery. No perioperative complications occurred in either group and a good outcome was achieved in 25 of the 27 patients.

CONCLUSION

Laparoscopic reoperative antireflux surgery is feasible. Reoperation is likely to be more difficult following failure of an open procedure than a laparoscopic one.

Pediatric research and the parens patriae jurisdiction in Canada and England

This paper considers the issue of enrolling non-autonomous minors as participants in pediatric research in light of two high court decisions concerning the sterilization of non-autonomous individuals in Canada and England. In particular, this paper looks at the 1986 case of Re Eve in which the Supreme Court of Canada found that sterilization of such persons under the parens patriae jurisdiction can be justified only if direct, therapeutic benefit to the person has been established. It is compared to the 1987 decision in Re B (a minor), in which the English Law Lords repudiated the Canadian decision and upheld the broader, traditional interpretation of the parens patriae jurisdiction which allowed best interests as justification for the non-therapeutic sterilization of non-autonomous persons. With reference to differences in the interpretations of the parens patriae jurisdiction by these two courts, it is suggested that until such time that the Canadian courts consider a case directly on point, pediatric researchers in that country must presume greater restrictions when enrolling non-autonomous subjects in research protocols than in countries such as England.

Cell cycle control in the terminally differentiated myocyte. A platform for myocardial repair?

Currently available pharmaceuticals exert beneficial effects on morbidity and mortality in heart failure. Only cardiac transplantation, however, provides a definitive solution to the irreversible loss of cardiomyocytes in the failing heart. The limited availability of donor hearts leaves the vast majority of afflicted patients in need. The need for innovative approaches to improve care for these patients is apparent.

Mice without myoglobin

Myoglobin, an intracellular haemoprotein expressed in the heart and oxidative skeletal myofibres of vertebrates, binds molecular oxygen and may facilitate oxygen transport from erythrocytes to mitochondria, thereby maintaining cellular respiration during periods of high physiological demand. Here we show, however, that mice without myoglobin, generated by gene-knockout technology, are fertile and exhibit normal exercise capacity and a normal ventilatory response to low oxygen levels (hypoxia). Heart and soleus muscles from these animals are depigmented, but function normally in standard assays of muscle performance in vitro across a range of work conditions and oxygen availability. These data show that myoglobin is not required to meet the metabolic requirements of pregnancy or exercise in a terrestrial mammal, and raise new questions about oxygen transport and metabolic regulation in working muscles.

Collaborative interactions between MEF-2 and Sp1 in muscle-specific gene regulation

Previous investigations have demonstrated synergistic interactions in vivo between CCAC and A/T-rich nucleotide sequence motifs as functional components of muscle-specific transcriptional enhancers. Using CCAC and A/T-rich elements from the myoglobin and muscle creatine kinase (MCK) gene enhancers, Sp1 and myocyte-specific enhancer factor-2 (MEF-2) were identified as cognate binding proteins that recognize these sites. Physical interactions between Sp1 and MEF-2 were demonstrated by immunological detection of both proteins in DNA binding complexes formed in vitro by nuclear extracts in the presence of only the A/T sequence motif, by coprecipitation of recombinant MEF-2 in the presence of a glutathione-S-transferase-Sp1 fusion protein bound to glutathione beads, and by a two-hybrid assay in Saccharomyces cerevisiae. The interaction with Sp1 in vitro and in vivo is specific for MEF-2 and was not observed with serum response factor, a related MADS domain protein. Forced expression of Sp1 and MEF-2 in insect cells otherwise lacking these factors promotes synergistic transcriptional activation of a promoter containing binding sites for both proteins. These data expand the repertoire of functional and physical interactions between lineage-restricted (MEF-2) and ubiquitous (Sp1) transcription factors that may be important for myogenic differentiation.

A calcineurin-dependent transcriptional pathway controls skeletal muscle fiber type

Slow- and fast-twitch myofibers of adult skeletal muscles express unique sets of muscle-specific genes, and these distinctive programs of gene expression are controlled by variations in motor neuron activity. It is well established that, as a consequence of more frequent neural stimulation, slow fibers maintain higher levels of intracellular free calcium than fast fibers, but the mechanisms by which calcium may function as a messenger linking nerve activity to changes in gene expression in skeletal muscle have been unknown. Here, fiber-type-specific gene expression in skeletal muscles is shown to be controlled by a signaling pathway that involves calcineurin, a cyclosporin-sensitive, calcium-regulated serine/threonine phosphatase. Activation of calcineurin in skeletal myocytes selectively up-regulates slow-fiber-specific gene promoters. Conversely, inhibition of calcineurin activity by administration of cyclosporin A to intact animals promotes slow-to-fast fiber transformation. Transcriptional activation of slow-fiber-specific transcription appears to be mediated by a combinatorial mechanism involving proteins of the NFAT and MEF2 families. These results identify a molecular mechanism by which different patterns of motor nerve activity promote selective changes in gene expression to establish the specialized characteristics of slow and fast myofibers.