Age-dependent sexual dimorphism in hippocampal cornu ammonis-1 perineuronal net expression in rats

INTRODUCTION

Perineuronal nets (PNNs) are extracellular matrices that encompass parvalbumin-expressing parvalbumin positive (PVALB+) fast-spiking inhibitory interneurons where they protect and stabilize afferent synapses. Recent observations that gonadal hormones influence PVALB+ neuron development suggest that PNN regulation may be sexually dimorphic. Sex differences in PNN abundance and complexity have been reported in sexually dimorphic nuclei in zebra finch brains; however, corresponding differences in mammalian brains have not been investigated.

METHODS

In this study we assessed the number of cortical and hippocampal PNNs in juvenile and young adult male and female rats using fluorescent immunohistochemistry for PVALB and the PNN marker Wisteria Floribunda Lectin.

RESULTS

We report here that PNNs are numerous and well developed in hippocampal cornu ammonis-1 of adult males but are lower in juvenile and possibly adult females. No significant differences were observed between sexes in cornu ammonis-3 or adjacent neocortex. There was an observed developmental difference in the neocortex as juveniles had more PVALB+ cells, but fewer PNN+ cells, than adults.

CONCLUSIONS

Because PNNs are integral for several hippocampal-mediated learning and memory tasks, these observations have potential sex-dependent translational implications for clinical strategies targeting cognitive dysfunction.

Ethics and communication: does students' comfort addressing: ethical issues vary by specialty team?

Ethics education aims to train physicians to identify and resolve ethical issues. To address ethical concerns, physicians may need to confront each other. We surveyed medical students to determine if their comfort challenging members of their ward teams about ethical issues varies by specialty and what attributes of students and their teams contributed to that comfort. Compared to other specialties, students felt significantly less comfortable challenging team members about ethical issues on surgery and obstetrics/gynecology. We suggest that ethics education must address the atmosphere on ward teams and give students skills to help them speak out despite their discomfort.

Calorie use and obesity among diabetic and non-diabetic Mvskoke Indians

Type 2 diabetes is a major cause of death among American Indians and obesity and physical inactivity are modifiable risk factors in the development of type 2 diabetes. Physical activity may have both a preventive effect and a secondary preventive effect of lessening insulin resistance in persons with type 2 diabetes. Moreover, for some individuals participation in daily regimens of physical activity is very difficult. Culture-specific physical activity may be an intervention to reduce obesity and prevent diabetes-related complications. Therefore, the research questions for this study were: (1) What is the body fat percentage of diabetic and non-diabetic Mskoke Indians?, (2) How does body fat percentage of Mvskoke Indians compare with recommended percentages for age and gender?, (3) What is the caloric use of Mvskoke Indians during daily and traditional cultural activities of dancing and stickball?, and (4) Are there relationships among body fat percentage, calorie use, gender, and diabetic status? The findings revealed that female diabetics' percentage of body fat in three age cohorts (40-49, 50-59, and 70+) was higher than that of non-diabetic females. By contrast, male diabetics had lower percentage of body fat than non-diabetic males. The actual mean percentage of body fat of the female participants ranged from 38.5% to 44%, roughly twice the standard recommended percentages of body fat of 20-24%. No significant difference was found in calorie use by gender or diabetic status. Analysis of calories during traditional activities revealed that 30 minutes of stickball used an average of 135.7 calories. Dancing for 33 minutes used an average of 149 calories. No significant relationship was found among percentage of body fat, caloric use, gender, and diabetic status.

Drosophila stretchin-MLCK is a novel member of the Titin/Myosin light chain kinase family

Members of the titin/myosin light chain kinase family play an essential role in the organization of the actin/myosin cytoskeleton, especially in sarcomere assembly and function. In Drosophila melanogaster, projectin is so far the only member of this family for which a transcription unit has been characterized. The locus of another member of this family, a protein related to Myosin light chain kinase, was also identified. The cDNA and genomic sequences published explain only the shorter transcripts expressed by this locus. Here, we report the complete molecular characterization of this transcription unit, which spans 38 kb, includes 33 exons and accounts for transcripts up to 25 kb in length. This transcription unit contains both the largest exon (12,005 nt) and the largest coding region (25,213 nt) reported so far for Drosophila. This transcription unit features both internal promoters and internal polyadenylation signals, which enable it to express seven different transcripts, ranging from 3.3 to 25 kb in size. The latter encodes a huge, titin-like, 926 kDa kinase that features two large PEVK-rich repeats, 32 immunoglobulin and two fibronectin type-III domains, which we designate stretchin-MLCK. In addition, the 3' end of the stretchin-MLCK transcription unit expresses shorter transcripts that encode 86 to 165 kDa isoforms of stretchin-MLCK that are analogous to vertebrate Myosin light chain kinases. Similarly, the 5' end of the Stretchin-Mlck transcription unit can also express transcripts encoding kettin and Unc-89-like isoforms, which share no sequences with the MLCK-like transcripts. Thus, this locus can be viewed as a single transcription unit, Stretchin-Mlck (genetic abbreviation Strn-Mlck), that expresses large, composite transcripts and protein isoforms (sequences available at http://www.academicpress.com/jmb), as well as a complex of two independent transcription units, the Stretchin and Mlck transcription units (Strn and Mlck, respectively) the result of a "gene fission" event, that encode independent transcripts and proteins with distinct structural and enzymatic functions.

Multiple forces contribute to cell sheet morphogenesis for dorsal closure in Drosophila

The molecular and cellular bases of cell shape change and movement during morphogenesis and wound healing are of intense interest and are only beginning to be understood. Here, we investigate the forces responsible for morphogenesis during dorsal closure with three approaches. First, we use real-time and time-lapsed laser confocal microscopy to follow actin dynamics and document cell shape changes and tissue movements in living, unperturbed embryos. We label cells with a ubiquitously expressed transgene that encodes GFP fused to an autonomously folding actin binding fragment from fly moesin. Second, we use a biomechanical approach to examine the distribution of stiffness/tension during dorsal closure by following the response of the various tissues to cutting by an ultraviolet laser. We tested our previous model (Young, P.E., A.M. Richman, A.S. Ketchum, and D.P. Kiehart. 1993. Genes Dev. 7:29-41) that the leading edge of the lateral epidermis is a contractile purse-string that provides force for dorsal closure. We show that this structure is under tension and behaves as a supracellular purse-string, however, we provide evidence that it alone cannot account for the forces responsible for dorsal closure. In addition, we show that there is isotropic stiffness/tension in the amnioserosa and anisotropic stiffness/tension in the lateral epidermis. Tension in the amnioserosa may contribute force for dorsal closure, but tension in the lateral epidermis opposes it. Third, we examine the role of various tissues in dorsal closure by repeated ablation of cells in the amnioserosa and the leading edge of the lateral epidermis. Our data provide strong evidence that both tissues appear to contribute to normal dorsal closure in living embryos, but surprisingly, neither is absolutely required for dorsal closure. Finally, we establish that the Drosophila epidermis rapidly and reproducibly heals from both mechanical and ultraviolet laser wounds, even those delivered repeatedly. During healing, actin is rapidly recruited to the margins of the wound and a newly formed, supracellular purse-string contracts during wound healing. This result establishes the Drosophila embryo as an excellent system for the investigation of wound healing. Moreover, our observations demonstrate that wound healing in this insect epidermal system parallel wound healing in vertebrate tissues in situ and vertebrate cells in culture (for review see Kiehart, D.P. 1999. Curr. Biol. 9:R602-R605).

Informed decision making in outpatient practice: time to get back to basics

CONTEXT

Many clinicians have called for an increased emphasis on the patient's role in clinical decision making. However, little is known about the extent to which physicians foster patient involvement in decision making, particularly in routine office practice.

OBJECTIVE

To characterize the nature and completeness of informed decision making in routine office visits of both primary care physicians and surgeons.

DESIGN

Cross-sectional descriptive evaluation of audiotaped office visits during 1993.

SETTING AND PARTICIPANTS

A total of 1057 encounters among 59 primary care physicians (general internists and family practitioners) and 65 general and orthopedic surgeons; 2 to 12 patients were recruited from each physician's community-based private office.

MAIN OUTCOME MEASURES

Analysis of audiotaped patient-physician discussions for elements of informed decision making, using criteria that varied with the level of decision complexity: basic (eg, laboratory test), intermediate (eg, new medication), or complex (eg, procedure). Criteria for basic decisions included discussion of the nature of the decision and asking the patient to voice a preference; other categories had criteria that were progressively more stringent.

RESULTS

The 1057 audiotaped encounters contained 3552 clinical decisions. Overall, 9.0% of decisions met our definition of completeness for informed decision making. Basic decisions were most often completely informed (17.2%), while no intermediate decisions were completely informed, and only 1 (0.5%) complex decision was completely informed. Among the elements of informed decision making, discussion of the nature of the intervention occurred most frequently (71 %) and assessment of patient understanding least frequently (1.5%).

CONCLUSIONS

Informed decision making among this group of primary care physicians and surgeons was often incomplete. This deficit was present even when criteria for informed decision making were tailored to expect less extensive discussion for decisions of lower complexity. These findings signal the need for efforts to encourage informed decision making in clinical practice.

Drosophila wing melanin patterns form by vein-dependent elaboration of enzymatic prepatterns

BACKGROUND

Animal melanin patterns are involved in diverse aspects of their ecology, from thermoregulation to mimicry. Many theoretical models have simulated pigment patterning, but little is known about the developmental mechanisms of color pattern formation. In Drosophila melanogaster, several genes are known to be necessary for cuticular melanization, but the involvement of these genes in melanin pattern evolution is unknown. We have taken a genetic approach to elucidate the developmental mechanisms underlying melanin pattern formation in various drosophilids.

RESULTS

We show that, in D. melanogaster, tyrosine hydroxylase (TH) and dopa decarboxylase (DDC) are required for melanin synthesis. Ectopic expression of TH, but not DDC, alone was sufficient to cause ectopic melanin patterns in the wing. Thus, changes in the level of expression of a single gene can result in a new level of melanization. The ontogeny of this ectopic melanization resembled that found in Drosophila species bearing wing melanin patterns and in D. melanogaster ebony mutants. Importantly, we discovered that in D. melanogaster and three other Drosophila species these wing melanin patterns are dependent upon and shaped by the circulation patterns of hemolymph in the wing veins.

CONCLUSIONS

Complex wing melanin patterns are determined by two distinct developmental mechanisms. Spatial prepatterns of enzymatic activity are established late in wing development. Then, in newly eclosed adults, melanin precursors gradually diffuse out from wing veins and are oxidized into dark brown or black melanin. Both the prepatterning and hemolymph-supplied components of this system can change during evolution to produce color pattern diversity.

Mechanical Resistance to Shear Stress: The Role of Echinoderm Egg Extracellular Layers

Extracellular layers (jelly coats) on echinoderm eggs are composed of a fibrous network imbedded in a gelatinous material. This type of fibrous network has the potential to protect eggs from mechanical stress. To determine the effects of shear stress and the role of jelly coats in protecting eggs from these stresses, eggs of the sea urchin Lytechinus variegatus, both with and without intact jelly coats, were exposed to shear stresses ranging from 0.3 to 2 Pa in a cone and plate viscometer. The percentage of eggs remaining intact after exposure to the shear stress was assessed. The results indicate that shear stress can damage eggs and that jelly coats may play a role in decreasing the effects of these stresses. Eggs with jelly coats remained intact and fertilizable at greater shear stresses than those with the coats removed. This is the first evidence that extracellular layers on invertebrate eggs can provide protection from mechanical forces.

Diabetes research in an American Indian community

PURPOSE

To describe field experiences of a nurse-led team conducting collaborative research on diabetes with an American Indian community. Diabetes is of epidemic proportions among Indians. Methodological reports can assist nurse researchers to make important contributions to Indian health and diabetes care.

ORGANIZING FRAMEWORK

Wax's stages of fieldwork: Initiation, fieldwork, post-field work. SCOPE AND METHOD: Report of key research experiences from all phases of a study with an Indian community (1988-1996). Based on review of classic literature, field notes, and team meetings.

FINDINGS

Methodological literature on research with Indians and cultural tutelage by Indians were helpful but neither sufficient nor infallible. A long period of investigator presence in the community before beginning the research was extremely useful. The need for researchers to explain their presence and the contribution of research to the community was ongoing.

CONCLUSIONS

Wax's conception of field work as a dialectic process was supported. A collaborative, community focus and willingness to spend much time acquiring cultural knowledge can facilitate successful research on Indian health.

GFP-moesin illuminates actin cytoskeleton dynamics in living tissue and demonstrates cell shape changes during morphogenesis in Drosophila

Moesin, ezrin, and radixin (MER) are components of the cortical actin cytoskeleton and membrane processes such as filopodia and microvilli. Their C-terminal tails contain an extended region that is predicted to be helical, an actin binding domain, and a region(s) that participates in self-association. We engineered an in vivo fluorescent actin binding protein (GFP-moe) by joining sequences that encode the jellyfish green fluorescent protein (GFP) to sequences that encode the C-terminal end of the sole Drosophila MER homolog, moesin [Moesin-like gene product, referred to previously as the D17 MER-like protein; Edwards et al., 1994, Proc. Natl. Acad. Sci. USA 91, 4589], and Dmoesin [McCartney and Fehon, 1996, J. Cell Biol. 133, 843]. Transgenic flies expressing this fusion protein under control of the hsp70 promoter were generated and used for analysis of cell shape changes during morphogenesis of various developmental stages and tissues. Following heat shock, high levels of stable fusion protein are produced by all somatic tissues. GFP-moe localizes to the cortical actin cytoskeleton, providing a strong in vivo marker for cell shape and pattern during epithelial morphogenesis. The protein also becomes highly enriched in pseudopods, microvilli, axons, denticles, the border cell process, and other membrane projections, potentially by binding to endogenous moesin as well as actin. We show that GFP-moe can be used to examine the development and behavior of these dynamic structures in live specimens. We observe a bright green fluorescent, presumably actin-rich, polar cell proboscis that inserts itself into the forming micropyle and appears to maintain an opening for sperm passage around which the chorion is formed. We also confirm the existence of an actin-rich purse string at the leading edge of the lateral epidermis and provide a dynamic analysis of its behavior as it migrates during dorsal closure. Observations of embryos, larvae, and pupae show that GFP-moe is also useful for labeling the developing nervous system and will be a good general marker of dynamic cell behavior during morphogenesis in live tissues and demonstrate that fusion of a subcellular localization signal to GFP greatly increases its utility as a cell marker.

Myosin heavy chain isoforms regulate muscle function but not myofibril assembly

Myosin heavy chain (MHC) is the motor protein of muscle thick filaments. Most organisms produce many muscle MHC isoforms with temporally and spatially regulated expression patterns. This suggests that isoforms of MHC have different characteristics necessary for defining specific muscle properties. The single Drosophila muscle Mhc gene yields various isoforms as a result of alternative RNA splicing. To determine whether this multiplicity of MHC isoforms is critical to myofibril assembly and function, we introduced a gene encoding only an embryonic MHC into Drosophila melanogaster. The embryonic transgene acts in a dominant antimorphic manner to disrupt flight muscle function. The transgene was genetically crossed into an MHC null background. Unexpectedly, transformed flies expressing only the embryonic isoform are viable. Adult muscles containing embryonic MHC assemble normally, indicating that the isoform of MHC does not determine the dramatic ultrastructural variation among different muscle types. However, transformed flies are flightless and show reduced jumping and mating ability. Their indirect flight muscle myofibrils progressively deteriorate. Our data show that the proper MHC isoform is critical for specialized muscle function and myofibril stability.

Drosophila nonmuscle myosin II has multiple essential roles in imaginal disc and egg chamber morphogenesis

Morphogenesis is characterized by orchestrated changes in the shape and position of individual cells. Many of these movements are thought to be powered by motor proteins. However, in metazoans, it is often difficult to match specific motors with the movements they drive. The nonmuscle myosin II heavy chain (MHC encoded by zipper is required for cell sheet movements in Drosophila embryos. To determine if myosin II is required for other processes, we examined the phenotypes of strong and weak larval lethal mutations in spaghetti squash (sqh), which encodes the nonmuscle myosin II regulatory light chain (RLC). sqh mutants can be rescued to adulthood by daily induction of a sqh cDNA transgene driven by the hsp70 promoter. By transiently ceasing induction of the cDNA, we depleted RLC at specific times during development. When RLC is transiently depleted in larvae, the resulting adult phenotypes demonstrate that RLC is required in a stage-specific fashion for proper development of eye and leg imaginal discs. When RLC is depleted in adult females, oogenesis is reversibly disrupted. Without RLC induction, developing egg chambers display a succession of phenotypes that demonstrate roles for myosin II in morphogenesis of the interfollicular stalks, three morphologically and mechanistically distinct types of follicle cell migration, and completion of nurse cell cytoplasm transport (dumping). Finally, we show that in sqh mutant tissues, MHC is abnormally localized in punctate structures that do not contain appreciable amounts of filamentous actin or the myosin tail-binding protein p127. This suggests that sqh mutant phenotypes are chiefly caused by sequestration of myosin into inactive aggregates. These results show that myosin II is responsible for a surprisingly diverse array of cell shape changes throughout development.

Transcriptional basis for hyporesponsiveness of the human inducible nitric oxide synthase gene to lipopolysaccharide/interferon-gamma

The work reported here resolves, at the level of gene regulation, the controversy as to whether or not human monocytes/macrophages can produce nitric oxide (NO) when stimulated with lipopolysaccharide (LPS), with or without co-stimulation by interferon-gamma (IFN-gamma). Studies included structural comparison of the promoters for human and mouse inducible NO synthase (iNOS) genes, transfection and assay of human and mouse iNOS promoter regions in response to LPS +/- IFN-gamma, and electrophoretic mobility shift assays of kappa B response elements. Two explanations for hyporesponsiveness of the human iNOS promoter to LPS +/- IFN-gamma were found: (1) multiple inactivating nucleotide substitutions in the human counterpart of the enhancer element that has been shown to regulate LPS/IFN-gamma induced expression of the mouse iNOS gene; and (2) and absence of one or more nuclear factors in human macrophages (e.g., an LPS-inducible nuclear factor-kappa B/Rel complex), that is (are) required for maximal expression of the gene. The importance of resolution of this controversy is that future research in this area should be directed toward the understanding of alternative mechanisms that can result in the successful production of NO.

Research methodology. Part IV: Understanding canonical correlation analysis

Canonical correlation is presented as a technique to determine how sets of dependent variables are related with sets of independent variables. Canonical correlation reveals the strength of the relationship between the clusters using case data as illustration, three pairs of clusters (factors or profiles) emerged. Interpretation of the clusters are presented. As indicated in the case presentation, Canonical Correlation (CA) is the fourth in a series of methodologies selected for illustration as precursors to advanced statistics and modeling. In this paper, background will be given, a schematic example presented, sample size and CA, SPSS procedure to perform CA, and interpretation of CA and possible uses of CA in nursing research.

Research methodology. Part III: understanding multiple correlation analysis and multiple regression

This is part III of a case series on research methodology with additional case demographic information. The relationship of a dependent variable with two or more independent variables is explained and used to illustrate multiple correlation and multiple regression.

Essential light chain of Drosophila nonmuscle myosin II

We have cloned and sequenced a cDNA encoding the essential (alkaline) light chain of nonmuscle myosin from Drosophila melanogaster. The protein predicted from the cDNA matches partial amino acid sequence derived from essential light chain protein that copurifies with native nonmuscle myosin heavy chain. This completes the sequence of the three myosin subunits, two of which have been shown genetically to be required for morphogenesis and cytokinesis (the heavy chain encoded by zipper and the regulatory light chain encoded by spaghetti squash). The essential light chain protein is 147 amino acids in length and is 53% identical to human smooth muscle essential light chain. The sequence is consistent with the presence of four helix-loop-helix domains seen in crystallographic structures of the striated muscle myosin light chains and their close relative, calmodulin. We identified the most conserved residues among essential light chain sequences from multiple phyla and present their locations on the crystallographic structure of striated muscle essential light chain. This highlights several conserved contacts among the myosin subunits that may be important for the structure and regulation of the myosin motor. The gene encoding Drosophila nonmuscle essential light chain (Mlc-c) localizes to cytological position 5A6 and we discuss prospects for genetic analysis in this region.

Research methodology. Part I: Understanding correlational analysis

This paper is part one of a four part series on basic statistical analytical methods. Using a case method presentation, the basic essentials of correlational analysis is described.

Identification of Drosophila cytoskeletal proteins by induction of abnormal cell shape in fission yeast

To clone metazoan genes encoding regulators of cell shape, we have developed a functional assay for proteins that affect the morphology of a simple organism, the fission yeast Schizosaccharomyces pombe. A Drosophila melanogaster cDNA library was constructed in an inducible expression vector and transformed into S. pombe. When expression of the Drosophila sequences was induced, aberrant cell shapes were found in 0.2% of the transformed colonies. Four severe phenotypes representing defects in cytokinesis and/or cell shape maintenance were examined further. Each displayed drastic and specific reorganizations of the actin cytoskeleton. Three of the cDNAs responsible for these defects appear to encode cytoskeletal components: the actin binding proteins profilin and cofilin/actin depolymerizing factor and a membrane-cytoskeleton linker of the ezrin/merlin family. These results demonstrate that a yeast phenotypic screen efficiently identifies conserved genes from more complex organisms and sheds light on their potential in vivo functions.

Muscle-specific accumulation of Drosophila myosin heavy chains: a splicing mutation in an alternative exon results in an isoform substitution

We show that the molecular lesions in two homozygousviable mutants of the Drosophila muscle myosin heavy chain gene affect an alternative exon (exon 9a) which encodes a portion of the myosin head that is highly conserved among both cytoplasmic and muscle myosins of all organisms. In situ hybridization and Northern blotting analysis in wild-type organisms indicates that exon 9a is used in indirect flight muscles whereas both exons 9a and 9b are utilized in jump muscles. Alternative exons 9b and 9c are used in other larval and adult muscles. One of the mutations in exon 9a is a nonsense allele that greatly reduces myosin RNA stability. It prevents thick filament accumulation in indirect flight muscles and severely reduces the number of thick filaments in a subset of cells of the jump muscles. The second mutation affects the 5' splice site of exon 9a. This results in production of an aberrantly spliced transcript in indirect flight muscles, which prevents thick filament accumulation. Jump muscles of this mutant substitute exon 9b for exon 9a and consequently have normal levels of thick filaments in this muscle type. This isoform substitution does not obviously affect the ultrastructure or function of the jump muscle. Analysis of this mutant illustrates that indirect flight muscles and jump muscles utilize different mechanisms for alternative RNA splicing.

The regulatory light chain of nonmuscle myosin is encoded by spaghetti-squash, a gene required for cytokinesis in Drosophila

Two independent approaches to understanding the molecular mechanism of cytokinesis have converged on the gene spaghetti-squash (sqh). A genetic screen for mitotic mutants identified sqh1, a mutation that disrupts cytokinesis, which was then cloned by transposon tagging. Independently, the gene that encodes the regulatory light chain of the biochemically defined nonmuscle myosin (MRLC-C) was also cloned. We show here that sqh encodes MRLC-C and that in sqh1 mutants, the level of stable light chain transcript is greatly reduced. Reversion by transposon excision or transformation with a wild-type copy of the sqh transcription unit rescues cytokinesis failure and other defects in sqh1. Vertebrate homologs of MRLC-C are phosphorylatable and regulate myosin activity in vitro. These studies provide genetic proof that MRLC-C is required for cytokinesis, suggest a role for the protein in regulating contractile ring function, and establish a genetic system to evaluate its function.

Alternative myosin hinge regions are utilized in a tissue-specific fashion that correlates with muscle contraction speed

By comparing the structure of wild-type and mutant muscle myosin heavy chain (MHC) genes of Drosophila melanogaster, we have identified the defect in the homozygous-viable, flightless mutant Mhc10. The mutation is within the 3' splice acceptor of an alternative exon (exon 15a) that encodes the central region of the MHC hinge. The splice acceptor defect prevents the accumulation of mRNAs containing exon 15a, whereas transcripts with a divergent copy of this exon (exon 15b) are unaffected by the mutation. In situ hybridization and Northern blot analysis of wild-type organisms reveals that exon 15b is used in larval MHCs, whereas exons 15a and/or 15b are used in adult tissues. Because Mhc10 mutants fail to accumulate transcripts encoding MHC protein with hinge region a, analysis of their muscle-specific reduction in thick filament number serves as a sensitive assay system for determining the pattern of accumulation of MHCs with alternative hinge regions. Electron microscopic comparisons of various muscles from wild-type and Mhc10 adults reveals that those that contract rapidly or develop high levels of tension utilize only hinge region a, those that contract at moderate rates accumulate MHCs of both types, and those that are slowly contracting have MHCs with hinge region b. The presence of alternative hinge-coding exons and their highly tissue-specific usage suggests that this portion of the MHC molecule is important to the isoform-specific properties of MHC that lead to the different physiological and ultrastructural characteristics of various Drosophila muscle types. The absence of other alternative exons in the rod-coding region, aside from those shown previously to encode alternative carboxyl termini, demonstrates that the bulk of the myosin rod is not involved in the generation of isoform-specific properties of the MHC molecule.

Inverse effects of ethidium bromide on superoxide dismutase and lactate dehydrogenase of Artemia salina embryos

Development of Artemia salina embryos in the presence of ethidium bromide, an inhibitor of mitochondrial transcription, results in a dose dependent increase in the specific activity of lactate dehydrogenase, and a concomitant decrease in the specific activity of a cyanide-resistant superoxide dismutase. The inhibition of mitochondrial function by ethidium bromide appears to exert opposite effects on the nuclear cistrons encoding lactate dehydrogenase and superoxide dismutase, and suggests that a common mitochondrial signal may exert diametric effects on nuclear cistrons whose products are characteristic of alternate states of respiration.

Purification and characterization of a type II DNA topoisomerase from bovine calf thymus

We report here the large scale purification of DNA topoisomerase II from calf thymus glands, using the unknotting of naturally knotted P4 phage DNA as an assay for enzymatic activity. Topoisomerase II was purified more than 1300-fold as compared to the whole cell homogenate, with 22% yield. Analysis of the purified enzyme by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed two bands of apparent molecular masses of 125 and 140 kDa. Tryptic maps of the two bands indicated that they derive from the same protein. Using these fragments, specific polyclonal antisera to topoisomerase II were raised in rabbits. Immunoblotting of whole cell lysates from various species indicated that topoisomerase II is well conserved among mammals and has a native subunit molecular mass of 180 kDa. Analytical sedimentation and gel filtration were used to determine a sedimentation coefficient of 9.8 S and a Stokes radius of 68 A. The calculated solution molecular mass of 277 kDa implies a dimer structure in solution. The purified topoisomerase II unknots P4 DNA in an ATP-dependent manner and is highly stimulated in its relaxation activity by ATP. A DNA-stimulated ATPase activity, as has been found with other type II topoisomerases, is associated with the purified enzyme. Approximate kinetic parameters for the ATPase reaction were determined to be: a Vmax of 0.06 nmol of ATP/(micrograms of protein) (min) and Km of 0.2 mM in the absence of DNA, and a Vmax of 0.2 nmol of ATP/(micrograms of protein) (min) and Km of 0.4 mM ATP in the presence of supercoiled plasmid DNA.

Recognition sites of eukaryotic DNA topoisomerase I: DNA nucleotide sequencing analysis of topo I cleavage sites on SV40 DNA

Eukaryotic DNA topoisomerase I introduces transient single-stranded breaks on double-stranded DNA and spontaneously breaks down single-stranded DNA. The cleavage sites on both single and double-stranded SV40 DNA have been determined by DNA sequencing. Consistent with other reports, the eukaryotic enzymes, in contrast to prokaryotic type I topoisomerases, links to the 3'-end of the cleaved DNA and generates a free 5'-hydroxyl end on the other half of the broken DNA strand. Both human and calf enzymes cleave SV40 DNA at the identical and specific sites. From 827 nucleotides sequenced, 68 cleavage sites were mapped. The majority of the cleavage sites were present on both double and single-stranded DNA at exactly the same nucleotide positions, suggesting that the DNA sequence is essential for enzyme recognition. By analyzing all the cleavage sequences, certain nucleotides are found to be less favored at the cleavage sites. There is a high probability to exclude G from positions -4, -2, -1 and +1, T from position -3, and A from position -1. These five positions (-4 to +1 oriented in the 5' to 3' direction) around the cleavage sites must interact intimately with topo I and thus are essential for enzyme recognition. One topo I cleavage site which shows atypical cleavage sequence maps in the middle of a palindromic sequence near the origin of SV40 DNA replication. It occurs only on single-stranded SV40 DNA, suggesting that the DNA hairpin can alter the cleavage specificity. The strongest cleavage site maps near the origin of SV40 DNA replication at nucleotide 31-32 and has a pentanucleotide sequence of 5'-TGACT-3'.

Intra- and intermolecular strand transfer by HeLa DNA topoisomerase I

The major type I DNA topoisomerase (topo I) has been purified from HeLa cell nuclei to a homogeneous, monomeric protein (Mr = 100,000). Similar to the nicking-closing enzyme (Mr = 67,000) from rat liver (Been, M. D., and Champoux, J. J. (1981) Proc. Natl. Acad. Sci. U. S. A. 78, 2883-2887), HeLa topo I has the following properties: (a) HeLa topo I breaks down single-stranded DNA to smaller fragments, each with an enzyme-linked 3'-phosphoryl end and a free 5'-OH end. This cleavage is not dependent upon protein denaturant or protease treatment. (b) HeLa topo I produces single-stranded DNA circles from linear single-stranded DNA. Such DNA circles are believed to be produced by the intramolecular cyclization of topo I-linked, single-stranded DNA fragments. (c) HeLa topo I-linked, single-stranded fragments (donors) can join covalently to double-stranded DNA possessing a 5'-OH group (acceptors). The donor is transferred to the 5'-OH end of the acceptor, independent of the position of the end (internal nick or end of linear DNA) or the configuration of the end (flush, 5'-protruding, or 5'-recessed end) of the acceptor. (d) HeLa topo I cleavage of single-stranded DNA is site-specific, but no special sequence at the ends of the acceptor molecule is apparently required for a successful heterologous strand transfer. These results suggest that HeLa topo I may be involved in DNA sequence rearrangements in addition to its possible role as a swivelase for transcription and replication.

An index for assessing weight change in children: weight/height ratios

Weight and height data from two studies were recomputed, and original data were computed using a Weight Index formula that accounts for the interaction of actual weight/height changes in growing children and compares this ratio with that of normed weight/height ratios for equal-aged children. Recomputing the data of one study showed that the Weight Index is a more sensitive procedure for assessing long-term behavioral treatment of obesity for girls than weight alone. Recomputing the data of a second study showed that the Weight Index formula is consistent for boys and girls and is a more sensitive procedure for assessing long-term effects of a variety of medical treatments for obesity than the Ponderal Index or weight alone. Computation of the data for 17 "normal" children in a preschool class showed a zero Weight Index score before and after a six-month interval elapsed without treatment. The procedure may be useful in assessing ponderosity or anorexia over intervals of six months or more with growing children or difference between actual and normed weight over shorter intervals.