Transcripts of individual Drosophila actin genes are differentially distributed during embryogenesis

Actomyosin contraction during cellularization is regulated in part by Src64 control of Actin 5C protein levels

Src64 is required for actomyosin contraction during cellularization of the Drosophila embryonic blastoderm. The mechanism of actomyosin ring constriction is poorly understood even though a number of cytoskeletal regulators have been implicated in the assembly, organization, and contraction of these microfilament rings. How these cytoskeletal processes are regulated during development is even less well understood. To investigate the role of Src64 as an upstream regulator of actomyosin contraction, we conducted a proteomics screen to identify proteins whose expression levels are controlled by src64. Global levels of actin are reduced in src64 mutant embryos. Furthermore, we show that reduction of the actin isoform Actin 5C causes defects in actomyosin contraction during cellularization similar to those caused by src64 mutation, indicating that a relatively high level of Actin 5C is required for normal actomyosin contraction and furrow canal structure. However, reduction of Actin 5C levels only slows down actomyosin ring constriction rather than preventing it, suggesting that src64 acts not only to modulate actin levels, but also to regulate the actomyosin cytoskeleton by other means.

Absence of the Drosophila jump muscle actin Act79B is compensated by up-regulation of Act88F

BACKGROUND

Actins are structural components of the cytoskeleton and muscle, and numerous actin isoforms are found in most organisms. However, many actin isoforms are expressed in distinct patterns allowing each actin to have a specialized function. Numerous studies have demonstrated that actin isoforms both can and cannot compensate for each other under specific circumstances. This allows for an ambiguity of whether isoforms are functionally distinct.

RESULTS

In this study, we analyzed mutants of Drosophila Act79B, the predominant actin expressed in the adult jump muscle. Functional and structural analysis of the Act79B mutants found the flies to have normal jumping ability and sarcomere structure. Analysis of actin gene expression determined that expression of Act88F, an actin gene normally expressed in the flight muscles, was significantly up-regulated in the jump muscles of mutants. This indicated that loss of Act79B caused expansion of Act88F expression. When we created double mutants of Act79B and Act88F, this abolished the jump ability of the flies and resulted in severe defects in myofibril formation.

CONCLUSIONS

These results indicate that Act88F can functionally substitute for Act79B in the jump muscle, and that the functional compensation in actin expression in the jump muscles only occurs through Act88F. Developmental Dynamics 247:642-649, 2018. © 2018 Wiley Periodicals, Inc.

An undergraduate laboratory class using CRISPR/Cas9 technology to mutate drosophila genes

CRISPR/Cas9 genome editing technology is used in the manipulation of genome sequences and gene expression. Because of the ease and rapidity with which genes can be mutated using CRISPR/Cas9, we sought to determine if a single-semester undergraduate class could be successfully taught, wherein students isolate mutants for specific genes using CRISPR/Cas9. Six students were each assigned a single Drosophila gene, for which no mutants currently exist. Each student designed and created plasmids to encode single guide RNAs that target their selected gene; injected the plasmids into Cas9-expressing embryos, in order to delete the selected gene; carried out a three-generation cross to test for germline transmission of a mutated allele and generate a stable stock of the mutant; and characterized the mutant alleles by PCR and sequencing. Three genes out of six were successfully mutated. Pre- and post- survey evaluations of the students in the class revealed that student attitudes towards their research competencies increased, although the changes were not statistically significant. We conclude that it is feasible to develop a laboratory genome editing class, to provide effective laboratory training to undergraduate students, and to generate mutant lines for use by the broader scientific community. © 2016 by The International Union of Biochemistry and Molecular Biology, 44:263-275, 2016.

Postsynaptic actin regulates active zone spacing and glutamate receptor apposition at the Drosophila neuromuscular junction

Synaptic communication requires precise alignment of presynaptic active zones with postsynaptic receptors to enable rapid and efficient neurotransmitter release. How transsynaptic signaling between connected partners organizes this synaptic apparatus is poorly understood. To further define the mechanisms that mediate synapse assembly, we carried out a chemical mutagenesis screen in Drosophila to identify mutants defective in the alignment of active zones with postsynaptic glutamate receptor fields at the larval neuromuscular junction. From this screen we identified a mutation in Actin 57B that disrupted synaptic morphology and presynaptic active zone organization. Actin 57B, one of six actin genes in Drosophila, is expressed within the postsynaptic bodywall musculature. The isolated allele, act(E84K), harbors a point mutation in a highly conserved glutamate residue in subdomain 1 that binds members of the Calponin Homology protein family, including spectrin. Homozygous act(E84K) mutants show impaired alignment and spacing of presynaptic active zones, as well as defects in apposition of active zones to postsynaptic glutamate receptor fields. act(E84K) mutants have disrupted postsynaptic actin networks surrounding presynaptic boutons, with the formation of aberrant actin swirls previously observed following disruption of postsynaptic spectrin. Consistent with a disruption of the postsynaptic actin cytoskeleton, spectrin, adducin and the PSD-95 homolog Discs-Large are all mislocalized in act(E84K) mutants. Genetic interactions between act(E84K) and neurexin mutants suggest that the postsynaptic actin cytoskeleton may function together with the Neurexin-Neuroligin transsynaptic signaling complex to mediate normal synapse development and presynaptic active zone organization.

First comparative transcriptomic analysis of wild adult male and female Lutzomyia longipalpis, vector of visceral leishmaniasis

Leishmaniasis is a vector-borne disease with a complex epidemiology and ecology. Visceral leishmaniasis (VL) is its most severe clinical form as it results in death if not treated. In Latin America VL is caused by the protist parasite Leishmania infantum (syn. chagasi) and transmitted by Lutzomyia longipalpis. This phlebotomine sand fly is only found in the New World, from Mexico to Argentina. However, due to deforestation, migration and urbanisation, among others, VL in Latin America is undergoing an evident geographic expansion as well as dramatic changes in its transmission patterns. In this context, the first VL outbreak was recently reported in Argentina, which has already caused 7 deaths and 83 reported cases. Insect vector transcriptomic analyses enable the identification of molecules involved in the insect's biology and vector-parasite interaction. Previous studies on laboratory reared Lu. longipalpis have provided a descriptive repertoire of gene expression in the whole insect, midgut, salivary gland and male reproductive organs. Nevertheless, the study of wild specimens would contribute a unique insight into the development of novel bioinsecticides. Given the recent VL outbreak in Argentina and the compelling need to develop appropriate control strategies, this study focused on wild male and female Lu. longipalpis from an Argentine endemic (Posadas, Misiones) and a Brazilian non-endemic (Lapinha Cave, Minas Gerais) VL location. In this study, total RNA was extracted from the sand flies, submitted to sequence independent amplification and high-throughput pyrosequencing. This is the first time an unbiased and comprehensive transcriptomic approach has been used to analyse an infectious disease vector in its natural environment. Transcripts identified in the sand flies showed characteristic profiles which correlated with the environment of origin and with taxa previously identified in these same specimens. Among these, various genes represented putative targets for vector control via RNA interference (RNAi).

Cardiac remodeling in Drosophila arises from changes in actin gene expression and from a contribution of lymph gland-like cells to the heart musculature

Understanding the basis of normal heart remodeling can provide insight into the plasticity of the cardiac state, and into the potential for treating diseased tissue. In Drosophila, the adult heart arises during metamorphosis from a series of events, that include the remodeling of an existing cardiac tube, the elaboration of new inflow tracts, and the addition of a layer of longitudinal muscle fibers. We have identified genes active in all these three processes, and studied their expression in order to characterize in greater detail normal cardiac remodeling. Using a Transglutaminase-lacZ transgenic line, that is expressed in the inflow tracts of the larval and adult heart, we confirm the existence of five inflow tracts in the adult structure. In addition, expression of the Actin87E actin gene is initiated in the remodeling cardiac tube, but not in the longitudinal fibers, and we have identified an Act87E promoter fragment that recapitulates this switch in expression. We also establish that the longitudinal fibers are multinucleated, characterizing these cells as specialized skeletal muscles. Furthermore, we have defined the origin of the longitudinal fibers, as a subset of lymph gland cells associated with the larval dorsal vessel. These studies underline the myriad contributors to the formation of the adult Drosophila heart, and provide new molecular insights into the development of this complex organ.

The transcriptional diversity of 25 Drosophila cell lines

Drosophila melanogaster cell lines are important resources for cell biologists. Here, we catalog the expression of exons, genes, and unannotated transcriptional signals for 25 lines. Unannotated transcription is substantial (typically 19% of euchromatic signal). Conservatively, we identify 1405 novel transcribed regions; 684 of these appear to be new exons of neighboring, often distant, genes. Sixty-four percent of genes are expressed detectably in at least one line, but only 21% are detected in all lines. Each cell line expresses, on average, 5885 genes, including a common set of 3109. Expression levels vary over several orders of magnitude. Major signaling pathways are well represented: most differentiation pathways are "off" and survival/growth pathways "on." Roughly 50% of the genes expressed by each line are not part of the common set, and these show considerable individuality. Thirty-one percent are expressed at a higher level in at least one cell line than in any single developmental stage, suggesting that each line is enriched for genes characteristic of small sets of cells. Most remarkable is that imaginal disc-derived lines can generally be assigned, on the basis of expression, to small territories within developing discs. These mappings reveal unexpected stability of even fine-grained spatial determination. No two cell lines show identical transcription factor expression. We conclude that each line has retained features of an individual founder cell superimposed on a common "cell line" gene expression pattern.

Mutations in many genes affect aggressive behavior in Drosophila melanogaster

Background

Aggressive behavior in animals is important for survival and reproduction. Identifying the underlying genes and environmental contexts that affect aggressive behavior is important for understanding the evolutionary forces that maintain variation for aggressive behavior in natural populations, and to develop therapeutic interventions to modulate extreme levels of aggressive behavior in humans. While the role of neurotransmitters and a few other molecules in mediating and modulating levels of aggression is well established, it is likely that many additional genetic pathways remain undiscovered. Drosophila melanogaster has recently been established as an excellent model organism for studying the genetic basis of aggressive behavior. Here, we present the results of a screen of 170 Drosophila P-element insertional mutations for quantitative differences in aggressive behavior from their co-isogenic control line.

Results

We identified 59 mutations in 57 genes that affect aggressive behavior, none of which had been previously implicated to affect aggression. Thirty-two of these mutants exhibited increased aggression, while 27 lines were less aggressive than the control. Many of the genes affect the development and function of the nervous system, and are thus plausibly relevant to the execution of complex behaviors. Others affect basic cellular and metabolic processes, or are mutations in computationally predicted genes for which aggressive behavior is the first biological annotation. Most of the mutations had pleiotropic effects on other complex traits. We characterized nine of these mutations in greater detail by assessing transcript levels throughout development, morphological changes in the mushroom bodies, and restoration of control levels of aggression in revertant alleles. All of the P-element insertions affected the tagged genes, and had pleiotropic effects on brain morphology.

Conclusion

This study reveals that many more genes than previously suspected affect aggressive behavior, and that these genes have widespread pleiotropic effects. Given the conservation of aggressive behavior among different animal species, these are novel candidate genes for future study in other animals, including humans.

CNAct-1 gene is differentially expressed in the subtropical mosquito Culex nigripalpus (Diptera: Culicidae), the primary West Nile Virus vector in Florida

Analysis of differentially expressed genes is a common molecular biological tool to investigate changes in mosquito genes after a bloodmeal or parasite exposure. We report here the characterization of a differentially expressed actin gene, CNAct-1, from the subtropical mosquito, Culex nigripalpus Theobald (Diptera: Culicidae). The CNAct-1 genomic clone is 1.525 kb, includes one 66-bp intron, and a 328-bp 3'-untranslated region. The 376-amino acid putative translation product shares high similarity with muscle-specific actin proteins from other insects, including Culex pipiens pipiens L., Aedes aegypti (L.), Anopheles gambiae Giles and Drosophila melanogaster (Meigen). CNAct-1 is expressed in second and third instars, late pupae, and adult females and males. Interestingly, Cx. nigripalpus actin was highly expressed in female mosquito midgut tissue isolated 6-12 h after ingestion of a bloodmeal. This expression profile indicates a unique function for CNAct-1 in midgut processes that are initiated after blood ingestion.

Global and comparative protein profiles of the pronotum of the southern pine beetle, Dendroctonus frontalis

The southern pine beetle (Dendroctonus frontalis Zimmermann) kills all pines within its range and is among the most important forest pest species in the US. Using a specialized mycangium surrounded by gland cells in the pronotum, adult females culture, transport, and inoculate two fungi into beetle galleries during oviposition. These fungal symbionts, to varying degrees, exclude antagonistic fungi and provide nutrients to larvae. However, the mechanisms (e.g. secreted antibiotic chemicals or nutrients, proteins or pathways) by which this relationship is maintained are not known. Here we present the first global and differential proteome profile of the southern pine beetle pronotum. Two-dimensional polyacrylamide electrophoresis, tandem mass spectrometry, and database searches revealed that the majority of pronotal proteins were related to energy-yielding metabolism, contractile apparati, cell structure, and defence. The identified proteins provide important insights into the molecular and biochemical processes of, and candidates for functional genomics to understand mycangia and pronotum functions in, the southern pine beetle.

CF2 activity and enhancer integration are required for proper muscle gene expression in Drosophila

The creation of the contractile apparatus in muscle involves the co-activation of a group of genes encoding muscle-specific proteins and the production of high levels of protein in a short period of time. We have studied the transcriptional control of six Drosophila muscle genes that have similar expression profiles and we have compared these mechanisms with those employed to control the distinct expression profiles of other Drosophila genes. The regulatory elements controlling the transcription of co-expressed muscle genes share an Upstream Regulatory Element and an Intronic Regulatory Element. Moreover, similar clusters of MEF2 and CF2 binding sites are present in these elements. Here, we demonstrate that CF2 depletion alters the relative expression of thin and thick filament components. We propose that the appropriate rapid gene expression responses during muscle formation and the maintenance of each muscle type is guaranteed in Drosophila by equivalent duplicate enhancer-like elements. This mechanism may be exceptional and restricted to muscle genes, reflecting the specific requirement to mediate rapid muscle responses. However, it may also be a more general mechanism to control the correct levels of gene expression during development in each cell type.

Myocyte enhancer factor 2 and chorion factor 2 collaborate in activation of the myogenic program in Drosophila

The process of myogenesis requires the coordinated activation of many structural genes whose products are required for myofibril assembly, function, and regulation. Although numerous reports have documented the importance of the myogenic regulator myocyte enhancer factor 2 (MEF2) in muscle differentiation, the interaction of MEF2 with cofactors is critical to the realization of muscle fate. We identify here a genomic region required for full MEF2-mediated activation of actin gene expression in Drosophila, and we identify the zinc finger transcriptional regulator chorion factor 2 (CF2) as a factor functioning alongside MEF2 via this region. Furthermore, although both MEF2 and CF2 can individually activate actin gene expression, we demonstrate that these two factors collaborate in regulating the Actin57B target gene in vitro and in vivo. More globally, MEF2 and CF2 synergistically activate the enhancers of a number of muscle-specific genes, and loss of CF2 function in vivo results in reductions in the levels of several muscle structural gene transcripts. These findings validate a general importance of CF2 alongside MEF2 as a critical regulator of the myogenic program, identify a new regulator functioning with MEF2 to control cell fate, and provide insight into the network of regulatory events that shape the developing musculature.

Identification and expression analysis of an actin gene from the soft tick, Ornithodoros moubata (Acari: Argasidae)

Actin genes are found in all living organisms and highly conserved in various animals as shown by numerous studies on actin gene expression and function. Because of this ubiquitous nature of actin, it is often used as an internal control in gene expression studies. To clarify the suitability of actin gene as an internal control in soft ticks, isolation and expression analyses of an actin gene from Ornithodoros moubata was performed. An actin gene of Ornithodoros moubata (OmAct2, GenBank accession no. AB208021) with 1,131 bp and 376 amino acid residues was identified. The homology of OmAct2 with other arthropod actin genes was greater than 80% in nucleotides and 99% in amino acids. OmAct2 gene was classified as a cytoskeletal actin type by absence of muscle-specific amino acids commonly found in insects and ubiquitous expression in all stages and both sexes. Southern blot revealed that O. moubata has four to seven actin genes. In addition, actin expression analyzed by real-time PCR before and after blood feeding was not significantly different indicating OmAct2 is an appropriate internal control for the analysis of gene expression in these ticks.

Interaction of cytoskeleton genes with NSF2-induced neuromuscular junction overgrowth

N-Ethylmaleimide sensitive factor (NSF) is an ATPase whose activity is important for intracellular trafficking. Previous genetic analysis of Drosophila NSF2 revealed a potential link between NSF and the actin cytoskeleton. The present study was therefore undertaken to specifically examine genetic interactions between the cytoskeleton and NSF. First, we tested for loss-of-function interaction and, indeed, we found that the combination of flies heterozygous for Act5C and NSF2 alleles led to reduced viability. Second, we expanded our gain-of-function approach to include cytoskeletal genes that were not included in our previous screen. Thirteen of 30 genes tested were found to suppress neuromuscular junction (NMJ) overgrowth. Altogether, these data support the idea that diverse NSF2 developmental and physiological phenotypes are related to disruption of the cytoskeleton and the large number of genes which can partially restore NMJ overgrowth and suggests that NSF may function near the top of the actin regulatory pathway.

Transcriptional regulation by Modulo integrates meiosis and spermatid differentiation in male germ line

Transcriptional activation in early spermatocytes involves hundreds of genes, many of which are required for meiosis and spermatid differentiation. A number of the meiotic-arrest genes have been identified as general regulators of transcription; however, the gene-specific transcription factors have remained elusive. To identify such factors, we purified the protein that specifically binds to the promoter of spermatid-differentiation gene Sdic and identified it as Modulo, the Drosophila homologue of nucleolin. Analysis of gene-expression patterns in the male sterile modulo mutant indicates that Modulo supports high expression of the meiotic-arrest genes and is essential for transcription of spermatid-differentiation genes. Expression of Modulo itself is under the control of meiotic-arrest genes and requires the DAZ/DAZL homologue Boule that is involved in the control of G(2)/M transition. Thus, regulatory interactions among Modulo, Boule, and the meiotic-arrest genes integrate meiosis and spermatid differentiation in the male germ line.

Expression profiling of a hypercontraction-induced myopathy in Drosophila suggests a compensatory cytoskeletal remodeling response

Mutations that alter muscle contraction lead to a large array of diseases, including muscular dystrophies and cardiomyopathies. Although the molecular lesions underlying many hereditary muscle diseases are known, the downstream pathways that contribute to disease pathogenesis and compensatory muscle remodeling are poorly defined. We have recently identified and characterized mutations in Myosin Heavy Chain (Mhc) that lead to hypercontraction and subsequent degeneration of flight muscles in Drosophila. To characterize the genomic response to hypercontraction-induced myopathy, we performed expression analysis using Affymetrix high density oligonucleotide microarrays in Drosophila Mhc hypercontraction alleles. The altered transcriptional profile of dystrophic Mhc muscles suggests an actin-dependent remodeling of the muscle cytoskeleton. Specifically, a subset of the highly up-regulated transcripts is involved in actin regulation and structural support for the contractile machinery. In addition, we identified previously uncharacterized proteins with putative actin-interaction domains that are up-regulated in Mhc mutants and differentially expressed in muscles. Several of the up-regulated proteins, including the dystrophin-related protein, MSP-300, and the homolog of the neuronal activity-regulated protein, ARC, localize to specific subcellular muscle structures that may provide key structural sites for cytoskeletal remodeling in dystrophic muscles. Defining the genome-wide transcriptional response to muscle hypercontraction in Drosophila has revealed candidate loci that may participate in the pathogenesis of muscular dystrophy and in compensatory muscle repair pathways through modulation of the actin cytoskeleton.

Positive selection drives the evolution of rhino, a member of the heterochromatin protein 1 family in Drosophila

Heterochromatin comprises a significant component of many eukaryotic genomes. In comparison to euchromatin, heterochromatin is gene poor, transposon rich, and late replicating. It serves many important biological roles, from gene silencing to accurate chromosome segregation, yet little is known about the evolutionary constraints that shape heterochromatin. A complementary approach to the traditional one of directly studying heterochromatic DNA sequence is to study the evolution of proteins that bind and define heterochromatin. One of the best markers for heterochromatin is the heterochromatin protein 1 (HP1), which is an essential, nonhistone chromosomal protein. Here we investigate the molecular evolution of five HP1 paralogs present in Drosophila melanogaster. Three of these paralogs have ubiquitous expression patterns in adult Drosophila tissues, whereas HP1D/rhino and HP1E are expressed predominantly in ovaries and testes respectively. The HP1 paralogs also have distinct localization preferences in Drosophila cells. Thus, Rhino localizes to the heterochromatic compartment in Drosophila tissue culture cells, but in a pattern distinct from HP1A and lysine-9 dimethylated H3. Using molecular evolution and population genetic analyses, we find that rhino has been subject to positive selection in all three domains of the protein: the N-terminal chromo domain, the C-terminal chromo-shadow domain, and the hinge region that connects these two modules. Maximum likelihood analysis of rhino sequences from 20 species of Drosophila reveals that a small number of residues of the chromo and shadow domains have been subject to repeated positive selection. The rapid and positive selection of rhino is highly unusual for a gene encoding a chromosomal protein and suggests that rhino is involved in a genetic conflict that affects the germline, belying the notion that heterochromatin is simply a passive recipient of “junk DNA” in eukaryotic genomes.

Eukaryotic genomes are organized into good and bad neighborhoods. In fruit fly genomes, most genes are found in euchromatin—good neighborhoods that tend to be amenable to gene expression and deficient in selfish mobile elements. Conversely, heterochromatic regions are deficient in genes but chock full of mobile genetic elements, both dead and alive. Cells expend considerable effort to maintain this organization, to prevent bad neighborhoods from exerting their negative influence on the rest of the genome. At the forefront of this organization are the HP1 proteins, which are involved in the compaction and silencing of heterochromatic sequences. First discovered in Drosophila, HP1 proteins have been subsequently found in virtually all fungi, plants, and animals.

Most HP1 proteins evolve under stringent evolutionary pressures, suggesting that they lack any discriminatory power in their action. However, a recent paper by Vermaak finds that one of the five HP1 encoding genes in Drosophila genomes, rhino, bucks the trend and evolves rapidly. rhino is predominantly expressed in ovaries, which is where many mobile elements are also active. Their results suggest that rhino has been constantly evolving to police a particularly dynamic, novel compartment in heterochromatin with exquisite specificity. Thus, instead of a genomic wasteyard that genes shun and where transposons go to die, heterochromatin now appears to have been shaped by a constant struggle for evolutionary dominance.

Invertebrate Muscles: Muscle Specific Genes and Proteins

This is the first of a projected series of canonic reviews covering all invertebrate muscle literature prior to 2005 and covers muscle genes and proteins except those involved in excitation-contraction coupling (e.g., the ryanodine receptor) and those forming ligand- and voltage-dependent channels. Two themes are of primary importance. The first is the evolutionary antiquity of muscle proteins. Actin, myosin, and tropomyosin (at least, the presence of other muscle proteins in these organisms has not been examined) exist in muscle-like cells in Radiata, and almost all muscle proteins are present across Bilateria, implying that the first Bilaterian had a complete, or near-complete, complement of present-day muscle proteins. The second is the extraordinary diversity of protein isoforms and genetic mechanisms for producing them. This rich diversity suggests that studying invertebrate muscle proteins and genes can be usefully applied to resolve phylogenetic relationships and to understand protein assembly coevolution. Fully achieving these goals, however, will require examination of a much broader range of species than has been heretofore performed.

Regulated chromatin domain comprising cluster of co-expressed genes in Drosophila melanogaster

Recently, the phenomenon of clustering of co-expressed genes on chromosomes was discovered in eukaryotes. To explore the hypothesis that genes within clusters occupy shared chromatin domains, we performed a detailed analysis of transcription pattern and chromatin structure of a cluster of co-expressed genes. We found that five non-homologous genes (Crtp, Yu, CK2betates, Pros28.1B and CG13581) are expressed exclusively in Drosophila melanogaster male germ-line and form a non-interrupted cluster in the 15 kb region of chromosome 2. The cluster is surrounded by genes with broader transcription patterns. Analysis of DNase I sensitivity revealed 'open' chromatin conformation in the cluster and adjacent regions in the male germ-line cells, where all studied genes are transcribed. In contrast, in somatic tissues where the cluster genes are silent, the domain of repressed chromatin encompassed four out of five cluster genes and an adjacent non-cluster gene CG13589 that is also silent in analyzed somatic tissues. The fifth cluster gene (CG13581) appears to be excluded from the chromatin domain occupied by the other four genes. Our results suggest that extensive clustering of co-expressed genes in eukaryotic genomes does in general reflect the domain organization of chromatin, although domain borders may not exactly correspond to the margins of gene clusters.

Expression of a nonpolymerizable actin mutant in Sf9 cells

We have succeeded in expressing actin in the baculovirus/Sf9 cell system in high yield. The wild-type (WT) actin is functionally indistinguishable from tissue-purified actin in its ability to activate ATPase activity and to support movement in an in vitro motility assay. Having achieved this feat, we used a mutational strategy to express a monomeric actin that is incapable of polymerization. Native actin requires actin binding proteins or chemical modification to maintain it in a monomeric state. The mutant actin sediments in the analytical ultracentrifuge as a homogeneous monomeric species of 3.2 S in 100 mM KCl and 2 mM MgCl(2), conditions that cause WT actin to polymerize. The two point mutations that render actin nonpolymerizable are in subdomain 4 (A204E/P243K; "AP-actin"), distant from the myosin binding site. AP-actin binds to skeletal myosin subfragment 1 (S1) and forms a homogeneous complex as demonstrated by analytical ultracentrifugation. The ATPase activity of a cross-linked AP-actin.S1 complex is higher than that of S1 alone, although less than that supported by filamentous actin (F-actin). AP-Actin is an excellent candidate for structural studies of complexes of actin with motor proteins and other actin-binding proteins.

Stage-specific expression of two actin genes in the yellow fever mosquito, Aedes aegypti

Abstract The expression patterns of two muscle-specific actin genes were studied in the yellow fever mosquito, Aedes aegypti. The coding sequence of AeAct-2 exhibits between 82 and 85% similarity with coding sequences of the Drosophila melanogaster and predicted Anopheles gambiae actin genes. The transcription of the AeAct-2 gene was differentially regulated during developmental stages with higher levels of expression in larvae and lower levels in pupae and adults. The AeAct-2 gene is mainly expressed in the head and body wall tissues. Transcripts of the AeAct-3 gene are not detectable in larvae until late 4th instar and the level increased in male pupae and early male adults. The main site of expression of the AeAct-3 gene was the thoracic tissue. Thus, AeAct-3 is the first reported male-specific actin gene in mosquitoes.

One of the two cytoplasmic actin isoforms in Drosophila is essential

Actin is a highly conserved protein found in all eukaryotic organisms. Most organisms have multiple cytoplasmic actin genes that encode isoforms with slightly different amino acid sequences. These different isoforms are coexpressed in many cell types. Why organisms have multiple very similar cytoplasmic actin genes is unclear. We have addressed this question with the cytoplasmic actins in Drosophila, Act5C, and Act42A. These isoforms differ by only two amino acids and both genes are expressed in all cells at all times during development. We identified P element insertions in the Act5C gene that resulted in a lethal phenotype. The lethal phenotype is rescued by a transgene with a genomic fragment that includes Act5C regulatory and amino acid coding sequences. A hybrid transgene containing the protein coding sequence for the Act42A isoform, under the control of the regulatory regions of the Act5C gene, also rescues the lethality of the Act5C mutants. Furthermore, flies that carry only one copy each of Act5C and Act42A are viable. These results suggest the amino acid differences between these two cytoplasmic actin isoforms are not important for function and the need for increased gene dosage to provide more actin is not likely to explain the existence of multiple genes. Instead, our results suggest that regulated expression of Act5C is essential to the fly.

Expression and function of the Drosophila ACT88F actin isoform is not restricted to the indirect flight muscles

Most higher eukaryotic genomes contain multiple actin genes, yet the sequence differences between isoforms are few. In Drosophila melanogaster it was previously established that one of the six actin genes, Act88F, is expressed only in the indirect flight muscles (IFMs). These muscles are highly specialised for oscillatory contractions to power flight. The implication was that this isoform had tissue-specific properties. In this paper we show using two reporter constructs expressing either beta-galactosidase, Act88F-lacZ, or the green fluorescent protein, Act88F-GFP, that the Act88F promoter is active in a small number of other muscles, including leg (femoral) and uterine muscles. However, the levels of Act88F driven non-IFM expression are much less than in the IFMs. We have confirmed endogenous Act88F gene expression in these other muscles by in situ hybridisation studies. Using null and antimorphic mutants to show decreased walking ability and delayed/reduced oviposition we demonstrated that Act88F expression is functionally important in multiple muscle groups. Since the mutant effects are mild, this supports the expectation that other actin genes are also expressed in these muscles. The Act88F-GFP promoter-reporter also detects Act88F-driven expression in the bristle-forming cells in the pupal wings. The implications of these results for the functions and developmental expression of the Drosophila ACT88F isoform are discussed.

Drosophila MEF2 is a direct regulator of Actin57B transcription in cardiac, skeletal, and visceral muscle lineages

To identify regulatory events occurring during myogenesis, we characterized the transcriptional regulation of a Drosophila melanogaster actin gene, Actin 57B. Act57B transcription is first detected in visceral muscle precursors and is detectable in all embryonic muscles by the end of embryogenesis. Through deletion analysis we identified a 595 bp promoter element that was sufficient for high levels of expression in all three muscle lineages. This fragment contained a MEF2 binding site conserved between D. melanogaster and Drosophila virilis which bound MEF2 protein in embryo nuclear extracts. Mutation of the MEF2 site severely reduced promoter activity in embryos, and in Mef2 mutants Act57B expression was severely decreased, demonstrating MEF2 is an essential regulator of Act57B. We also showed that MEF2 likely acts synergistically with factors bound to additional sequences within the 595 bp element. These findings underline the importance of MEF2 in controlling differentiation in all muscle lineages. Our experiments reveal a novel regulatory mechanism for a structural gene where high levels of expression in all embryonic muscles is regulated through a single transcription factor binding site.

Characterization of muscle actin genes in Drosophila virilis reveals significant molecular complexity in skeletal muscle types

Actin is a ubiquitous and highly conserved eukaryotic protein required for cell motility and locomotion. In this manuscript, we characterize the four muscle actin genes of the insect Drosophila virilis and demonstrate strong similarities between the D. virilis genes and their homologues in Drosophila melanogaster; intron locations are conserved, and there are few amino acid differences between homologues. We also found strong conservation in temporal expression patterns of the muscle actin genes--the homologues of the D. melanogaster genes Act57B and Act87E are expressed throughout the life cycle, whereas the other two D. virilis genes, homologous to Act79B and Act88F are specific to pupal and adult stages. In situ hybridization revealed that each D. virilis gene is expressed in a unique pattern in the muscles of the thorax and abdomen. These muscle-specific patterns of actin isoforms suggest a greater physiological diversity for the adult muscles of insects than has been appreciated to date from their categorization into fibrillar, tubular (non-fibrillar) and supercontractile muscle types.

Drosophila OVO regulates ovarian tumor transcription by binding unusually near the transcription start site

Evolutionarily conserved ovo loci encode developmentally regulated, sequence-specific, DNA-binding, C(2)H(2)-zinc-finger proteins required in the germline and epidermal cells of flies and mice. The direct targets of OVO activity are not known. Genetic experiments suggest that ovo acts in the same regulatory network as ovarian tumor (otu), but the relative position of these genes in the pathway is controversial. Three OVO-binding sites exist in a compact regulatory region that controls germline expression of the otu gene. Interestingly, the strongest OVO-binding site is very near the otu transcription start, where basal transcriptional complexes must function. Loss-of-function, gain-of-function and promoter swapping constructs demonstrate that OVO binding near the transcription start site is required for OVO-dependent otu transcription in vivo. These data unambiguously identify otu as a direct OVO target gene and raise the tantalizing possibility that an OVO site, at the location normally occupied by basal components, functions as part of a specialized core promoter.

Spatially and temporally regulated expression of myosin heavy chain alternative exons during Drosophila embryogenesis

We used alternative exon-specific probes to determine the accumulation of transcripts encoding myosin heavy chain (MHC) isoforms in Drosophila melanogaster embryos. Six isoforms accumulate in body wall muscles. Transverse (external) muscles express a different major form than intermediate and internal muscles, suggesting different physiological properties. Cardioblasts express one of the somatic muscle transcripts; visceral muscles express at least two transcript types. The pharyngeal muscle accumulates a unique Mhc transcript, suggesting unique contractile abilities. Mhc transcription begins in stage 12 in visceral and somatic muscles, but as late as stage 15 in cardioblasts. This is the first study of myosin isoform localization during insect embryogenesis, and forms the basis for transgenic and biochemical experiments designed to determine how MHC domains regulate muscle physiology.

Expression of actin in the central nervous system is switched off during diapause in the gypsy moth, Lymantria dispar

Diapause-regulated proteins were identified in the CNS of pharate 1st instar larvae of the gypsy moth, Lymantria dispar. Expression of two proteins (130kDa and 45kDa) declined at the time of diapause initiation and remained low during diapause. At diapause termination, following exposure to 5 degrees C for at least 60 days, the 45-kDa protein was again highly expressed. Treatment of young pharate larvae with KK-42 averted diapause, and in such larvae, continued synthesis of the 45 kDa protein in the CNS was observed. These results suggest that expression of the 45-kDa protein is strongly down-regulated in the central nervous system (CNS) during diapause. Partial amino acid sequence determination suggested that the 45-kDa protein is actin, and this was confirmed using anti-actin antibodies. RT-PCR using primers designed from the sequence of the gypsy moth midgut actin mRNA indicated that appearance of actin mRNA in the CNS followed the same pattern as that of the 45-kDa protein. The results indicate that diapause controls actin gene expression in the gypsy moth CNS and regulation is at the transcriptional level.

Three main patterns in the expression of six actin genes in the plerocercoid and adult Diphyllobothrium dendriticum tapeworm (Cestoda)

The expression of six actin genes was examined in adult and plerocercoid Diphyllobothrium dendriticum tapeworms using in situ hybridization. On the basis of their structures, these genes are divided into three groups, the cestoda-I, -II and -III actins. Current studies show that the expression of actins belonging to different groups vary to a great extent. The three cestoda-I actins are expressed primarily in muscle cells of both adult and plerocercoid tapeworms, the expression being restricted to fewer cells in the plerocercoid larva. The two cestoda-II actins are cytoplasmic actin isoforms, expressed in a variety of cells, i.e. in cells dividing, differentiating and migrating. Expression of the cestoda-III actin gene is detected merely in the peripheral part of the outer parenchyma, mainly in the tegument cell bodies. This pattern is very weak in plerocercoids. The results indicate that actins also in D. dendriticum can be divided into cytoplasmic and muscle-specific isoforms. In this organism, one major pattern of muscle actin gene expression (cestoda-I) and two major patterns of non-muscle actin gene expression (cestoda-II and -III) were found.

Actin-encoding cDNAs and gene expression during the intermolt cycle of the Bermuda land crab Gecarcinus lateralis

Two actin-encoding cDNAs (act1 and act2) from Gecarcinus lateralis have been sequenced or partially sequenced and the corresponding proteins deduced. The act1 cDNA has a complete ORF; the act2 cDNA lacks most of the 5' end of the coding region. The nucleotide (nt) sequences of both clones are very similar to act sequences of many organisms, the most closely related being from another arthropod, the silkmoth Bombyx mori. The proteins Act1 and Act2 are more similar to vertebrate cytoplasmic actin isoforms (beta-actins) than to vertebrate muscle actins (alpha-actins); they are also more similar to animal actins than to those of fungi or plants. Codon usage is strongly biased toward C or G in the third position. The deduced number of amino acid (aa) residues and calculated Mr for Act1 are 376 aa and 41.94 kDa, respectively. The deduced aa sequence of Act1 is very similar to those of muscle actins of B. mori and Drosophila melanogaster. Southern blots indicated seven to eleven act genes in the crab genome. Northern blots probed with a segment from the 3' UTR of act1 showed a single band of approx. 1.6 kb in poly(A)+ mRNAs from epidermis, limb bud or claw muscle and in total RNAs from ovary and gill, and two bands of approx. 1.6 and 1.8 kb in total RNA from midgut gland. Western blots of one-dimensional gels of proteins from the four layers of the exoskeleton, epidermis, limb buds and claw muscle were probed with a monoclonal Ab against chicken gizzard actin; tissue- and stage-specific changes in actin content were observed. The presence of several isoforms, and differences in their number and occurrence at various stages of the intermolt cycle, were detected on Western blots of two-dimensional gels.

The actin gene family in the oriental fruit fly Bactrocera dorsalis. Muscle specific actins

The actin protein is a critical protein in eukaryotic cells. Four actin genes, constituting what appear to be a set of muscle specific actin genes, have been isolated from the genome of the oriental fruit fly Bactrocera dorsalis. DNA sequences have been determined for the coding as well as 3' and 5' flanking regions for each of these genes. These genes have also been characterized in terms of RNA expression patterns, and comparisons have been made to actin genes from other species. Consistent with other actins, there is a high degree of amino acid sequence conservation in the coding regions of these genes. However, even within the coding regions codon usage patterns in the oriental fruit fly are quite different from some other well characterized species. In addition, the DNA sequences in the intermediate 3' and 5' flanking regions exhibit virtually no detectable sequence homology both within and between species. In terms of introns, three of the four actin genes from the oriental fruit fly described here have a single intervening sequence. Two of these genes share the same intron position with the two muscle specific actin genes act79B and act88F from Drosophila melanogaster and with one muscle specific actin gene CcA1 from the Mediterranean fruit fly, Ceratitis capitata. Another gene from the oriental fruit fly shares the same intron position as the muscle specific actin gene act57B from D. melanogaster. Such conservation of intron positioning between species is highly unusual among previously characterized actin genes. Using unique sequences found in the 3' untranslated regions, gene specific probes have also been constructed. These have been used to detect the expression patterns of individual genes in a temporal and spatial manner. Each of the four genes examined here show differential patterns of expression. The patterns indicate that all four genes are most likely to encode muscle specific actins.

Actin-encoding genes of the hydrozoan Podocoryne carnea

We have isolated and characterized one genomic clone and five actin-encoding cDNA clones of Podocoryne carnea. The complete nucleotide (nt) sequences of the genomic clone and two cDNA clones were determined. The genomic clone contains two introns at positions also found in actin-encoding genes (Act) of other species. The transcription start point has been mapped, and the promoter sequences CAAT and TATA were identified. The sequenced Act cDNA clones encode identical proteins. The deduced amino acid (aa) sequence differs from the genomic clone in 5 aa residues. All aa substitutions occur in a small region between aa 211 and 303. This variable region has also been sequenced from the remaining Act cDNA clones. From these data, it was concluded that the six Act genes probably code for only two actin proteins (Act). The nt sequences were compared to those of Act from other species. A closer relationship of coelenterate Act to deuterostome than to protostome Act is proposed.

A cytoplasmic actin gene from the silkworm Bombyx mori is expressed in tissues of endodermal origin and previtellogenic germ cells of transgenic Drosophila

A cytoplasmic actin gene from Bombyx mori introduced into Drosophila melanogaster by P-element mediated transformation, is efficiently transcribed in larvae, pupae and adults of the host. The exogenous mRNA has the same size as the one observed in the Bombyx cells and the intron located within the coding region is properly excised, indicating a correct recognition of the exogenous sequences by the Drosophila transcriptional and splicing machineries. The expression of the Bombyx gene in Drosophila tissues was determined by transforming flies with a hybrid gene in which a large part of the Bombyx actin coding sequences was replaced by those of the bacterial lac Z gene. This chimaeric gene is specifically and highly expressed, from the embryo to the adult of the transgenic lines, in tissues of endodermal origin, the midgut and its derivatives, i.e. gastric caeca, the outer layer of the proventriculus, and in the Malpighian tubules. This gene is also expressed, at a lower level, in germ cells but restricted to the sixteen cell cysts during previtellogenesis. The expression of the Bombyx gene during development of transgenic flies was compared to that of the two Drosophila endogenous cytoplasmic actin genes and the results are discussed.

twist and snail as positive and negative regulators during Drosophila mesoderm development

twist and snail are members of the helix-loop-helix and zinc-finger protein families, respectively, and determine the development of the mesoderm in Drosophila. This paper analyzes their role in mesoderm development by examining how they affect the expression of downstream genes. twist and snail act by regulating gene expression in the mesoderm and in neighboring regions, and have distinct roles in this process. snail prevents expression in the mesoderm of genes that are destined to be active only in more lateral or dorsal regions. twist is required for the activation of downstream mesodermal genes. twist is also required for the full expression of snail and for the maintenance of its own expression. Only the absence of both twist and snail results in the complete loss of all mesodermal characteristics.

Both genes for EF-1 alpha in Candida albicans are translated

In previous work, we showed that Candida albicans has two genes, TEF-1 and TEF-2, which encode identical polypeptides for the highly conserved, essential, protein synthesis factor EF-1 alpha (Breviario et al., 1988). This result prompted questions as to whether C. albicans preferentially uses one of the genes over the other and whether both genes are actually translated into protein. Gene-specific sequence differences in the untranslated portion of each gene made it possible to prepare gene-specific oligonucleotide hybridization probes. Results with the probes showed that the relative steady-state mRNA levels of the two genes were equivalent and that the mRNA for each gene was present in active translation complexes.