What's new in edition 46 part 3/5 April 2006 F-M

Updates at previously included gene sites:

genes F-M listed below

Folded gastrulation Fruitless Glass bottom boat Glial cells missing G protein oalpha 47A Highwire Histone H3 HP1 Lethal giant larvae

Leukocyte-antigen-related-like/Dlar Lozenge Medea Meiotic 41 Miranda Mirror Moesin Myc/Dimunitive Myocyte enhancerfactor 2

What's new in edition 46:
part 1/5 new genes | updates: part 2/5 genes A-E | part 4/5 genes N-R | part 5/5 genes S-Z

Folded gastrulation: Signaling downstream of Fog: folded gastrulation, cell shape change and the control of myosin localization

The global cell movements that shape an embryo are driven by intricate changes to the cytoarchitecture of individual cells. In a developing embryo, these changes are controlled by patterning genes that confer cell identity. However, little is known about how patterning genes influence cytoarchitecture to drive changes in cell shape. This paper analyzes the function of the folded gastrulation gene (fog), a known target of the patterning gene twist. Analysis of fog function therefore illuminates a molecular pathway spanning all the way from patterning gene to physical change in cell shape. Secretion of Fog protein is apically polarized, making this the earliest polarized component of a pathway that ultimately drives myosin to the apical side of the cell. fog is both necessary and sufficient to drive apical myosin localization through a mechanism involving activation of myosin contractility with actin. This contractility driven form of localization involves RhoGEF2 and the downstream effector Rho kinase. This distinguishes apical myosin localization from basal myosin localization; the latter does not require actinomyosin contractility or FOG/RhoGEF2/Rho-kinase signaling. Furthermore, once localized apically, myosin continues to contract. The force generated by continued myosin contraction is translated into a flattening and constriction of the cell surface through a tethering of the actinomyosin cytoskeleton to the apical adherens junctions. Therefore, this analysis of fog function provides a direct link from patterning to cell shape change (Dawes-Hoang, 2005).

Fruitless: fruitless splicing specifies male courtship behavior in Drosophila

All animals exhibit innate behaviors that are specified during their development. Drosophila melanogaster males (but not females) perform an elaborate and innate courtship ritual directed toward females (but not males). Male courtship requires products of the fruitless (fru) gene, which is spliced differently in males and females. Alleles of fru have been generated that are constitutively spliced in either the male or the female mode. Male splicing is essential for male courtship behavior and sexual orientation. More importantly, male splicing is also sufficient to generate male behavior in otherwise normal females. These females direct their courtship toward other females (or males engineered to produce female pheromones). The splicing of a single neuronal gene thus specifies essentially all aspects of a complex innate behavior (Demir, 2005).

Fruitless: Fruitless specifies sexually dimorphic neural circuitry in the Drosophila brain

Fruitless has been postulated to be a neural sex determination factor that directs development of the central nervous system (CNS), thereby producing male-typical courtship behaviour and inducing male-specific muscle. Male-specific Fru protein is expressed in small groups of neurons scattered throughout the CNS of male, but not female. Collectively, these observations suggest that Fru 'masculinizes' certain neurons, thereby establishing neural substrates for male-typical behaviour. However, specific differences between neurons resulting from the presence or absence of Fru are unknown. Previous studies have suggested that Fru might result in sexual differences in the CNS at the functional level, because no overt sexual dimorphism in CNS structure was discernible. This study identifies a subset of fru-expressing interneurons in the brain that show marked sexual dimorphism in their number and projection pattern. This study also demonstrates that Fru supports the development of neurons with male-specific dendritic fields, that are programmed to die during female development as a result of the absence of Fru. Thus, Fru expression can produce a male-specific neural circuit, probably used during heterosexual courtship, by preventing cell death in identifiable neurons (Kimura, 2005).

Fruitless: Neural circuitry that governs Drosophila male courtship behavior

Male-specific fruitless (fru) products (Fru^M) are both necessary and sufficient to 'hardwire' the potential for male courtship behavior into the Drosophila nervous system. Fru^M is expressed in ~2% of neurons in the male nervous system, but not in the female. The insertion of GAL4 was targeted into the fru locus, allowing visualization and manipulation of the Fru^M-expressing neurons in the male as well as their counterparts in the female. Evidence suggests that these neurons are directly and specifically involved in male courtship behavior and that at least some of them are interconnected in a circuit. This circuit includes olfactory neurons required for the behavioral response to sex pheromones. Anatomical differences in this circuit that might account for the dramatic differences in male and female sexual behavior are not apparent (Stockinger, 2005).

Glass bottom boat: BMP signaling is required for controlling somatic stem cell self-renewal in the Drosophila ovary: Glass bottom boat is essential for controlling somatic stem cell maintenance

BMP signaling is essential for promoting self-renewal of mouse embryonic stem cells and Drosophila germline stem cells and for repressing stem cell proliferation in the mouse intestine and skin. However, it remains unknown whether BMP signaling can promote self-renewal of adult somatic stem cells. In this study, BMP signaling is shown to be necessary and sufficient for promoting self-renewal and proliferation of somatic stem cells (SSCs) in the Drosophila ovary. BMP signaling, via the ligand Glass bottom boat, is required in SSCs to directly control their maintenance and division, but is dispensable for proliferation of their differentiated progeny. Furthermore, BMP signaling is required to control SSC self-renewal, but not survival. Moreover, constitutive BMP signaling prolongs the SSC lifespan. Therefore, this study clearly demonstrates that BMP signaling directly promotes SSC self-renewal and proliferation in the Drosophila ovary. This work further suggests that BMP signaling could promote self-renewal of adult stem cells in other systems (Kirilly, 2005)

Glial cells missing: glial cells missing and gcm2 cell autonomously regulate both glial and neuronal development in the visual system of Drosophila

The transcription factors Glial cells missing (Gcm) and Gcm2 are known to play a crucial role in promoting glial-cell differentiation during Drosophila embryogenesis. A central function for gcm genes has been revealed in regulating neuronal development in the postembryonic visual system. Gcm and Gcm2 are expressed in both glial and neuronal precursors within the optic lobe. Removal of gcm and gcm2 function shows that the two genes act redundantly and are required for the formation of a subset of glial cells. They also cell-autonomously control the differentiation and proliferation of specific neurons. The transcriptional regulator Dachshund acts downstream of gcm genes and is required to make lamina precursor cells and lamina neurons competent for neuronal differentiation through regulation of epidermal growth factor receptor levels. These findings further suggest that gcm genes regulate neurogenesis through collaboration with the Hedgehog-signaling pathway (Chotard, 2005).

G protein oalpha 47A: GPCR signaling is required for blood-brain barrier formation in Drosophila

The blood-brain barrier of Drosophila is established by surface glia, which ensheath the nerve cord and insulate it against the potassium-rich hemolymph by forming intercellular septate junctions. The mechanisms underlying the formation of this barrier remain obscure. The G protein-coupled receptor (GPCR) Moody, the G protein subunits Galphai and Galphao, and the regulator of G protein signaling Loco are required in the surface glia to achieve effective insulation. The data suggest that the four proteins act in a complex common pathway. At the cellular level, the components function by regulating the cortical actin and thereby stabilizing the extended morphology of the surface glia, which in turn is necessary for the formation of septate junctions of sufficient length to achieve proper sealing of the nerve cord. This study demonstrates the importance of morphogenetic regulation in blood-brain barrier development and places GPCR signaling at its core (Schwab, 2005).

Highwire: Highwire regulates presynaptic BMP signaling essential for synaptic growth; Highwire interacts with Medea

Highwire, a putative RING finger E3 ubiquitin ligase, negatively regulates synaptic growth at the neuromuscular junction (NMJ) in Drosophila. hiw mutants have dramatically larger synaptic size and increased numbers of synaptic boutons. Hiw binds to the Smad protein Medea (Med). Med is part of a presynaptic bone morphogenetic protein (BMP) signaling cascade consisting of three receptor subunits, Wit, Tkv, and Sax, in addition to the Smad transcription factor Mad. When compared to wild-type, mutants of BMP signaling components have smaller NMJ size, reduced neurotransmitter release, and aberrant synaptic ultrastructure. BMP signaling mutants suppress the excessive synaptic growth in hiw mutants. Activation of BMP signaling, which in wild-type does not cause additional growth, in hiw mutants does lead to further synaptic expansion. These results reveal a balance between positive BMP signaling and negative regulation by Highwire, governing the growth of neuromuscular synapses (McCabe, 2004).

Highwire: Highwire function at the Drosophila neuromuscular junction: spatial, structural, and temporal requirements

Highwire is a large, evolutionarily conserved protein that is required to restrain synaptic growth and promote synaptic transmission at the Drosophila neuromuscular junction. Current models of highwire function suggest that it may act as a ubiquitin ligase to regulate synaptic development. However, it is not known in which cells highwire functions, whether its putative ligase domain is required for function, or whether highwire regulates the synapse during development or alternatively sets cell fate in the embryo. A series of transgenic rescue experiments were performed to test the spatial, structural, and temporal requirements for highwire function. Presynaptic activity of highwire is both necessary and sufficient to regulate both synapse morphology and physiology. The Highwire RING domain, which is postulated to function as an E3 ubiquitin ligase, is required for highwire function. In addition, highwire acts throughout larval development to regulate synaptic morphology and function. Finally, it is shown that the morphological and physiological phenotypes of highwire mutants have different dosage and temporal requirements for highwire, demonstrating that highwire may independently regulate the molecular pathways controlling synaptic growth and function (Wu, 2005).

Histone H3: Drosophila Paf1 modulates chromatin structure at actively transcribed genes; modification of methylation status of H3

The Paf1 complex in yeast influences a multitude of steps in gene expression through interactions with RNA polymerase II (Pol II) and chromatin-modifying complexes; however, it is unclear which of these many activities are primary functions of Paf1 and are conserved in metazoans. The Drosophila homologs of three subunits of the yeast Paf1 complex have been identified and characterized and striking differences were found between the yeast and Drosophila Paf1 complexes. Although Drosophila Paf1 (CG2503), Rtf1 (CG10955), and Cdc73 (CG11990) colocalize broadly with actively transcribing phosphorylated Pol II, and all are recruited to activated heat shock genes with similar kinetics, Rtf1 does not appear to be a stable part of the Drosophila Paf1 complex. RNA interference (RNAi)-mediated depletion of Paf1 or Rtf1 leads to defects in induction of Hsp70 RNA, but tandem RNAi-chromatin immunoprecipitation assays show that loss of neither Paf1 nor Rtf1 alters the density or distribution of phosphorylated Pol II on the active Hsp70 gene. However, depletion of Paf1 reduces trimethylation of histone H3 at lysine 4 in the Hsp70 promoter region and significantly decreases the recruitment of chromatin-associated factors Spt6 and FACT, suggesting that Paf1 may manifest its effects on transcription through modulating chromatin structure (Adelman, 2006).

HP1: Sex-specific role of Drosophila melanogaster HP1 in regulating chromatin structure and gene transcription

Drosophila melanogaster heterochromatin protein 1 (HP1a or HP1) is believed to be involved in active transcription, transcriptional gene silencing and the formation of heterochromatin. But little is known about the function of HP1 during development. Using a Gal4-induced RNA interference system, it has been shown that conditional depletion of HP1 in transgenic flies results in preferential lethality in male flies. Cytological analysis of mitotic chromosomes shows that HP1 depletion causes sex-biased chromosomal defects, including telomere fusions. The global levels of specific histone modifications, particularly the hallmarks of active chromatin, are preferentially increased in males as well. Expression analysis shows that approximately twice as many genes are specifically regulated by HP1 in males than in females. Furthermore, HP1-regulated genes show greater enrichment for HP1 binding in males. Taken together, these results indicate that HP1 modulates chromosomal integrity, histone modifications and transcription in a sex-specific manner (Liu, 2005).

Lethal giant larvae: Lgl, Pins and aPKC regulate neuroblast self-renewal versus differentiation

How a cell chooses to proliferate or to differentiate is an important issue in stem cell and cancer biology. Drosophila neuroblasts undergo self-renewal with every cell division, producing another neuroblast and a differentiating daughter cell, but the mechanisms controlling the self-renewal/differentiation decision are poorly understood. This study tested whether cell polarity genes, known to regulate embryonic neuroblast asymmetric cell division, also regulate neuroblast self-renewal. Clonal analysis in larval brains shows that pins mutant neuroblasts rapidly fail to self-renew, whereas lethal giant larvae (lgl) mutant neuroblasts generate multiple neuroblasts. Notably, lgl pins double mutant neuroblasts all divide symmetrically to self-renew, filling the brain with neuroblasts at the expense of neurons. The lgl pins neuroblasts show ectopic cortical localization of atypical protein kinase C (aPKC), and a decrease in aPKC expression reduces neuroblast numbers, suggesting that aPKC promotes neuroblast self-renewal. In support of this hypothesis, neuroblast-specific overexpression of membrane-targeted aPKC, but not a kinase-dead version, induces ectopic neuroblast self-renewal. It is concluded that cortical aPKC kinase activity is a potent inducer of neuroblast self-renewal (Lee, 2005).

Leukocyte-antigen-related-like/Dlar: The heparan sulfate proteoglycan syndecan is an in vivo ligand for the Drosophila LAR receptor tyrosine phosphatase

Receptor tyrosine phosphatases (RPTPs) are essential for axon guidance and synaptogenesis in Drosophila. Each guidance decision made by embryonic motor axons during outgrowth to their muscle targets requires a specific subset of the five neural RPTPs. The logic underlying these requirements, however, is still unclear, partially because the ligands recognized by RPTPs at growth cone choice points have not been identified. RPTPs in general are still 'orphan receptors' because, while they have been found to interact in vitro with many different proteins, their in vivo ligands are unknown. This study uses a new type of deficiency screen to identify the transmembrane heparan sulfate proteoglycan Syndecan (Sdc) as a ligand for the neuronal RPTP LAR. LAR interacts with the glycosaminoglycan chains of Syndecan in vitro with nanomolar affinity. Genetic interaction studies using Sdc and Lar LOF mutations demonstrate that Sdc contributes to LAR's function in motor axon guidance. Overexpression of Sdc on muscles is shown to generate the same phenotype as overexpression of LAR in neurons, and genetic removal of LAR suppresses the phenotype produced by ectopic muscle Sdc. Finally, it is shown that there is at least one additional, nonproteoglycan, ligand for LAR encoded in the genome. Taken together, these results demonstrate that Sdc on muscles can interact with neuronal LAR in vivo and that binding to Sdc increases LAR's signaling efficacy. Thus, Sdc is a ligand that can act in trans to positively regulate signal transduction through LAR within neuronal growth cones (Fox, 2005).

Lozenge: Resolving embryonic blood cell fate choice in Drosophila: interplay of GCM and RUNX factors

The differentiation of Drosophila embryonic blood cell progenitors (prohemocytes) into plasmatocytes or crystal cells is controlled by lineage-specific transcription factors. The related proteins Glial cells missing (Gcm) and Gcm2 control plasmatocyte development, whereas the RUNX factor Lozenge (Lz) is required for crystal cell differentiation. The segregation process that leads to the formation of these two cell types, and the interplay between La and Gcm/Gcm2 was investigated. Surprisingly, Gcm is initially expressed in all prohemocytes but is rapidly downregulated in the anterior-most row of prohemocytes, which then initiates lz expression. However, the lz⁺ progenitors constitute a mixed-lineage population whose fate depends on the relative levels of Lz and Gcm/Gcm2. Notably, Gcm/Gcm2 play a key role in controlling the size of the crystal cell population by inhibiting lz activation and maintenance. Furthermore, prohemocytes are bipotent progenitors, and downregulation of Gcm/Gcm2 is required for lz-induced crystal cell formation. These results provide new insight into the mechanisms controlling Drosophila hematopoiesis and establish the basis for an original model for the resolution of the choice of blood cell fate (Bataille, 2005).

Medea: DNA-binding domain mutations in SMAD genes yield dominant-negative proteins or a neomorphic protein that can activate WG target genes in Drosophila

Mutations in SMAD tumor suppressor genes are involved in approximately 140,000 new cancers in the USA each year. How the absence of a functional SMAD protein leads to a tumor is unknown. However, clinical and biochemical studies suggest that all SMAD mutations are loss-of-function mutations. One prediction of this hypothesis is that all SMAD mutations cause tumors via a single mechanism. To test this hypothesis, five tumor-derived alleles of human SMAD genes and five mutant alleles of Drosophila SMAD genes were expressed in flies. All of the DNA-binding domain mutations conferred gain-of-function activity, thereby falsifying the hypothesis. Furthermore, two types of gain-of-function mutation were identified -- dominant negative and neomorphic. In numerous assays, the neomorphic allele SMAD4^100T appears to be capable of activating the expression of Wingless target genes. These results imply that SMAD4^100T may induce tumor formation by a fundamentally different mechanism from other SMAD mutations, perhaps via the ectopic expression of WNT target genes -- an oncogenic mechanism associated with mutations in Adenomatous Polyposis Coli. These results are likely to have clinical implications, because gain-of-function mutations may cause tumors when heterozygous, and the life expectancy of individuals with SMAD4^100T is likely to be different from those with other SMAD mutations. From a larger perspective, this study shows that the genetic characterization of missense mutations, particularly in modular proteins, requires experimental verification (Takaesu, 2005).

Meiotic 41: Drosophila ATM and ATR checkpoint kinases control partially redundant pathways for telomere maintenance

In higher eukaryotes, the ataxia telangiectasia mutated (ATM) and ATM and Rad3-related (ATR) checkpoint kinases play distinct, but partially overlapping, roles in DNA damage response. Yet their interrelated function has not been defined for telomere maintenance. The two proteins control partially redundant pathways for telomere protection in Drosophila: the loss of ATM (encoded by telomere fusion) leads to the fusion of some telomeres, whereas the loss of both ATM and ATR (encoded by mei-41) renders all telomeres susceptible to fusion. The ATM-controlled pathway includes the Mre11 and Nijmegen breakage syndrome complex but not the Chk2 kinase, whereas the ATR-regulated pathway includes its partner ATR-interacting protein but not the Chk1 kinase. This finding suggests that ATM and ATR regulate different molecular events at the telomeres compared with the sites of DNA damage. This compensatory relationship between ATM and ATR is remarkably similar to that observed in yeast despite the fact that the biochemistry of telomere elongation is completely different in the two model systems. Evidence is provided suggesting that both the loading of telomere capping proteins and normal telomeric silencing require ATM and ATR in Drosophila and it is proposed that ATM and ATR protect telomere integrity by safeguarding chromatin architecture that favors the loading of telomere-elongating, capping, and silencing proteins (Bi, 2005).

Miranda: Induction of tumor growth by altered stem-cell asymmetric division in Drosophila melanogaster

Loss of cell polarity and cancer are tightly correlated, but proof for a causative relationship has remained elusive. In stem cells, loss of polarity and impairment of asymmetric cell division could alter cell fates and thereby render daughter cells unable to respond to the mechanisms that control proliferation. To test this hypothesis, Drosophila larval neuroblasts were generated containing mutations in various genes that control asymmetric cell division and then their proliferative potential was assayed after transplantation into adult hosts. It was found that larval brain tissue carrying neuroblasts with mutations in raps (also called pins), mira, numb or pros grew to more than 100 times their initial size, invading other tissues and killing the hosts in 2 weeks. These tumors became immortal and can be retransplanted into new hosts for years. Six weeks after the first implantation, genome instability and centrosome alterations, two traits of malignant carcinomas, appeared in these tumors. Increasing evidence suggests that some tumors may be of stem cell origin. These results show that loss of function of any of several genes that control the fate of a stem cell's daughters may result in hyperproliferation, triggering a chain of events that subverts cell homeostasis in a general sense and leads to cancer (Caussinus, 2005).

Mirror: Iroquois transcription factors recognize a unique motif to mediate transcriptional repression in vivo

Iroquois transcription factors regulate diverse aspects of developmental patterning in all metazoans. Despite their widespread importance, the direct targets of the Iroquois are poorly understood. This study used in vitro site selection to define the DNA-binding preference of the Drosophila Iroquois Mirror. Electrophoretic mobility shift assays were used to determine the critical nucleotides for Mirror binding and to show that this site is recognized by other Drosophila Iroquois transcription factors. This site also is recognized by vertebrate Iroquois transcription factors. Transgenic analysis demonstrates that Drosophila Iroquois proteins recognize this site in vivo to mediate transcriptional repression. It was further shown that Iroquois transcription factors form homodimers and heterodimers, suggesting that combinatorial binding may contribute to gene regulation by this family (Bilioni, 2005).

Moesin: Light-regulated interaction of Moe with TRP and TRPL channels is required for maintenance of photoreceptors

Recent studies in Drosophila retina indicate that absorption of light causes the translocation of signaling molecules and actin from the photoreceptor's signaling membrane to the cytosol, but the underlying mechanisms are not fully understood. Since ezrin-radixin-moesin (ERM) proteins are known to regulate actin-membrane interactions in a signal-dependent manner, the role of Drosophila Moesin (Moe), the unique D. melanogaster ERM, was examined in response to light. Illumination of dark-raised flies triggers the dissociation of Moe from the light-sensitive transient receptor potential (TRP) and TRP-like channels, followed by the migration of Moe from the membrane to the cytoplasm. Furthermore, light-activated migration of Moe results from the dephosphorylation of a conserved threonine in Moe. The expression of a Moe mutant form that impairs this phosphorylation inhibits Moe movement and leads to light-induced retinal degeneration. Thus, these data strongly suggest that the light- and phosphorylation-dependent dynamic association of Moe to membrane channels is involved in maintenance of the photoreceptor cells (Chorna-Ornan, 2005).

Myc/Diminutive: Human c-Myc isoforms differentially regulate cell growth and apoptosis in Drosophila melanogaster

The human c-myc proto-oncogene, implicated in the control of many cellular processes including cell growth and apoptosis, encodes three isoforms differing in their N-terminal region. The functions of these isoforms have never been addressed in vivo. This study used Drosophila to examine the functions of these isoforms in a fully integrated system. First, it was established that the human c-Myc protein can rescue lethal mutations of the Drosophila myc ortholog, dmyc, demonstrating the biological relevance of this model. Then, a new lethal dmyc insertion allele was characterized, that permits expression of human c-Myc in place of dMyc; this allele was used to compare physiological activities of these isoforms in whole-organism rescue, transcription, cell growth, and apoptosis. The isoforms differ both quantitatively and qualitatively. Most remarkably, while the small c-MycS form truncated for much of its N-terminal trans-activation domain efficiently rescues viability and cell growth, it does not induce detectable programmed cell death. The data indicate that the main functional difference between c-Myc isoforms resides in their apoptotic properties and that the N-terminal region, containing the conserved MbI motif, is decisive in governing the choice between growth and death (Benassayag, 2005).

Myocyte enhancer factor 2: Transcription of Myocyte enhancer factor-2 in adult Drosophila myoblasts is induced by the steroid hormone ecdysone

The steroid hormone 20-hydroxyecdysone (ecdysone) activates a relatively small number of immediate-early genes during Drosophila pupal development, yet is able to orchestrate distinct differentiation events in a wide variety of tissues. This study demonstrates that expression of the muscle differentiation gene Myocyte enhancer factor-2 (Mef2) is normally delayed in twist-expressing adult myoblasts until the end of the third larval instar. The late up-regulation of Mef2 transcription in larval myoblasts is an ecdysone-dependent event that acts upon an identified Mef2 enhancer, and enhancer sequences have been identified required for up-regulation. Evidence is presented that the ecdysone-induced Broad Complex of zinc finger transcription factor genes is required for full activation of the myogenic program in these cells. Since forced early expression of Mef2 in adult myoblasts leads to premature muscle differentiation, these results explain how and why the adult muscle differentiation program is attenuated prior to pupal development. A mechanism is proposed for the initiation of adult myogenesis whereby twist expression in myoblasts provides a cellular context upon which an extrinsic signal builds to control muscle-specific differentiation events, and the general relevance of this model for gene regulation in animals is discussed (Lovato, 2005).

What's new in edition 46 of the Interactive Fly :

part 1/5 new genes | updates: part 2/5 genes A-E | part 4/5 genes N-R | part 5/5 genes S-Z

Home page: The Interactive Fly © 1995, 1996 Thomas B. Brody, Ph.D.