What's new in edition 50 part August 2007 Gene sites new with this edition

The Interactive Fly was first released July/August 1996, with updates provided at approximately one month intervals, through September 1997 (edition 13). Updating quarterly started with edition 14. With edition 40, the Interactive Fly began to schedule updates three times a year: fall, winter and spring.

Gene sites new with this edition of the Interactive Fly:

Basigin

Synapses can undergo rapid changes in size as well as in their vesicle release function during both plasticity processes and development. This fundamental property of neuronal cells requires the coordinated rearrangement of synaptic membranes and their associated cytoskeleton, yet remarkably little is known of how this coupling is achieved. In a GFP exon-trap screen, Drosophila Basigin (Bsg) was identified as an immunoglobulin domain-containing transmembrane protein accumulating at periactive zones of neuromuscular junctions. Bsg is required pre- and post-synaptically to restrict synaptic bouton size, its juxtamembrane cytoplasmic residues being important for that function. Bsg controls different aspects of synaptic structure, including distribution of synaptic vesicles and organization of the presynaptic cortical actin cytoskeleton. Strikingly, bsg function is also required specifically within the presynaptic terminal to inhibit nonsynchronized evoked vesicle release. It is thus proposed that Bsg is part of a transsynaptic complex regulating synaptic compartmentalization and strength, and coordinating plasma membrane and cortical organization (Besse, 2007).

dawdle

Proper axon pathfinding requires that growth cones execute appropriate turns and branching at particular choice points en route to their synaptic targets. The Drosophila metalloprotease tolloid-related (tlr) is required for proper fasciculation/defasciculation of motor axons in the CNS and for normal guidance of many motor axons enroute to their muscle targets. Tlr belongs to a family of developmentally important proteases that process various extracellular matrix components, as well as several TGF-ß inhibitory proteins and pro-peptides. Tlr is a circulating enzyme that processes the pro-domains of three Drosophila TGF-ß-type ligands, and, in the case of the Activin-like protein Dawdle (Daw), this processing enhances the signaling activity of the ligand in vitro and in vivo. Null mutants of daw, as well as mutations in its receptor babo and its downstream mediator Smad2, all exhibit axon guidance defects that are similar to but less severe than tlr. It is suggested that by activating Daw and perhaps other TGF-ß ligands, Tlr provides a permissive signal for axon guidance (Serpe, 2006).

Eb1

End binding 1 (EB1) is an evolutionarily conserved protein that localizes to and controls the plus ends of growing microtubules (Vaughan, 2005). EB1 targets other MT-associated proteins to the plus end and thereby regulates interactions of MTs with the cell cortex, mitotic kinetochores, and different cellular organelles. EB1 also localizes to centrosomes and is required for centrosomal MT anchoring and organization of the MT network. Using a novel preparation of the Drosophila S2 cell line that promotes cell attachment and spreading, dynamics of single microtubules were visualized in real time, and it was found that depletion of EB1 by RNA-mediated inhibition (RNAi) in interphase cells causes a dramatic increase in nondynamic microtubules (neither growing nor shrinking), but does not alter overall microtubule organization. In contrast, several defects in microtubule organization are observed in RNAi-treated mitotic cells, including a drastic reduction in astral microtubules, malformed mitotic spindles, defocused spindle poles, and mispositioning of spindles away from the cell center. Similar phenotypes were observed in mitotic spindles of Drosophila embryos that were microinjected with anti-EB1 antibodies. In addition, live cell imaging of mitosis in Drosophila embryos reveals defective spindle elongation and chromosomal segregation during anaphase after antibody injection. These results reveal crucial roles for EB1 in mitosis, which is postulated to involve its ability to promote the growth and interactions of microtubules within the central spindle and at the cell cortex (Rogers, 2002).

Fer1HCH and Fer2LCH

Ferritin is a symmetric, 24-subunit iron-storage complex assembled of H and L chains. H and L heteropolymers have distinct physicochemical properties, owing to the ferroxidase activity of the H subunit, which is necessary for iron uptake by the ferritin molecule, and the ability of the L subunit to facilitate iron core formation inside the protein shell. Ferritin is found in bacteria, plants and animals, and two classes of mutations in the human L-chain gene result in hereditary hyperferritinemia cataract syndrome or in neuroferritinopathy. This study examined systemic and cellular ferritin regulation and trafficking in Drosophila; ferritin H and L transcripts are co-expressed during embryogenesis and both subunits are essential for embryonic development. Ferritin overexpression impairs the survival of iron-deprived flies. In vivo expression of GFP-tagged holoferritin confirmed that iron-loaded ferritin molecules traffic through the Golgi organelle and are secreted into hemolymph. A constant ratio of ferritin H and L subunits, secured via tight post-transcriptional regulation, is characteristic of the secreted ferritin in flies. Differential cellular expression, conserved post-transcriptional regulation via the iron regulatory element, and distinct subcellular localization of the ferritin subunits prior to the assembly of holoferritin are all important steps mediating iron homeostasis. This study revealed both conserved features and insect-specific adaptations of ferritin nanocages and provides novel imaging possibilities for their in vivo characterization (Missirlis, 2007).

fizzy

Meiosis is a highly specialized cell division that requires significant reorganization of the canonical cell-cycle machinery and the use of meiosis-specific cell-cycle regulators. The anaphase-promoting complex (APC, a machine for degrading proteins; see APC subunits Cdc27 and morula; for review see Acquaviva, 2006) and a conserved APC adaptor/activator, Cdc20 (also known as Fizzy), are required for anaphase progression in mitotic cells. The APC has also been implicated in meiosis, although it is not yet understood how it mediates these non-canonical divisions. Cortex (Cort) is a diverged Fzy homologue that is expressed in the female germline of Drosophila, where it functions with the Cdk1-interacting protein Cks30A to drive anaphase in meiosis II. This study shows that Cort functions together with the canonical mitotic APC adaptor Fzy to target the three mitotic cyclins (A, B and B3) for destruction in the egg and drive anaphase progression in both meiotic divisions. In addition to controlling cyclin destruction globally in the egg, Cort and Fzy appear to both be required for the local destruction of cyclin B on spindles. Cyclin B associates with spindle microtubules throughout meiosis I and meiosis II, and dissociates from the meiotic spindle in anaphase II. Fzy and Cort are required for this loss of cyclin B from the meiotic spindle. These results lead to a model in which the germline-specific APC^Cort cooperates with the more general APC^Fzy, both locally on the meiotic spindle and globally in the egg cytoplasm, to target cyclins for destruction and drive progression through the two meiotic divisions (Swan, 2007).

hugin

Feeding is a fundamental activity of all animals that can be regulated by internal energy status or external sensory signals. A zinc finger transcription factor, klumpfuss, is required for food intake in Drosophila larvae. Microarray analysis indicates that expression of the neuropeptide gene hugin (hug) in the brain is altered in klu mutants and that hug itself is regulated by food signals. Neuroanatomical analysis demonstrates that hug-expressing neurons project axons to the pharyngeal muscles, to the central neuroendocrine organ, and to the higher brain centers, whereas hug dendrites are innervated by external gustatory receptor-expressing neurons, as well as by internal pharyngeal chemosensory organs. The use of tetanus toxin to block synaptic transmission of hug neurons results in alteration of food intake initiation, which is dependent on previous nutrient condition. These results provide evidence that hug neurons function within a neural circuit that modulates taste-mediated feeding behavior (Melcher, 2005).

hu-li tai shao

Drosophila hu-li tai shao (hts; meaning 'too little nursing'), encoding a homolog of mammalian adducin, is required for ring canal formation during Drosophila oogenesis (Yue, 1992). Mammalian adducins comprise a protein family encoded by three genes (α, þ, and γ). The α and γ isoforms (Mr of 103,000 and 84-86,000, respectively) are ubiquitously expressed in human cells; the β isoform (Mr of 97,000) is abundant in erythrocytes and the brain. Subunits assemble into heterodimers, or larger oligomers, through interactions in the globular amino-terminal head domains. In addition, assembly probably occurs through interactions near or within a myristoylated alanine-rich C-kinase substrate (MARCKS) domain by the carboxyl-terminus (Hughes, 1995), which contains PKC phosphorylation sites (Bennett, 1988) as well as binding sites for calcium/calmodulin (Gardner, 1986) and possibly phospholipids. Adducin caps the barbed ends of actin filaments (Kuhlman, 1996; Li, 1998) and promotes their association with spectrin (Gardner, 1987). However, phosphorylation of purified adducin by PKC diminishes its interaction with actin and spectrin (Matsuoka, 1998), whereas addition of exogenous calcium/calmodulin releases adducin from actin (Kuhlman, 1996). Together, these findings indicate that adducin may be involved in exposing actin filament barbed ends in motile cells after activation of certain signal transduction cascades. Consequently, adducin may be implicated in the development of actin assembly sites (Falet, 2002; Ichetovkin, 2002). Furthermore, signaling cascades that elevate intracellular calcium or activate PKC would destabilize the triadic interaction of adducin, actin filament barbed end, and spectrin, thereby potentially triggering perturbations in the spectrin network (Barkalow, 2003 and references therein).

Patj

Planar cell polarity (PCP) is a common feature of many vertebrate and invertebrate epithelia and is perpendicular to the cellular apical/basal (A/B) polarity axis. While apical localization of PCP determinants such as Frizzled (Fz1) is critical for protein function, the relationship between A/B polarity and PCP is poorly understood. A direct molecular link is described between A/B determinants and Fz1-mediated PCP establishment in the Drosophila eye. Patj (Pals1-associated tight junction protein) binds the cytoplasmic tail of Fz1 and is proposed to recruit aPKC, which in turn phosphorylates and inhibits Fz1. Accordingly, components of the aPKC complex and Patj produce PCP defects in the eye. During PCP signaling, aPKC and Patj are downregulated, while Bazooka is upregulated, suggesting an antagonistic effect of Bazooka on Patj/aPKC. A model is proposed whereby the Patj/aPKC complex regulates PCP by inhibiting Fz1 in cells where it should not be active (Djiane, 2005).

Ptpmeg

Ptpmeg is a cytoplasmic tyrosine phosphatase containing FERM and PDZ domains. Drosophila Ptpmeg and its vertebrate homologs PTPN3 and PTPN4 are expressed in the nervous system, but their developmental functions have been unknown. This study found that ptpmeg is involved in neuronal circuit formation in the Drosophila central brain, regulating both the establishment and the stabilization of axonal projection patterns. In ptpmeg mutants, mushroom body (MB) axon branches are elaborated normally, but the projection patterns in many hemispheres become progressively abnormal as the animals reach adulthood. The two branches of MB α/ß neurons are affected by ptpmeg in different ways; ptpmeg activity inhibits α lobe branch retraction while preventing ß lobe branch overextension. The phosphatase activity of Ptpmeg is essential for both α and ß lobe formation, but the FERM domain is required only for preventing α lobe retraction, suggesting that Ptpmeg has distinct roles in regulating the formation of α and ß lobes. ptpmeg is also important for the formation of the ellipsoid body (EB), where it influences the pathfinding of EB axons. ptpmeg function in neurons is sufficient to support normal wiring of both the EB and MB. However, ptpmeg does not act in either MB or EB neurons, implicating ptpmeg in the regulation of cell-cell signaling events that control the behavior of these axons (Whited, 2007).

reptin

Histone acetyltransferase (HAT) complexes have been linked to activation of transcription. Reptin is a subunit of different chromatin-remodeling complexes, including the TIP60 HAT complex. In Drosophila, Reptin also copurifies with the Polycomb group (PcG) complex PRC1, which maintains genes in a transcriptionally silent state. Genetic interactions have been demonstrated between reptin mutant flies and PcG mutants, resulting in misexpression of the homeotic gene Scr. Genetic interactions are not restricted to PRC1 components, but are also observed with another PcG gene. In reptin homozygous mutant cells, a Polycomb response-element-linked reporter gene is derepressed, whereas endogenous homeotic gene expression is not. Furthermore, reptin mutants suppress position-effect variegation (PEV), a phenomenon resulting from spreading of heterochromatin. These features are shared with three other components of TIP60 complexes, namely Enhancer of Polycomb, Domino, and dMRG15. It is concluded that Drosophila Reptin participates in epigenetic processes leading to a repressive chromatin state as part of the fly TIP60 HAT complex rather than through the PRC1 complex. This shows that the TIP60 complex can promote the generation of silent chromatin (Qi, 2006).

RhoGEF2

Members of the Rho/Rac/Cdc42 superfamily of GTPases and their upstream activators, guanine nucleotide exchange factors (GEFs), have emerged as key regulators of actin and microtubule dynamics. In their GTP bound form, these proteins interact with downstream effector molecules that alter actin and microtubule behavior. During Drosophila embryogenesis, a Gα subunit (Concertina) and a Rho-type guanine nucleotide exchange factor (DRhoGEF2) have been implicated in the dramatic epithelial-cell shape changes that occur during gastrulation. Using Drosophila S2 cells as a model system, this study shows that DRhoGEF2 induces contractile cell shape changes by stimulating myosin II via the Rho1 pathway. Unexpectedly, it was found that DRhoGEF2 travels to the cell cortex on the tips of growing microtubules by interaction with the microtubule plus-end tracking protein EB1. The upstream activator Concertina, in its GTP but not GDP bound form, dissociates DRhoGEF2 from microtubule tips and also causes cellular contraction. It is proposed that DRhoGEF2 uses microtubule dynamics to search for cortical subdomains of receptor-mediated Gα activation, which in turn causes localized actomyosin contraction associated with morphogenetic movements during development (Rogers, 2004).

sneaky

Fertilization typically involves membrane fusion between sperm and eggs. In Drosophila, however, sperm enter eggs with membranes intact. Consequently, sperm plasma membrane breakdown (PMBD) and subsequent events of sperm activation occur in the egg cytoplasm. It has been proposed that mutations in the sneaky (snky) gene result in male sterility due to failure in PMBD. This study supports this proposal by demonstrating persistence of a plasma membrane protein around the head of snky sperm after entry into the egg. It is further shown that snky is expressed in testes and encodes a predicted integral membrane protein with multiple transmembrane domains, a DC-STAMP-like domain, and a variant RING finger. Using a transgene that expresses an active Snky-Green fluorescent protein fusion (Snky-GFP), it is shown that the protein is localized to the acrosome, a membrane-bound vesicle located at the apical tip of sperm. Snky-GFP also allowed following the fate of the protein and the acrosome during fertilization. In many animals, the acrosome is a secretory vesicle with exocytosis essential for sperm penetration through the egg coats. Surprisingly, the Drosophila acrosome is a paternally inherited structure. Evidence is presented that the acrosome induces changes in sperm plasma membrane, exclusive of exocytosis and through the action of the acrosomal membrane protein Snky. Existence of testis-expressed Snky-like genes in many animals, including humans, suggests conserved protein function. The characteristics of Drosophila Snky, acrosome function and sperm PMBD is related to membrane fusion events that occur in other systems (Wilson, 2006).

Son of sevenless

Son of sevenless (Sos) is a dual specificity guanine nucleotide exchange factor (GEF) that regulates both Ras and Rho family GTPases and thus is uniquely poised to integrate signals that affect both gene expression and cytoskeletal reorganization. Sos is recruited to the plasma membrane, where it forms a ternary complex with the Roundabout receptor and the SH3-SH2 adaptor protein Dreadlocks (Dock) to regulate Rac-dependent cytoskeletal rearrangement in response to the Slit ligand. Intriguingly, the Ras and Rac-GEF activities of Sos can be uncoupled during Robo-mediated axon repulsion; Sos axon guidance function depends on its Rac-GEF activity, but not its Ras-GEF activity. These results provide in vivo evidence that the Ras and RhoGEF domains of Sos are separable signaling modules and support a model in which Robo recruits Sos to the membrane via Dock to activate Rac during midline repulsion (Yang, 2006).

Thrombospondin

Organogenesis of the somatic musculature in Drosophila is directed by the precise adhesion between migrating myotubes and their corresponding ectodermally derived tendon cells. Whereas the PS integrins mediate the adhesion between these two cell types, their extracellular matrix (ECM) ligands have been only partially characterized. This study shows that the ECM protein Thrombospondin (Tsp), produced by tendon cells, is essential for the formation of the integrin-mediated myotendinous junction. Tsp expression is induced by the tendon-specific transcription factor Stripe, and accumulates at the myotendinous junction following the association between the muscle and the tendon cell. In tsp mutant embryos, migrating somatic muscles fail to attach to tendon cells and often form hemiadherens junctions with their neighboring muscle cells, resulting in nonfunctional somatic musculature. Talin accumulation at the cytoplasmic faces of the muscles and tendons is greatly reduced, implicating Tsp as a potential integrin ligand. Consistently, purified Tsp C-terminal domain polypeptide mediates spreading of PS2 integrin-expressing S2 cells in a KGD- and PS2-integrin-dependent manner. A model is proposed in which the myotendinous junction is formed by the specific association of Tsp with multiple muscle-specific PS2 integrin receptors and a subsequent consolidation of the junction by enhanced tendon-specific production of Tsp secreted into the junctional space (Subramanian, 2007).

tudor

Tudor domains are found in many organisms and have been implicated in protein-protein interactions in which methylated protein substrates bind to these domains. Evidence is presented for the involvement of specific Tudor domains in germline development. Drosophila Tudor, the founder of the Tudor domain family, contains 11 Tudor domains and is a component of polar granules and nuage, electron-dense organelles characteristic of the germline in many organisms, including mammals. This study investigated whether the 11 Tudor domains fulfil specific functions for polar granule assembly, germ cell formation and abdomen formation. It was found that even a small number of non-overlapping Tudor domains or a substantial reduction in overall Tudor protein is sufficient for abdomen development. In stark contrast, a requirement was found for specific Tudor domains in germ cell formation, Tudor localization and polar granule architecture. Combining genetic analysis with structural modeling of specific Tudor domains, it is proposed that these domains serve as 'docking platforms' for polar granule assembly (Arkov, 2006).

Verprolin 1

Formation of syncytial muscle fibers involves repeated rounds of cell fusion between growing myotubes and neighboring myoblasts. Wsp, the Drosophila homolog of the WASp family of microfilament nucleation-promoting factors, is an essential facilitator of myoblast fusion in Drosophila embryos. D-WIP (termed Verprolin 1 in FlyBase), a homolog of the conserved Verprolin/WASp Interacting Protein family of WASp-binding proteins, performs a key mediating role in this context. D-WIP, which is expressed specifically in myoblasts, associates with both the WASp-Arp2/3 system and with the myoblast adhesion molecules Dumbfounded and Sticks and Stones, thereby recruiting the actin-polymerization machinery to sites of myoblast attachment and fusion. This analysis demonstrates that D-WIP recruitment is normally required late in the fusion process, for enlargement of nascent fusion pores and breakdown of the apposed cell membranes. These observations identify cellular and developmental roles for the WASp-Arp2/3 pathway, and provide a link between force-generating actin polymerization and cell fusion (Massarwa, 2007).

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