What's new in edition 41 part 1/5 November 2004 Gene sites new with this edition

A search engine for the SDB website, including the Interactive Fly, is now available through the Society for Developmental Biology.

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 this edition, the Interactive Fly has scheduled updates three times a year: fall, winter and spring.

The 'What's New' sections are more accurately termed, 'Some of What's New'. Every new gene site is included, but only about 10% of the information added to previously included gene sites is listed in the What's New sections for any given edition.

Your comments and corrections are most welcome, and needed. Please keep them coming to brodyt@codon.nih.gov

Gene sites new with this edition of the Interactive Fly:

Archipelago

The Myc oncoprotein is an important regulator of cellular growth in metazoan organisms. Its levels and activity are tightly controlled in vivo by a variety of mechanisms. In normal cells, Myc protein is rapidly degraded, but the mechanism of its degradation is not well understood. Genetic and biochemical evidence is presented that Archipelago (Ago), the F box component of an SCF-ubiquitin ligase and the Drosophila ortholog of a human tumor suppressor, negatively regulates the levels and activity of Drosophila Myc (dMyc) protein in vivo. Mutations in archipelago (ago) result in strongly elevated dMyc protein levels and increased tissue growth. Genetic interactions indicate that ago antagonizes dMyc function during development. Archipelago binds dMyc and regulates its stability, and the ability of Ago to bind dMyc in vitro correlates with its ability to inhibit dMyc accumulation in vivo. These data indicate that archipelago is an important inhibitor of dMyc in developing tissues. Because archipelago can also regulate Cyclin E levels and Notch activity, these results indicate how a single F box protein can be responsible for the degradation of key components of multiple pathways that control growth and cell cycle progression (Moberg, 2004).

Bursicon

To accommodate growth, insects must periodically replace their exoskeletons. After shedding the old cuticle, the new soft cuticle must sclerotize. Sclerotization has long been known to be controlled by the neuropeptide hormone bursicon [Fraenkel, 1962; Cottrell, 1962), but its large size of 30 kDa has frustrated attempts to determine its sequence and structure. Using partial sequences obtained from purified cockroach bursicon (Honegger, 2002), the Drosophila gene CG13419 was identified as a candidate bursicon gene. CG13419 encodes a peptide with a predicted final molecular weight of 15 kDa, which likely functions as a dimer. This predicted Bursicon protein belongs to the cystine knot family, which includes vertebrate transforming growth factor-ß (TGF-ß) and glycoprotein hormones. Point mutations in the bursicon gene cause defects in cuticle sclerotization and wing expansion behavior. Bioassays show that these mutants have decreased Bursicon bioactivity. In situ hybridization and immunocytochemistry reveal that Bursicon is co-expressed with crustacean cardioactive peptide (CCAP). Transgenic flies that lack CCAP neurons also lack Bursicon bioactivity. These results indicate that CG13419 encodes Bursicon, the last of the classic set of insect developmental hormones. It is the first member of the cystine knot family to be assigned a defined function in invertebrates. Mutants show that the spectrum of Bursicon actions is broader than formerly demonstrated (Dewey, 2004).

Chromosome bows

Maintenance of genetic stability during cell division requires binding of chromosomes to the mitotic spindle, a process that involves attachment of spindle microtubules to chromosomal kinetochores. This enables chromosomes to move to the metaphase plate, to satisfy the spindle checkpoint and finally to segregate during anaphase. Studies on the function of Orbit/MAST (FlyBase designation: Chromosome bows or Chb for short) in Drosophila and its human homolog CLASP1 (Maiato, 2003a: CLASP stand for CLIP-associated protein), have revealed that these microtubule-associated proteins play an essential role for the kinetochore-microtubule interaction. CLASP1 localizes to the plus ends of growing microtubules and to the most external kinetochore domain. Depletion of CLASP1 causes abnormal chromosome congression, collapse of the mitotic spindle and attachment of kinetochores to very short microtubules that do not show dynamic behavior. CLASP1 is therefore required at kinetochores to regulate the dynamic behavior of attached microtubules (reviewed by Maiato, 2003b).

Dysfusion

The development of the mature insect trachea requires a complex series of cellular events, including tracheal cell specification, cell migration, tubule branching, and tubule fusion. The Drosophila dysfusion gene encodes a basic helix-loop-helix (bHLH)-PAS protein conserved between Caenorhabditis elegans, insects, and humans; dysfusion controls tracheal fusion events. The Dysfusion protein functions as a heterodimer with the Tango bHLH-PAS protein in vivo to form a putative DNA-binding complex. The dysfusion gene is expressed in a variety of embryonic cell types, including tracheal-fusion, leading-edge, foregut atrium cells, nervous system, hindgut, and anal pad cells. RNAi experiments indicate that dysfusion is required for dorsal branch, lateral trunk, and ganglionic branch fusion but not for fusion of the dorsal trunk. The escargot gene, which is also expressed in fusion cells and is required for tracheal fusion, precedes dysfusion expression. Analysis of escargot mutants indicates a complex pattern of dysfusion regulation, such that dysfusion expression is dependent on escargot in the dorsal and ganglionic branches but not the dorsal trunk. Early in tracheal development, the Trachealess bHLH-PAS protein is present at uniformly high levels in all tracheal cells, but when the levels of Dysfusion rise in wild-type fusion cells, the levels of Trachealess in fusion cells decline. The downregulation of Trachealess is dependent on dysfusion function. These results suggest the possibility that competitive interactions between basic helix-loop-helix-PAS proteins (Dysfusion, Trachealess, and possibly Similar) may be important for the proper development of the trachea (Jiang, 2003).

Encore

In Drosophila, egg development starts at the anterior tip of the ovary, in the germarium, where the germline stem cells divide to produce a cystoblast and a self-renewing stem cell. Each cystoblast undergoes four mitotic divisions with incomplete cytokinesis. The resulting 16 cells of each egg chamber are connected by intercellular bridges called ring canals. Exit from the cell cycle at the end of these four mitotic divisions requires the downregulation of Cyclin/Cdk activity. In the ovary of Drosophila, Encore activity is necessary in the germline to exit this division program. In encore mutant germaria, Cyclin A persists longer than in wild type. In addition, Cyclin E expression is not downregulated after the fourth mitosis and accumulates in a polyubiquitinated form. Mutations in genes coding for components of the ubiquitin-protease pathway such as cul1, UbcD2 and effete enhance the extra division phenotype of encore. Encore physically interacts with the proteasome, Cul1 and Cyclin E. The association of three factors, Cul1, phosphorylated Cyclin E, and the proteasome 19S-RP subunit S1, with the fusome is affected in encore mutant germaria. It is proposed that in encore mutant germaria the proteolysis machinery is less efficient and, in addition, reduced association of Cul1 and S1 with the fusome may compromise Cyclin E destruction and consequently promote an extra round of mitosis (Ohlmeyer, 2003).

Foraging

Naturally occuring polymorphisms in behavior are difficult to map genetically and thus are refractory to molecular characterization. An exception is the Drosophila melanogaster foraging (for) gene, which has two naturally occurring variants relating to food-search behavior: 'rover' and 'sitter'. Molecular mapping placed foraging mutations in the dg2 gene, which encodes a cyclic guanosine monophosphate (cGMP)-dependent protein kinase (PKG). Rovers have higher PKG activity than sitters, and transgenic sitters expressing a dg2 complementary DNA from rover show transformation of behavior to rover type. Thus, PKG levels affect food-search behavior, and natural variation in PKG activity accounts for a behavioral polymorphism (Osborne, 1997).

Kinesin associate protein 3

Kinesin II-mediated anterograde intraflagellar transport (IFT) is essential for the assembly and maintenance of flagella and cilia in various cell types. Kinesin associated protein (KAP) is identified as the non-motor accessory subunit of Kinesin II, but its role in the corresponding motor function has not been characterized. Mutations in the Drosophila KAP (DmKap) gene eliminate the sensory cilia as well as the sound-evoked potentials of Johnston's organ (JO) neurons. Ultrastructure analysis of these mutants reveals that the ciliary axonemes are absent. Mutations in Klp64D, which codes for a Kinesin II motor subunit in Drosophila, show similar ciliary defects. All these defects are rescued by exclusive expression of DmKAP and KLP64D/KIF3A in the JO neurons of respective mutants. Furthermore, reduced copy number of the DmKap gene was found to enhance the defects of hypomorphic Klp64D alleles. Unexpectedly, however, both the DmKap and the Klp64D mutant adults produce vigorously motile sperm with normal axonemes. It is concluded that KAP plays an essential role in Kinesin II function, which is required for the axoneme growth and maintenance of the cilia in Drosophila type I sensory neurons. However, the flagellar assembly in Drosophila spermatids does not require Kinesin II and is independent of IFT (Sarpal, 2003).

Lipid storage droplet-2

In Drosophila, the masses and sheets of adipose tissue that are distributed throughout the fly are collectively called the fat body. Like mammalian adipocytes, insect fat body cells provide the major energy reserve of the animal organism. Both cell types accumulate triacylglycerols (TAG) in intracellular lipid droplets; this finding suggests that the strategy of energy storage as well as the machinery and the control to achieve fat storage might be evolutionarily conserved. Studies addressing the control of lipid-based energy homeostasis of mammals identified proteins of the PAT domain family, such as Perilipin, which reside on lipid droplets. Perilipin knockout mice are lean and resistant to diet-induced obesity. Conversely, Perilipin expression in preadipocyte tissue culture increases lipid storage by reducing the rate of TAG hydrolysis. Factors that mediate corresponding processes in invertebrates are still unknown. The function of Lsd2, one of only two PAT domain-encoding genes in the Drosophila genome has been analyzed. Lsd2 acts in a Perilipin-like manner, suggesting that components regulating homeostasis of lipid-based energy storage at the lipid droplet membrane are evolutionarily conserved. Lsd2 is predominantly expressed in tissues engaged in high levels of lipid metabolism, the fat body and the germ line of females. Ultrastructural analysis in the germ line shows that Lsd2 localizes to the surface of lipid droplets. Mutant adults have a reduced level of neutral lipid content compared to wild type, showing that Lsd2 is required for normal lipid storage. Ovaries from Lsd2 mutant females exhibit an abnormal pattern of accumulation of neutral lipids from mid-oogenesis, which results in reduced deposition of lipids in the egg. Consistent with its expression in the female germ line, Lsd2 is shown to be a maternal effect gene that is required for normal embryogenesis (Gronke, 2003; Teixeira; 2003).

Moesin-like

Two prominent characteristics of epithelial cells, apical-basal polarity and a highly ordered cytoskeleton, depend on the existence of precisely localized protein complexes associated with the apical plasma membrane and on a separate machinery that regulates the spatial order of actin assembly. ERM (ezrin, radixin, moesin) proteins have been proposed to link transmembrane proteins to the actin cytoskeleton in the apical domain, suggesting a structural role in epithelial cells, and they have been implicated in signalling pathways. The sole Drosophila ERM protein Moesin functions to promote cortical actin assembly and apical-basal polarity. As a result, cells lacking Moesin lose epithelial characteristics and adopt invasive migratory behaviour. These data demonstrate that Moesin facilitates epithelial morphology not by providing an essential structural function, but rather by antagonizing activity of the small GTPase Rho. Thus, Moesin functions in maintaining epithelial integrity by regulating cell-signalling events that affect actin organization and polarity. Furthermore, these results show that there is negative feedback between ERM activation and activity of the Rho pathway (Speck, 2003).

Nkx6

The homeodomain protein Nkx6 is a key member of the genetic network of transcription factors that specifies neuronal fates in Drosophila. Nkx6 collaborates with the homeodomain protein Hb9/ExEx to specify ventrally projecting motoneuron fate and to repress dorsally projecting motoneuron fate. While Nkx6 acts in parallel with hb9 to regulate motoneuron fate, Nkx6 plays a distinct role to promote axonogenesis; axon growth of Nkx6-positive motoneurons is severely compromised in Nkx6 mutant embryos. Furthermore, Nkx6 is necessary for the expression of the neural adhesion molecule Fasciclin III in Nkx6-positive motoneurons. Thus, this work demonstrates that Nkx6 acts in a specific neuronal population to link neuronal subtype identity to neuronal morphology and connectivity (Broihier, 2004).

Radish

In both vertebrate and invertebrate animals, anesthetic agents cause retrograde amnesia for recently experienced events. In contrast, older memories are resistant to the same treatments. In Drosophila, anesthesia-resistant memory (ARM) and long-term memory (LTM) are genetically distinct forms of long-lasting memory that exist in parallel for at least a day after training. ARM is disrupted in radish mutants but is normal in transgenic flies overexpressing a CREB repressor transgene. In contrast, LTM is normal in radish mutants but is disrupted in CREB repressor transgenic flies. To date, nothing is known about the molecular, genetic, or cell biological pathways underlying ARM. This study reports the molecular identification of radish as a phospholipase-A2, providing the first clue about signaling pathways underlying ARM in any animal. An enhancer-trap allele of radish (C133) reveals expression in a novel anatomical pathway. Transgenic expression of PLA2 under control of C133 restores normal levels of ARM to radish mutants, whereas transient disruption of neural activity in C133 neurons inhibits memory retention. Notably, expression of C133 is not in mushroom bodies, the primary anatomical focus of olfactory memory research in Drosophila. Identification of radish as a phospholipase-A2 and the neural expression pattern of an enhancer-trap allele significantly broaden our understanding of the biochemistry and anatomy underlying olfactory memory in Drosophila (Chiang, 2004).

Spastin

Hereditary Spastic Paraplegia (HSP) is a devastating neurological disease causing spastic weakness of the lower extremities and eventual axonal degeneration. Over 20 genes have been linked to HSP in humans; however, mutations in one gene, spastin (SPG4), are the cause of >40% of all cases. Spastin is a member of the ATPases Associated with diverse cellular Activities (AAA) protein family, and contains a microtubule interacting and organelle transport (MIT) domain. Previous work in cell culture has proposed a role for Spastin in regulating microtubules. Employing Drosophila transgenic methods for overexpression and RNA interference (RNAi), the role of Spastin in vivo was investigated in vitro. Drosophila Spastin (DSpastin) is enriched in axons and synaptic connections. At neuromuscular junctions (NMJ), Dspastin RNAi causes morphological undergrowth and reduced synaptic area. Moreover, Dspastin overexpression reduces synaptic strength, whereas Dspastin RNAi elevates synaptic currents. By using antibodies against posttranslationally modified alpha-Tubulin, it has been found that Dspastin regulates microtubule stability. Functional synaptic defects caused by Dspastin RNAi and overexpression were pharmacologically alleviated by agents that destabilize and stabilize microtubules, respectively. It is concluded that loss of Dspastin in Drosophila causes an aberrantly stabilized microtubule cytoskeleton in neurons and defects in synaptic growth and neurotransmission. These in vivo data strongly support previous reports, providing a probable cause for the neuronal dysfunction in spastin-linked HSP disease. The role of Spastin in regulating neuronal microtubule stability suggests therapeutic targets for HSP treatment and may provide insight into neurological disorders linked to microtubule dysfunction (Trotta, 2004).

Src homology 2, ankyrin repeat, tyrosine kinase

Shark (SH2 domain ankyrin repeat kinase, Ferrante, 1995) is a Drosophila nonreceptor tyrosine kinase that contains from amino to carboxyl terminus, a Src homology 2 (SH2) domain (N-SH2), five ankyrin repeats, a second SH2 domain (C-SH2), a proline-rich and basic region, and a tyrosine kinase domain. Analysis of the phenotypes associated with a shark loss-of-function mutation demonstrates that Shark activity is essential for the migration of the dorsolateral epidermis of the embryo during dorsal closure (DC). Shark kinase functions in DC upstream of Dpp expression by leading edge cells (Fernandez, 2000).

Telomere fusion

ATM is a large, multifunctional protein kinase that regulates responses required for surviving DNA damage, including functions such as DNA repair, apoptosis, and cell cycle checkpoints. Drosophila ATM (accepted FlyBase name: Telomere fusion) function is essential for normal adult development. Extensive, inappropriate apoptosis occurs in proliferating atm mutant tissues, and in clonally derived atm mutant embryos, frequent mitotic defects are seen. At a cellular level, spontaneous telomere fusions and other chromosomal abnormalities are common in atm larval neuroblasts, suggesting a conserved and essential role for dATM in the maintenance of normal telomeres and chromosome stability. Evidence from other systems supports the idea that DNA double-strand break (DSB) repair functions of ATM kinases promote telomere maintenance by inhibition of illegitimate recombination or fusion events between the legitimate ends of chromosomes and spontaneous DSBs. Drosophila will be an excellent model system for investigating how these ATM-dependent chromosome structural maintenance functions are deployed during development. Because neurons appear to be particularly sensitive to loss of ATM in both flies and humans, this system should be particularly useful for identifying cell-specific factors that influence sensitivity to loss of dATM and are relevant for understanding the human disease, ataxia-telangiectasia (Silva, 2004).

Tout-velu

Hedgehog (Hh) proteins act through both short-range and long-range signaling to pattern tissues during invertebrate and vertebrate development. The mechanisms allowing Hedgehog to diffuse over a long distance and to exert its long-range effects are not understood. A new Drosophila gene, named tout-velu, meaning 'all hair,' has been identified: it is required for diffusion of Hedgehog. Ttv is involved in heparan sulfate proteoglycan (HSPG) biosynthesis, suggesting that HSPGs control Hh distribution (The, 1999). ttv was identified in a screen for maternal-effect mutations associated with segment polarity. ttv clones prove to have a non-cell-autonomous effect. Hh signal is shown to be unable to reach wild-type cells located anterior to ttv mutant cells. It is proposed that ttv functions in the receiving cells for the movement of Hh from sending to receiving cells (Bellaiche, 1998). Subsequent studies have shown striking defects in both Dpp signalling and the range of extracellular Wg protein distribution in ttv and the mutant sister of tout velu (sotv or Ext2), a gene that encodes a co-polymerase that synthesizes HSPG glycosaminoglycan (GAG) chains. Therefore, the previous view that Ttv is involved only in Hh signalling should be revised (Han, 2004b).

Wunen and Wunen-2

In many animals, primordial germ cells (PGCs) migrate through the embryo toward the future gonad, a process guided by attractive and repulsive cues provided from surrounding somatic cells. In Drosophila, the two related lipid phosphate phosphatases (LPPs), Wunen (Wun) and Wun2, are thought to degrade extracellular attractive substrates and to act redundantly in somatic cells to provide a repulsive environment to steer the migration of PGCs, or pole cells. Wun and Wun2 also affect the viability of pole cells, because overexpression of either one in somatic cells causes pole cell death. However, the means by which they regulate pole cell migration and survival remains elusive. Wun2 has a maternal function required for the survival of pole cells during their migration to the gonad. Maternal wun2 RNA was found to be concentrated in pole cells and pole cell-specific expression of wun2 rescues the pole cell death phenotype of the maternal wun2 mutant, suggesting that wun2 activity in pole cells is required for their survival. Furthermore, genetic evidence was obtained that pole cell survival requires a proper balance of LPP activity in pole cells and somatic cells. In somatic cells, Wun and Wun2 may provide a repulsive environment for pole cell migration by depleting this extracellular, attractive substrate. Upon Wun2 expression, cultured insect cells dephosphorylate and internalize exogenously supplied lipid phosphate. It is proposed that Wun2 in pole cells competes with somatic Wun and Wun2 for a common lipid phosphate substrate, which is required by pole cells to produce their survival signal (Renault, 2004; Hanyu-Nakamura, 2004).

What's new in this edition [41] November 2004 continues:

Updates for previously included genes:
part 2/5 genes A-E | part 3/5 genes F-M | part 4/5 genes N-R | part 5/5 genes S-Z

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

Please e-mail comments/corrections to brodyt@codon.nih.gov