The genetics of the dorsal-Bicaudal-D region of Drosophila melanogaster

The Toll gene in Drosophila pattern formation

Toll-like receptors (TLRs) play a crucial role in innate immunity in animals. Their discovery was rewarded a Nobel Prize to Jules Hoffmann and Bruce Beutler in 2011. The name Toll stems from a Drosophila mutant that was isolated in 1980 by Eric Wieschaus and myself as a byproduct of our screen for segmentation genes in Drosophila for which we received the Nobel Prize in 1995. It was named Toll due to its amazing dominant phenotype displayed in embryos from Toll/+ females. The analysis of Toll by Kathryn Anderson in my laboratory in Tübingen and subsequently in her own laboratory in Berkeley singled out Toll as a central component of the complex pathway regulating dorsoventral polarity and pattern of the Drosophila embryo. The Drosophila Toll story provides a striking example for the value of curiosity-driven research in providing fundamental insights that later gain strong impact on applied medical research.

Neuronal Roles of the Bicaudal D Family of Motor Adaptors

All cell types rely on active intracellular cargo transport to shuttle essential cellular components such as proteins, lipids, RNA, and even organelles from the center to the periphery and vice versa. Additionally, several signaling pathways take advantage of intracellular transport to propagate their signals by moving activated receptors and protein effectors to specific locations inside the cell. Neurons particularly, being a very polarized cell type, are highly dependent on molecular motors for the anterograde and retrograde delivery of essential cellular components and signaling molecules. For these reasons, motor adaptor proteins have been extensively investigated in regard to their role in physiology and pathology of the nervous system. In this chapter, we will concentrate on a family of motor adaptor proteins, Bicaudal D (BICD), and their function in the context of the nervous system. BicD was originally described as essential for the correct localization of maternal mRNAs in Drosophila's oocyte and a regulator of the Golgi to ER retrograde transport in mammalian cells. Both mammalian BICD1 and BICD2 are highly expressed in the nervous system during development, and their importance in neuronal homeostasis has been recently under scrutiny. Several mutations in BICD2 have been linked to the development of neuromuscular diseases, and BICD2 knockout (KO) mice display migration defects of the radial cerebellar granule cells. More in line with the overall topic of this book, BICD1 was identified as a novel regulator of neurotrophin (NT) signaling as its deletion leads to defective sorting of ligand-activated NT receptors with dramatic consequences on the NT-mediated signaling pathway.

Drug resistance genomics of the antimalarial drug artemisinin

Across the globe, over 200 million annual malaria infections result in up to 660,000 deaths, 77% of which occur in children under the age of five years. Although prevention is important, malaria deaths are typically prevented by using antimalarial drugs that eliminate symptoms and clear parasites from the blood. Artemisinins are one of the few remaining compound classes that can be used to cure multidrug-resistant Plasmodium falciparum infections. Unfortunately, clinical trials from Southeast Asia are showing that artemisinin-based treatments are beginning to lose their effectiveness, adding renewed urgency to the search for the genetic determinants of parasite resistance to this important drug class. We review the genetic and genomic approaches that have led to an improved understanding of artemisinin resistance, including the identification of resistance-conferring mutations in the P. falciparum kelch13 gene.

Crystallographic characterization of the C-terminal coiled-coil region of mouse Bicaudal-D1 (BICD1)

Bicaudal-D1 (BICD1) is an α-helical coiled-coil protein which is evolutionarily conserved from Drosophila to mammals and facilitates the attachment of specific cargo factors to the dynein motor complex. The C-terminal coiled-coil region (CC3) of BICD1 plays an important role in sorting cargo, linking proteins such as the small GTPase Rab6 and the nuclear pore complex component Ran-binding protein 2 (RanBP2) to the dynein motor complex. This report describes the crystallization and X-ray data collection of the BICD1 CC3 region, as well as the preparation of the complex of BICD1 CC3 with a constitutively active mutant of Rab6. The crystals of the BICD1 CC3 region belonged to space group C2, with unit-cell parameters a = 59.0, b = 36.8, c = 104.3 Å, α = γ = 90, β = 99.8°. The X-ray diffraction data set was collected to 1.50 Å resolution.

Regulators of the cytoplasmic dynein motor

Eukaryotic cells use cytoskeletal motor proteins to transport many different intracellular cargos. Numerous kinesins and myosins have evolved to cope with the various transport needs that have arisen during eukaryotic evolution. Surprisingly, a single cytoplasmic dynein (a minus end-directed microtubule motor) carries out similarly diverse transport activities as the many different types of kinesin. How is dynein coupled to its wide range of cargos and how is it spatially and temporally regulated? The answer could lie in the several multifunctional adaptors, including dynactin, lissencephaly 1, nuclear distribution protein E (NUDE) and NUDE-like, Bicaudal D, Rod-ZW10-Zwilch and Spindly, that regulate dynein function and localization.

Vertebrate rel proteins exhibit dorsal-like activities in earlyDrosophila embryogenesis

In Drosophila, the Toll/Dorsal pathway triggers the nuclear entry of the Rel protein Dorsal, which controls dorsoventral patterning in early embryogenesis and plays an important role in innate immunity of the adult fly. In vertebrates, the homologous Toll/IL-1 receptor signaling pathway directs the nuclear localization of Rel/NF-kappaB complexes, which activate genes involved in proliferation, apoptosis, and immune response. Recently, first evidence has been reported for the activity of vertebrate Rel proteins and a Toll-like signaling pathway in the dorsoventral patterning process of Xenopus laevis embryos. Given the evolutionary divergence of the fly and frog model organisms, these findings raise the question, to what extent the effector functions of this pathway have been conserved? Here, we report the ability of two Xenopus Rel proteins to partially substitute for several, but not all, functions of the Dorsal protein in Drosophila embryos. Our results suggest the interaction between Rel proteins and their cytoplasmic inhibitors as an important interface of evolutionary adaptation.

Suppression of muscle hypercontraction by mutations in the myosin heavy chain gene of Drosophila melanogaster

The indirect flight muscles (IFM) of Drosophila melanogaster provide a good genetic system with which to investigate muscle function. Flight muscle contraction is regulated by both stretch and Ca(2+)-induced thin filament (actin + tropomyosin + troponin complex) activation. Some mutants in troponin-I (TnI) and troponin-T (TnT) genes cause a "hypercontraction" muscle phenotype, suggesting that this condition arises from defects in Ca(2+) regulation and actomyosin-generated tension. We have tested the hypothesis that missense mutations of the myosin heavy chain gene, Mhc, which suppress the hypercontraction of the TnI mutant held-up(2) (hdp(2)), do so by reducing actomyosin force production. Here we show that a "headless" Mhc transgenic fly construct that reduces the myosin head concentration in the muscle thick filaments acts as a dose-dependent suppressor of hypercontracting alleles of TnI, TnT, Mhc, and flightin genes. The data suggest that most, if not all, mutants causing hypercontraction require actomyosin-produced forces to do so. Whether all Mhc suppressors act simply by reducing the force production of the thick filament is discussed with respect to current models of myosin function and thin filament activation by the binding of calcium to the troponin complex.

A genetic screen for suppressors and enhancers of the Drosophila cdk1-cyclin B identifies maternal factors that regulate microtubule and microfilament stability

Coordination between cell-cycle progression and cytoskeletal dynamics is important for faithful transmission of genetic information. In early Drosophila embryos, increasing maternal cyclin B leads to higher Cdk1-CycB activity, shorter microtubules, and slower nuclear movement during cycles 5-7 and delays in nuclear migration to the cortex at cycle 10. Later during cycle 14 interphase of six cycB embryos, we observed patches of mitotic nuclei, chromosome bridges, abnormal nuclear distribution, and small and large nuclei. These phenotypes indicate disrupted coordination between the cell-cycle machinery and cytoskeletal function. Using these sensitized phenotypes, we performed a dosage-sensitive genetic screen to identify maternal proteins involved in this process. We identified 10 suppressors classified into three groups: (1) gene products regulating Cdk1 activities, cdk1 and cyclin A; (2) gene products interacting with both microtubules and microfilaments, Actin-related protein 87C; and (3) gene products interacting with microfilaments, chickadee, diaphanous, Cdc42, quail, spaghetti-squash, zipper, and scrambled. Interestingly, most of the suppressors that rescue the astral microtubule phenotype also reduce Cdk1-CycB activities and are microfilament-related genes. This suggests that the major mechanism of suppression relies on the interactions among Cdk1-CycB, microtubule, and microfilament networks. Our results indicate that the balance among these different components is vital for normal early cell cycles and for embryonic development. Our observations also indicate that microtubules and cortical microfilaments antagonize each other during the preblastoderm stage.

Drosophila quail, a villin-related protein, bundles actin filaments in apoptotic nurse cells

Drosophila Quail protein is required for the completion of fast cytoplasm transport from nurse cells to the oocyte, an event critical for the production of viable oocytes. The abundant network of cytoplasmic filamentous actin, established at the onset of fast transport, is absent in quail mutant egg chambers. Previously, we showed that Quail is a germline-specific protein with sequence homology to villin, a vertebrate actin-regulating protein. In this study, we combined biochemical experiments with observations in egg chambers to define more precisely the function of this protein in the regulation of actin-bundle assembly in nurse cells. We report that recombinant Quail can bind and bundle filamentous actin in vitro in a manner similar to villin at a physiological calcium concentration. In contrast to villin, Quail is unable to sever or cap filamentous actin, or to promote nucleation of new actin filaments at a high calcium concentration. Instead, Quail bundles the filaments regardless of the calcium concentration. In vivo, the assembly of nurse-cell actin bundles is accompanied by extensive perforation of the nurse-cell nuclear envelopes, and both of these phenomena are manifestations of nurse-cell apoptosis. To investigate whether free calcium levels are affected during apoptosis, we loaded egg chambers with the calcium indicator Indo-1. Our observations indicate a rise in free calcium in the nurse-cell cytoplasm coincident with the permeabilization of the nuclear envelopes. We also show that human villin expressed in the Drosophila germline could sense elevated cytoplasmic calcium; in nurse cells with reduced levels of Quail protein, villin interfered with actin-bundle stability. We conclude that Quail efficiently assembles actin filaments into bundles in nurse cells and maintains their stability under fluctuating free calcium levels. We also propose a developmental model for the fast phase of cytoplasm transport incorporating findings presented in this study.

Nuclear import of the Drosophila Rel protein Dorsal is regulated by phosphorylation

In Drosophila, dorsal-ventral polarity is determined by a maternally encoded signal transduction pathway that culminates in the graded nuclear localization of the Rel protein, Dorsal. Dorsal is retained in the cytoplasm by the IkappaB protein, Cactus. Signal-dependent phosphorylation of Cactus results in the degradation of Cactus and the nuclear targeting of Dorsal. We present an in-depth study of the functional importance of Dorsal phosphorylation. We find that Dorsal is phosphorylated by the ventral signal while associated with Cactus, and that Dorsal phosphorylation is essential for its nuclear import. In vivo phospholabeling of Dorsal is limited to serine residues in both ovaries and early embryos. A protein bearing mutations in six conserved serines abolishes Dorsal activity, is constitutively cytoplasmic, and appears to eliminate Dorsal phosphorylation, but still interacts with Cactus. Two individual serine-to-alanine mutations produce unexpected results. In a wild-type signaling background, a mutation in the highly conserved PKA site (S312) produces only a weak loss-of-function; however, it completely destabilizes the protein in a cactus mutant background. Significantly, the phosphorylation of another completely conserved serine (S317) regulates the high level of nuclear import found in ventral cells. We conclude that the formation of a wild-type Dorsal nuclear gradient requires the phosphorylation of both Cactus and Dorsal. The strong conservation of the serines suggests that phosphorylation of other Rel proteins is essential for their proper nuclear targeting.

TAFII mutations disrupt Dorsal activation in the Drosophila embryo

In this study, we present evidence that the Dorsal activator interacts with limiting amounts of the TFIID complex in the Drosophila embryo. In vitro transcription reactions and protein binding assays implicate the TAFII110 and TAFII60 subunits of the TFIID complex in contributing to Dorsal-mediated activation. Mutations in TAFII110 and TAFII60 result in altered patterns of snail and twist transcription in embryos derived from dl/+ females. These results suggest that TAFIIs contribute to the activation of transcription in vivo and support the hypothesis that subunits of TFIID may serve as targets of enhancer binding proteins.

A screen to identify Drosophila genes required for integrin-mediated adhesion

Drosophila integrins have essential adhesive roles during development, including adhesion between the two wing surfaces. Most position-specific integrin mutations cause lethality, and clones of homozygous mutant cells in the wing do not adhere to the apposing surface, causing blisters. We have used FLP-FRT induced mitotic recombination to generate clones of randomly induced mutations in the F1 generation and screened for mutations that cause wing blisters. This phenotype is highly selective, since only 14 lethal complementation groups were identified in screens of the five major chromosome arms. Of the loci identified, 3 are PS integrin genes, 2 are blistered and bloated, and the remaining 9 appear to be newly characterized loci. All 11 nonintegrin loci are required on both sides of the wing, in contrast to integrin alpha subunit genes. Mutations in 8 loci only disrupt adhesion in the wing, similar to integrin mutations, while mutations in the 3 other loci cause additional wing defects. Mutations in 4 loci, like the strongest integrin mutations, cause a "tail-up" embryonic lethal phenotype, and mutant alleles of 1 of these loci strongly enhance an integrin mutation. Thus several of these loci are good candidates for genes encoding cytoplasmic proteins required for integrin function.

Genetic analysis of the Drosophila alphaPS2 integrin subunit reveals discrete adhesive, morphogenetic and sarcomeric functions

The integrin family of cell surface receptors mediates cell-substrate and cell-to-cell adhesion and transmits intracellular signals. In Drosophila there is good evidence for an adhesive role of integrins, but evidence for integrin signalling has remained elusive. Each integrin is an alphabeta heterodimer, and the Drosophila betaPS subunit forms at least two integrins by association with different alpha subunits: alphaPS1betaPS (PS1) and alphaPS2betaPS (PS2). The complex pattern of PS2 integrin expression includes, but is more extensive than, the sites where PS2 has a known requirement. In order to investigate whether PS2 integrin is required at these additional sites and/or has functions besides mediating adhesion, a comprehensive genetic analysis of inflated, the gene that encodes alphaPS2, was performed. We isolated 35 new inflated alleles, and obtained 10 alleles from our colleagues. The majority of alleles are amorphs (36/45) or hypomorphs (4/45), but five alleles that affect specific developmental processes were identified. Interallelic complementation between these alleles suggests that some may affect distinct functional domains of the alphaPS2 protein, which specify particular interactions that promote adhesion or signalling. One new allele reveals that the PS2 integrin is required for the development of the adult halteres and legs as well as the wing.

Implication of a 5' coding sequence in targeting maternal mRNA to the Drosophila oocyte

Early accumulation of maternal mRNA in one of the cells of the cluster of 16 cystocytes is a critical event in the determination of the Drosophila oocyte. A number of developmentally important mRNAs have been shown to accumulate in the early oocyte. We report here the early expression of the yemanuclein-alpha (yem-alpha) transcript, its accumulation in the germarial oocyte and its dynamic localization in the growing oocyte. We have investigated the mechanisms involved in these processes. Microtubules are likely to be involved in both transport and localization as was shown for other maternal transcripts which behave similarly. However, unlike all the cases reported so far, transport and localization are not dependent on 3'UTR sequences. We show that the 5' coding sequence is necessary for the early accumulation of yem-alpha RNA in the oocyte and for its localization pattern during oogenesis.

Axon patterning requires DN-cadherin, a novel neuronal adhesion receptor, in the Drosophila embryonic CNS

We identified DN-cadherin, a novel Drosophila cadherin that is expressed in axons and in the mesoderm. Although DN-cadherin has diverged from vertebrate classic cadherins in terms of its extracellular structure, it still can form a complex with catenins and induce cell aggregation, as do the vertebrate molecules. Loss-of-function mutations of the gene resulted in either embryonic lethality or uncoordinated locomotion of adults. In the central nervous system of null mutant embryos, subsets of ipsilateral axons displayed a variety of aberrant trajectories including failure of position shifts, defective bundling, and errors in directional migration of growth cones. These results suggest that processes of axon patterning critically depend on DN-cadherin-mediated axon-axon interactions.

Homeless is required for RNA localization in Drosophila oogenesis and encodes a new member of the DE-H family of RNA-dependent ATPases

The homeless (hls) gene of Drosophila is required for anteroposterior and dorsoventral axis formation during oogenesis. At a low frequency, females homozygous for mutations in hls generate early egg chambers in which the oocyte is positioned incorrectly within the cyst. At a high frequency, late-stage egg chambers exhibit a ventralized chorion. Sequence analysis of the hls cDNA predicts a protein with amino-terminal homology to members of the DE-H family of RNA-dependent ATPases and putative helicases. Similarity of 51% in the amino-terminal third of the protein was found to two yeast splicing factors, PRP2 and PRP16, and to Drosophila Maleless, which is required for dosage compensation. To analyze Hls function, RNA localization patterns were determined for seven different transcripts in hls mutant ovaries. Previtellogenic transport to the oocyte was unaffected for all transcripts examined. Transport and localization of bicoid and oskar messages during vitellogenic stages were strongly disrupted, and the distribution and/or quantity of gurken, orb, and fs(1)K10 mRNAs were also affected, but to a lesser degree. In contrast, hu-li tai shao and Bicaudal-D transcripts were transported and localized normally in hls mutants. In addition, Kinesin heavy chain:beta-Galactosidase fusion protein failed to localize correctly to the posterior of the oocyte in vitellogenic egg chambers. Examination of the microtubule structure with anti-alpha-Tubulin antibodies revealed aberrant microtubule organizing center movement and an abnormally dense cytoplasmic microtubule meshwork. We discuss potential roles for Hls in organizing a cytoskeletal framework essential for localizing specific RNAs.

The genetic and molecular organization of the Dopa decarboxylase gene cluster of Drosophila melanogaster

We report the complete molecular organization of the Dopa decarboxylase gene cluster. Mutagenesis screens recovered 77 new Df(2L)TW130 recessive lethal mutations. These new alleles combined with 263 previously isolated mutations in the cluster to define 18 essential genes. In addition, seven new deficiencies were isolated and characterized. Deficiency mapping, restriction fragment length polymorphism (RFLP) analysis and P-element-mediated germline transformation experiments determined the gene order for all 18 loci. Genomic and cDNA restriction endonuclease mapping, Northern blot analysis and DNA sequencing provided information on exact gene location, mRNA size and transcriptional direction for most of these loci. In addition, this analysis identified two transcription units that had not previously been identified by extensive mutagenesis screening. Most of the loci are contained within two dense subclusters. We discuss the effectiveness of mutagens and strategies used in our screens, the variable mutability of loci within the genome of Drosophila melanogaster, the cytological and molecular organization of the Ddc gene cluster, the validity of the one band-one gene hypothesis and a possible purpose for the clustering of genes in the Ddc region.

Cytoskeletal functions during Drosophila oogenesis

Organismal morphogenesis is driven by a complex series of developmentally coordinated changes in cell shape, size, and number. These changes in cell morphology are in turn dependent on alterations in basic cytoarchitecture. Elucidating the mechanisms of development thus requires an understanding of the cytoskeletal elements that organize the cytoplasm of differentiating cells. Drosophila oogenesis has emerged as a versatile system for the study of cytoskeletal function during development. A series of highly coordinated changes in cytoskeletal organization are required to produce a mature Drosophila oocyte, and these cytoskeletal transformations are amenable to a variety of experimental approaches. Genetic, molecular, and cytological studies have shed light on the specific functions of the cytoskeleton during oogenesis. The results of these studies are reviewed here, and their mechanistic implications are considered.

The villin-like protein encoded by the Drosophila quail gene is required for actin bundle assembly during oogenesis

Mutations in the Drosophila quail gene result in female sterility due to the disruption of cytoplasmic transport from the nurse cells into the oocyte late in oogenesis. Nurse cells from quail mutant egg chambers fail to assemble cytoplasmic actin filament bundles correctly. We have cloned the quail gene and found that it encodes a protein with homology to the vertebrate actin-regulating protein villin. Unlike vertebrate villin, which is restricted to specialized absorptive epithelial cells, the villin-like protein encoded by quail is germline specific in adult flies. Antibodies directed against the quail protein show a striking colocalization with filamentous actin in the nurse cells and the oocyte. Our results demonstrate that the villin-like product of quail is required for the formation of cytoplasmic actin filament bundles in nurse cells, possibly by regulating both the polymerization and organization of actin filaments as demonstrated for vertebrate villin in vitro.

Regulation of the dorsal morphogen by the Toll and torso signaling pathways: a receptor tyrosine kinase selectively masks transcriptional repression

The dorsal (dl) nuclear gradient initiates the differentiation of the mesoderm, neuroectoderm, and dorsal ectoderm by activating and repressing gene expression in the early Drosophila embryo. This gradient is organized by a Toll signaling pathway that shares many common features with the mammalian IL-1 cytokine pathway. Here we present evidence that a second signaling pathway, controlled by the torso (tor) receptor tyrosine kinase, also modulates dl activity. Evidence is presented that the tor pathway selectively masks the ability of dl to repress gene expression but has only a slight effect on activation. Intracellular kinases that are thought to function downstream of tor, such as D-raf and the rolled MAP kinase, mediate this selective block in repression. Normally, the Toll and tor pathways are both active only at the embryonic poles, and consequently, target genes (zen and dpp) that are repressed in middle body regions are expressed at these sites. Constitutive activation of the tor pathway causes severe embryonic defects, including disruptions in gastrulation and mesoderm differentiation, as a result of misregulation of dl target genes. These results suggest that RTK signaling pathways can control gene expression by antirepression, and that multiple pathways can fine-tune the activities of a single transcription factor.

Null alleles reveal novel requirements for Bic-D during Drosophila oogenesis and zygotic development

In the Drosophila ovary, the Bicaudal-D (Bic-D) gene is required for the differentiation of one of 16 interconnected cystocyte sister cells into an oocyte. A new class of Bic-Dnull alleles reveals a novel requirement for Bic-D for zygotic viability. In the germ line, the null mutations show that developmental processes that take place in germarial region 1, even those that create asymmetry, are independent of Bic-D function. Bic-D is then required to establish oocyte identity in one cystocyte and is essential, not only for the oocyte-specific accumulation of all oocyte markers that we have tested so far, but also for the posterior migration of the oocyte. In addition, normal polarity amongst the nurse cells requires Bic-D, indicating that the creation of different nurse cell identities may depend on oocyte determination. Our results show that different processes in early oogenesis require different amounts of Bic-D in a process-specific way and certain later processes can proceed at low levels of Bic-D. This suggests that the patterning of the female germ line and the development of an oocyte depend on differential responses to a single activity that is capable of initiating distinct oogenesis processes and can establish different cell fates.

Dissociation of the dorsal-cactus complex and phosphorylation of the dorsal protein correlate with the nuclear localization of dorsal

The formation of dorsal-ventral polarity in Drosophila requires the asymmetric nuclear localization of the dorsal protein along the D/V axis. This process is regulated by the action of the dorsal group genes and cactus. We show that dorsal and cactus are both phosphoproteins that form a stable cytoplasmic complex, and that the cactus protein is stabilized by its interaction with dorsal. The dorsal-cactus complex dissociates when dorsal is targeted to the nucleus. While the phosphorylation of cactus remains apparently unchanged during early embryogenesis, the phosphorylation state of dorsal correlates with its release from cactus and with its nuclear localization. This differential phosphorylation event is regulated by the dorsal group pathway.

In vivo self-association of the Drosophila rel-protein dorsal

The Drosophila morphogen dorsal, KBF1, NF-kappa B, and the proto-oncogene c-rel belong to the rel family of transcription factors whose function is regulated post-translationally by selective nuclear import. In the early Drosophila embryo, dorsal protein is proposed to be retained in the cytoplasm through its interaction with cactus protein. The maternal dorsal group genes constitute a signal transduction pathway, which results in targeting cytoplasmic dorsal protein into the nuclei of the syncytial blastoderm embryo, in a ventral-to-dorsal gradient. The asymmetric transcriptional regulation of zygotic genes along the dorsoventral axis by the dorsal morphogen gradient establishes embryonic dorsoventral polarity. In the lymphocytes, the functional equivalent of cactus is I kappa B, which appears to retain NF-kappa B in the cytoplasm. This retention is relieved by extracellular signals in tissue culture. NF-kappa B and rel proteins each are known to function as oligomeric complexes. Here we present genetic and biochemical evidence for the existence and functional importance of an oligomeric dorsal complex in vivo.

Female sterile mutations on the second chromosome of Drosophila melanogaster. II. Mutations blocking oogenesis or altering egg morphology

In mutagenesis screens for recessive female sterile mutations on the second chromosome of Drosophila melanogaster 528 lines were isolated which allow the homozygous females to survive but cause sterility. In 62 of these lines early stages of oogenesis are affected, and these females usually do not lay any eggs. In 333 lines oogenesis proceeds apparently normally to stage 8 of oogenesis, but morphological defects become often apparent during later stages of oogenesis, and are visible in the defective eggs produced by these females whereas 133 lay eggs that appear morphologically normal, but do not support normal embryonic development. Of the lines 341 have been genetically characterized and define a total of 140 loci on the second chromosome. Not all the loci are specific for oogenesis. From the numbers obtained we estimate that the second chromosome of Drosophila contains about 13 loci that are relatively specific for early oogenesis, 70 loci that are specifically required in mid to late oogenesis, and around 30 maternal-effect lethals.

Requirement for phosphorylation and localization of the Bicaudal-D protein in Drosophila oocyte differentiation

In the Drosophila female the product of the germline stem cell, the cystoblast, gives rise to 16 interconnected cystocytes. One of them differentiates into the oocyte, while the 15 others become polyploid nurse cells. Bic-D is required for the differentiation of an oocyte and hence for fertility. Recessive mutations in Bic-D block the oocyte-specific accumulation of its own and other RNAs. Based on its properties and distribution, the Bic-D protein appears to be a component of a cytoskeletal transport or anchoring system. Additional results suggest that the phosphorylation of the Bic-D protein is essential for its accumulation in the pro-oocyte and that this process leads to the gradual localization to the pro-oocyte of factors required for oocyte differentiation.

The temperature-sensitive mutation vir ts(virilizer) identifies a new gene involved in sex determination of Drosophila

When XX animals homozygous for the temperature-sensitive mutation vir ^tsof virilizer (2-103.9) are raised at the restrictive temperature of 29° C, they are transformed into sterile intersexes with a morphology comparable to XX flies mutant at the sex-determining gene doublesex (dsx). The gonads of the vir ^tsintersexes are ovaries in which the germ cells undergo abortive oogenesis. At the permissive temperature of 25° C or below, XX vir ^tsanimals develop into marginally fertile females. The temperature-sensitive period of vir ^tsis within the third larval instar. XY males are not affected by the mutation. Animals that are homozygous for vir ^tsand either transformer (tra) or tra2 develop as pseudomales; on the other hand, constitutive expression of a female-specific tra product rescues XX animals from the effect of vir ^ts, but these females are sterile. The data show that tra and tra2 are epistatic to vir. Animals with only one wildtype copy of either tra or tra2 and mutant for vir ^tsare already transformed into intersexes at 25° C. Conversely, the presence of three copies of the tra ⁺ gene largely prevents the effect of vir ^tsat 29° C; such flies are practically female, but sterile. Animals homozygous for vir ^tsand heterozygous for dsx ^D/+, raised at 29° C, are transformed into severely masculinized intersexes or almost pseudomales. The observations suggest that vir acts above and via tra and tra2 to achieve proper female-specific expression of the dsx gene in XX zygotes.

The genetics of a small autosomal region of Drosophila melanogaster containing the structural gene for alcohol dehydrogenase. VII. Characterization of the region around the snail and cactus loci

The genetic interval 35C to 36A on chromosome arm 2L of Drosophila melanogaster has been saturated for mutations with visible or lethal phenotypes. 38 loci have been characterized, including several maternal-effect lethals (vasa, Bic-C, chiffon, cactus and cornichon) and several early embryonic lethals, including snail and fizzy. About 130 deletions have been used to order these loci. Complex interactions between mutant alleles have been uncovered in the immediate genetic environs of the snail gene, as has further evidence for an interaction between this region and that including the nearby genes no-ocelli and elbow.

Cloning of the p50 DNA binding subunit of NF-kappa B: homology to rel and dorsal

The DNA binding subunit of the transcription factor NF-kappa B, p50, has been cloned. p50 appears to be synthesized as a larger protein that is then processed to its functional size. Sequence analysis reveals remarkable homology for over 300 amino acids at the amino-terminal end to the oncogene v-rel, its cellular homolog c-rel, and the Drosophila maternal effect gene dorsal. This establishes NF-kappa B as a member of the rel family of proteins, all of which display nuclear-cytosolic translocation. Protein sequence from the p65 polypeptide has established that it is not encoded in the same mRNA as p50. However, p65 appears homologous to c-rel, suggesting that c-rel may form heterodimers with p50 and rel may include a homodimerization motif.

Structure of the Drosophila BicaudalD protein and its role in localizing the posterior determinant nanos

Mutations in the BicaudalD (BicD) gene lead to a global reorganization of the Drosophila body pattern such that the head, thoracic, and anterior abdominal segments are replaced by posterior abdominal segments and terminalia. We first provide evidence that the primary cause of this phenotype is the inhibition of two anterior factors, bicoid and hunchback, by mislocalized activity of the posterior determinant nanos. We then describe the isolation of the BicD gene and show that it encodes a coiled-coil protein similar to the carboxy-terminal portion of the myosin heavy chain. Finally, we find that BicD protein is uniformly distributed throughout wild-type oocytes but is concentrated at the anterior pole of BicD mutant oocytes together with ectopic nanos activity. Taken together, these results suggest that BicD encodes a cytoskeleton-like protein involved in transporting or anchoring the nanos morphogen within the oocyte cytoplasm.

Developmental genetics of loci at the base of the X chromosome of Drosophila melanogaster

We have conducted a genetic and developmental analysis of the 26 contiguous genetic complementation groups within the 19D3-20F2 interval of the base of the X chromosome, a region of 34 polytene bands delimited by the maroon-like and suppressor of forked loci. Within this region there are four loci which cause visible phenotypes but which have little or no effect on zygotic viability (maroon-like, little fly, small optic lobes and sluggish). There are 22 loci which, when mutated, are zygotic lethals and three of these, legless/runt, folded gastrulation and 13E3, have severe effects on embryonic development. In addition, three visible phenotypes have been defined only by overlapping deficiencies (melanized-like, tumorous head, and varied outspread). We have analyzed the lethal phases and maternal requirement of 58 mutations at 22 of the zygotic lethal loci by means of germline clone analysis using the dominant female sterile technique. Additionally, all lethal complementation groups, as well as a specific subset of deficiencies, have been studied histologically for defects in the development of the central and peripheral embryonic nervous systems.

Female sterile mutations on the second chromosome of Drosophila melanogaster. I. Maternal effect mutations

In mutagenesis screens for recessive female sterile mutations on the second chromosome of Drosophila melanogaster 529 chromosomes were isolated which allow the homozygous females to survive, but cause them to be sterile. In 136 of these lines, mutant females produce morphologically normal eggs which cannot support normal embryonic development. These "maternal-effect" mutations fall into 67 complementation groups which define 23 multiply hit and 44 singly hit loci. In eggs from 14 complementation groups development is blocked before the formation of a syncytial blastoderm. In eggs from 12 complementation groups development is abnormal before cellularization, 17 complementation groups cause abnormal cellularization, 12 complementation groups cause changes in cellular morphology in early gastrulation stages, and 12 complementation groups seem to affect later embryonic development.

Characterization and cloning of fasciclin III: a glycoprotein expressed on a subset of neurons and axon pathways in Drosophila

To identify candidates for neuronal recognition molecules in Drosophila, we used monoclonal antibodies to search for surface glycoproteins expressed on subsets of axon bundles (or fascicles) during development. Here we report on the characterization and cloning of fasciclin III, which is expressed on a subset of neurons and axon pathways in the Drosophila embryo. Fasciclin III is also expressed at other times and places including transient segmentally repeated patches in the neuroepithelium and segmentally repeated stripes in the body epidermis. Antisera generated against each of four highly related forms of the protein were used for cDNA expression cloning to identify a single gene, which was confirmed to encode fasciclin III by tissue in situ hybridization and genetic deficiency analysis.

The Drosophila sex determination gene daughterless has different functions in the germ line versus the soma

As a regulator of the female-specific gene Sxl, da+ provides an essential maternal component in the control of sex determination and dosage compensation; nevertheless, neither the maternal nor zygotic phenotypes of the original mutant da allele is sex-specific. Here we clarify the role of da+ in Drosophila development, finding: this sex determination gene is indeed pleiotropic; zygotic functioning of da+ is essential in both sexes for somatic cell development, but not for germ cell development; da female sterility results from a somatic, rather than germ-line, defect; and expression of da+ in the maternal germ line is required only for daughters in the subsequent generation, as expected for a specific regulator of Sxl+. These conclusions follow from the characterization of new da null alleles isolated by a selection for defects in maternally acting positive regulators of Sxl.

Electrophysiological study of Drosophila rhodopsin mutants

Electrophysiological investigations were carried out on several independently isolated mutants of the ninaE gene, which encodes opsin in R1-6 photoreceptors, and a mutant of the ninaD gene, which is probably important in the formation of the rhodopsin chromophore. In these mutants, the rhodopsin content in R1-6 photoreceptors is reduced by 10(2)-10(6)-fold. Light-induced bumps recorded from even the most severely affected mutants are physiologically normal. Moreover, a detailed noise analysis shows that photoreceptor responses of both a ninaE mutant and a ninaD mutant follow the adapting bump model. Since any extensive rhodopsin-rhodopsin interactions are not likely in these mutants, the above results suggest that such interactions are not needed for the generation and adaptation of light-induced bumps. Mutant bumps are strikingly larger in amplitude than wild-type bumps. This difference is observed both in ninaD and ninaE mutants, which suggests that it is due to severe depletion of rhodopsin content, rather than to any specific alterations in the opsin protein. Lowering or buffering the intracellular calcium concentration by EGTA injection mimics the effects of the mutations on the bump amplitude, but, unlike the mutations, it also affects the latency and kinetics of light responses.