Molecular organization of an individual Drosophila polytene chromomere: transcribed sequences in the 10A1-2 band

Complete cloning of the DNA in the cytogenetic region 9F12-10A7 has allowed us to analyze the fine structure of an individual polytene chromomere in Drosophila melanogaster. In this report we identify the transcriptionally active fragments within the 10A1-2 band. At least 22 DNA fragments representing multiple distinct transcription units are active during embryogenesis, in third-instar larva or in isolated larval tissues. The transcribed fragments are significantly (at least sevenfold) more numerous than the three genetically defined complementation groups in the 10A1-2 band. One of the transcriptionally active zones detected encompasses a previously unsuspected homologue of the genes Delta and Serrate.

The autosomal chorion locus of the medfly Ceratitis capitata. I. Conserved synteny, amplification and tissue specificity but sequence divergence and altered temporal regulation

We report the isolation, full sequence characterization, amplification and expression properties of medfly chorion genes corresponding to the autosomal chorion locus of Drosophila. These genes are found adjacent to the paramyosin gene and are organized in the same order and tandem orientation as their Drosophila homologues, although they are spaced further apart. They show substantial sequence divergence from their Drosophila homologues, including novel peptide repeats and a new spacing of the tyrosines, which are known to be cross-linked in Dipteran chorion. The genes are amplified and expressed during oogenesis, as in Drosophila. Three of them are expressed in the same relative temporal order as in Drosophila but the fourth gene, the homologue of s15, shows a clear shift to an earlier expression period. This is the first known instance of changed temporal regulation in dipteran chorion genes.

Plasmodium activates the innate immune response of Anopheles gambiae mosquitoes

Innate immune-related gene expression in the major disease vector mosquito Anopheles gambiae has been analyzed following infection by the malaria parasite, Plasmodium berghei. Substantially increased levels of mRNAs encoding the antibacterial peptide defensin and a putative Gram-negative bacteria-binding protein (GNBP) are observed 20-30 h after ingestion of an infected blood-meal, at a time which indicates that this induction is a response to parasite invasion of the midgut epithelium. The induction is dependent upon the ingestion of infective, sexual-stage parasites, and is not due to opportunistic co-penetration of resident gut micro-organisms into the hemocoel. The response is activated following infection both locally (in the midgut) and systemically (in remaining tissues, presumably fat body and/or hemocytes). The observation that Plasmodium can trigger a molecularly defined immune response in the vector constitutes an important advance in our understanding of parasite-vector interactions that are potentially involved in malaria transmission, and extends knowledge of the innate immune system of insects to encompass responses to protozoan parasites.

Molecular immune responses of the mosquito Anopheles gambiae to bacteria and malaria parasites

Immune responses of the malaria vector mosquito Anopheles gambiae were monitored systematically by the induced expression of five RNA markers after infection challenge. One newly isolated marker encodes a homologue of the moth Gram-negative bacteria-binding protein (GNBP), and another corresponds to a serine protease-like molecule. Additional previously described markers that respond to immune challenge encode the antimicrobial peptide defensin, a putative galactose lectin, and a putative serine protease. Specificity of the immune responses was indicated by differing temporal patterns of induction of specific markers in bacteria-challenged larvae and adults, and by variations in the effectiveness of different microorganisms and their components for marker induction in an immune-responsive cell line. The markers exhibit spatially distinct patterns of expression in the adult female mosquito. Two of them are highly expressed in different regions of the midgut, one in the anterior and the other in the posterior midgut. Marker induction indicates a significant role of the midgut in insect innate immunity. Immune responses to the penetration of the midgut epithelium by a malaria parasite occur both within the midgut itself and elsewhere in the body, suggesting an immune-related signaling process.

Antisense suppression of the putative ribosomal protein S3A gene disrupts ovarian development in Drosophila melanogaster

The Drosophila melanogaster homologue of the Anopheles gambiae C3 cDNA has been isolated and characterized by sequence analysis. The encoded protein was localized by immunochemical and immunocytochemical methods. The Drosophila C3 protein is highly similar to homologues of disputed function, which have previously been identified in fungi, plants and animals. The protein is ubiquitous and localized in the cytoplasm. Cell fractionation followed by detection with a specific antibody preparation shows that the protein is associated with the 40S ribosomal subunit. The C3 gene is located in section 101F of chromosome 4. Antisense transgenic analysis shows that this gene is essential for oogenesis. The most prominent phenotype resulting from antisense depletion of C3 RNA is disappearance of the follicular cells of the ovary (where the concentration of C3 protein is normally high) and abnormalities of the associated germline derivatives, leading to failure of egg production.

One-hundred and five new potential Drosophila melanogaster genes revealed through STS analysis

Complementation analysis had suggested that the Drosophila melanogaster genome contains approximately 5000 genes, but it is now generally accepted that the actual number is several times as high. We report here an analysis of 1788 anonymous sequence tagged sites (STSs) from the European Drosophila Genome Project (EDGP), totalling 463 kb. The data reveal a substantial number of previously undescribed potential genes, amounting to 6.1% of the number of Drosophila genes already in the sequence databases.

Isolation and properties of Drosophila melanogaster ferritin--molecular cloning of a cDNA that encodes one subunit, and localization of the gene on the third chromosome

Ferritin was purified from iron-fed Drosophila melanogaster extracts by centrifugation in a gradient of potassium bromide. On polyacrylamide gel electrophoresis, the product showed two protein bands corresponding to the ferritin monomer and dimer. Electrophoresis following dissociation with SDS and 2-mercaptoethanol revealed three strong bands of approximately 25, 26, and 28 kDa. N-terminal amino acid sequences were identical for the 25-kDa and 26-kDa subunits, but different for the 28-kDa subunit. Conserved ferritin PCR primers were used to amplify a 360-bp cDNA product, which was used to isolate a clone from a D. melanogaster cDNA library that contained the complete coding sequence for a ferritin subunit. Additional 5' sequence obtained by the RACE method revealed the presence of a putative iron regulatory element. The PCR product was also used to locate the position of the ferritin subunit gene at region 99F on the right arm of the third chromosome. The deduced amino acid sequence of the D. melanogaster ferritin subunit contained a signal sequence and resembled most closely ferritin of the mosquito Aedes aegypti. The evolution of ferritin sequences is discussed.

The Drosophila bunched gene is a homologue of the growth factor stimulated mammalian TSC-22 sequence and is required during oogenesis

A Drosophila melanogaster sequence homologous to the mammalian growth factor-stimulated TSC-22 gene was isolated in an enhancer trap screen for genes expressed in anterodorsal follicle cells during oogenesis. This sequence includes a 225 aa residue open reading frame that encompasses a leucine zipper motif immediately preceded by a highly conserved region (TSC box), similarly located but distinct from the basic domain of bZIP proteins. The gene encoding this sequence, bunched (bun), has been independently isolated and characterized with respect to its role in peripheral nervous system development and eye development (Treisman, J.E., Lai, Z.-C. and Rubin, G.M. (1995) Shortsighted acts in the decapentaplegic pathway in the Drosophila eye development and has homology to a mouse TGF-beta-responsive gene. Development 121, 2835-2845). In agreement with the expression of the enhancer detector insertion, in situ hybridization reveals that bun transcripts localize to the anterior dorsal follicle cells at stages 10-12 of oogenesis. Changes in bun enhancer trap expression in genetic backgrounds that disrupt the grk/Egfr signaling pathway suggest that bun is regulated by growth factor patterning of dorsal anterior follicle cell fates. Clonal analysis shows that bun is required for the proper elaboration of dorsal cell fates leading to the formation of the dorsal appendages.

Progress in the map-based cloning of the Anopheles gambiae genes responsible for the encapsulation of malarial parasites

A genetically selected strain of the mosquito Anopheles gambiae, the major vector of malaria in sub-Saharan Africa, is able to encapsulate and kill Plasmodium ookinetes after they have penetrated the midgut cells and come to rest between the midgut epithelial cells and the surrounding basal lamina. The genetic basis of this phenotype has now been examined by high-resolution mapping using microsatellite loci. Results of this mapping indicate that three genes contribute to this phenotype, with one gene on the left arm of chromosome 2 accounting for the most of the effect. These genes, called Pen1, Pen2, and Pen3 (for Plasmodium encapsulation genes 1, 2 and 3) have also been physically localized to relatively small and well defined regions of the polytene chromosome complement. Strategies for cloning these genes by genetic and physical mapping methods are discussed.

Quantitative trait loci for refractoriness of Anopheles gambiae to Plasmodium cynomolgi B

The severity of the malaria pandemic in the tropics is aggravated by the ongoing spread of parasite resistance to antimalarial drugs and mosquito resistance to insecticides. A strain of Anopheles gambiae, normally a major vector for human malaria in Africa, can encapsulate and kill the malaria parasites within a melanin-rich capsule in the mosquito midgut. Genetic mapping revealed one major and two minor quantitative trait loci (QTLs) for this encapsulation reaction. Understanding such antiparasite mechanisms in mosquitoes may lead to new strategies for malaria control.

Cloning and characterization of cDNAs preferentially expressed in the ovary of the mosquito, Anopheles gambiae

We used differential screening to isolate from an ovarian cDNA library two expressed sequences that are enriched substantially in ovaries of blood-fed female Anopheles gambiae, as compared to female carcass and male mosquitoes. One of these clones encodes an isoform of histone H2B, whose transcript is polyadenylated at the 3' end. The other cDNA clone encodes a protein that is highly conserved in evolution and has been implicated in growth control although its function is still obscure. Both genes can be used to study gene activation during An. gambiae oogenesis.

Identification and characterization of differentially expressed cDNAs of the vector mosquito, Anopheles gambiae

The isolation and study of Anopheles gambiae genes that are differentially expressed in development, notably in tissues associated with the maturation and transmission of the malaria parasite, is important for the elucidation of basic molecular mechanisms underlying vector-parasite interactions. We have used the differential display technique to screen for mRNAs specifically expressed in adult males, females, and midgut tissues of blood-fed and unfed females. We also screened for mRNAs specifically induced upon bacterial infection of larval stage mosquitoes. We have characterized 19 distinct cDNAs, most of which show developmentally regulated expression specificity during the mosquito life cycle. The most interesting are six new sequences that are midgut-specific in the adult, three of which are also modulated by blood-feeding. The gut-specific sequences encode a maltase, a V-ATPase subunit, a GTP binding protein, two different lectins, and a nontrypsin serine protease. The latter sequence is also induced in larvae subjected to bacterial challenge. With the exception of a mitochondrial DNA fragment, the other 18 sequences constitute expressed genomic sequence tags, 4 of which have been mapped cytogenetically.

Immune factor Gambif1, a new rel family member from the human malaria vector, Anopheles gambiae

A novel rel family member, Gambif1 (gambiae immune factor 1), has been cloned from the human malaria vector, Anopheles gambiae, and shown to be most similar to Drosophila Dorsal and Dif. Gambif1 protein is translocated to the nucleus in fat body cells in response to bacterial challenge, although the mRNA is present at low levels at all developmental stages and is not induced by infection. DNA binding activity to the kappaB-like sites in the A.gambiae Defensin and the Drosophila Diptericin and Cecropin promoters is also induced in larval nuclear extracts following infection. Gambif1 has the ability to bind to kappaB-like sites in vitro. Co-transfection assays in Drosophila mbn-2 cells show that Gambif1 can activate transcription by interacting with the Drosophila Diptericin regulatory elements, but is not functionally equivalent to Dorsal in this assay. Gambif1 protein translocation to the nucleus and the appearance of kappaB-like DNA binding activity can serve as molecular markers of activation of the immune system and open up the possibility of studying the role of defence reactions in determining mosquito susceptibility/refractoriness to malaria infection.

An integrated genetic map of the African human malaria vector mosquito, Anopheles gambiae

We present a genetic map based on microsatellite polymorphisms for the African human malaria vector, Anopheles gambiae. Polymorphisms in laboratory strains were detected for 89% of the tested microsatellite markers. Genotyping was performed for individual mosquitos from 13 backcross families that included 679 progeny. Three linkage groups were identified, corresponding to the three chromosomes. We added 22 new markers to the existing X chromosome map, for a total of 46 microsatellite markers spanning a distance of 48.9 cM. The second chromosome has 57 and the third 28 microsatellite markers spanning a distance of 72.4 and 93.7 cM, respectively. The overall average distance between markers is 1.6 cM (or 1.1, 1.2, and 3.2 cM for the X, second, and third chromosomes, respectively). In addition to the 131 microsatellite markers, the current map also includes a biochemical selectable markers, Dieldrin resistance (Dl), on the second chromosome and five visible markers, pink-eye (p) and white (w) on the X, collarless (c) and lunate (lu) on the second, and red-eye (r) on the third. The cytogenetic locations on the nurse cell polytene chromosomes have been determined for 47 markers, making this map an integrated tool for cytogenetic, genetic, and molecular analysis.

The transcriptional factor CF2 is a mediator of EGF-R-activated dorsoventral patterning in Drosophila oogenesis

Establishment of dorsoventral polarity during Drosophila oogenesis requires localized intercellular communication between the follicular cells and the oocyte. This is initiated by the transmission of a "dorsal signal" from the oocyte to the anterior dorsal follicle cells by the EGF receptor (EGF-R) pathway and is followed by transmission of a second signal from the ventral follicle cells back to the embryo. We show that the zinc finger transcription factor CF2 participates in these processes. CF2 is suppressed by EGF-R signaling in the anterior dorsal follicle cells. Altered expression patterns of CF2 result in specific dorsoventral patterning defects in egg chambers and in embryos, as demonstrated phenotypically and with molecular markers. CF2 appears to act as a repressor of dorsal follicle cell fates and specifically as a repressor of the rhomboid gene transcription.

Integrated genetic map of Anopheles gambiae: use of RAPD polymorphisms for genetic, cytogenetic and STS landmarks

Randomly amplified polymorphic DNA (RAPD) markers have been integrated in the genetic and cytogenetic maps of the malaria vector mosquito, Anopheles gambiae. Fifteen of these markers were mapped by recombination, relative to microsatellite markers that had been mapped previously. Thirty-four gel-purified RAPD bands were cloned and sequenced, generating sequence tagged sites (STSs) that can be used as entry points to the A. gambiae genome. Thirty one of these STSs were localized on nurse cell polytene chromosomes through their unique hybridization signal in in situ hybridization experiments. Five STSs map close to the breakpoints of polymorphic inversions, which are notable features of the Anopheles genome. The usefulness and limitations of this integrated mosquito map are discussed.

A gene complex acting downstream of dpp in Drosophila wing morphogenesis

Localized expression of the transforming growth factor-beta (TGF-beta) homologue decapentaplegic (dpp) is crucial for Drosophila wing development. Here we show that spalt and spalt-related (sal and salr), two closely related genes that encode transcription factors, are expressed in response to dpp in a central territory of the wing imaginal disc, where they are required for the patterning of the wing. They are among the first identified elements that act downstream of dpp in wing development. The phenotypic consequences of misexpression of sal and salr suggest that an important outcome of dpp activity is the subdivision of the wing disc into territories smaller than lineage compartments, through the regulation of transcription-factor-encoding genes such as sal and salr.

Recognition of diverse sequences by class I zinc fingers: asymmetries and indirect effects on specificity in the interaction between CF2II and A+T-rich elements

The Drosophila CF2II protein, which contains zinc fingers of the Cys2His2 type and recognizes an A+T-rich sequence, behaves in cell culture as an activator of a reporter chloramphenicol acetyltransferase gene. This activity depends on C-terminal but not N-terminal zinc fingers, as does in vitro DNA binding. By site-specific mutagenesis and binding site selection, we define the critical amino acid-base interactions. Mutations of single amino acid residues at the leading edge of the recognition helix are rarely neutral: many result in a slight change in affinity for the ideal DNA target site; some cause major loss of affinity; and others change specificity for as many as two bases in the target site. Compared to zinc fingers that recognize G+C-rich DNA, CF2II fingers appear to bind to A+T-rich DNA in a generally similar manner, but with additional flexibility and amino acid-base interactions. The results illustrate how zinc fingers may be evolving to recognize an unusually diverse set of DNA sequences.

Regulation, function and potential origin of the Drosophila gene spalt adjacent, which encodes a secreted protein expressed in the early embryo

During early embryogenesis of Drosophila the spatial and temporal expression patterns of the region-specific homeotic gene spalt (sal) and the neighbouring gene spalt adjacent (sala) extensively overlap. We show that the initial expression patterns of the two genes in the blastoderm also have identical genetic controls. However, while sal encodes a transcription factor, sala encodes a precursor protein from which a functional signal peptide is cleaved off to generate the secreted sala protein. Ectopic expression or absence of sala protein does not affect embryonic development, adult viability or fertility. In addition to sal and sala, we identified a third gene nearby, termed spalt related (salr), which shares coding sequence similarity and a late embryonic expression pattern with sal, but lacks the early expression domains that are shared by sal and sala. These results suggest that the three genes and their present cis-regulatory regions arose through a chromosomal rearrangement involving local duplication and transposition events in the 32F/33A region on the left arm of the second chromosome.

Analysis of regulatory elements of the developmentally controlled chorion s15 promoter in transgenic Drosophila

The Drosophila s15 chorion gene is expressed only in the follicular epithelium surrounding the developing oocyte, with tight quantitative control and a very narrow temporal specificity. We have used germ-line transformation analysis to conduct an extensive mutational dissection of its promoter between -189 and -39 bp relative to the transcriptional start site. Quantitative control and temporal specificity are disrupted by several of these mutations. The results suggest that this 150-bp DNA region encompasses many positive and negative, at least partially degenerate, cis-regulatory elements, which are involved in specifying the highly precise expression pattern of the s15 gene during development.

Immunity to eukaryotic parasites in vector insects

Mosquitoes and blackflies have been the focus of recent efforts to elucidate factors influencing the susceptibility of vector insects to metazoan and protozoan parasites of medical significance. Vector species exhibit variation in cellular and humoral immune responses, as highlighted by studies of melanotic encapsulation and components of the phenoloxidase system. Significant progress has been made in the development of genetic maps based upon molecular markers, leading to the genetic analysis of loci influencing susceptibility. The identification of specific inducible antibacterial peptides, and the cloning of genes encoding immune effector proteins as well as potential regulatory factors, open the path to fruitful studies of vector insect innate immunity and its relationship to insect-parasite interactions.

The white gene of Ceratitis capitata: a phenotypic marker for germline transformation

Reliable germline transformation is required for molecular studies and ultimately for genetic control of economically important insects, such as the Mediterranean fruit fly (medfly) Ceratitis capitata. A prerequisite for the establishment and maintenance of transformant lines is selectable or phenotypically dominant markers. To this end, a complementary DNA clone derived from the medfly white gene was isolated, which showed substantial similarity to white genes in Drosophila melanogaster and other Diptera. It is correlated with a spontaneous mutation causing white eyes in the medfly and can be used to restore partial eye color in transgenic Drosophila carrying a null mutation in the endogenous white gene.

Two genes encoding midgut-specific maltase-like polypeptides from Anopheles gambiae

Full-length cDNA clones of two genes have been isolated from the African malaria vector mosquito, Anopheles gambiae. These genes, designated Agm1 and Agm2, encode maltase-like polypeptides of 498 and 599 residues, respectively. Deduced amino acid sequences contain a putative signal peptide sequence and four potential glycosylation sites. Agm1 and Agm2 show highest similarities to the Mal1 gene from Aedes aegypti and three clustered maltase genes from Drosophila melanogaster. Both genes are located at position 46D, in the terminal division of the left arm of the third chromosome. Agm2 has very strict tissue and temporal specificity, being expressed exclusively in the adult midgut. The specificity of Agm1 is similar but appears slightly broader; transcripts of this gene are detected at a low level in the pupae, and occasionally in the adult carcass after removal of the midgut.