Malaria entomology: can genomics help?

The field of genomics has advanced over the last decades to the forefront of molecular genetic research. Many genomes, including that of yeast, have already been sequenced and the determination of the genome sequence of several higher organisms is now within sight, including the complete DNA sequence of Homo sapiens. Here I review the state of the Anopheles gambiae genomic research and I present the current plans for an 'Anopheles Genome Project'. An understanding of the structure and function of the vector's genome may ultimately provide better tools for the control of the malaria mosquito.

Molecular identification of chromosomal forms of Anopheles gambiae sensu stricto

The Afrotropical malaria vectors Anopheles gambiae sensu stricto and An. arabiensis, responsible for more than 3/4 of the world Plasmodium falciparum inoculations, are members of the Anopheles gambiae complex, a group consisting of six sibling species. The nominal species (An. gambiae s.s.) is by far the most anthropophilic vector and its adaptation to man and his environment involves further ongoing speciation processes. This fact is shown by the existence of a number of incipient taxonomic units characterised by different chromosomal arrangements derived from the presence of polymorphic paracentric inversions. This speciation process is centered in West Africa, where five so-called 'chromosomal forms' have been described, designated with a non-Linnean nomenclature: Forest, Bissau, Savanna, Bamako, and Mopti. Studies on the distribution and the ecology of these incipient species have highlighted specific adaptations to eco-ethological parameters, which might reflect on their relative efficiency as malaria vectors. Cytogenetic analysis, in spite of some inherent difficulties, has proved to be a powerful tool for the identification of An. gambiae sibling species and the individual chromosomal forms. Yet, modern molecular tools are now available, providing alternative faster low-cost technologies, and we discuss here their relative merits.

Salivary gland-specific gene expression in the malaria vector Anopheles gambiae

Molecular studies on the tissue-specific gene expression in the salivary glands of Anopheles gambiae may provide useful tools for the development of new strategies for the control of the most efficient malaria vector in the sub-Saharan Africa. We summarize here the results of a recent investigation focused on the isolation of secreted factors and putative receptors from the salivary glands of An. gambiae. Using the Signal Sequence Trap technique we have identified the first cDNAs specifically expressed in the An. gambiae salivary glands. Among these, four are exclusively expressed in female glands and encode factors presumably involved in blood-feeding, whereas two other cDNAs seem to be expressed both in male and in female glands and are likely implicated in sugar-feeding. Homologues of genes previously identified in the yellow fever mosquito Aedes aegypti, like the apyrase and D7, as well as novel salivary gland-specific cDNAs, were identified. The isolation and characterization of promoter sequences from the corresponding genes may prove useful for the expression of anti parasitic agents in the salivary glands of transgenic mosquitoes.

[Contralateral transinguinal laparoscopy in unilateral inguinal hernia]

BACKGROUND

Indication for surgical exploration of the contralateral groin during unilateral herniorraphy in children is the subject of a worldwide debate. Routine exploration based on the likelihood of a patent processus vaginalis (PV) according to age, gender or side to some extent leads to unnecessary procedures, while routine abstention may leave a peritoneal sac, likely to later induce a symptomatic hernia in about 10% of cases.

METHODS AND PATIENTS

One hundred and twenty-five children aged from 1 month to 15 years underwent transinguinal laparoscopic assessment of the contralateral groin, using a 3 mm trocar and a 70 degrees telescope gently introduced through the exposed PV. Surgical exploration was performed only in those patients who exhibited a patent PV, and in patients where the groin was poorly visualized due to technical problems.

RESULTS

Regardless of age, contralateral surgery was not considered in 88 (70%) of the 125 children. Among the 37 patients that were operated upon, eight had a negative exploration due to an erroneous endoscopic evaluation. Surgery was avoided in 35 (56%) of the 62 infants aged less than 2 years, including nine of the 13 prematures who were previously routinely operated upon. Conversely, in the 63 older patients who were readily spared from surgical exploration, the videoscopic evaluation allowed appropriate selection for contralateral surgery in six.

CONCLUSION

A routine policy, either of surgery or observation, is no longer indicated as a quick, safe and cost-effective method is available to detect a patent PV. The transinguinal laparoscopy is safe and could be easily performed by surgeons already skilled in pediatric herniorraphy. Therefore, the videoscopic transinguinal contralateral evaluation is worth being promoted to ensure an appropriate surgery tailored to the anatomical features.

[Skin gangrene of the external genitalia. Report of 44 cases]

STUDY AIM

The aim of this study is to report 44 cases of male external genitalia cutaneous gangrene which have been observed at the Principal Hospital of Dakar (Senegal) during a 4-year period.

PATIENTS AND METHODS

The patients all belonged to a black and poor population (mean age: 60 years). Diabetes was present in 11% of the patients. In ten patients, no aetiology was found. The other 34 cases were secondary mainly to urogenital pathology (50%). In 50% of the cases, the lesions were localised on the external genitalia, in the other 50%, the lesions had spread to the hypogastrium and/or the perineum. Medical treatment included intensive care and triple antibiotic therapy, penicillin, gentamycin and metronidazole. A hyperbaric oxygen therapy was associated in 25% of the cases. The surgical treatment in the acute period included incising, debridement, paring, draining, urinary derivation (n = 36), and colostomy (n = 5). Thirteen patients had the benefit of sequential and prospective bacteriological tests.

RESULTS

Spontaneous healing was obtained in 48% of the patients within 2 to 3 months. Secondary reconstructive surgery consisted mainly in cutaneous grafts. Global mortality rate was 34%, mortality rate was 30% in the secondary gangrenes, 40% in the primitive gangrenes. Mean hospitalisation duration was 6 weeks. Main sequelae were cheiloïd scars.

CONCLUSIONS

The authors try to clarify the nosological imprecisions of this pathology by distinguishing between the secondary types and the primitive types corresponding to Fournier's gangrene, which still inspires many questions concerning its etio-pathogenesis. The surgical treatment must eradicate all necrosis by suited iterative procedures, associated with local care. Hyperbaric oxygen therapy was not efficient in this series. This pathology, although rare, needs to be better known, because only an early and efficient surgical and medical treatment will be able to decrease the exceptional gravity of the prognosis.

P-element insertion alleles of essential genes on the third chromosome of Drosophila melanogaster: correlation of physical and cytogenetic maps in chromosomal region 86E-87F

We have established a collection of 2460 lethal or semi-lethal mutant lines using a procedure thought to insert single P elements into vital genes on the third chromosome of Drosophila melanogaster. More than 1200 randomly selected lines were examined by in situ hybridization and 90% found to contain single insertions at sites that mark 89% of all lettered subdivisions of the Bridges' map. A set of chromosomal deficiencies that collectively uncover approximately 25% of the euchromatin of chromosome 3 reveal lethal mutations in 468 lines corresponding to 145 complementation groups. We undertook a detailed analysis of the cytogenetic interval 86E-87F and identified 87 P-element-induced mutations falling into 38 complementation groups, 16 of which correspond to previously known genes. Twenty-one of these 38 complementation groups have at least one allele that has a P-element insertion at a position consistent with the cytogenetics of the locus. We have rescued P elements and flanking chromosomal sequences from the 86E-87F region in 35 lines with either lethal or genetically silent P insertions, and used these as probes to identify cosmids and P1 clones from the Drosophila genome projects. This has tied together the physical and genetic maps and has linked 44 previously identified cosmid contigs into seven "super-contigs" that span the interval. STS data for sequences flanking one side of the P-element insertions in 49 lines has identified insertions in the alphagamma element at 87C, two known transposable elements, and the open reading frames of seven putative single copy genes. These correspond to five known genes in this interval, and two genes identified by the homology of their predicted products to known proteins from other organisms.

Infection of the gonads of the SimES strain of Drosophila simulans by the hereditary reovirus DSV

The S character of Drosophila simulans SimES-st strain undergoes a non-mendelian transmission. It has been postulated that a virus, Drosophila S virus (DSV), could be the causative agent. Electron microscopy analysis of gonads of flies showing a strong S phenotype revealed the presence of virus in or near the germ cells. The S character transmission rate is greater in females than that in males. Similarly, the level of infection by DSV is higher in ovaries than that in testes. Flies treated at a nonpermissive temperature do not present the S phenotype and appear to be cured from the virus. This information, taken together with previous work, makes the hypothesis that DSV is the causative agent of the S phenotype more than likely.

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.

Mapping of microsatellite markers developed from a flow-sorted swine chromosome 6 library

Swine Chromosome (Chr) 6-enriched libraries, generated with size-fractionated DNA isolated from chromosomes sorted by flow cytometry, have been used to develop new Chr 6 microsatellite markers. Chromosome isolation procedures were established to reproducibly prepare high quality chromosomes from phytohemagglutinin (PHA)-stimulated swine peripheral blood lymphocytes and to sort individual chromosomes after staining with Hoechst 33258 and chromomycin A3. Chromosome purity was verified by specific staining of swine Chr 6 with fluorescence in situ hybridization (FISH) by use of painting probes generated by degenerate oligonucleotide-primed polymerase chain reaction (DOP-PCR) amplification of as few as 300 sorted Chr 6. For library construction, DNA was extracted from flow-sorted pools representing Chr 6, amplified, size selected for fragments from 300 to 700 bp, and ligated into pBluescript SK II+ or Lambda ZAP Express. The libraries were then screened with a radiolabeled poly-(dCA) DNA probe. Of 107 (CA)n repeat-containing clones verified by sequencing, 21 were polymorphic and used to genotype the University of Illinois swine reference families. Linkage analysis was then performed with CRIMAP 2.4 (LOD > 3.0), and the results showed that 15 of the microsatellites mapped to swine Chr 6. At least three of these new markers map to locations where there were gaps in the consensus Chr 6 map. Another four markers, because of their PIC values, should provide more informative markers in other areas of the map. Most of the new markers can also be used for automated genotyping with fluorescent labeling. This set of 15 new Chr 6 markers will, therefore, be useful in helping to define QTL associated with swine Chr 6.

The aphid transmission factor of cauliflower mosaic virus forms a stable complex with microtubules in both insect and plant cells

We analyzed the distribution of the cauliflower mosaic virus (CaMV) aphid transmission factor (ATF), produced via a baculovirus recombinant, within Sf9 insect cells. Immunogold labeling revealed that the ATF colocalizes with an atypical cytoskeletal network. Detailed observation by electron microscopy demonstrated that this network was composed of microtubules decorated with paracrystalline formations, characteristic of the CaMV ATF. A derivative mutant of the ATF, unable to self-assemble into paracrystals, was also analyzed. This mutant formed a net-like structure, with a mesh of four nanometers, tightly sheathing microtubules. Both the ATF- and the derivative mutant-microtubule complexes were highly stable. They resisted dilution-, cold-, and calcium-induced microtubule disassembly as well as a combination of all three for over 6 hr. CaMV ATF cosedimented with microtubules and, surprisingly, it bound to Taxol-stabilized microtubules at high ionic strength, thus suggesting an atypical interaction when compared with that usually described for microtubule-binding proteins. Using immunofluorescence double labeling we also demonstrated that the CaMV ATF colocalizes with the microtubule network when expressed in plant cells.

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.

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.

To outsource or not to outsource

Outsourcing work can be a positive intervention if the environment and strategies are properly coordinated, but there is no guarantee of success. Today, more than ever before, hospitals are suffering from two pressures: economic constraints and the migration of managerial talent out of the field to other sectors of the economy. With these two pressures, hospitals are searching for ways to reduce costs and find skilled personnel. A common strategy is to seek support from the open market and outsource. This article looks at tools for making the outsourcing decision, such as risk and force field analysis.

Isolation and characterization of three serine protease genes in the mosquito Anopheles gambiae

Three genes encoding serine proteases (Sp6A, Sp6T and Sp8T) were isolated from the malaria mosquito An. gambiae. The proteins that are conceptually translated from these genes contain all amino acids that have been described for this class of proteolytic enzymes, namely the His, Asp and Ser residues at the active site, and the six cysteine residues that form the three disulphide bridges in invertebrate serine proteases. The genes are expressed at low levels and the transcripts were detected only by PCR. Analysis of the nucleotide sequences of the three genes and their pattern of expression indicate that none of the genes code for digestive enzymes, but rather that the proteins have features of the tethered type of serine proteases.

Conserved function of anopheles gambiae midgut-specific promoters in the fruitfly

Control of malaria by a methodology that would permit the effective blockage of the Anopheles gambiae midgut wall penetration by Plasmodium parasites requires a detailed understanding of both the physiology of the mosquito's digestion, and of the interactions between the parasite and its host. We have transformed Drosophila melanogaster with several constructs that allow the study of the promoter region of two of the major late trypsin genes of A. gambiae. Using several deletions, we have identified, for both genes, small genomic segments that are sufficient to confer tissue specificity to the promoter in a species that is far away in evolution from the mosquito. This will allow further studies that will enable both the understanding of the blood meal digestion, and may potentially be useful for the design of anti-plasmodial constructs at a later stage.

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.