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M J Lehane

Publications and source records attributed to M J Lehane.

At least 19 recordsLinked to original sources
PubMed1999

Pteridine fluorescence for age determination of Anopheles mosquitoes.

The age structure of mosquito populations is of great relevance to understanding the dynamics of disease transmission and in monitoring the success of control operations. Unfortunately, the ovarian dissection methods currently available for determining the age of adult mosquitoes are technically difficult, slow and may be of limited value, because the proportion of diagnostic ovarioles in the ovary declines with age. By means of reversed-phase HPLC this study investigated the malaria vectors Anopheles gambiae and An. stephensi to see if changes in fluorescent pteridine pigments, which have been used in other insects to determine the age of field-caught individuals, may be useful for age determination in mosquitoes. Whole body fluorescence was inversely proportional to age (P < 0.001, r2 > 91%) up to 30 days postemergence, with the regression values: y = 40580-706x for An. gambiae, and y = 52896-681x for An. stephensi. In both species the main pteridines were 6-biopterin, pterin-6-carboxylic acid and an unidentified fluorescent compound. An. gambiae had only 50-70% as much fluorescence as An. stephensi, and fluorescent compounds were relatively more concentrated in the head than in the thorax (ratios 1:0.8 An. gambiae; 1:0.5 An. stephensi). The results of this laboratory study are encouraging. It seems feasible that this simpler and faster technique of fluorescence quantification could yield results of equivalent accuracy to the interpretation of ovarian dissection. A double-blind field trial comparing the accuracy of this technique to marked, released and recaptured mosquitoes is required to test the usefulness of the pteridine method in the field.

Age Factors↗
PubMed1998

Factors influencing the prevalence of trypanosome infection of Glossina pallidipes on the Ruvu flood plain of Eastern Tanzania.

We report the pattern of infection of Glossina pallidipes with Trypanosoma vivax and T. congolense at a site in the Coast region of eastern Tanzania, studied between November 1993 and December 1994. Of the 2315 flies dissected 114 (4.9%) were T. congolense positive, 77 (3.3%) were T. vivax positive and 2 (0.1%) were T. brucei positive. Fly age was determined by the pteridine fluorescence method. Prevalence of infection was most strongly affected by month and the linear effect of age with the interaction of month and age having an effect for T. congolense-type infections. Sex and sex by month also have some predictive capacity when data for T. congolense and T. vivax-type infections are combined. In contrast to other similar studies our results suggest that the infection rate is non-linearly related to age of the tsetse fly, with older flies having progressively more chance of infection. The potential biological factors underpinning these interactions are discussed.

Aging↗
PubMed1998

Cloning, sequencing, temporal expression and tissue-specificity of two serine proteases from the midgut of the blood-feeding fly Stomoxys calcitrans.

Using highly degenerate, serine-protease-specific PCR primers on a midgut-specific cDNA library it was estimated that a minimum of 24 independent serine proteases were expressed in the midgut of Stomoxys calcitrans. The relative abundance of these 24 independent serine proteases has been estimated by restriction analysis of PCR products, showing that 69% fall into six almost equally abundant groups. Two highly abundant serine protease cDNAs (Ssp1 and Ssp2) were isolated and sequenced. They encode preproenzymes of 272 amino acids (Mr 28521) and 255 amino acids (Mr 27097) with putative signal peptides of 17 amino acids and 16 amino acids, putative activation peptides of 15 amino acids and 10 amino acids and mature enzymes of 239 amino acids (Mr 25322; pI 4.89) and 228 amino acids (Mr 24182; pI 7.59), respectively. Both deduced amino acid sequences contain the Asp/His/Ser catalytic triad and the highly conserved sequences surrounding it. Ssp2 also has the aspartate and two glycine residues in the specificity pocket, marking this as a typical trypsin. The positioning of the residues in the specificity pocket of Sspl is unusual; aspartate and glycine residues are present, which is typical of trypsin, but both are separated from surrounding conserved residues by additional amino acids; the second glycine found in the specificity pocket of trypsin is replaced by a serine, which is typical of chymotrypsin. Although a serine protease, the precise substrate specificity of Sspl remains to be determined. Northern analysis shows that both serine proteases are expressed constitutively with only a 20% change in the levels of expression of Ssp1 and Ssp2 through the digestive cycle, and that expression occurs predominantly in the opaque region of the midgut, the region responsible for secretion of digestive enzymes.

Amino Acid Sequence↗
PubMed1997

Midgut-specific immune molecules are produced by the blood-sucking insect Stomoxys calcitrans.

We have cloned and sequenced two defensins, Smd1 and Smd2, from anterior midgut tissue of the blood-sucking fly Stomoxys calcitrans. The DNA and N-terminal protein sequences suggest both are produced as prepropeptides. Smd1 differs from the classic defensin pattern in having an unusual six-amino acid-long N-terminal sequence. Both Smd1 and Smd2 have lower pI points and charge than insect defensins derived from fat body/hemocytes. Northern analysis shows both of these defensin molecules are tissue specific; both are produced by the anterior midgut tissue and, unlike the other insect defensins reported to date, neither appears to be expressed in fat body or hemocytes. Northern analysis also shows that mRNAs for both defensins are constitutively produced in the anterior midgut tissues and that these transcripts are up-regulated in response to sterile as well as a lipopolysaccharide-containing blood meal. However, anti-Gram-negative biological activity in the midgut is substantially enhanced by lipopolysaccharide. These findings suggest that the insect midgut has its own tissue-specific immune mechanisms and that this invertebrate epithelium is, like several vertebrate epithelia, protected by specific antibacterial peptides.

Amino Acid Sequence↗
PubMed1996

Vector insects and their control.

This paper emphasizes the huge influence that vector-transmitted disease has on humans using plague, epidemic typhus and nagana as examples. The continuing need for vector control in campaigns against insect-transmitted disease is shown by reference to current control programmes mounted against Chagas' disease, onchocerciasis, lymphatic filariasis and nagana. These successful campaigns have not been reliant on new breakthroughs but on the forging of available tools into effective strategies widely and efficiently used by the control authorities, and the long-lasting political commitment to the success of the schemes in question. A brief mention is made of current fashions in vector control research and that great care needs to be taken by policy-makers to achieve a balance between long-term research aiming at the production of fundamentally new control technologies and operational research aiming to forge the often highly effective tools we already have into sound control strategies.

Animals↗
PubMed1996

Composition of the peritrophic matrix of the tsetse fly, Glossina morsitans morsitans.

The three-layered peritrophic matrix of Glossina morsitans morsitans is shown, by histochemistry, to be formed of a mixture of glycosaminoglycans, glycoproteins and chitin. In all three layers the glycosaminoglycans contain GlcNAc-hexuronic and Gal-GlcNAc moieties, together with chitin. Glycosaminoglycans in layer 3 are sulphated and sulphated sites have a mean interspace distance of 53 nm - similar to the spacing of fixed charge sites in glomerular basement membrane suggesting a rôle for these sites in the filtration properties of the peritrophic matrix. O-linked oligo- saccharides are present in all three layers. Layer 1 contains the widest variety of glycoprotein oligosaccharide constructs GlcNac and alphalinked GalNAc possibly as GalNAcalpha1,3GalNAc, the latter apparently distal to Galbeta1-4GlcNAc. Lectin binding suggests that layer 2 contains GalNAcalpha1,3Galbeta1,3GlcNAc and that layer 3 contains GalNAc and Galbeta1,4GlcNAc. The evidence for N-linked oligosaccharides is more equivocal. Two dimensional electrophoresis showed that the peritrophic matrix contains a range of proteins, most of which require relatively harsh treatment for their solubilization.

Animals↗
PubMed1996

An immunocytochemical investigation of trypsin secretion in the midgut of the stablefly, Stomoxys calcitrans.

Musca domestica trypsin antibody cross-reacts with polypeptide bands of M(r) 25,000 and 30,000 showing proteolytic activity from Stomoxys calcitrans midgut extracts. Secretory granules from the main enzyme-secreting region, the opaque zone, stained heavily with the trypsin antibody in both unfed and blood-fed flies. Heterogeneous staining of granules suggests the unequal distribution of trypsin in secretory granules. This is also consistent with the occurrence of non-parallel secretion, which is also suggested by the possible preferential release of smaller, heavily stained secretory granules in fed flies. The predigestive, anterior midgut region responsible for rapid dehydration of the blood meal, the reservoir zone, contains a different population of secretory granules which stain heavily with trypsin antibody. This zone contains 20% of the midgut trypsin activity in unfed flies; trypsins are held here as proenzymes which are probably only activated postsecretion. In the midgut lumen of both unfed and blood-fed flies, trypsin is mainly immunolocalized in the ectoperitrophic space. Enzyme assays suggest that 5-15% of the lumenal trypsin is associated with the peritrophic matrix. The finding of intact secretory granules plus cell debris in the ectoperitrophic space of opaque and lipoid zones of blood-fed flies supports the contention that some trypsin is released by apocrine secretion in this insect.

Animals↗
PubMed1995

Tyrosinase-type prophenoloxidase distribution in the alimentary canal of strains of Anopheles gambiae refractory and susceptible to Plasmodium infection.

Tyrosinase-type prophenoloxidase distribution was investigated in the posterior midgut and salivary glands of strains of noninfected adult Anopheles gambiae refractory (Blue strain) and susceptible (G3 strain) to infection with malaria parasites. Immunocytochemical localization showed that in the posterior midgut epithelium tyrosinase-type prophenoloxidase was almost entirely restricted to apical granules. These are known to be a mixture of secretory granules and lysosomes; it was not possible to distinguish between the two in this study. The secretory product in the lumen of the distal median lobe of the salivary gland was heavily labeled; the secretory product in the lumen of the distal lateral lobes was also labeled but to a lesser extent. Subjectively, no differences in the degree or pattern of labeling of either midgut or salivary glands between the strains of mosquito were apparent.

Animals↗
PubMed1995

Fluorescence as a tool for age determination in Culicoides variipennis sonorensis (Diptera: Ceratopogonidae).

Adult culicoides variipennis sonorensis Wirth & Jones were tested using fluorescence spectrophotometry to determine whether age or sex influenced fluorescence. Males and nulliparous females 0.5, 2.5, and 5.5 d after eclosion were processed, as were uniparous and biparous females 14 d after eclosion. Variability among insects within a sex and age group was moderately high. Males and nulliparous females showed significantly greater fluorescence when very young (0.5 d old). Parous females had significantly lower levels of fluorescence compared with younger nulliparous females and males, but uniparous females could not be differentiated from biparous females of the same absolute age. Fluorescence as applied here appears to have limited utility as a tool for age determination in this vector species.

Aging↗
PubMed1994

Digestive enzymes, haemolysins and symbionts in the search for vaccines against blood-sucking insects.

Control of blood-sucking insects by vaccination of the host is an appealing possibility. In this overview the potential of digestive enzymes, haemolysins and symbionts as targets for vaccines are discussed. Blood-sucking insects are largely dependent on proteases for digestion. This is advantageous in the search for a vaccine as there is a considerable fund of biochemical knowledge for this group of molecules. Also there are a range of inhibitors available which can be used to mimic the effects of a vaccine providing a useful guide to the potential usefulness of such a vaccine before the considerable investment needed in producing one. Weighing against this, proteolytic enzymes by their nature will attack antibodies approaching them making it questionable if antibodies ingested by the insect could succeed before they themselves are destroyed by their target. Proteolytic enzymes are also poor immunogens, probably because they attack the antibody making machinery approaching them and because the complexes formed between the abundant vertebrate antiproteolytic molecules and proteases provide a different antigenic target to the native enzymes. Despite their relative paucity, evidence suggests that lipid digesting enzymes deserve attention as potential vaccine targets. Because about 80% of the nutrients in blood are locked up in its formed elements haemolysins are a strong potential target of a vaccine. The obligate haematophages rely on symbionts to provide essential nutrients and in consequence these are also potential vaccine targets in these insects.

Animals↗
PubMed1992

The role of temperature and nutritional status in flight initiation by Triatoma infestans.

Flight initiation in Triatoma infestans is associated with low nutritional status and increases with rising temperature; it appears to be largely independent of bug age and sex. A predictive model for the probability of flight initiation was constructed based on weight:length ratios of the bugs and maximum ambient temperature, both of which can be ascertained in the field. The model accurately predicted the proportion of bugs initiating flight in > 85% of the groups used in our study. The predictive equation was found to give significant fits with two independent data sets. From our results it might be expected that flight would be rare during colder (< 20 degrees C) months but that 5-10% of the normal population of an infested house would fly on any given night during the hotter months when temperatures approach 30 degrees C. If bug nutritional status falls significantly, this proportion could be expected to rise to 30%.

Animal Nutritional Physiological Phenomena↗
PubMed1992

Dispersive flight by Triatoma infestans under natural climatic conditions in Argentina.

Male and female T. infestans were released on two consecutive nights in the salinas of Cordoba Province, Argentina, when air temperatures during the flying period averaged 28.5 degrees C. 136 males (43% of the total released) and 170 females (57%) flew on the first night, and 6 males (18%) and 7 females (27%) on the second. Of these, we recovered 23 males and 14 females within 100 m, and a further female within 200 m, all from the first night's release. The remainder appear to have flown more than 100 m and possibly more than 200 m. In support of this conclusion 4 male and 5 female bugs were recovered in an abandoned brick house 550 m from the release point. Since the proportion of bugs apparently flying more than 200 m is considerably greater than that deduced from previous experiments at lower temperatures (Lehane & Schofield, 1981) it is possible that temperature influences not only the proportion of bugs flying but also the distance flown. Flight appears to be affected by wind speed. On the first night, when there was negligible wind, 43% of male and 57% of female bugs flew. On the second night, with winds gusting at 4-5 m/s, only 18% of the male and 27% of the female bugs flew.

Animals↗
PubMed1991

Lectin and peritrophic membrane development in the gut of Glossina m.morsitans and a discussion of their role in protecting the fly against trypanosome infection.

Newly emerged Glossina m.morsitans Westwood tsetse flies lack a peritrophic membrane which develops to fully line the midgut after c. 80-90 h. Midgut lectins are mainly associated with the peritrophic membrane. Lectin levels in the blood-free gut of adult flies rise slowly up to 8 days and then rapidly to at least 14 days post-eclosion (when the last of our recordings was made). Despite starving flies for 4 days prior to the agglutination assay, gut lectin levels in older flies are 100-200 times more than those in newly ecloded flies. This is inconsistent with the idea that there is a simple relationship between lectins and the protection of tsetse flies against trypanosome infection. Various theories put forward to account for age-dependent variation in the ability of tsetse to become infected with trypanosomes are discussed in the light of these findings.

Animals↗
PubMed1989

The intracellular pathway and kinetics of digestive enzyme secretion in an insect midgut cell.

The opaque zone cells of the midgut of the stablefly, Stomoxys calcitrans display a cyclical series of ultrastructural events in response to feeding, which it has been suggested are related to the synthesis and secretion of digestive enzymes. These cells have been studied in vivo using a combination of biochemical, morphometric and electron microscopical autoradiographic techniques. The cyclical nature, timing and relationship of the ultrastructural events to enzyme secretion has been confirmed. The autoradiographic data presented is in good agreement with the classical synthetic pathway for exported proteins. The kinetics of the cellular process have been described: transfer of newly synthesized product from the rough endoplasmic reticulum to Golgi apparatus begins ca. 13-14 min after labelling of the fly and from the Golgi apparatus to secretory granules after ca. 24-26 min. Secretion of this newly synthesized material begins before 60 min and possibly as early as 30 min after labelling of the fly. The data are discussed in relation to the comparable studies in other tissues.

Animals↗
PubMed1984

Peritrophic membrane formation in three temperate simuliids, Simulium ornatum, S. equinum and S. lineatum, with respect to the migration of onchocercal microfilariae.

Engorged females of three temperate simuliid species, Simulium ornatum, S. lineatum and S. equinum, were collected immediately after their bloodfeeds from a cow host. Midguts were dissected out at selected time intervals thereafter, from two minutes to 24 hours post engorgement (p.e.) and peritrophic membrane formation observed. There was an initial rapid secretion of peritrophic membrane (PM) material from the midgut epithelium. The peritrophic membrane produced is Type 1, being formed by delamination from the entire midgut epithelium. This secretory phase continued for approximately two hours p.e. in all three species and was followed by a period of organization within the membrane. At between 12 and 24 hours p.e., the PM appeared more organized and was associated with the formation of several distinct laminae in both S. ornatum and S. lineatum, although in S. equinum it consisted of only a single homogenous layer. Both the rate of secretion and the resulting morphological appearance of the PM appeared species-specific and there was great variation in its thickness in all three species at all time intervals examined. It is suggested that microfilariae penetrate the PM during the initial period of its secretion before it has condensed to form a distinct structure. Furthermore, the migration of microfilariae may be restricted to, or enhanced by, the presence of very thin areas within the membrane where erythrocytes lie almost adjacent to the midgut epithelium.

Animals↗
PubMed1982

A kinetic and ultrastructural comparison of alphavirus infection of cultured mosquito and vertebrate cells.

Vero cells and Aedes pseudoscutellaris cells showed rapid production of Semliki Forest virus (SFV) whereas in Aedes aegypti and Anopheles stephensi cells no rapid production of SFV was observed. Ultrastructurally the only virally induced cell inclusion in early infection was the cytopathic vacuole type 1. Later in infection, in mosquito cells, electron-dense bodies appear and budding of new virions appears to be very efficient. In Vero cells large accumulations of envelope proteins and nucleocapsids saturate the plasma membrane suggesting an inefficient budding process. After this time cytopathic vacuoles type 2 appear in Vero cells and a mechanism for their formation is proposed. Subsequent death of Vero cells appears to centre on progressive build-up of envelope protein on the rough endoplasmic reticulum (which is never seen in mosquito cells) and subsequent vacuolation of the rough endoplasmic reticulum followed by cell lysis.

Aedes↗