The characterization of the fat bodies and oenocytes in the adult females of the sand fly vectors Lutzomyia longipalpis and Phlebotomus papatasi.

The fat body (FB) is responsible for the storage and synthesis of the majority of proteins and metabolites secreted into the hemolymph. Oenocytes are responsible for lipid processing and detoxification. The FB is distributed throughout the insect body cavity and organized as peripheral and perivisceral portions in the abdomen, with trophocytes and oenocytes attached to the peripheral portion. Here, we investigated the morphology and the subcellular changes in the peripheral and perivisceral FBs and in oenocytes of the sand flies Lutzomyia longipalpis and Phlebotomus papatasi after blood feeding. In L. longipalpis two-sized oenocytes (small and large) were identified, with both cell types displaying well-developed reticular system and smooth endoplasmic reticulum, whereas in P. papatasi, only small cells were observed. Detailed features of FBs of L. longipalpis and P. papatasi are shared either prior to or after blood feeding. The peripheral and perivisceral FBs responded to blood feeding with the development of glycogen zones and rough endoplasmic reticulum. This study provides the first detailed description of the FBs and oenocytes in sand flies, contributing significantly towards are better understanding of the biology of such important disease vectors.

A comparative study of fat body morphology in five mosquito species.

The insect fat body plays major roles in the intermediary metabolism, in the storage and transport of haemolymph compounds and in the innate immunity. Here, the overall structure of the fat body of five species of mosquitoes (Aedes albopictus, Aedes fluviatilis, Culex quinquefasciatus, Anopheles aquasalis and Anopheles darlingi) was compared through light, scanning and transmission electron microscopy. Generally for mosquitoes, the fat body consists of lobes projecting into the haemocoel and is formed by great cell masses consisting of trophocytes and oenocytes. Trophocytes are rich in lipid droplets and protein granules. Interestingly, brown pigment granules, likely ommochromes, were found exclusively in the trophocytes located within the thorax and near the dorsal integument of Anopheles, which is suggestive of the role these cells play in detoxification via ommochrome storage. This study provides a detailed comparative analysis of the fat body in five different mosquito species and represents a significant contribution towards the understanding of the structural-functional relationships associated with this organ.

A comparative study of fat body morphology in five mosquito species

The insect fat body plays major roles in the intermediary metabolism, in the storage and transport of haemolymph compounds and in the innate immunity. Here, the overall structure of the fat body of five species of mosquitoes (Aedes albopictus, Aedes fluviatilis, Culex quinquefasciatus, Anopheles aquasalis and Anopheles darlingi) was compared through light, scanning and transmission electron microscopy. Generally for mosquitoes, the fat body consists of lobes projecting into the haemocoel and is formed by great cell masses consisting of trophocytes and oenocytes. Trophocytes are rich in lipid droplets and protein granules. Interestingly, brown pigment granules, likely ommochromes, were found exclusively in the trophocytes located within the thorax and near the dorsal integument of Anopheles, which is suggestive of the role these cells play in detoxification via ommochrome storage. This study provides a detailed comparative analysis of the fat body in five different mosquito species and represents a significant contribution towards the understanding of the structural-functional relationships associated with this organ.

Insights into the transcriptome of oenocytes from Aedes aegypti pupae.

Oenocytes are ectodermic cells present in the fat body of several insect species and these cells are considered to be analogous to the mammalian liver, based on their role in lipid storage, metabolism and secretion. Although oenocytes were identified over a century ago, little is known about their messenger RNA expression profiles. In this study, we investigated the transcriptome of Aedes aegypti oenocytes. We constructed a cDNA library from Ae. aegypti MOYO-R strain oenocytes collected from pupae and randomly sequenced 687 clones. After sequences editing and assembly, 326 high-quality contigs were generated. The most abundant transcripts identified corresponded to the cytochrome P450 superfamily, whose members have roles primarily related to detoxification and lipid metabolism. In addition, we identified 18 other transcripts with putative functions associated with lipid metabolism. One such transcript, a fatty acid synthase, is highly represented in the cDNA library of oenocytes. Moreover, oenocytes expressed several immunity-related genes and the majority of these genes were lysozymes. The transcriptional profile suggests that oenocytes play diverse roles, such as detoxification and lipid metabolism, and increase our understanding of the importance of oenocytes in Ae. aegypti homeostasis and immune competence.

Insights into the transcriptome of oenocytes from Aedes aegypti pupae

Oenocytes are ectodermic cells present in the fat body of several insect species and these cells are considered to be analogous to the mammalian liver, based on their role in lipid storage, metabolism and secretion. Although oenocytes were identified over a century ago, little is known about their messenger RNA expression profiles. In this study, we investigated the transcriptome of Aedes aegypti oenocytes. We constructed a cDNA library from Ae. aegypti MOYO-R strain oenocytes collected from pupae and randomly sequenced 687 clones. After sequences editing and assembly, 326 high-quality contigs were generated. The most abundant transcripts identified corresponded to the cytochrome P450 superfamily, whose members have roles primarily related to detoxification and lipid metabolism. In addition, we identified 18 other transcripts with putative functions associated with lipid metabolism. One such transcript, a fatty acid synthase, is highly represented in the cDNA library of oenocytes. Moreover, oenocytes expressed several immunity-related genes and the majority of these genes were lysozymes. The transcriptional profile suggests that oenocytes play diverse roles, such as detoxification and lipid metabolism, and increase our understanding of the importance of oenocytes in Ae. aegypti homeostasis and immune competence.

Histochemical and ultrastructural studies of the mosquito Aedes aegypti fat body: effects of aging and diet type.

Aedes aegypti is the principal vector of dengue world wide and a major vector of urban yellow fever. Despite its epidemiological importance, not much is known regarding cellular and structural changes in the fat body in this mosquito. Here, we applied light and transmission electron microscopies to investigate structural changes in the fat body of three groups of A. aegypti females: newly emerged, 18-day-old sugar-fed, and 18-day-old blood-fed. The fat body consists of a layer of cells attached to the abdomen integument, formed by trophocytes and oenocytes. Trophocytes are strongly positive for carbohydrates, while oenocytes are strongly positive for proteins and lipids. Ultrastructural analyses of trophocytes from newly emerged and 18-day-old blood-fed indicate that these cells are rich in glycogen and free ribosomes. Many lipid droplets and protein granules, which are broken down after the blood meal, are also detected. In 18-day-old sugar-fed, trophocytes display a disorganized cytoplasm filled with lipid droplets, and reduced numbers of free ribosomes, glycogen, rough endoplasmic reticulum (RER) and mitochondria. Following a blood meal, the RER and mitochondria display enlarged sizes, suggestive of increased activity. With regard to oenocytes, these cells display an electron-dense cytoplasm and plasma membrane infoldings facing the hemolymph. As the A. aegypti female ages, trophocyte and oenocyte cell nuclei become larger but decrease in diameter after blood feeding. Our findings suggest that the trophocytes and oenocytes remodeling is likely involved in functional changes of fat body that take place during aging and following a blood meal in A. aegypti females.

Constitutive and blood meal-induced trypsin genes in Lutzomyia longipalpis.

Trypsins constitute some of the most abundant midgut digestive proteases expressed by hematophagous insects upon blood feeding. In addition to their role in the digestion of the blood meal, these proteases also have been implicated in the ability of certain pathogens to infect their natural vector. In sand flies, digestive proteases including trypsins were associated with early killing of Leishmania and are believed to play a role in the species-specificity dictating sand fly vectorial capacity. Our group is involved in studies of midgut digestive proteases in the sand fly Lutzomyia longipalpis, the principal vector of visceral leishmaniasis in Brazil. Here we report on the identification of two cDNAs, Lltryp1 and Lltryp2, which code for putative midgut trypsins in L. longipalpis. Analyses of RNA abundance using semi-quantitative RT-PCR show a different pattern of expression between the two genes. Lltryp1 expression remains undetected until blood feeding and reaches a peak at 12 h post-blood meal (PBM), returning to pre-blood meal levels at 72 h PBM. Additionally, Lltryp1 expression is undetected during larval development. Lltryp2, on the other hand, is constitutively expressed as high levels in the non-blood fed female, but is reduced upon blood feeding. At the end of the digestive cycle, Lltryp2 regains its pre-blood meal levels. This cDNA also is present in all developmental stages and in adult males. This pattern of expression is reminiscent of what is seen in mosquitoes and Old World sand flies, but has characteristics that are unique to L. longipalpis.