Lipoprotein assembly and function in an evolutionary perspective

Lipids in Insect Reproduction: Where, How, and Why

Modern insects have inhabited the earth for hundreds of millions of years, and part of their successful adaptation lies in their many reproductive strategies. Insect reproduction is linked to a high metabolic rate that provides viable eggs in a relatively short time. In this context, an accurate interplay between the endocrine system and the nutrients synthetized and metabolized is essential to produce healthy offspring. Lipids guarantee the metabolic energy needed for egg formation and represent the main energy source consumed during embryogenesis. Lipids availability is tightly regulated by a complex network of endocrine signals primarily controlled by the central nervous system (CNS) and associated endocrine glands, the corpora allata (CA) and corpora cardiaca (CC). This endocrine axis provides hormones and neuropeptides that significatively affect tissues closely involved in successful reproduction: the fat body, which is the metabolic center supplying the lipid resources and energy demanded in egg formation, and the ovaries, where the developing oocytes recruit lipids that will be used for optimal embryogenesis. The post-genomic era and the availability of modern experimental approaches have advanced our understanding of many processes involved in lipid homeostasis; therefore, it is crucial to integrate the findings of recent years into the knowledge already acquired in the last decades. The present chapter is devoted to reviewing major recent contributions made in elucidating the impact of the CNS/CA/CC-fat body-ovary axis on lipid metabolism in the context of insect reproduction, highlighting areas of fruitful research.

SDS-PAGE-Based Quantitative Assay of Hemolymph Proteins in Honeybees: Progress and Prospects for Field Application

In human and veterinary medicine, serum proteins are considered to be useful biomarkers for assessing the health and nutritional status of the organism. Honeybee hemolymph has a unique proteome that could represent a source of valuable biomarkers. Therefore, the aims of this study were to separate and identify the most abundant proteins in the hemolymph of worker honeybees to suggest a panel of these proteins that could represent useful biomarkers for assessing the nutritional and health status of the colonies and, finally, to analyze them in different periods of the year. Four apiaries were selected in the province of Bologna, and the bees were analyzed in April, May, July, and November. Thirty specimens from three hives of each apiary were sampled and their hemolymph was collected. The most represented bands obtained after 1D sodium-dodecyl-sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) were cut from the gel, and the proteins were identified using an LC-ESI-Q-MS/MS System. A total of twelve proteins were unmistakably identified; the two most abundant proteins were apolipophorin and vitellogenin, which are known biomarkers of bee trophic and health status. The two other proteins identified were transferrin and hexamerin 70a, the first being involved in iron homeostasis and the second being a storage protein. Most of these proteins showed an increase from April to November, mirroring the physiological changes of honeybees during the productive season. The current study suggests a panel of biomarkers from honeybee hemolymph worth testing under different physiological and pathological field conditions.

Lipids as a key element of insect defense systems

The relationship between insect pathogenic fungi and their insect hosts is a classic example of a co-evolutionary arms race between pathogen and target host: parasites evolve towards mechanisms that increase their advantage over the host, and the host increasingly strengthens its defenses. The present review summarizes the literature data describing the direct and indirect role of lipids as an important defense mechanism during fungal infection. Insect defense mechanisms comprise anatomical and physiological barriers, and cellular and humoral response mechanisms. The entomopathogenic fungi have the unique ability to digest the insect cuticle by producing hydrolytic enzymes with chitin-, lipo- and proteolytic activity; besides the oral tract, cuticle pays the way for fungal entry within the host. The key factor in insect resistance to fungal infection is the presence of certain types of lipids (free fatty acids, waxes or hydrocarbons) which can promote or inhibit fungal attachment to cuticle, and might also have antifungal activity. Lipids are considered as an important source of energy, and as triglycerides are stored in the fat body, a structure analogous to the liver and adipose tissue in vertebrates. In addition, the fat body plays a key role in innate humoral immunity by producing a range of bactericidal proteins and polypeptides, one of which is lysozyme. Energy derived from lipid metabolism is used by hemocytes to migrate to the site of fungal infection, and for phagocytosis, nodulation and encapsulation. One polyunsaturated fatty acid, arachidonic acid, is used in the synthesis of eicosanoids, which play several crucial roles in insect physiology and immunology. Apolipoprotein III is important compound with antifungal activity, which can modulate insect cellular response and is considered as important signal molecule.

From worms to humans: Understanding intestinal lipid metabolism via model organisms

The intestine is responsible for efficient absorption and packaging of dietary lipids before they enter the circulatory system. This review provides a comprehensive overview of how intestinal enterocytes from diverse model organisms absorb dietary lipid and subsequently secrete the largest class of lipoproteins (chylomicrons) to meet the unique needs of each animal. We discuss the putative relationship between diet and metabolic disease progression, specifically Type 2 Diabetes Mellitus. Understanding the molecular response of intestinal cells to dietary lipid has the potential to undercover novel therapies to combat metabolic syndrome.

Lipophorin receptor is required for the accumulations of cuticular hydrocarbons and ovarian neutral lipids in Locusta migratoria

Lipophorin is the most abundant lipoprotein particle in insect hemolymph. Lipophorin receptor (LPR) is a glycoprotein that binds to the lipophorin and mediates cellular uptake and metabolism of lipids by endocytosis. However, the roles of LPR in uptake of lipids in the integument and ovary remain unknown in the migratory locust (Locusta migratoria). In present study, we characterized the molecular properties and biological roles of LmLPR in L. migratoria. The LmLPR transcript level was high in the first 2 days of the adults after eclosion, then gradually declined. LmLPR was predominately expressed in fat body, ovary and integument. Using immuno-detection methods, we revealed that LmLPR was mainly localized in the membrane of oenocytes, epidermal cells, fat body cells and follicular cells. RNAi-mediated silencing of LmLPR led to a slight decrease of the cuticle hydrocarbon contents but with little effect on the cuticular permeability. However, the neutral lipid content was significantly decreased in the ovary after RNAi against LmLPR, which led to a retarded ovarian development. Taken together, our results indicated that LmLPR is involved in the uptake and accumulation of lipids in the ovary and plays a crucial role in ovarian development in L. migratoria. Therefore, LmLPR could be a promising RNAi target for insect pest management by disrupting insect ovarian development.

High-density lipoprotein revisited: biological functions and clinical relevance

Previous interest in high-density lipoproteins (HDLs) focused on their possible protective role in atherosclerotic cardiovascular disease (ASCVD). Evidence from genetic studies and randomized trials, however, questioned that the inverse association of HDL-cholesterol (HDL-C) is causal. This review aims to provide an update on the role of HDL in health and disease, also beyond ASCVD. Through evolution from invertebrates, HDLs are the principal lipoproteins, while apolipoprotein B-containing lipoproteins first developed in vertebrates. HDLs transport cholesterol and other lipids between different cells like a reusable ferry, but serve many other functions including communication with cells and the inactivation of biohazards like bacterial lipopolysaccharides. These functions are exerted by entire HDL particles or distinct proteins or lipids carried by HDL rather than by its cholesterol cargo measured as HDL-C. Neither does HDL-C measurement reflect the efficiency of reverse cholesterol transport. Recent studies indicate that functional measures of HDL, notably cholesterol efflux capacity, numbers of HDL particles, or distinct HDL proteins are better predictors of ASCVD events than HDL-C. Low HDL-C levels are related observationally, but also genetically, to increased risks of infectious diseases, death during sepsis, diabetes mellitus, and chronic kidney disease. Additional, but only observational, data indicate associations of low HDL-C with various autoimmune diseases, and cancers, as well as all-cause mortality. Conversely, extremely high HDL-C levels are associated with an increased risk of age-related macular degeneration (also genetically), infectious disease, and all-cause mortality. HDL encompasses dynamic multimolecular and multifunctional lipoproteins that likely emerged during evolution to serve several physiological roles and prevent or heal pathologies beyond ASCVD. For any clinical exploitation of HDL, the indirect marker HDL-C must be replaced by direct biomarkers reflecting the causal role of HDL in the respective disease.

HDL as Bidirectional Lipid Vectors: Time for New Paradigms

The anti-atherogenic properties of high-density lipoproteins (HDL) have been explained mainly by reverse cholesterol transport (RCT) from peripheral tissues to the liver. The RCT seems to agree with most of the negative epidemiological correlations between HDL cholesterol levels and coronary artery disease. However, therapies designed to increase HDL cholesterol failed to reduce cardiovascular risk, despite their capacity to improve cholesterol efflux, the first stage of RCT. Therefore, the cardioprotective role of HDL may not be explained by RCT, and it is time for new paradigms about the physiological function of these lipoproteins. It should be considered that the main HDL apolipoprotein, apo AI, has been highly conserved throughout evolution. Consequently, these lipoproteins play an essential physiological role beyond their capacity to protect against atherosclerosis. We propose HDL as bidirectional lipid vectors carrying lipids from and to tissues according to their local context. Lipid influx mediated by HDL appears to be particularly important for tissue repair right on site where the damage occurs, including arteries during the first stages of atherosclerosis. In contrast, the HDL-lipid efflux is relevant for secretory cells where the fusion of intracellular vesicles drastically enlarges the cytoplasmic membrane with the potential consequence of impairment of cell function. In such circumstances, HDL could deliver some functional lipids and pick up not only cholesterol but an integral part of the membrane in excess, restoring the viability of the secretory cells. This hypothesis is congruent with the beneficial effects of HDL against atherosclerosis as well as with their capacity to induce insulin secretion and merits experimental exploration.

The metabolism and role of free fatty acids in key physiological processes in insects of medical, veterinary and forensic importance

Insects are the most widespread group of organisms and more than one million species have been described. These animals have significant ecological functions, for example they are pollinators of many types of plants. However, they also have direct influence on human life in different manners. They have high medical and veterinary significance, stemming from their role as vectors of disease and infection of wounds and necrotic tissue; they are also plant pests, parasitoids and predators whose activities can influence agriculture. In addition, their use in medical treatments, such as maggot therapy of gangrene and wounds, has grown considerably. They also have many uses in forensic science to determine the minimum post-mortem interval and provide valuable information about the movement of the body, cause of the death, drug use, or poisoning. It has also been proposed that they may be used as model organisms to replace mammal systems in research. The present review describes the role of free fatty acids (FFAs) in key physiological processes in insects. By focusing on insects of medical, veterinary significance, we have limited our description of the physiological processes to those most important from the point of view of insect control; the study examines their effects on insect reproduction and resistance to the adverse effects of abiotic (low temperature) and biotic (pathogens) factors.

Two apolipoproteins in salmon louse (Lepeophtheirus salmonis), apolipoprotein 1 knock down reduces reproductive capacity

The salmon louse, Lepeophtheirus salmonis is an ectoparasite of salmonid fish in the Northern Hemisphere, causing large economical losses in the aquaculture industry and represent a threat to wild populations of salmonids. Like other oviparous animals, it is likely that female lice use lipoproteins for lipid transport to maturing oocytes and other organs of the body. As an important component of lipoproteins, apolipoproteins play a vital role in the transport of lipids through biosynthesis of lipoproteins. Apolipoproteins have been studied in detail in different organisms, but no studies have been done in salmon lice. Two apolipoprotein encoding genes (LsLp1 and LsLp2) were identified in the salmon lice genome. Transcriptional analysis revealed both genes to be expressed at all stages from larvae to adult with some variation, LsLp1 generally higher than LsLp2 and both at their highest levels in adult stages of the louse. In adult female louse, the LsLp1 and LsLp2 transcripts were found in the sub-epidermal tissue and the intestine. RNA interference-mediated knockdown of LsLp1 and LsLp2 in female lice resulted in reduced expression of both transcripts. LsLp1 knockdown female lice produced significantly less offspring than control lice, while knockdown of LsLp2 in female lice caused no reduction in the number of offspring. These results suggest that LsLp1 has an important role in reproduction in female salmon lice.

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Salmon lice are ectoparasites and a major threat to aquaculture industry and wild salmon.

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Two apolipoproteins in salmon louse (Lepeophtheirus salmonis).

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Expressed at all stages from larvae to adult, sub-epidermal tissue and the intestine .

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RNA interference-mediated knockdown of LsLp1 and LsLp2.

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LsLp1 knockdown female lice produced significantly less offspring than control lice.

Streptomyces griseocarneus R132 expresses antimicrobial genes and produces metabolites that modulate Galleria mellonella immune system

Actinobacteria is a phylum composed of aerobic, Gram-positive, and filamentous bacteria with a broad spectrum of biological activity, including antioxidant, antitumor, and antibiotic. The crude extract of Streptomyces griseocarneus R132 was fractionated on a C18 silica column and the isolated compound was identified by ¹H and ¹³C nuclear magnetic resonance as 3-(phenylprop-2-enoic acid), also known as trans-cinnamic acid. Antimicrobial activity against human pathogens was assayed in vitro (disk-diffusion qualitative test) and in vivo using Galleria mellonella larvae (RT-qPCR). The methanol fractions 132-F30%, 132-F50%, 132-F70%, and 132-F100% inhibited the Escherichia coli (ATCC 25922) and Staphylococcus aureus (MRSA) growth in vitro the most effectively. Compared with the untreated control (60-80% of larvae death), the fractions and isolated trans-cinnamic acid increased the survival rate and modulated the immune system of G. mellonella larvae infected with pathogenic microorganisms. The anti-infection effect of the S. griseocarneus R132 fermentation product led us to sequence its genome, which was assembled and annotated using the Rast and antiSMASH platforms. The assembled genome consisted of 227 scaffolds represented on a linear chromosome of 8.85 Mb and 71.3% of GC. We detected conserved domains typical of enzymes that produce molecules with biological activity, such as polyketides and non-ribosomal and ribosomal peptides, indicating a great potential for obtaining new antibiotics and molecules with biotechnological application.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02942-1.

Large lipid transfer proteins in hepatopancreas of the mud crab Scylla paramamosain

Large lipid transfer proteins (LLTPs) are extensively involved in various physiological processes. In the present study, five LLTP sequences encoding apolipocrustacein 1 (apoCr 1), apoCr 2, precursor of the large discoidal lipoprotein (dLp) and high density lipoprotein/β-glucan binding protein (HDL-BGBP) (dLp-BGBP), microsomal triglyceride transfer protein (MTP) and clotting protein (CP) were identified in the hepatopancreas of Scylla paramamosain. Of these, apoCr 2, dLp-BGBP, and MTP were newly identified in this species, and the former two proteins were classified into the APO family while the later into the MTP family in phylogenetic trees. The apoCr 1 expression level was dramatically increased in the hepatopancreas towards ovarian maturation, which was extremely greater than that in the ovaries concurrently, likely to meet the considerable requirements of yolk protein and lipids for embryo development. The dLp-BGBP expression level in male crabs was comparable to that in female crabs, supporting HDL-BGBP acts as a major circulatory lipid carrier. The close phylogenetic relationship between dLp-BGBP and the scaffolding protein of lipid transfer particle implied dLp might facilitate lipid transfer between the hepatopancreas and HDL-BGBP-containing lipoproteins. The MTP expression level was positively related to ovarian development in both the hepatopancreas and ovaries, indicating MTP may be involved in lipoprotein assembly in the hepatopancreas and lipid droplet maturation in the ovaries. CP may play a crucial role in embryo development based on high expression level observed in the testes of mature crabs. Our findings provide novel insights into LLTP superfamily members and their functions in decapods.

pH-Dependent Interactions of Apolipophorin-III with a Lipid Disk

Apolipophorin-III (ApoLp-III) is required for stabilization of molecular shuttles of lipid fuels in insects and is found to contribute to the insect immune reaction. Rearrangement of its five [Formula: see text]-helices enables ApoLp-III to reversibly associate with lipids. We investigate computationally the conformational changes of ApoLp-III and the pH-dependence of the binding free energy of ApoLp-III association with a lipid disk. A dominant binding mode along with several minor, low population, modes of the ApoLp-III binding to a lipid disk was identified. The pH-dependence of the binding energy for ApoLp-III with the lipid disk is predicted to be significant, with the pH-optimum at pH[Formula: see text]. The calculations suggest that there are no direct interactions between the lipid head groups and titratable residues of ApoLp-III. In the physiological pH range from 6.0 to 9.0, the binding free energy of ApoLp-III with the lipid disk decreases significantly with respect to its optimal value at pH 8.0 (at pH[Formula: see text], it is 1.02[Formula: see text]kcal/mol and at pH[Formula: see text] it is 0.23[Formula: see text]kcal/mol less favorable than at the optimal pH[Formula: see text]), indicating that the pH is an important regulator of ApoLp-III lipid disk association.

Apolipophorin-II/I Contributes to Cuticular Hydrocarbon Transport and Cuticle Barrier Construction in Locusta migratoria

Apolipophorins are carrier proteins that bind lipids and mediate their transport from tissue to tissue in animals. Apolipophorin I and II (apoLp-II/I) are the major apolipophorins in insects. The implication of apoLp-II/I in cuticle lipid-barrier formation in insects has not been addressed to date. In the present study, we investigated the function of apoLp-II/I in the migratory locust Locusta migratoria (LmapoLp-II/I). During the development of fifth instar nymphs, LmapoLp-II/I transcript levels increased until mid-instar, and then decreased gradually until molting to the adult stage. We found that LmapoLp-II/I was predominately expressed in the fat body and the integument including oenocytes and epidermal cells. Immunodetection experiments revealed that LmapoLp-I mainly localized in the cytoplasm of oenocytes and epidermal cells. Silencing of LmapoLp-II/I caused molting defects in nymphs. Importantly, RNA interference against LmapoLp-II/I resulted in a significant decrease in the content of cuticle surface lipids including alkanes and methyl alkanes. Cuticular permeability was significantly enhanced in these nymphs in Eosin Y penetration assays. By consequence, desiccation resistance and insecticide tolerance of dsLmapoLp-II/I-treated locusts were reduced. Taken together, our results indicate that LmapoLp-II/I is involved in the transport and deposition of surface-cuticular lipids that are crucial for maintaining normal cuticle barrier function in L. migratoria.

Lipids in Insect Oocytes: From the Storage Pathways to Their Multiple Functions

In insect physiology, the mechanisms involved in the buildup and regulation of yolk proteins in developing oocytes have been thoroughly researched during the last three decades. Comparatively, the study of lipid metabolism in oocytes had received less attention. The importance of this issue lies in the fact that lipids make up to 40% of the dry weight of an insect egg, being the most important supply of energy for the developing embryo. Since the oocyte has a very limited capacity to synthesize lipids de novo, most of the lipids in the mature eggs arise from the circulation. The main lipid carriers in the insect circulatory system are the lipoproteins lipophorin and vitellogenin. In some species, the endocytosis of lipophorin and vitellogenin may account for about 10% of the lipids present in mature eggs. Thus, most of the lipids are transferred by a lipophorin-mediated pathway, in which the lipoprotein unloads its lipid cargo at the surface of oocytes without internalization. This chapter recapitulates the current status on lipid storage and its utilization in insect oocytes and discusses the participation of key factors including lipoproteins, transfer proteins, lipolytic enzymes, and dynamic organelles such as lipid droplets. The new findings in the field of lipophorin receptors are presented in the context of lipid accumulation during egg maturation, and the roles of lipids beyond energy source are summarized from the perspective of oogenesis and embryogenesis. Finally, prospective and fruitful areas of future research are suggested.

TGL-mediated lipolysis in Manduca sexta fat body: possible roles for lipoamide-dehydrogenase (LipDH) and high-density lipophorin (HDLp)

Triglyceride-lipase (TGL) is a major fat body lipase in Manduca sexta. The knowledge of how TGL activity is regulated is very limited. A WWE domain, presumably involved in protein-protein interactions, has been previously identified in the N-terminal region of TGL. In this study, we searched for proteins partners that interact with the N-terminal region of TGL. Thirteen proteins were identified by mass spectrometry, and the interaction with four of these proteins was confirmed by immunoblot. The oxidoreductase lipoamide-dehydrogenase (LipDH) and the apolipoprotein components of the lipid transporter, HDLp, were among these proteins. LipDH is the common component of the mitochondrial α-keto acid dehydrogenase complexes whereas HDLp occurs in the hemolymph. However, subcellular fractionation demonstrated that these two proteins are relatively abundant in the soluble fraction of fat body adipocytes. The cofactor lipoate found in typical LipDH substrates was not detected in TGL. However, TGL proved to have critical thiol groups. Additional studies with inhibitors are consistent with the notion that LipDH acting as a diaphorase could preserve the activity of TGL by controlling the redox state of thiol groups. On the other hand, when TG hydrolase activity of TGL was assayed in the presence of HDLp, the production of diacylglycerol (DG) increased. TGL-HDLp interaction could drive the intracellular transport of DG. TGL may be directly involved in the lipoprotein assembly and loading with DG, a process that occurs in the fat body and is essential for insects to mobilize fatty acids. Overall the study suggests that TGL occurs as a multi-protein complex supported by interactions through the WWE domain.

Genetic studies of spectrin in the larval fat body of Drosophila melanogaster: evidence for a novel lipid uptake apparatus

Spectrin cytoskeleton defects produce a host of phenotypes affecting the plasma membrane, cell polarity, and secretory membrane traffic. However, many of the underlying molecular mechanisms remain unexplained by prevailing models. Here we used the larval fat body of Drosophila melanogaster as a genetic model system to further elucidate mechanisms of αβ-spectrin function. The results provide unexpected new insights into spectrin function as well as mechanisms of dietary fat uptake and storage. We show that loss of α- or β-spectrin in the fat body eliminated a population of small cortical lipid droplets and altered plasma membrane architecture, but did not affect viability of the organism. We present a novel model in which αβ-spectrin directly couples lipid uptake at the plasma membrane to lipid droplet growth in the cytoplasm. In contrast, strong overexpression of β-spectrin caused fat body atrophy and larval lethality. Overexpression of β-spectrin also perturbed transport of dietary fat from the midgut to the fat body. This hypermorphic phenotype appears to be the result of blocking secretion of the lipid carrier lipophorin from fat cells. However, this midgut phenotype was never seen with spectrin loss of function, suggesting that spectrin is not normally required for lipophorin secretion or function. The β-spectrin hypermorphic phenotype was ameliorated by co-overexpression of α-spectrin. Based on the overexpression results here, we propose that β-spectrin family members may be prone to hypermorphic effects (including effects on secretion) if their activity is not properly regulated.

Developmental changes in the protein composition of Manduca sexta lipid droplets

The lipid droplets (LDs) are intracellular organelles mainly dedicated to the storage and provision of fatty acids. To accomplish these functions the LDs interact with other organelles and cytosolic proteins. In order to explore possible correlations between the physiological states of cells and the protein composition of LDs we have determined and compared the proteomic profiles of lipid droplets isolated from the fat bodies of 5th-instar larvae and adult Manduca sexta insects and from ovaries. These LD-rich tissues represent three clearly distinct metabolic states in regard to lipid metabolism: 1) Larval fat body synthesizes fatty acids (FA) and accumulates large amounts as triglyceride (TG); 2) Fat body from adult insects provides FA to support reproduction and flight; 3) Ovaries do not synthesize FA, but accumulate considerable amounts of TG in LDs. Major qualitative and semi-quantitative variations in the protein compositions of the LDs isolated from these three tissues were observed by MS/MS and partially validated by immuno-blotting. The differences observed included changes in the abundance of lipid droplet specific proteins, cytosolic proteins, mitochondrial proteins and also proteins associated with the machinery of protein synthesis. These results suggest that changes in the interaction of LDs with other organelles and cytosolic proteins are tightly related to the physiological state of cells. Herein, we summarize and compare the protein compositions of three subtypes of LDs and also describe for the first time the proteomic profile of LDs from an insect ovary. The compositions and compositional differences found among the LDs are discussed to provide a platform for future studies on the role of LDs, and their associated proteins, in cellular metabolism.

Lipophorin acts as a shuttle of lipids to the milk gland during tsetse fly pregnancy

During pregnancy in the viviparous tsetse fly, lipid mobilization is essential for the production of milk to feed the developing intrauterine larva. Lipophorin (Lp) functions as the major lipid transport protein in insects and closely-related arthropods. In this study, we assessed the role of Lp and the lipophorin receptor (LpR) in the lipid mobilization process during tsetse reproduction. We identified single gene sequences for GmmLp and GmmLpR from the genome of Glossinamorsitansmorsitans, and measured spatial and temporal expression of gmmlp and gmmlpr during the female reproductive cycle. Our results show that expression of gmmlp is specific to the adult fat body and larvae. In the adult female, gmmlp expression is constitutive. However transcript levels increase in the larva as it matures within the mother's uterus, reaching peak expression just prior to parturition. GmmLp was detected in the hemolymph of pregnant females and larvae, but not in the uterine fluid or larval gut contents ruling out the possibility of direct transfer of GmmLp from mother to offspring. Transcripts for gmmlpr were detected in the head, ovaries, midgut, milk gland/fat body, ovaries and developing larva. Levels of gmmlpr remain stable throughout the first and second gonotrophic cycles with a slight dip observed during the first gonotrophic cycle. GmmLpR was detected in multiple tissues, including the midgut, fat body, milk gland, spermatheca and head. Knockdown of gmmlp by RNA interference resulted in reduced hemolymph lipid levels, delayed oocyte development and extended larval gestation. Similar suppresion of gmmlpr did not significantly reduce hemolymph lipid levels or oogenesis duration, but did extend the duration of larval development. Thus, GmmLp function as the primary shuttle for lipids originating from the midgut and fat body to the ovaries and milk gland to supply resources for developing oocytes and larval nourishment, respectively. Once in the milk gland however, lipids are apparently transferred into the developing larva not by lipophorin but by another carrier lipoprotein.