Vitellogenin Uptake Research Articles

Vitellogenin uptake, not synthesis, is dependent on juvenile hormone in adults of Phormia regina (Meigen)

When Phormia regina larvae were raised on an artificial diet, topical applications of either methoprene (2.5 μg/fly) or juvenile hormone III (5 μg/fly) to adult, sugar-fed, females on days 3, 4 and 5 after emergence caused from 10.2 to 17.5% to have stage 4 follicles (i.e. as judged by the presence of a little opaque material in the oöcytes); whereas, in both the untreated and the acetone controls, oöcytes remained in stage 3, in nearly all flies, without any opaque material. Previous studies by other researchers on methoprene-treated, sugar-fed P. regina referred to the opaque material in stage 4 follicles as yolk. In this present study, however, examination, using a specific enzyme-linked immunosorbent assay (ELISA) for vitellin and vitellogenin, of stage 4 follicles as well as the haemolymph from sugar-fed and methoprene (or juvenile hormone III)-treated flies, revealed no vitellin or vitellogenin, respectively. These results are consistent with our previous data, which have shown that juvenile hormone is mainly involved with vitellogenin uptake but not vitellogenin biosynthesis. Thus our present results are inconsistent with a previous conclusion indicating that methoprene treatment would cause vitellogenin biosynthesis and complete egg development in sugar-fed P. regina raised as larvae on pork liver. When we raised larvae on pork liver, we found that topical application of methoprene (three times) to 195 sugar-fed females resulted in only one female containing stage 10 ovaries and 112 contained stage 3, 74 stage 4, and eight stages 5–9 ovaries. None of the methoprene induced stage 4 follicles showed any detectable quantity of vitellin. Since methoprene treatment resulted in only one fly (out of 195) to have stage 10 follicles (albeit the vitellin deficiency), our results do not support the idea that juvenile hormone treatment alone is sufficient to initiate and sustain vitellogenin biosynthesis and uptake in sugar-fed P. regina.

Effect of cobalt and other divalent cations on oöcyte development of the black blowfly, Phormia regina (Meigen)

Results showed that injections of the divalent cation cobalt, a calcium channel blocker, at effective haemolymph concentrations of 2.1, 3.4 or 5.0 mM, immediately prior to liver feeding, retarded or inhibited egg development by influencing vitellogenin uptake in Phormia regina. Topical application of methoprene (a juvenile hormone analogue) to cobalt-injected flies partially restored the otherwise inhibited egg development. Since vitellogenin uptake in this fly is controlled by juvenile hormone, cobalt may affect oöcyte development at least partly through its effect on juvenile hormone biosynthesis. Rates of juvenile hormone biosynthesis by the corpus allatum, in vitro, in cobalt-injected flies fell into three levels of 0.48 ± 0.01, 0.72 ± 0.12 and 0.97 ± 0.08 pmol/gland pair/h. These three levels of rates of juvenile hormone biosynthesis corresponded well with the three categories of ovary development observed in cobalt-injected flies: undeveloped, partially developed and fully developed. In comparison, the rates of juvenile hormone biosynthesis were 0.03 ± 0.00, 1.16 ± 0.08 and 1.23 ± 0.10 pmol/gland pair/h for sugar-fed, liver-fed, and liver-fed but water-injected control flies, respectively. Effects or lack of effects of several different calcium-replacement divalent cations and a dihydropyridine calcium channel blocker (i.e. nifedipine) on oöcyte development in P. regina suggested that calcium channels of the corpora allata may be involved in the regulation of juvenile hormone biosynthesis, which then affected oöcyte development.

Vitellogenin in Winter Flounder (Pleuronectes americanus) from Long Island Sound and Boston Harbor

Vitellogenin is an egg-yolk precursor protein in teleosts which is crucial to the survival of larvae. Manufactured in the liver, where pollutants are known to accumulate, and transported to the ovary by the blood, its synthesis by the liver or uptake by the gonad can be compromised by accumulation of xenobiotics. In three studies, winter flounder (Pleuronectes americanus) blood samples were taken to determine normal levels of vitellogenin during the reproductive cycle, and to learn how its production might be affected in degraded environments. Specifically, these studies followed the seasonal cycle of vitellogenin production in winter flounder through monthly sampling at relatively clean (Shoreham, New York) and degraded areas (Black Rock and New Haven harbors, Connecticut) in Long Island Sound; examined the relationship between parental vitellogenin levels and survival of offspring by sampling fish that had been spawned at the Milford Laboratory for a reproductive success study; and determined the effect of gross liver lesions on vitellogenin production by sampling flounder from Boston Harbor, Massachusetts, which have been reported to have a high prevalence of liver tumors. Blood vitellogenin levels were determined by measuring alkali-labile phosphate (ALP). Large fish (>30 cm) from the two degraded sites had elevated serum ALP levels relative to those from the clean area. Lowered total ovarian lipid levels in large fish from Black Rock Harbor suggested impaired vitellogenin uptake. There were no significant differences in serum ALP among the small (≤30 cm) fish from the three sampling sites. Boston Harbor flounder with gross liver lesions had lower ALP values than fish without such lesions. There were no significant differences in ALP values among the spawned fish.

Ovarian ecdysteroid levels and basal oöcyte development during maturation in the cockroach Blattella germanica (L.)

By using enzyme immunoassay techniques we have quatified the ovarian ecdysteroids during the 7-day cycle of oöcyte maturation in Blattella germanica. Immunoreactive ecdysteroid levels were low on days 0–2, increased to higher values on days 3–6, and peaked on day 7 (about 5 ng of 20-hydroxyecdysone equivalents per pair of ovaries). The predominant non-conjugated ovarian ecdysteroid detected by HPLC analysis was 20-hydroxyecdysone. During oöcyte maturation, the dynamics of patency, vitellogenin uptake, increase in follicle cells diameter (suggested to be due to polyploidy), and choriogenesis was studied. A comparison of the ovarian ecdysteroid profile with the succession of physiological processes occurring within the oöcyte maturation cycle suggests that these hormones could be directly or indirectly involved in the control of patency, polyploidy and choriogenesis in the follicle cells.

Isolation and characterization of two follicle-specific proteins from eggs of Manduca sexta

Two proteins synthesized exclusively in developing follicles have been isolated from eggs of Manduca sexta. One protein has a molecular mass of 130 kDa and is composed of two identical 65 kDa subunits. This protein is glycosylated and phosphorylated. The second protein has a molecular mass of 140 kDa and is composed of two 40 and two 35 kDa subunits. The second protein is glycosylated but not phosphorylated. The proteins are made after active vitellogenin uptake by the developing egg but before chorion formation. Both proteins are extremely sensitive to hydrolysis by proteases found in the egg. We propose the generic term follicle-specific protein (FSP) for these proteins.

Involvement of gonadotropin in the uptake of vitellogenin into vitellogenic oocytes of the rainbow trout, Oncorhynchus mykiss

The effects of two fully characterized, structurally distinct gonadotropins, GtH I and GtH II, on the uptake of vitellogenin (VTG) into oocytes of the rainbow trout, Oncorhynchus mykiss, were investigated both in vivo and in vitro. GtH I, injected into maturing vitellogenic females at a dose of 10 μg · kg body wt −1, increased the rate of [ 3H]VTG uptake into oocytes by more than two-fold, effectively doubling their rate of growth. Ovaries from females similarly treated with GtH II sequestered VTG at rates similar to controls. In vitro, GtH I stimulated VTG uptake in a dose-dependent manner. At a GtH I concentration of 100 ng · ml −1 and above, the rate of VTG uptake was significantly greater than that of the controls and at 1000 ng · ml −1 the rate of uptake was more than doubled. GtH II did not significantly increase VTG sequestration into isolated oocytes at concentrations up to, and including, 1000 ng · ml −1. These data provide the first evidence that GtH I has a primary function in stimulating VTG uptake and strongly support the contention that at least two functionally distinct GtHs occur in fish.

Effects of benzodioxole on microtubule formation in the ovaries of Drosophila melanogaster

Benzodioxole J2581 (5-ethoxy-6-(4-methoxyphenyl)methyl-1,3-benzodioxole), a known chemosterilant that inhibits vitellogenin uptake, was shown to prevent microtubule formation in the ovaries of Drosophila melanogaster. When female flies were topically treated with benzodioxole at emergence, ultrastructural studies revealed that the follicular epithelium was not patent, thus preventing the entry of vitellogenin into the oocytes. Closer examination revealed that the submembrane space of follicular cells in benzodioxole-treated ovaries had reduced numbers of microtubules. In addition, coated vesicles that are responsible for the endocytotic uptake of vitellogenin were nearly nonexistent in the submembrane space of the oolemma of treated ovaries. Since the movements of these organelles are dependent on an intact microtubule matrix, we hypothesize that benzodioxole exerts its effects at least in part via disruption of the microtubule system. Application of the JH analog, 7 s-methoprene, reversed the effects of benzodioxole on patency, microtubule assembly, and coated vesicle numbers at the oolemma.

Uptake of vitellogenin into oocytes during early vitellogenic development in the rainbow trout, Oncorhynchus mykiss (Walbaum)

Uptake of 3H‐vitellogenin (3H‐VTG) into oocytes of various sizes was investigated during early vitellogenic development in the rainbow trout, Oncorhynchus mykiss (Walbaum). Females were injected with 3H‐VTG and uptake into oocytes of different sizes (<0.4,0.4–0.59, 0.6–0.79, 0.8–0.99 and 1.0 1.2 mm in diameter) measured. Oocytes measuring less than 0.6 mm in diameter appeared unable to sequester VTG and were therefore considered pre‐vitellogenic. Oocytes measuring 0.6 mm or more all sequestered VTG. The larger the oocyte, the more 3H‐VTG it sequestered, even when uptake was expressed per unit surface area. The latter observation could be due to an increase in the number of VTG receptors per unit surface area, an increase in the rate of turnover of the VTG receptor, greater access of VTG to the receptors as oocytes grow, or a combination of any of these factors. The data suggest that the ability to sequester VTG is developmentally regulated.

Initiation of vitellogenin uptake and protein synthesis in the mosquito ( Aedes aegypti) ovary in response to a blood meal

We studied the initiation of both vitellogenin endocytosis and non-vitellogenin protein synthesis in the mosquito ovary after a blood meal. Both these processes exhibited activation in two phases. The rate of endocytosis increased slowly during the first 2 h after feeding and was followed by a more rapid increase that peaked at 24 h after feeding. The rate of ovarian protein synthesis, which increased dramatically within the first 30 min after feeding, declined for the next 2 h and then increased again, gradually, reaching a peak at 8 h after a blood meal. Following a slight decline at 12 h, a steady rate was maintained for the next 12 h. Decapitation or isolation of the abdomen, within 5 min of the beginning of blood feeding, eliminated the second activation phase, but not the first one, for both these processes. In contrast, neither vitellogenin endocytosis nor ovarian protein synthesis was stimulated in abdomens isolated from previtellogenic females given an enema of blood and assayed 4 h later. The rate of ovarian protein synthesis became independent from the head at 8 h after feeding. In order to maintain the normal rates of vitellogenin endocytosis, the presence of the head was required for 16–20 h after a blood meal. Thus, both protein synthesis and vitellogenin endocytosis were first activated as a result of blood feeding itself. The second activation phase was also dependent on the head factors, and their continued release was essential for the maintenance of these ovarian functions.

The effect of ions, ion channel blockers, and ionophores on uptake of vitellogenin into cockroach follicles

Since calcium plays an important role in vitellogenin binding and uptake in Nauphoeta cinerea and because calcium channels have been described in follicles of this species, we investigated the effect of various ions, ionophores, and ion channel blockers on vitellogenin uptake in vitro. Calcium significantly stimulated vitellogenin uptake; this effect could be substituted best by barium and less well by strontium and magnesium. The stimulatory effect of calcium, and to a certain extent also that of barium, was dependent on the vitellogenin concentration, whereas the effect of strontium and magnesium was not. In the presence of calcium, vitellogenin uptake was inhibited by barium, strontium, and magnesium as well as by the transition elements nickel, cobalt, and zinc, but not by manganese which had a stimulatory effect. Valinomycin, verapamil, tetraethylammonium, and atropin reduced vitellogenin uptake, while amiloride and ouabain were ineffective. Our results indicate that calcium inward (and possibly potassium outward) fluxes play an important role in vitellogenin uptake.

Ultrastructural aspects of oogenesis and oocyte growth in fish and amphibians

Oogenesis, the early events of primary oocyte growth (meiotic arrest, synapsis, ribosomal gene duplication), and folliculogenesis can be seen to particular advantage in the germinal ridge of the syngnathan ovary. After budding off the germinal ridge (a compartment of the luminal epithelium), nascent follicles then enter into a linear array of developing follicles within which temporal and stage-specific events can be correlated with spatial distribution. Prominent features of the later phase of primary oocyte growth include intense transcriptional activity and the formation and subsequent dispersal of the Balbiani vitelline body (mitochondrial cloud) concomitant with an increase in cytoplasmic organelles and volume. Further oocyte growth is characterized by a period of cortical alveolus (in teleosts) or cortical granule (in anurans) formation, in which Golgi elements play a predominant role, and finally vitellogenesis. The latter process, which is responsible for the preponderance of oocyte growth, includes the hepatic synthesis and secretion of vitellogenin (VTG), the uptake of VTG from the bloodstream into the oocyte by receptor-mediated endocytosis, and the transport of VTG via endosomes and multivesicular bodies to forming yolk platelets. In the process, VTG is proteolytically cleaved into the yolk proteins, which assume either a monoclinic (in cyclostomes) or orthorhombic (in teleosts and amphibians) crystalline array. Other structures associated with the growing oocyte are also briefly discussed, including nuage, the vitelline envelope, intercellular junctions between the oocyte and overlying follicle cells, pigment, intramitochondrial crystals in ranidae, and annulate lamellae.

An in vitro culture system for studying vitellogenin uptake into ovarian follicles of the rainbow trout, Salmo gairdneri

AbstractThe development of a short‐term culture system to study vitellogenin (VTG) sequestration in vitro into vitellogenic follicles of the rainbow trout, Salmo gairdneri, is described. The outer epithelial cell layer of the trout follicle restricted VTG uptake considerably and its removal was a prerequisite to study VTG uptake in vitro. Vitellogenic follicles divested of the surface epithelium sequestered VTG at rates of up to 170 ng·mm2 follicle surface−1·h−1 (ng·mm−2·h−1). Uptake of VTG over an 8 h period of incubation was linear.Increasing the titre of VTG in the culture medium induced greater rates of sequestration in a dose‐dependent manner; follicles cultured in medium containing 45 mg VTG·ml−1 sequestered 170 ± 9ng·mm−2·h−1 whereas those follicles cultured in medium containing 2 mg·ml−1 only incorporated 6 ± 0.5 ng·mm−2·h−1.Uptake of VTG was temperature dependent with higher temperatures inducing higher levels of incorporation. Sequestration of VTG persisted at temperatures below 5°C, showing that the uptake mechanisms are adapted to low temperatures in this species.Size of follicles also had a considerable bearing on the rate of VTG sequestration; follicles of less than 1 mm diameter (pre‐vitellogenic follicles) did not sequester VTG in amounts that were detectable. All follicles measuring 1 mm or greater in diameter sequestered VTG. As the follicles increased in size between approximately 1 and 3 mm in diameter there was an increase in both the total amount of VTG sequestered and the rate of uptake of VTG relative to surface area. Limited data suggested that in follicles closely approaching ovulation the rate of VTG sequestration was considerably reduced.

Regulation of oogenesis: The piscine receptor for vitellogenin

The receptor-mediated uptake of vitellogenin (VTG), a plasmatic lipophosphoglycoprotein, is crucial for oocyte growth in egg-laying animals. The plasma membrane receptor for VTG was characterized from oocytes of coho salmon, Oncorhynchus kisutch. In direct binding studies, the receptor exhibited high affinity ( K d , 180 nM) for salmonid VTG, and by ligand blotting with radiolabelled VTG it was visualized as a protein with an apparent M r of 100000, under non-reducing conditions. The fish VTG receptor was shown to share key structural elements with VTG receptors from chicken and Xenopus laevis. Namely, cross-reactivity at the level of ligand recognition was observed among VTG receptors from these species and immunological relatedness was demonstrated by immunoblotting with anti-chicken VTG receptor antibodies. In addition, as in chicken and Xenopus, binding of VTG to fish oocyte receptors was shown to be mediated by the lipovitellin domain of VTG. These results clearly indicate that regulation of oocyte growth at the level of yolk formation has been accomplished by the conservation of structural features of receptors required for internalization of VTG.

The dynamics of vitellogenin sequestration into vitellogenic ovarian follicles of the rainbow trout, Salmo gairdneri

This study provides quantitative data on the dynamics of protein sequestration into vitellogenic follicles of the rainbow trout, Salmo gairdneri. The ovarian uptake of both radiolabelled vitellogenin (VTG) and bovine serum albumin (BSA) were investigated in a homogenous population of maturing vitellogenic females.Ten fish were injected with (3)H. VTG directly into the bloodstream. Concomitantly, five of these fish received an equal amount of (14)C.BSA. Twenty two hours after injection, of the tissues sampled, the greatest proportions of (3)H. VTG were present in the blood (into which the radio labels were administered) and in the ovary (up to 28% and 46% of that originally present in the blood, respectively). VTG uptake was both selective, rates of uptake far exceeding that of the (14)C.BSA, and rapid. (3)H. VTG was sequestered at rates of between 35 to 390 ng.mm(2) follicle surface(-1).h(-1) in the different fish. The rates of VTG uptake into similarly sized follicles varied both between different sites within the ovary (by up to 30%) and also between the ovaries (by up to 38%) of an individual fish.

Ovarian uptake of vitellogenin and another very high density lipoprotein in winter flounder (Pseudopleuronectes americanus) and their relationship with yolk proteins

Ultracentrifugation analysis of female winter flounder plasma confirmed that in addition to vitellogenin another different lipoprotein is found as very high density lipoprotein (VHDL). Accordingly this protein (formerly known as peak A protein) has been named VHDL II, with respect to vitellogenin which we designate VHDL I. Both these proteins were shown to be taken up in vivo by the ovary of vitellogenic females. Based on total mass, vitellogenin and VHDL II could potentially contribute in similar amounts to yolk protein accumulated by developing oocytes. Sodium dodecyl sulfate – polyacrylamide gel electrophoresis of vitellogenic oocyte yolk proteins revealed five major protein subunits of 101.4, 94.4, 68.7, 25.5, and 22.5 kilodaltons (kDa). Western blots of these yolk protein subunits established three of them (104.4, 94.4, and 22.5 kDa) as originating from vitellogenin. Similar Western blots utilizing a VHDL II antisera identified the 68.7-kDa yolk protein subunit as arising from incorporated serum VHDL II.Key words: VHDL II, vitellogenin, oocyte yolk proteins, in vivo uptake, Western blot.

Interspecific ovarian transplantations in Drosophila: vitellogenin uptake as an index of evolutionary relatedness

Evolutionary divergence is measured either by comparing homologous characters in related species or by assessing the compatibility of genes, cells or tissues from different species to sustain normal development and function. Here we examine vitellogenin accumulation in interspecifically transplanted ovaries as a measure of evolutionary divergence of the second kind. We report on the results from about 400 ovary transplantations involving 27 species from four different species groups of Drosophila. With the exception of one species, no vitellogenin accumulation was observed in inter-group transplantations, but accumulation occurred at varying degrees in intra-group transplantations. This degree is in good agreement with intra-group phylogenetic relationship established on other criteria and it can, therefore, be a useful complementary index of relative evolutionary divergence among members of the same species group.

Relationship between feeding, mating, vitellogenin production and vitellogenesis in the tick Dermacentor variabilis.

Anti-vitellin IgG directed against Dermacentor variabilis egg vitellin was used in sodium dodecyl sulfate polyacrylamide (SDS-PAGE) gradient gel immunoblots to detect the presence of vitellin and its precursor, vitellogenin, in the organs of feeding adults and in the immature stages of this tick. Vitellin polypeptides were found in the egg, larvae, nymph, and in the unfed adult stages of both sexes. Vitellin polypeptides were first detected in the ovary of mated females during the rapid-engorgement feeding period. These polypeptides were also present in the ovaries of ovipositing females, unmated females fed for extended periods, and fed unmated females that were detached from the host and held for 12 h before dissection. The same anti-vitellin antibody was used in immunoblots to monitor the appearance of vitellogenin in the organs and hemolymph of female ticks. Immunoreactive peptides of vitellogenin were found in the fat body, midgut, and hemolymph of pre-rapid-engorging mated and unmated females. These polypeptides were not found in fed males nor in Malpighian tubes of feeding or ovipositing females. Our data supported the following conclusions: 1) presence of immunoreactive vitellogenin in the adult female fat body, hemolymph, and midgut was dependent upon feeding; 2) in mated feeding females, we could not detect the uptake of vitellogenin by the ovary until rapid engorgement; 3) in unmated females, vitellogenesis did not begin unless prolonged feeding occurred; and 4) during the early developmental stages of this tick, vitellin served as an embryonic nutrient reserve and as a reserve against starvation between feedings.

Onset of vitellogenin production and vitellogenesis, and their relationship to changes in the midgut epithelium and oocytes in the tickDermacentor variabilis

In Dermacentor variabilis (Say), the onset of vitellogenin production and vitellogenesis (uptake of vitellogenin into oocytes) began during the rapid-engorgement feeding period. Mating was required for both vitellogenin production and vitellogenesis to complete the tick's life cycle. Complete immunological identity, as measured by Ouchterlony's double diffusion test, existed between vitellogenin from the fat body, midgut and hemolymph, and vitellin from the ovaries and eggs. Antivitellin antibody did not react with host hemoglobin nor with fat body, midgut, and ovary extracts from feeding females prior to rapid engorgement, feeding unmated females, or unfed or fed males. Some unmated females fed for 13 days and then hand-detached from the host eventually began oviposition after going through a preoviposition period. In these ticks, organ extracts from the midgut, fat body and ovary reacted with antivitellin antibody. The presence or absence of presumed vitellogenic cells in the midgut and yolk bodies in oocytes corresponded with the presence or absence of vitellogenin and vitellogenesis as measured by Ouchterlony's test. Presumed vitellogenic cells increased in size during the preoviposition period. These cells reached their greatest size during the time when the most eggs were being produced, and then declined in size toward the end of oviposition. Vitellogenin was deposited directly into developing yolk bodies in oocytes and was not processed through lysosomes. Feeding was the process that initiated the formation of eggshell cuticle. Detachment from the host was required for the initiation of oviposition.

Ovarian follicle development during vitellogenesis in the house cricket Acheta domesticus.

To determine the morphological correlates of vitellogenin uptake and distribution, vitellogenic ovarian follicles of Acheta domesticus were examined by light and transmission electron microscopy. Yolk deposition was usually restricted to the terminal follicle of each panoistic ovariole, but if the terminal follicle had completed vitellogenesis and had not yet been ovulated, the penultimate follicle was often vitellogenic. Vitellogenesis occurred only in the ovaries of adults, with follicles representing all stages of vitellogenic development occurring simultaneously within a single ovary. Vitellogenic follicles were 0.75 to >2.0 mm long. The single irregularly shaped nucleus of each follicle cell contained two to three nucleoli. During vitellogenesis the epithelium of individual follicles progressed from columnar to cuboidal to squamous. The distribution of cytoplasmic organelles within individual follicle cells was polarized during early and middle stages of vitellogenesis. Near the end of vitellogenesis, polarity disappeared, the follicular epithelium became squamous, and the frequency of vesicular and multivesicular bodies in the follicle cell cytoplasm increased. A well-developed capability for follicle cell protein synthesis and secretion throughout vitellogenesis was indicated by abundant rough endoplasmic reticulum and Golgi bodies. Receptor-mediated endocytotic activity by the follicle cells during all stages of vitellogenesis was suggested by omnipresent coated pits on all surfaces. Septate junctions, gap-like junctions, and desmosomes all occurred in the lateral membranes, while gap-like junctions predominated at the oocyte-follicle cell interface. In follicles longer than 1 mm, adjacent follicle cells were separated by intercellular channels that widened to as much as 10 m̈m by the completion of vitellogenesis. The channels contained a flocculent material, and a similar-appearing material filled the space between the oolemma and follicle cell apical membranes. The oolemma contained a profusion of coated pits throughout vitellogenesis.

Selective endocytosis of vitellogenin by oocytes of the mosquito, Aedes aegypti: An in vitro study

An in vitro assay was used to study the uptake of vitellogenin (VG) by oocytes of the mosquito, Aedes aegypti. The VG, obtained from the culture of fat bodies in vitro, was metabolically labeled to a high specific activity ( 3–6 × 10 5 cpm/μg) using [ 35S]methionine. Purification of both VG and vitellin (VN) from ovaries was achieved with ion-exchange chromatography on DEAE-Sepharose CL-6B. In an optimized in vitro system, mosquito oocytes in intact ovaries maintained stable endocytotic activity for at least 4 h. The rate of VG uptake was maximal at pH 7.5. It declined at acid pH and ceased abruptly at pH 6.3. Accumulation of VG by mosquito oocytes demonstrated features of receptor-mediated endocytosis; i.e. temperature dependence, saturability, selectivity and tissue specificity. The uptake of VG was inhibited at 4°C with only 6% of uptake achieved at 27°C. At 24 h post-blood meal, uptake of VG by oocytes at 27°C, neared saturation with a VG concentration in the medium of 8 μg/μl. Saturation kinetics generated for VG endocytosis by these oocytes produced a V max = 3.2 μg/μl/h and an apparent K uptake = 8.4 × 10 −6 M. Ovaries accumulated 10 times the amount of VG compared to mouse IgG, while uptake of VN was 71.6% of that for VG, indicating that oocytes from Aedes are able to distinguish these proteins. Non-ovarian tissues, fat body and Malpighian tubules, accumulated both VG and IgG at equally low levels. During the vitellogenic cycle, the rate of VG uptake by oocytes showed a steep and linear increase between 6 and 24 h post-blood meal. The peak of VG uptake occurred between 24 and 30 h post-blood meal, followed by a precipitous decline and cessation of uptake by 36 h.