Protein Synthesis In Fat Body Research Articles

Exogenous substances regulate silkworm fat body protein synthesis through MAPK and PI3K/Akt signaling pathways

Insect fat body is an important intermediate metabolic organ that plays an important role in protein metabolism and detoxification. In order to study the effects of TiO2 NPs and phoxim on fat body protein synthesis through MAPK and PI3K/Akt signaling pathways in silkworms, we determined the effects of TiO2 NPs and phoxim, alone and in combination, on fat body protein content of silkworms, analyzed the gene expression profile of the fat body, and verified the expression of characteristic genes. We found that TiO2 NPs and phoxim alone increased the total protein content of the fat body, and up-regulated MAPK and PI3K/Akt signaling pathway genes. TiO2 NPs up-regulated the expression of two growth and development-related genes-insulin-like peptide and neuropeptide receptor B-by 5.17 and 3.89-fold, respectively. Phoxim up-regulated the expression of detoxification genes-P450, GST, and CarE2. Pretreatment with TiO2 NPs could reduce phoxim-increased total protein content and up-regulated MAPK and PI3K/Akt signaling pathway genes and detoxification genes; the activities of detoxification enzymes were consistent with the gene expression pattern. Our results showed that MAPK and PI3K/Akt signaling pathways both regulate fat body protein synthesis in silkworms, but the target proteins induced to express were different under different inducing factors. Our finding may provide a reference for investigating the mechanism of protein synthesis regulation through MAPK and PI3K/Akt signaling pathways.

The role of adipokinetic hormone in the control of vitellogenesis in locusts

Vitellogenesis in locusts is synchronized with the cyclic maturation of oocytes. Vitellogenesis by excised fat body of gravid females is differentially inhibited 80–90% when locust adipokinetic hormone I (AKH-I) is added to the incubation media. Hemolymph methanolic extracts completely inhibit fat body protein synthesis in vitro when the donor females are at the end of the ovarian cycle (6 mm stage), but not when taken from earlier stages. Hemolymph methanolic extracts from vitellogenic females at the 6 mm stage are separated by HPLC into three distinct inhibitors of protein synthesis, one of which is AKH-I. AKH-RIA of hemolymph during the first ovarian cycle reveals no AKH-I during active vitellogenesis, but a marked increase to about 5 ng per female at the end of egg maturation. A development of responsiveness to AKH-I is evident in female fat body as vitellogenesis proceeds. AKH-I is involved in the negative control of vitellogenesis.

Neuroendocrine and juvenile hormone effects on fat body protein synthesis during the reproductive cycle in female Blaberus discoidalis cockroaches

Ovarian protein content and fat body protein synthesis were measured during the first gonotrophic cycle in virgin female Blaberus discoidalis cockroaches. Protein systhesis was measured for in vitro fat bodies from animals treated with combinations of a juvenile hor mone analog (JHA = methoprene) and corpora cardiaca (CC) extracts. Ovarian protein content began to increase on Day 5 of adult life and reached its maximum at Days 20–22. Synthesis of proteins secreted by the in vitro fat body increased by 12-fold between emergence and its maximum on Day 18, then declined to nearly its original level by Day 33. Synthesis of nonsecreted, fat body proteins increased by 4-fold between emergence and a maximum on Day 21, then declined. CC extracts and JHA were administered to decapitated females to determine their regulative effects on fat body protein synthesis. The synthesis by the fat body of nonsecreted proteins was increased by both JHA and CC extracts. In contrast, synthesis of secreted proteins increased only in the presence of JHA. CC extracts, alone, had no effects on the synthesis of secreted proteins, but administration of CC extracts in combination with JHA increased the synthesis of the secreted proteins by 55% above that observed with JHA alone. SDS-PAGE of proteins secreted into the medium by the in vitro fat body demonstrated that JHA stimulated the synthesis of specific polypeptides, whereas CC extracts did not affect the synthesis of specific-secreted polypeptides. These results suggest that JH regulates specific protein synthesis by the fat body of B. discoidalis; neurohormones elevate the general capacity of the fat body for protein synthesis and amplify the specific effects of JH.

Ovarian maturation in Leucophaea maderae: Juvenile hormone regulation of thymidine uptake into follicle cell DNA

Our research demonstrates that juvenile hormone (JH I) stimulates thymidine incorporation into ovarian follicle cell DNA in the ovoviviparous cockroach, Leucophaea maderae. A rapid, quantitative method for monitoring 3H-thymidine incorporation into ovarian DNA, in vitro, is described. Cultured ovarian tissue from L. maderae incorporates 3H-thymidine into DNA at a linear rate between 16 and 120 min; analysis of the incorporated label revealed at least 98% of it to be in DNA. Using L. maderae females that had been mated 7 days after adult emergence, we monitored the following biochemical phenomena during the 18–22 day period of terminal oöcyte growth: (1) 3H-thymidine incorporation into ovarian DNA: (2) general protein synthesis in fat body; and (3) specific fat body vitellogenin synthesis. Decapitation of mated females with maturing oöcytes arrested both ovarian DNA synthesis and fat body vitellogenin synthesis. Substantial restoration of both types of synthesis was induced by injection of JH I. The resumption of thymidine incorporation into DNA was localized in the follicular epithelium of the terminal oöcyte. In decapitated virgin females, injection of JH I stimulated oöcyte growth and 3H-thymidine incorporation into ovarian DNA. Dose and time response curves indicate that peak stimulation of ovarian DNA synthesis occurred between 72 and 96 hr after administration of a single optimal dose of 25 μg JH I. The concurrent manifestation of 3H-thymidine uptake into ovarian DNA and activity within the fat body indicates that a similar hormonal mode of action may be operative with respect to both tissue types in virgin females.

Inhibition of molting of the desert locust, Schistocerca gregaria, by the nematode parasite Mermis nigrescens

The older the host (Schistocerca gregaria) at infection, the greater the burden of parasitic Mermis nigrescens required to inhibit the next-but-one molt. Mermithid parasitism caused no change in ecdysone level in the host, but did cause a decrease in fat body protein synthesis. The effect of this decrease on host molting is discussed.

Protein and nucleic acid metabolism in insect fat body.

Summary1. The appearance of larval fat body as seen under the light or electron microscope depends on the nutritional state of the larva and on the stage of larval development at which the fat body is observed.2. Early in the last larval instar the cells usually possess a well‐developed endo‐plasmic reticulum rich in ribosomes, numerous mitochondria, glycogen granules, a Golgi complex and fat droplets, while later in the instar the endoplasmic reticulum is much reduced and mitochondria are few, but glycogen and fat droplets are present in greater amount together with the appearance of large numbers of proteinaceous spheres.3. Early in the last instar the fat body synthesizes proteins and exports them into the blood, while later in the instar proteins are sequestered from the blood into the fat body.4. The rate of protein synthesis by the fat body is high in the early to mid part of the last instar, but then falls off rapidly to a low level, at which it remains until the larva pupates. In diapausing pupae, protein synthesis remains at this low level.5. The similarity between the electrophoretic patterns of proteins from the fat body and those from the blood provides strong evidence that the fat body is the site of synthesis of many of the blood proteins.6. Some of the blood proteins have been shown to possess enzymic properties, while others are thought to play a role in the transportation of various types of compounds.7. Ecdysone and juvenile hormone both stimulate the rate of protein synthesis by larval fat body. Protein synthesis in fat body from diapausing pupae is stimulated after injury to the pupae.8. The appearance of adult fat body and the amount of protein it contains is often closely linked with the nutritional and reproductive states of the insect.9. An important role of the fat body in the adult female insect is the synthesis of yolk proteins, which are released into the blood and then taken up by the developing oocytes. This synthesis and uptake are under the control of hormones secreted by the corpora allata and by the median neurosecretory cells of the pars intercerebralis.10. The RNA content of fat body in final‐instar larvae is not constant throughout the instar. In some larvae it is at its highest level early in the instar, falling to a low level as the instar progresses, while in other larvae (e.g. Calliphora) the level of RNA in fat body does not decrease as the instar progresses.11. In some dipterous insects the base composition of total RNA is DNA‐like in that the guanine + cytosine content is low, accounting for 40 % of the bases. A similar composition is seen in rapidly labelled RNA isolated from insects of other orders (Coleoptera and Lepidoptera), but the base content of total RNA from these latter insects resembles ribosomal RNA from vertebrate tissues in that it has a high (ca. 60 %) guanine + cytosine content.12. The RNA/DNA ratios in blowfly larval tissues are high compared with those found in any vertebrate tissue.13. In larval fat body, RNA synthesis is low at the time of a moult, increases during the early and mid‐instar period and subsequently falls during the latter part of the instar. During the pupal period, especially during pupal diapause, the rate of RNA synthesis is very low and then increases during the subsequent development of the pharate adult. Injury to diapausing pupae results in an increased rate of RNA synthesis in most of their tissues.14. Ecdysone and juvenile hormone both stimulate RNA and DNA synthesis in larval and adult fat body and in other tissues, although there is evidence that in some tissues these two hormones may act antagonistically to each other. The insecticide DDT also has been shown to stimulate RNA synthesis in tissues of adult insects.

Protein synthesis in fat body of Trichoplusia ni during the course of a nuclear polyhedrosis virus infection

Protein synthesis in fat body of cabbage looper, Trichoplusia ni, larvae was investigated during the course of a nuclear polyhedrosis virus infection. Fat body total protein concentration increased late in the disease due to a large increase in the saline-insoluble protein fraction. Incorporation of 14C-leucine into fat body proteins in vitro revealed a slight increase in synthesis of both retained and released proteins on the first day of the disease followed by a rapid decrease in protein synthesis. The rate of decrease was more rapid in released than in retained proteins. Fat body soluble proteins of healthy larvae were separated into 22 bands by disc acrylamide gel electrophoresis. In diseased larvae, the concentration of major protein bands decreased during late stages of the disease. Electropherograms of the soluble fraction following 14C-leucine incorporation revealed most protein synthesized in the fifth instar of healthy larvae was in 2 zones close to the origin of the gels. These proteins were rapidly released following synthesis and accounted for all but trace amounts of the released protein. Synthesis of these major proteins decreased rapidly in diseased larvae after the first day as did synthesis of released proteins. Radioactivity in other areas of the gels was well maintained in retained proteins of diseased larvae until the fourth day when little radioactivity was present in any area of the gel.

Common electrophoretic properties of the fat body, haemolymph, and oöcytes of adult Tenebrio molitor

Electropherograms of the haemolymph indicated the presence, at a pH of 9·8, of eighteen negatively charged proteins of which at least five (bands Nos. 4, 13, 14, 15 and 16 from the origin) were common to the fat body and oöcytes. The distribution of the per cent composition of the five bands varied between unmated and mated females in the three tissues over the 4 days studied (days 3, 7, 8, and 10 after emergence). Circumstantial evidence suggested a three-step process of fat body protein synthesis followed by protein release into the haemolymph and its subsequent uptake by the oöcytes. Band No. 13 had the highest average per cent composition for both mated and unmated females in all three tissues reaching a maximum, on day 7 after emergence, of 56 (unmated females) or 58 (mated females) per cent of the total protein concentration in the oöcytes. Band No. 4, however, held the highest per cent composition of the five measured haemolymph protein bands on day 3 after emergence for both mated and unmated females, and on days 8 and 10 after emergence for unmated females when in the fat body it was also tied with band No. 13 for highest per cent composition. On day 3 after emergence fat body band No. 16, in mated females, represented the highest per cent composition of total protein and was four times higher than in unmated females of the same age, and similarly in the oöcytes, on day 3, band No. 16 was 34 per cent higher for mated than unmated females. Spectrophotometric analyses of fluctuations in the haemolymph protein concentration indicated a similar pattern for unmated and mated females from emergence to day 10 after emergence, the haemolymph protein concentration being significantly greater ( P<0·05) for mated females on days 4 and 9 after emergence (0·05> P>0·025). The mean value on day 9 was approximately 60 per cent higher for mated than unmated females. A possible relationship between the cyclic pattern of haemolymph protein concentration and the patterns of fat body protein and RNA synthesis is discussed.

Protein synthesis and nucleic acid metabolism in the fat body of the larva of the blowfly, Calliphora erythrocephala

The effect of culturing blowfly larvae at a low temperature (10°-larvae) for part of their larval period on the rate of protein synthesis by the fat body was investigated. In 10°-larvae this treatment prevented the rapid decline in protein synthesis which is seen in fat body from larvae cultured at 25°C for the whole of their larval period (25°-larvae). Protein synthesis in fat body from 25°-larvae was completely inhibited by 10 −4 M dinitrophenol, 7·8 × 10 −3 M chloramphenicol, and 10 −5 M cycloheximide. The RNA-P content per fat body from 25°-larvae increased from 2·8 to 14·0 μg over the age range 3 to 7 days and the protein content increased from 0·8 to 2·3 μg over the same period. Electron micrographs showed that fat body from 4-day-old 25°-larvae contained fat droplets, mitochondria, glycogen granules, and numerous ribosomes. On the other hand, fat body from 7-day-old larvae contained numerous albuminoid granules, but hardly any mitochondria and few ribosomes.

Effect of ecdysone on protein synthesis in the larval fat body of Calliphora

The effect of ecdysone on protein synthesis in the fat body of isolated abdomens of 6- and 8-day-old larvae of Calliphora erythrocephala has been investigated. A very rapid and significant stimulation of protein synthesis occurred in both the 6- and the 8-day-old larvae. The pattern of 14C-leucine (u.l.) incorporation was rather similar in both age groups. The 6-day-old larvae showed a stimulation of 152 per cent relative to their controls 1 hr after injection of the hormone and reached a maximal stimulation of 172 per cent at 2 hr after hormone administration. The 8-day-old larvae showed a maximal stimulation of 185 per cent relative to their controls within 1 hr after injection of the hormone.

Short-term effects of crustecdysone (20-hydroxyecdysone) on protein and RNA synthesis in third instar larvae of Calliphora

The effect of exogenous crustecdysone (20-hydroxyecdysone) on protein and RNA synthesis in body wall and fat body of third instar larvae of Calliphora stygia has been investigated in vivo. The effect of injury resulting from the injection and handling technique has been separated from responses to the hormone. Protein synthesis in body wall is most sensitive to crustecdysone in larvae aged 7 to 8 days, somewhat before the level of endogenous moulting hormone rises. Protein synthesis in fat body is stimulated over a wider age range. The time-course of the hormone effect on protein synthesis in 7 to 8 day larvae is similar in body wall and fat body, and is quantitatively the same for either ecdysone or crustecdysone. There is an initial depression of protein synthesis 1 hr after injection of hormone, followed by a burst of protein synthesis at 4 hr which is substantially over at 6 hr. The effect of crustecdysone on protein synthesis in body wall from treated 7 to 8 day larvae is proportional to the logarithm of the dose over the range 0·002 to 0·2 μg/larva. The response of protein synthesis in fat body to increasing dose in this range is slight. Gross RNA synthesis in body wall from 7–8 day larvae is greatly stimulated 2 hr after injection of crustecdysone but approximates control levels by 4 hr. An initial depression in gross RNA synthesis is apparent at 2 hr in fat body preparations from the same animals, but by 4 hr RNA synthesis shows marked enhancement above the control levels. A study of 3H-uridine incorporation into subcellular fractions from body wall and fat body shows that synthesis in nuclear, microsomal, and soluble RNA components is affected by the hormone, but at different times and to varying degrees.