Hormonal control of the follicular epithelium during vitellogenin uptake

Purification of an insect juvenile hormone receptor complex enables insights into its post-translational phosphorylation

Juvenile hormone (JH) plays vital roles in insect reproduction, development, and in many aspects of physiology. JH primarily acts at the gene-regulatory level through interaction with an intracellular receptor (JH receptor [JHR]), a ligand-activated complex of transcription factors consisting of the JH-binding protein methoprene-tolerant (MET) and its partner taiman (TAI). Initial studies indicated significance of post-transcriptional phosphorylation, subunit assembly, and nucleocytoplasmic transport of JHR in JH signaling. However, our knowledge of JHR regulation at the protein level remains rudimentary, partly because of the difficulty of obtaining purified and functional JHR proteins. Here, we present a method for high-yield expression and purification of JHR complexes from two insect species, the beetle T. castaneum and the mosquito Aedes aegypti. Recombinant JHR subunits from each species were coexpressed in an insect cell line using a baculovirus system. MET–TAI complexes were purified through affinity chromatography and anion exchange columns to yield proteins capable of binding both the hormonal ligand (JH III) and DNA bearing cognate JH-response elements. We further examined the beetle JHR complex in greater detail. Biochemical analyses and MS confirmed that T. castaneum JHR was a 1:1 heterodimer consisting of MET and Taiman proteins, stabilized by the JHR agonist ligand methoprene. Phosphoproteomics uncovered multiple phosphorylation sites in the MET protein, some of which were induced by methoprene treatment. Finally, we report a functional bipartite nuclear localization signal, straddled by phosphorylated residues, within the disordered C-terminal region of MET. Our present characterization of the recombinant JHR is an initial step toward understanding JHR structure and function.

Rhodnius, Golden Oil, and Met: A History of Juvenile Hormone Research

Juvenile hormone (JH) is a unique sesquiterpenoid hormone which regulates both insect metamorphosis and insect reproduction. It also may be utilized by some insects to mediate polyphenisms and other life history events that are environmentally regulated. This article details the history of the research on this versatile hormone that began with studies by V. B. Wigglesworth on the "kissing bug" Rhodnius prolixus in 1934, through the discovery of a natural source of JH in the abdomen of male Hyalophora cecropia moths by C. M. Williams that allowed its isolation ("golden oil") and identification, to the recent research on its receptor, termed Methoprene-tolerant (Met). Our present knowledge of cellular actions of JH in metamorphosis springs primarily from studies on Rhodnius and the tobacco hornworm Manduca sexta, with recent studies on the flour beetle Tribolium castaneum, the silkworm Bombyx mori, and the fruit fly Drosophila melanogaster contributing to the molecular understanding of these actions. Many questions still need to be resolved including the molecular basis of competence to metamorphose, differential tissue responses to JH, and the interaction of nutrition and other environmental signals regulating JH synthesis and degradation.

Sequential oogenesis is controlled by an oviduct factor in the locusts Locusta migratoria and Schistocerca gregaria: Overcoming the doctrine that patency in follicle cells is induced by juvenile hormone

In insects that lay eggs in large clutches, yolk accumulation in each of the many ovarioles is restricted to the basal (terminal) oocyte, the one closest to the lateral oviduct. All succeeding (subterminal) oocytes remain small until the terminal oocytes finished their development and were ovulated into the oviduct. The major step regulating yolk uptake by terminal oocytes is the formation of gaps between cells of the follicle layer, a process termed patency. In the migratory as well as in the desert locust, patency is induced by a Patency Inducing Factor (PIF) produced by the lateral oviducts. PIF is secreted in all regions of the lateral oviducts and interacts with the basal follicle cells via the pedicel, a fine duct that connects an ovariole with the oviduct. By this mechanism, patency is triggered in the follicle cells of the terminal oocyte only, restricting yolk accumulation to the oocytes next to ovulation. In contrast to the previous hypothesis, juvenile hormone (JH) is not necessary to induce patency, rather JH amplifies the effect of PIF.

Protein kinase C modulates transcriptional activation by the juvenile hormone receptor methoprene-tolerant

Juvenile hormone (JH) controls many biological events in insects by triggering dramatic changes in gene expression in target cells. The Methoprene-tolerant (MET) protein, an intracellular JH receptor, acts as a transcriptional regulator and binds to the promoters of tissue- and stage-specific JH target genes when JH is present. Our recent study has demonstrated that the transcriptional activation by MET is modulated by a membrane-initiated JH signaling pathway, involving phospholipase C (PLC) and calcium/calmodulin-dependent protein kinase II (CaMKII). Here we report that protein kinase C (PKC) is another essential intermediate of this pathway. PKC was activated by JH and this action was PLC-dependent. Inhibition of the PKC activity substantially weakened the JH-induced gene expression in mosquito cells. RNAi experiments indicated that several PKC isoforms were involved in the JH action during the post-emergence development of adult female mosquitoes. JH treatment considerably increased the binding of MET to the promoters of JH response genes in cultured mosquito abdomens that were collected from newly emerged female adults. The JH-induced DNA binding of MET was hindered when the abdomens were treated with a PKC inhibitor and JH. Therefore, the results suggest that PKC modulates the transactivation activity of MET by enhancing the binding of MET to JH response elements in the JH target genes. This mechanism may allow for variable and stage- and tissue-specific genomic responses to JH.

Juvenile hormone-activated phospholipase C pathway enhances transcriptional activation by the methoprene-tolerant protein

Juvenile hormone (JH) is a key regulator of a wide diversity of developmental and physiological events in insects. Although the intracellular JH receptor methoprene-tolerant protein (MET) functions in the nucleus as a transcriptional activator for specific JH-regulated genes, some JH responses are mediated by signaling pathways that are initiated by proteins associated with plasma membrane. It is unknown whether the JH-regulated gene expression depends on the membrane-mediated signal transduction. In Aedes aegypti mosquitoes, we found that JH activated the phospholipase C (PLC) pathway and quickly increased the levels of inositol 1,4,5-trisphosphate, diacylglycerol, and intracellular calcium, leading to activation and autophosphorylation of calcium/calmodulin-dependent protein kinase II (CaMKII). When abdomens from newly emerged mosquitoes were cultured in vitro, the JH-activated gene expression was repressed substantially if specific inhibitors of PLC or CaMKII were added to the medium together with JH. In newly emerged female mosquitoes, RNAi-mediated depletion of PLC or CaMKII considerably reduced the expression of JH-responsive genes, including the Krüppel homolog 1 gene (AaKr-h1) and the early trypsin gene (AaET). JH-induced loading of MET to the promoters of AaKr-h1 and AaET was weakened drastically when either PLC or CaMKII was inactivated in the cultured tissues. Therefore, the results suggest that the membrane-initiated signaling pathway modifies the DNA-binding activity of MET via phosphorylation and thus facilitates the genomic responses to JH. In summary, this study reveals an interplay of genomic and nongenomic signaling mechanisms of JH.

Oostatic peptides

Oostatic peptides are organic molecules, which influence an insect reproduction due to a regulation of the eggs development. It was proved that decapeptide-H-Tyr-Asp-Pro-Ala-Pro-Pro-Pro-Pro-Pro-Pro-OH (YDPAPPPPPP)-isolated from mosquito Aedes aegypti, inhibits trypsin activity in the midgut of the mosquito. Therefore, it was named trypsin-modulating oostatic factor (Aea-TMOF). Feeding the recombinant cells with cloned and expressed TMOF on the coat protein of tobacco mosaic virus (TMV) to mosquito larvae, caused larval mortality. The TMOF was therefore designed for usage as a new biorational insecticide against mosquito. Similarly, a hexapeptide-H-Asn-Pro-Thr-Asn-Leu-His-OH (NPTNLH)-was isolated from the grey flesh fly Neobellieria bullata. This peptide and some of its analogs inhibited trypsin-like synthesis by the midgut in female flies and was therefore entitled Neb-TMOF. Interestingly, the synthetic Aea-TMOF and mainly its C-terminus shorten analogs, including those containing D-amino acids or methylene-oxy isosteric bond, quickly and strongly inhibited the hatchability and egg development in the flesh fly N. bullata.

The Drosophila FTZ-F1 nuclear receptor mediates juvenile hormone activation of E75A gene expression through an intracellular pathway

Juvenile hormone (JH) regulates a wide variety of biological activities in holometabolous insects, ranging from vitellogenesis and caste determination in adults to the timing of metamorphosis in larvae. The mechanism of JH signaling in such a diverse array of processes remains either unknown or contentious. We previously found that the nuclear receptor gene E75A is activated in S2 cells as a primary response to JH. Here, by expressing an intracellular form of JH esterase, we demonstrate that JH must enter the cell in order to activate E75A. To find intracellular receptors involved in the JH response, we performed an RNAi screen against nuclear receptor genes expressed in this cell line and identified the orphan receptor FTZ-F1. Removal of FTZ-F1 prevents JH activation of E75A, whereas overexpression enhances activation, implicating FTZ-F1 as a critical component of the JH response. FTZ-F1 is bound in vivo to multiple enhancers upstream of E75A, suggesting that it participates in direct JH-mediated gene activation. To better define the role of FTZ-F1 in JH signaling, we investigated interactions with candidate JH receptors and found that the bHLH-PAS proteins MET and GCE both interact with FTZ-F1 and can activate transcription through the FTZ-F1 response element. Removal of endogenous GCE, but not MET, prevents JH activation of E75A. We propose that FTZ-F1 functions as a competence factor by loading JH signaling components to the promoter, thus facilitating the direct regulation of E75A gene expression by JH.

Study of oostatic peptide uptake and metabolism in developing ovaries of the flesh fly, Neobellieria bullata

The uptake and metabolism of the oostatic pentapeptide analogue of trypsin modulating oostatic factor (TMOF), H-Tyr-Asp-Pro-Ala-Pro-OH (5P), in ovaries of Neobellieria bullata (Parker) (Diptera: Sarcophagidae) were analyzed during their developmental stages. During selected stages of yolk deposition, the fate of [3HPro(3)]5P after its in vivo injection was compared to its uptake after in vitro incubation of dissected ovaries. The ovaries were analyzed from 30 s to 180 min after incubation. A detection sensitivity of 60-100 fmol of the labeled 5P was achieved using radio-high performance liquid chromatography. While the uptake of the applied radioactivity strongly depended on the stage of vitellogenesis, especially for the in vitro experiment, degradation of 5P was very quick and independent of whether the label was injected or incubated with the ovaries, regardless of the developmental stage of ovaries. No tracers of 5P were detected at 30 s after applying the labeled 5P in all tests.

Vitellogenesis in the hematophagous Dipetalogaster maxima (Hemiptera: Reduviidae), a vector of Chagas' disease

Oocyte extracts of anautogenous Dipetalogaster maxima were chromatographed on an ion-exchange column in order to purify vitellin (Vt), the main insect yolk protein precursor. Purified Vt (Mr ~443 kDa) was composed of four subunits with approximate molecular weights of 174, 170, 50, and 44 kDa. Polyclonal anti-Vt antibody, which cross-reacted equally with fat body extracts and hemolymph vitellogenin (Vg), was used to measure the kinetics of Vg expression in the fat body and the levels in hemolymph. In addition, morphological and immunohistochemical changes that took place in the ovary during vitellogenesis were analyzed. The study was performed between 2 and 8 days post-ecdysis and between 2 and 25 days post-blood feeding. During the post-ecdysis period, D. maxima showed decreased synthesis of Vg and concomitantly, low levels of Vg in hemolymph (4.5 x 10(-3) microg/microl at day 4). After a blood meal, Vg synthesis in the fat body and its levels in hemolymph increased significantly, reaching an average of 19.5 microg/microl at day 20. The biochemical changes observed in the fat body and hemolymph were consistent with the histological and immunohistochemical finds. These studies showed noticeable remodeling of tissue after blood feeding.

A DNA-binding protein, tfp1, involved in juvenile hormone-regulated gene expression in Locusta migratoria

A partially palindromic 15-nt. sequence upstream from a juvenile hormone-regulated gene (jhp21) was previously identified in the African migratory locust, Locusta migratoria. This sequence was proposed as a juvenile hormone (JH) response element (JHRE), and a protein that bound to it, as a transcription factor (TF). A yeast strain was constructed containing four tandem copies of the JHRE and after transfection with a cDNA library made to fat bodies from vitellogenic females, yeast one-hybrid experiments yielded sequences for four putative binding proteins. One of these sequences, corresponding to a transcript that was present in fat body irrespective of JH stimulation, encodes a 35kDa protein. This was designated tfp1 and appears to have a leucine zipper motif and a lipid-binding motif. Recombinant tfp1 bound to JHRE in electrophoretic mobility shift experiments and addition of tfp1 antibody in the binding reaction resulted in the disappearance or shift of TF. We suggest that JH induces the association of pre-existing proteins, including tfp1, to form an active complex, which binds to the JHRE upstream from jhp21 and regulates its transcription.

Pharmacological analysis of ovarial patency in Heliothis virescens

The insect oocyte sequesters nutritive proteins during patency, which is facilitated as a result of intercellular spaces occurring between follicular epithelial cells under the influence of juvenile hormone (JH). Patency was analyzed in the moth, Heliothis virescens, using a pharmacological approach, in which we used different JH homologues and chemicals that specifically target elements of two second-messenger pathways in vertebrates, the cAMP-dependent and inositol triphosphate/diacylglycerol signaling pathways. JH I and JH III evoked dose-dependent patency in H. virescens oocyte follicles, which was suppressed by the Na/K-ATPase inhibitor, ouabain. Patency was observed in follicular epithelial cells treated with either protein kinase C activator, PDBu, or protein kinase A activator, 8-Br-cAMP, by itself. The protein kinase C inhibitor, H-7, preferentially suppressed patency evoked by JH III, whereas the protein kinase A inhibitor, H89, preferentially suppressed that evoked by JH I. Additionally, patency was triggered by the adenylate cyclase activator, NKH 477, or peptide Gs-protein activator, cholera toxin, alone. Patency evoked by JH I was suppressed by the adenylate cyclase inhibitor, SQ 22,536, and GPAnt-2, a peptide antagonistic to Gs proteins that stimulates adenylate cyclase. Neither of these latter inhibitors, however, affected JH III-evoked patency. These results suggest that, in the process of patency in H. virescens ovarial follicles, JH I predominantly signals via the cAMP-dependent second messenger system, whereas JH III acts via the inositol triphosphate/diacylglycerol signaling pathway. Moreover, stimulation of patency by cholera toxin alone and inhibition of JH I-evoked patency by GPAnt-2, strongly suggest that JH I acts on the follicular epithelial cells via activation of G-protein, and-possibly-via G(s)-protein coupled receptor.

Ligand specificity and developmental expression of RXR and ecdysone receptor in the migratory locust

The ecdysone receptor(1), which is a heterodimer of EcR and the retinoic acid receptor (RXR) homolog, Ultraspiracle (USP), has been well studied in the evolutionarily advanced and derived insects, the flies and moths. It is less well characterized in more primitive insect orders such as the Orthoptera, which include the grasshoppers and locusts. Following our previous isolation from Locusta migratoria (Lm) of a shorter RXR isoform (now called LmRXR-S), the isolation of a second, longer isoform (LmRXR-L) that appears to have characteristics of a ligand-modulated nuclear receptor is reported here. Transcripts for both isoforms, as well as LmEcR, were detected in embryos and in females during oocyte maturation. After expression in E. coli, both LmRXR-S and LmRXR-L form heterodimers with recombinant LmEcR in vitro which bind the active ecdysteroid, ponasterone A. Binding was only weakly competed for by ecdysone agonists that are known to be toxic to more advanced insects, suggesting functionally significant divergence in EcR ligand binding domains. In contrast, the DNA binding domain of LmEcR is less divergent and a protein complex, presumably LmEcR/LmRXR, that bound the ecdysone response element, IR-1, was detected in locust nuclear extracts. Because of reports of juvenile hormone (JH III) binding to Drosophila USP and the observed in silico RXR-like ligand-binding site in LmRXR-L, the recombinant proteins were also tested for binding to JH III. Neither LmRXR isoform, alone or in combination with LmEcR, bound JH III at nanomolar concentrations.

Cloning, characterization, and developmental expression of a putative farnesoic acid O-methyl transferase in the female edible crab Cancer pagurus

Farnesoic acid methyl transferase (FAMTase) catalyzes methylation of farnesoic acid to yield the crustacean juvenoid, methyl farnesoate (MF). A full-length cDNA encoding a 275 amino acid putative FAMTase has been isolated from the mandibular organ of the female edible crab (Cancer pagurus) by reverse transcriptase-polymerase chain reaction in conjunction with cDNA library screening. A high degree of sequence identity was found between this and other putative crustacean FAMTases. Conceptual translation and protein sequence analysis suggested that phosphorylation could occur at multiple sites in the FAMTase. This finding is consistent with the recent observation that endogenous FAMTase activity in mandibular organ extracts can be regulated by phosphorylation in vitro. We demonstrated that the recombinant FAMTase could be expressed as a LacZ-fusion protein in Escherichia coli and have undertaken its partial purification from inclusion bodies. In an established assay system, the recombinant FAMTase lacked activity. Northern blotting demonstrated widespread expression of an approximately 1250-nucleotide FAMTase transcript in female C. pagurus tissues. Levels of FAMTase transcripts in mandibular organs of female C. pagurus were found to fluctuate during vitellogenesis and embryonic development. Throughout the spring of 2002, an HPLC-based method was used to measure hemolymph MF titers in more than 70 female specimens of C. pagurus, which segregated into "high MF" and "low MF" groups. The high MF titers, which occurred before or during early vitellogenesis, coincided with, or were preceded by, elevated levels of putative FAMTase mRNA in the mandibular organs.

Effect of age, diet, diapause and juvenile hormone on oogenesis and the amount of vitellogenin and vitellin in the twospotted stink bug, Perillus bioculatus (Heteroptera: pentatomidae)

Vitellogenic oocytes from Perillus bioculatus have two native vitellins, Vt1 and Vt2, with molecular masses of 553 and 228 kDa, respectively. The hemolymph contains a major vitellogenin, Vg, with a molecular mass of 528 kDa that consists of three apoproteins with masses of 177, 84 and 59 kDa, respectively. Antibodies to purified Vt2 reacted with ovary extracts, egg extracts and female hemolymph, but not with male hemolymph in immunodiffusion tests. Western blots showed that anti Vt2 reacted with both Vt1, Vt2 and with Vg. Vitellogenesis starts at an ovarian score of 12 at 2.4 days after emergence. The first cycle of egg development is completed in ovaries with a score of 112 at 7.7 days. During this 5.3 day period, the ovaries of a single female incorporated 1833 &mgr;g of protein to form vitellin. Vitellogenin levels start to increase in females 2.5 days after emergence and reached 17.8 &mgr;g/&mgr;l by 5.5 days. After 5.5 days vitellogenin levels fluctuated between 9.7 and 19.9 &mgr;g/&mgr;l. Most diapausing females contained no ovarian follicles in the vitellarium and their hemolymph contained less than 1 &mgr;g/&mgr;l of vitellogenin. Treating diapausing females with 1 &mgr;g of JH III increased vitellogenin levels over 120-fold. Insects maintained on a liver-based artificial diet had lower vitellogenin levels than the controls at all sample times and did not show an increase in vitellogenin concentration until 11.5 days. Treating insects on the artificial diet with 10 &mgr;g of JH III elevated vitellogenin levels to about a fourth of that found in prey-fed insects of a comparable age. This suggests that females fed the artificial diet have low levels of essential materials needed for vitellogenin production.

Role of juvenile hormone in the synthesis and sequestration of vitellogenins in the red cotton stainer, Dysdercus koenigii (Heteroptera: Pyrrhocoridae)

Investigations were carried out to determine the role of juvenile hormone (JH) and 20-hydroxy ecdysone in the synthesis and uptake of vitellogenins, which were earlier identified, purified and characterised, in Dysdercus koenigii. The concentration(s) of vitellogenin(s) in fat body, haemolymph and that of vitellin(s) in ovary were significantly lower after chemical allatectomy at eclosion. In addition, at 70 h after emergence, chemical allatectomy reduced ovarian vitellin concentration, but vitellogenin levels remained normal in the fat body and haemolymph. The haemolymph vitellogenins were not incorporated into oocytes in such insects. Administration of JH-III at 20 h after allatectomy restored vitellogenin levels in the fat body and haemolymph, but the ovary failed to incorporate the available vitellogenins from haemolymph in such insects. However, when JH-III was administered twice, one at 20 h and then at 70 h after allatectomy, vitellogenin concentrations in fat body and haemolymph and also vitellin concentrations in ovary approached control levels. It is suggested that JH has two separate roles, one in vitellogenin synthesis and the other in uptake. 20-hydroxy ecdysone had no apparent role in either vitellogenin synthesis or uptake in D. koenigii.

Do thyroid hormones function in insects?

Earlier work demonstrated that phenoxy-phenyl compounds such as fenoxycarb and thyroxine mimicked the effects of JH III in causing a reduction in volume of the follicle cells of Locusta migratoria. While these compounds were only moderately effective, a derivative of thyroxine, 3,3',5-triiodothyronine (T3) was as effective as JH III, and T3 has been shown to bind to the same membrane receptor and activate the same pathway as JH III. The current paper shows that other thyroxine derivatives vary in activity. 3,3', 5'-Triiodothyronine (reverse T3) is inactive. 3,5-Diiodothyronine (T2) is more active than JH III, while its relatives (iodines at 3', 5' or at 3,3') are inactive. When follicles are exposed in vitro to rhodamine conjugated T3, the fluorescent compound can be seen to enter the cells and accumulate there: this process is inhibited by cycloheximide or by a temperature of 0 degrees C. The accumulation is antagonised by JH III but not JH I (which does not bind to the JH III membrane receptor) and by an antiserum raised against the putative membrane receptor protein. The action of T3, but not T2, is inhibited by 6-n-propyl-2-thiouracil or by aurothioglucose, both known to inhibit deiodinases. The activity of T3, but not of T2, increases with time of exposure to the follicle cells. These facts suggest that T3 enters the cells by receptor mediated endocytosis and is converted to a more active compound. Immunoreactivity to T3, but not thyroxine, can be detected in the haemolymph of locusts, and the titre varies slightly with the gonotrophic cycle. The food shows immunoreactivity for both thyroxine and T3. These findings suggest that thyroid hormones are ingested by locusts and have the potential to be used as hormonal signals in the control of egg production.

The modes of action of juvenile hormones: some questions we ought to ask

This paper argues that the current dogma that juvenile hormones are structurally unique and constitute a family of derivatives of farnesoic acid which are produced by the corpus allatum (CA), secreted into the hemolymph, frequently transported by binding proteins, enter cells by diffusion across the cell membrane and there the products of the CA interact in some way with the genome, probably via nuclear receptors of the steroid superfamily, may not be tenable. It does so by examining the following questions. How many JHs are there? Are there other sources of JH in insects? Are there non-farnesoids with JH activity in insects? How does JH get into cells? Is the product of the CA the effective hormone? How many modes of action are there? How many receptors are there?

Changes in protein kinase C during vitellogenesis in the crayfish Cherax quadricarinatus--possible activation by methyl farnesoate

During ovarian maturation in the crayfish Cherax quadricarinatus, changes in ovarian protein kinase C (PKC) isoenzymes take place in parallel to yolk accumulation (as shown by immunoblot analysis). Significant changes were recorded in the amounts of specific isoenzymes and in their distribution between the cytosol and the membranes. Ovarian maturation was accompanied by the appearance of high- and low-molecular-weight immunoreactive PKC isoenzyme species. Among the isoenzymes tested, PKC alpha was the most clearly activated during ovarian maturation, as shown by significant translocation from the cytosol to the particulate fraction and the appearance of high-molecular-weight species. Moreover, a similar picture was obtained in the ovaries of intersex individuals upon induction of secondary vitellogenesis by androgenic gland ablation. Immunohistological staining showed PKC alpha to be localized mainly in the cytosol of premature oocytes, whereas in later maturation stages, it was concentrated around the nucleus in a vesicular structure and in the oocyte membrane. In secondary vitellogenic stages, PKC was localized in the plasma membrane and apparently in follicular cells. In addition, its activity was demonstrated by in vitro phosphorylation assays of a crayfish ovarian homogenate. Activation of total PKC phosphorylation of histone, an external substrate, was induced by phosphatidylserine plus 12-O-tetradecanoylphorbol-13-acetate (TPA) or methyl farnesoate. Both TPA and methyl farnesoate stimulated activation of PKC alpha in organ culture, causing its translocation from the cytosol to the membranes and inducing autophosphorylation of threonine residues. The changes in PKC isoenzymes during ovarian maturation in the crayfish suggest their involvement in this process as well as a possible regulatory role for methyl farnesoate through a direct effect on some PKC isoenzymes.

Juvenile hormone titers, juvenile hormone biosynthesis, ovarian development and social environment in Bombus terrestris

The effects of the social environment and age on juvenile hormone (JH) and reproduction were investigated by measuring ovarian development, hemolymph levels of JH III, and rates of JH biosynthesis from the same individual bumble bees (Bombus terrestris). Differences in social environment were associated with differences in rates of JH biosynthesis, JH titer and ovarian development. Young queenless workers had a higher rate of JH biosynthesis, JH titer and ovarian development than queenright (QR) workers of similar age. Dominant workers in QR colonies had a higher rate of JH biosynthesis, JH titer and ovarian development than low ranked workers of similar size. There was a positive correlation between JH titer and ovarian development, but no correlation between rate of JH biosynthesis and ovarian development or between JH biosynthesis and JH titer. Both JH titer and rate of JH biosynthesis increased with age from emergence to 3 days of age, but 6-day-old workers, egg-laying workers, and actively reproducing queens had high JH titers and highly developed ovaries but low rates of JH biosynthesis. These results show that reproduction in B. terrestris is strongly affected by the social environment and the influence of the environment on reproduction is mediated by JH. Our data also indicate that the rate of JH biosynthesis measured in vitro is not a reliable indicator of JH titer or ovarian development in B. terrestris; possible reasons are discussed.

Juvenile hormone effect on DNA synthesis and apoptosis in caste-specific differentiation of the larval honey bee (Apis mellifera L.) ovary

Caste-specific differentiation of the honey bee ovary commences in the last larval instar. In this process, formation of germ cell clusters by synchronous and incomplete mitoses occurs in the queen ovary, whereas in the worker ovary programmed cell death is the dominant feature. BrdU and TUNEL labeling were used to study dynamics of cell proliferation and apoptosis-dependent DNA degradation in ovaries of naturally developing queens and workers, as well as in juvenile hormone-treated worker larvae. Cell proliferation in ovaries of last-instar queen larvae generally exceeded that in workers, except for the late feeding phase. This inversion in cell proliferation patterns coincided with the onset of apoptosis in worker ovaries, as evidenced by TUNEL labeling. Juvenile hormone application to early-fifth-instar worker larvae had two noticeable effects. First, it diminished the number of S-phase nuclei in ovaries of late feeding-phase workers, bringing them to queen-like levels. Second, it prevented the induction of apoptotic DNA degradation. Caste-specific regulation of cell division in connection with programmed cell death can thus be attributed to the previously described differences in juvenile hormone titer in queen and worker larvae, adding a new facet to this hormone's multiple functions.