Cuticle deposition in imaginal disks: effects of juvenile hormone and fat body in vitro

Effects of juvenile hormone on 20-hydroxyecdysone-inducible EcR, HR3, E75 gene expression in imaginal wing cells of Plodia interpunctella lepidoptera

The IAL-PID2 cells derived from imaginal wing discs of the last larval instar of Plodia interpunctella were responsive to 20-hydroxyecdysone (20E). These imaginal cells respond to 20E by proliferative arrest followed by a morphological differentiation. These 20E-induced late responses were inhibited in presence of juvenile hormone (JH II). From these imaginal wing cells, we have cloned a cDNA sequence encoding a P. interpunctella ecdysone receptor-B1 isoform (PIEcR-B1). The amino acid sequence of PIEcR-B1 showed a high degree of identity with EcR-B1 isoforms of Bombyx mori, Manduca sexta and Choristoneura fumiferana. The pattern of PIEcR-B1mRNA induction by 20E was characterized by a biphasic response with peaks at 2 h and 18 h. The presence of the protein synthesis inhibitor anisomycin induced a slight reduction in level of PIEcR-B1 mRNA and prevented the subsequent declines observed in 20E-treated cells. Therefore, PIEcR-B1 mRNA was directly induced by 20E and its downregulation depended on protein synthesis. An exposure of imaginal wing cells to 20E in the presence of JH II caused an increased expression of Plodia E75-B and HR3 transcription factors but inhibited the second increase of PIEcR-B1 mRNA. These findings showed that in vitro JH II was able to prevent the 20E-induced differentiation of imaginal wing cells. This effect could result from a JH II action on the 20E-induced genetic cascade through a modulation of EcR-B1, E75-B and HR3 expression.

Effects of a fat body extract on larval midgut cells and growth of lepidoptera

Treatment with fat body extract (FBX) from pupae of the tobacco hornworm, Manduca sexta, caused mortality in larvae of two pest lepidopterans, the gypsy moth, Lymantria dispar, and the cotton leafworm, Spodoptera littoralis. In FBX-treated larvae, the feeding rate was depressed, causing reduced weight gain and then larval death. Their midgut showed formation of multicellular layers of midgut epidermis, indicating stem-cell hyperplasia. Hence, the integument of FBX-treated larvae had a double cuticle, indicating induction of premature molting. But radioimmunoassay measurements confirmed that the amount of ecdysteroids in FBX was too low to be responsible for the molt-inducing effects observed after treatment with FBX. With midgut stem cell cultures in vitro, addition of FBX to the culture medium stimulated cell proliferation and differentiation in a concentration-dependent manner. This effect was compared with those of insect molting hormones, ecdysone and 20-hydroxyecdysone; an ecdysteroid agonist, RH-2485; and a purified protein from FBX (multiplication factor). This article describes the mode of action of FBX and possible interplay between fat body factor(s) and insect hormones in the development and metamorphosis of the insect midgut.

Juvenile hormone and juvenile hormone mimics inhibit proliferation in a lepidopteran imaginal disc cell line

The action of juvenile hormone (JH) and JH mimics have been examined in vitro by utilizing the imaginal disc-derived cell line, IAL-PID2. We have discovered that the cell line was responsive to JH and a variety of JH mimics. The most consistent response obtained in our studies was inhibition of cell proliferation, in the absence of 20-hydroxyecdysone (20E), which characteristically reduces cell proliferation in its own right in this cell line. JH-I, JH-III, methoprene, fenoxycarb, and farnesol significantly inhibited cell proliferation after 3 days of exposure of the cells in vitro to each of the compounds. Linoleic acid controls had no effect on proliferation in the cultures. The cell proliferation assay demonstrates the JH responsiveness of this cell line, but the concentrations of JH required were high compared to the concentrations of 20E needed for inhibition of proliferation in these cells.

Two polypeptide factors that promote differentiation of insect midgut stem cells in vitro

Isolated stem cells from the midguts of Manduca sexta and Heliothis virescens can be induced to differentiate in vitro by either of two polypeptide factors. One of the peptides was isolated from culture medium conditioned by differentiating mixed midgut cells; we used high performance liquid chromatographic separation and Edman degradation of the most prominent active peak. It is a polypeptide with 30 amino acid residues (3,244 Da), with the sequence HVGKTPIVGQPSIPGGPVRLCPGRIRYFKI, and is identical to the C-terminal peptide of bovine fetuin. A portion of this molecule (HVGKTPIVGQPSIPGGPVRLCPGRIR) was synthesized and was found to be very active in inducing differentiation of H. virescens midgut stem cells. It was designated Midgut Differentiation Factor 1 (MDF1). Proteolysis of bovine fetuin with chymotrypsin allowed isolation of a pentamer, Midgut Differentiation Factor 2 (MDF2) with the sequence HRAHY corresponding to a portion of the fetuin molecule near MDF1. Synthetic MDF2 was also biologically active in midgut stem cell bioassays. Dose response curves indicate activity in physiological ranges from 10(-14) to 10(-9) M for MDF1 and 10(-15) to 10(-5) M for MDF2.

The effect of juvenile hormone on the response of the Drosophila imaginal disc cell line Cl 8+ to moulting hormone

The Drosophila wing imaginal disc cell line Cl 8+ was used to investigate the interaction between juvenile hormone III (JH) and 20-hydroxyecdysone (20HE). Cell cultures were exposed to either or both hormones at a range of concentrations and cell growth was observed. JH was found to ameliorate the effects of 20HE on cell growth, even when added after the cells had been exposed to 20HE for 4 or 24h.

Genital tract growth factors from a moth, the tobacco budworm, Heliothis virescens

Development and maturation of the genital tract of the moth, Heliothis virescens, takes place within a few days in the pupal stage. The insect steroid hormone, 20-hydroxyecdysone (20E), essential during this period, stimulated testis sheath and fat body tissue to secrete factors that, in turn, stimulated growth and development of pupal spermducts and genital imaginal discs in vitro. Factors could be extracted in aqueous solution from tissues incubated for 24 h in media containing 1000pg/microliters 20E, and partially purified by chromatography on polyacrylamide gels. Ten active molecular weight fractions were separated from testis sheath extracts, and 9 from fat body extracts. Most fractions were labile to protease, although the activity of six of the fractions was also destroyed by lipase. Testis sheath, fat body tissue, and active fractions, caused partial development of the genital tract in vitro, as well as increased incorporation of [3H]methionine into precipitable protein and [3H]thymidine into nuclear material.

Insect tissue culture systems: models for study of hormonal control of development

The regulation of growth and development of insects is under endocrine control and involves both juvenile hormones and ecdysteroids. Neuropeptides are master regulators which control the secretion of these hormones. Most experiments in insect endocrinology have been conducted in vivo, but tissue culture methodology is playing an increasing role due to the great interest in simpler model systems for the study of complex processes that occur in vivo. The availability of appropriate media has allowed the culture of a variety of insect organs and cell lines of defined origin which have kept certain properties of the parent tissues. Tissue culture approaches have been useful for studying hormonal control of morphogenetic processes. Cell lines are particularly suited to the study of hormonally regulated mechanisms of macromolecular biosynthesis and gene expression. Thus, the value of in vitro analysis in studies of regulation of hormone production is now recognized. Results obtained from tissue culture allow more precise definition of the hormonal requirements of insect cells and tissues for growth and differentiation and might make possible the discovery of new growth regulators.

Hormonal control of growth and differentiation of insect tissues cultured in vitro

This paper reviews the effects of insect hormones on lepidopteran imaginal discs cultured in vitro. Beta-ecdysone showed that RNA and protein synthesis was required for evagination and cuticle deposition. In particular, studies with actinomycin D and cycloheximide (at nontoxic levels) showed that RNA and protein synthesis during the ecdysone-dependent period was essential for subsequent development. These findings support the hypothesis that stimulation of macromolecular synthesis is fundamental to the action of ecdysone on imaginal discs. The influence of beta-ecdysone on chitin synthesis was also examined. Beta-ecdysone stimulated uptake and incorporation of tritiated-glucosamine by cultured P.interpunctella wing discs. Addition of hexosamines to the culture medium had no influence on ecdysone-induced cuticle deposition, but inhibition of glucose-uptake by cytochalasin B prevented the formation of cuticle. The action of ecdysone on particular enzymes in the chitin pathway remains to be elucidated.timulated both evatination and cuticle deposition of wing discs of Plodia interpunctella(Hubner). However, evagination required a shorter exposure to ecdysone than did cuticle deposition. Cuticle deposition was obtained under the following conditions: (a) a 24-hour pulse of beta-ecdysone (0.5-5.0 mug/ml); (b) continuous treatment with 0.2 mug/ml beta-ecdysone; or (c) continuous treatment with 0.5 to 50.0 mug/ml beta-ecdysone in medium conditioned with larval fat body...

The influence of hemolymph-binding protein on juvenile hormone stability and distribution in Manduca sexta fat body and imaginal discs in vitro

The wing discs and fat body of Manduca sexta larvae contain enzymes (i.e. carboxylesterase and epoxide hydratase) that can convert the C18 juvenile hormone (JH) to the acid, diol and acid diol. No evidence of oxidative degradation was noted. In vitro studies suggest that JH can be compartmentalized within the cells of the fat body where it is less accessible to degradative mechanisms. Experiments utilizing a hemolymph-binding protein fraction (BPF) in vitro with fat body and imaginal discs indicate that the BPF retards the uptake of JH by tissues and its subsequent degradation by tissue enzymes. BPF also appears to protect JH from degradation by enzymes released into the medium. By these mechanisms the insect can maintain elevated JH titers for relatively long periods. Binding protein may also keep JH in solution in the hemolymph allowing its rapid distribution throughout the insect. The data suggest that the binding protein plays a key role in maintaining juvenile hormone titers.