Joanna Michalik

Control of activity and regression of the silk glands in the last-larval instar of Galleria mellonella

Abstract The weight increase of silk glands in isolated larval abdomens is enhanced by brain implants which stimulate RNA and protein synthesis. It is proposed that, in intact last-instar larvae, a blood-borne factor from the brain promotes silk gland activity during the facultative feeding period. In the post-feeding larvae, some starving larvae and in isolated larval abdomens the silk glands regress. The regression is accelerated and the glands degenerate under the action of 20-hydroxyecdysone. This effect is not associated with an increase in protease and RN-ase activities. In the normal larvae, the protease activity increases gradually during the last instar to a maximum at the time of regression and drops in the degenerating glands. RN-ase activity is maintained at a high level in the fully active, regressing and degenerating glands The results indicate that regression and degeneration of the silk glands are caused by structural cell reorganization rather than by an appearance of cytolytic enzymes.

Brain factor fromGalleria mellonella (Lepidoptera) stimulating silk gland activity

Brain extracts from day 1–4 last instar larvae ofGalleria mellonella (Lepidoptera) stimulate RNA synthesis in cultured silk glands from day 3 last instar larvae. When the fibroin-synthesizing posterior parts of silk glands were incubated for 3 h in vitro in the presence of brain extract (0.1 brain equivalent), [3H]-uridine incorporation into RNA was stimulated more than twofold. The stimulating effect of brain extract showed a dose response relationship. It is suggested that the heat-resistant and protease-sensitive brain factor is a peptide.

Suboptimal Temperature-Dependent Changes in the Brain Development and Activity in Galleria mellonella Larvae

The development of Galleria mellonella larvae is strongly af- fected by suboptimal temperature (18°C). One-day-old last-in- star larvae react to 18°C with the arrest of further development for several months described as facultative larval diapause. The aim of this study was to find what type of changes, if any, in the brain correlate with the larval diapause induced by sub- optimal temperature. Morphological analysis demonstrated the gradual inhibition of brain development. Paraldehyde-fuchsin (PAF) staining revealed cyclicity in the activity of the medial neurosecretory cells (M-NSC) in the larval brain. SDS-PAGE was used to examine the brain proteins of larvae reared at 30°C and at 18°C. The rate of protein synthesis in the brain of the last instar larvae kept at 18°C, measured as L-( 35 S)methio- nine incorporation during 2-h incubation in vitro, was only about 40% of the value characteristic for this tissue during nor- mal development (at 30°C). Despite decrease in the rate of to- tal protein synthesis, suboptimal temperature induced an increase in the level of two major brain proteins: 112 and 84 kDa. In SDS-PAGE analysis, these two proteins appear 21-28 days after transfer to the lower temperature. Whether these proteins are specific for induction of larval diapause of Galle- ria mellonella remains to be further investigated. Arch. In- sect Biochem. Physiol. 38:66-73, 1998.