Epidermal cell development during the pupal-adult metamorphosis of Hyalophora cecropia

Cuticular cavities: storage chambers for cyanoglucoside-containing defensive secretions in larvae of a Zygaenid moth

As a defensive reaction against predators the larvae of Zygaena trifolii Esper. 1783, release highly viscous fluid droplets out of cuticular cavities. The fluid appears on the cuticular surface upon contraction of the irritated segments, with no specialized muscles being involved. Two morphologically different types of cavities have been found: the larger ones are located beneath pigment spots, the smaller ones occupy the remaining surface except in the ventral region. Both types have complicated cuticular opening structures. The defensive fluid contains the cyanoglucosides linamarin and lotaustralin, the amino acid beta-cyano-L-alanine, proteins and water. Although a considerable amount of fluid (3-6 microliter per sixth-instar larva) is stored in the cuticle, fine structural examinations of the epidermis do not show any specific cells or cell areas with morphological adaptations for secretion. Further, there do not exist any major cytological differences between the cells below the cavities and in the ventral region, where those cavities are absent.

The morphology of the honey bee (Apis mellifera L.) venom gland and reservoir

Hymenopteran venom glands are epidermal glands that have evolved from female accessory reproductive glands. In the honey bee, Apis mellifera L., the venom gland shows many of the fine structural features of primitive glands. A honey bee venom gland is a simple, long, thin, distally bifurcated structure, opening into an ovoid reservoir. Along most of the length of the gland are similar secretory units that have four major components (secretory cells, duct cells, ducts, and end apparatuses), except in the part of the gland proximal to the venom reservoir, where the secretory units resemble those around the venom reservoir. In the latter secretory units a funnel structure occurs between the duct (which is shorter than that of the secretory units of the gland) and the end apparatus. This funnel may be important in protecting the secretory cells around the reservoir from the cytolytic activity of the complex chemical mixture constituting the venom.

mRNA populations during wing development in the silkmoth Antheraea polyphemus

Pupal wing tissue of the American silkmoth Antheraea polyphemus has been used as a model system to study 20-hydroxyecdysone and juvenile hormone control of cuticle protein synthesis. Juvenile hormone does not affect either the content or rate of synthesis of RNA and protein of the wing tissue. both of which show linear increases during the first few days of hormonal treatment. Based on the fractionation of total RNA on oligo-dT columns the percent of mRNA remains the same throughout development after both hormone treatments. However, both the amount of poly-A+ RNA in the wing tissue, and its content of poly-A show considerable increases as a function of development. The products of translation of the various poly-A+ RNA populations in the cell-free wheatgerm system have been analyzed by one- and two-dimensional gel electrophoresis and fluorography. Qualitative changes occur during the first 24 h; the production of a mRNA coding for a protein of approx. 40 000 dalton is stimulated and the production of a mRNA coding for a protein of 29 000 dalton is greatly reduced. Only a few differences are observed between samples from the 2 hormone treatments. Over the next 5-15 days of development mainly quantitative changes are observed. Juvenile hormone application results in quantitative changes in specific mRNAs, but no new mRNAs unique to juvenile hormone action are observed. The data are consistent with the concept that in altering the epidermal developmental program, juvenile hormone is apparently modulating the action of 20-hydroxyecdysone.

Correlations between epidermal cell structure and endogenous hormone titers during the fifth larval instar of the tobacco hornworm, Manduca sexta

Epidermal cell morphology and cuticle production in Manduca sexta are directly influenced by both ecdysterone and juvenile hormone. Up to day 6 of the last larval instar, post-molt endocuticle is continuously deposited even though cells undergo a partial and temporary separation from the overlying cuticle at the time when a small ecdysteroid peak is detected (approximately day 3.5). At about days 6--7 when another, larger ecdysteroid peak is present, apolysis occurs accompanied by the appearance of edcysial droplets. Following apolysis, layers of pupal cuticle are deposited. Increased quantities of rough endoplasmic reticulum characterize the epidermis at times of peak endocuticle deposition (day 3, larval cuticle; day 9, pupal cuticle). Dense pigment inclusions are found in epidermis from the day of ecdysis to the last larval instar until they are eliminated 5 days later. These dense bodies migrate from cell apex to base in the absence of juvenile hormone (or in the presence of a negligible amount of juvenile hormone) and probably contain insecticyanin.

Effects of ecdysone and juvenile hormone on epidermal cell development in Hyalophora cecropia

Pupae of Hyalophora cecropia were injected with various doses of beta-ecdysone (molting hormone) or juvenile hormone and the epidermal cell ultrastructure was then studied with the electron microscope. The hormonal effects were rapidly manifested and appeared to be cell specific and dose dependent. The initial response to both hormones was an outward blebbing of the apical plasma membrane. Large doses of beta-ecdysone elicited both precocious cuticle deposition and premature autophagic vacuole formation. Juvenile hormone prevented the appearance of the autophagic vacuoles which normally preceded cell differentation into cells capable of adult synthesis. After prolonged exposure to juvenile hormone, there appeared to be an exaggerated separation of the epidermal cells at the basal region suggesting that the juvenile hormone may act at the membrane level.