Steroid transport through the surface of the prothoracic gland cells in Galleria mellonella L

Body-fat sensor triggers ribosome maturation in the steroidogenic gland to initiate sexual maturation in Drosophila

Fat stores are critical for reproductive success and may govern maturation initiation. Here, we report that signaling and sensing fat sufficiency for sexual maturation commitment requires the lipid carrier apolipophorin in fat cells and Sema1a in the neuroendocrine prothoracic gland (PG). Larvae lacking apolpp or Sema1a fail to initiate maturation despite accruing sufficient fat stores, and they continue gaining weight until death. Mechanistically, sensing peripheral body-fat levels via the apolipophorin/Sema1a axis regulates endocytosis, endoplasmic reticulum remodeling, and ribosomal maturation for the acquisition of the PG cells' high biosynthetic and secretory capacity. Downstream of apolipophorin/Sema1a, leptin-like upd2 triggers the cessation of feeding and initiates sexual maturation. Human Leptin in the insect PG substitutes for upd2, preventing obesity and triggering maturation downstream of Sema1a. These data show how peripheral fat levels regulate the control of the maturation decision-making process via remodeling of endomembranes and ribosomal biogenesis in gland cells.

The structure of the antennal heart ofAedes aegypti(Linnaeus)

The structure of the antennal heart of Aedes aegypti (L.) (Diptera: Culicidae) was observed using light and electron microscopy. The antennal heart consists of several distinct regions including a single layer of columnar cells, the chamber walls, the valve, the z-body, the muscle fibres, and the connective tissue filaments. The columnar cells are structurally similar to secretory and osmoregulatory cells. Features of tendinous epidermal cells typically involved in the attachment of muscles to the cuticle can be observed in various areas of the antennal heart when it is examined as a whole. A model describing the pumping mechanism of the antennal heart in A. aegypti is presented.

Ultrastructure of prothoracic glands during larval-pupal development of the tobacco hornworm, Manduca sexta: a reappraisal

The structure of Manduca sexta prothoracic glands was investigated using a protocol that preserves membranes. During the last larval stadium, prothoracic gland cells increase in diameter, volume, protein content, and perhaps number, enhancing their capacity to produce ecdysteroids. The glands' strand-of-cells morphology, their in situ location, the presence of gap junctions between cells, and junctional foot-like structures within cells support previous findings that prothoracicotropic hormone stimulates ecdysteroidogenesis via Ca(2+)-induced Ca2+ release. A different method of tissue fixation from that previously used to investigate the ultrastructure of Manduca sexta prothoracic glands has revealed a significantly different ultrastructure. These new findings begin to define roles for endoplasmic reticulum and mitochondria in ecdysteroid synthesis and support the hypothesis that the glands secrete the steroid hormone via exocytosis. The structural dynamics of the glands are discussed in the context of the glands' function during Manduca sexta larval-pupal development.

Interactions between digitonin and bilayer membranes

The morphology of interactions between digitonin and cholesterol has been investigated. When precipitated from ethanolic solutions, digitonin-cholesterol complexes form in flat lamellar sheets. In contrast, when the complex is formed in a bilayer membrane, the membrane is deformed into corrugations of hemitubules. The polarity of the deformations formed in bilayer membranes is highly correlated with the direction of entry of digitonin into the membrane. We suggest that the morphology of digitonin/cholesterol hemitubules is dependent upon the complex being formed within a bilayer and, in addition, is not correlated with asymmetry of cholesterol concentration across the membrane.

Correlations between endocrine gland ultrastructure and hormone titers in the fifth larval instar of Manduca sexta

Correlations were made between endocrine gland ultrastructure and circulating hormone titers of Manduca sexta to investigate the mechanisms of hormone biosynthesis and secretion. Both the prothoracic glands (PTG), which secrete ecdysone, and the corpora allata (CA), which secrete juvenile hormone (JH), were studied. In the prothoracic glands, the intracellular spaces increase in area and reach their maximum size following the major ecdysteroid peak in the fourth and fifth larval instars. Within the intercellular spaces are multivesicular sacs (MVS), structures which are clusters of vesicles bounded by another membrane. Since these sacs are largely depleted of their internal vesicles after the second cycle of tropic hormone stimulates the PTG to secrete ecdysone, the MVS probably release a gland cell product at this time. In the CA, concentric whorls of smooth endoplasmic reticulum are present in larval glands, when the JH titer is high, but are absent from pupal CA when the JH titer is low. The peak of JH at Days 6-8 of the fifth larval instar occurs after an increase is seen in the neurosecretory cell axon diameters suggesting that the CA are stimulated by a brain hormone to release JH. The number of Golgi complexes increases in pupal CA and dense bodies are present in pupal but not larval glands. These Golgi complexes may be involved in the manufacture of lysosomal enzymes which degrade JH within the gland itself.