The Structure and Formation of Protein Granules in the Fat Body of an Insect

Abstract

In the larva of the butterfly Calpodes ethlius, the fat body begins to store protein in the form of granules at about 30 to 35 hours before pupation, at a time when the endocuticle is being resorbed. At least two sorts of granule can be distinguished. The first granules to arise are those within vesicles of the Golgi complex. These may increase in size by incorporating material from microvesicles at their surface and by coalescence with one another. Later, at about 10 hours before pupation, another sort of granule arises by the isolation of regions of the endoplasmic reticulum (ER) within paired membranes derived from Golgi vesicles. Several of these ER isolation bodies coalesce, with fusion of their outer isolating membranes. The ribosomes and membranes may then disappear and the granules become indistinguishable from the protein granules formed from Golgi vesicles, or the ribosomes may remain and be embedded in dense crystalline protein, forming a storage body for both protein and RNA. Mitochondria are isolated within paired membranes in the same way as regions of the ER. The isolated mitochondria also coalesce in a similar manner. When the inner membranes are lost, the structure of a group of isolation bodies is indistinguishable from that of a cytolysome. Isolation within paired membranes, as described here, may be of general importance in segregating regions of massive lysis or massive sequestration.

Surface Membranes, Golgi Complexes, and Vacuolar Systems

“…At the end of the fifth larval intermolt, the fat body of a caterpillar switches from larval synthesis and secretion to storage for re-utilization during pupal and adult development (9,27,28,39,42,45). The switch involves the selective removal of organelles and is induced by β-ecdysone in vitro (10).…”

“…Autophagic vacuoles, especially those in late stages containing RER, often fuse with endocytosed hemolymph protein to create mixed auto-and heterophagic vacuoles that go on to become storage granules. At the completion of autophagy, the fat body has been turned into a store for iron, protein, lipid, glycogen, and urate, everything needed for adult development (9,39,42,44).…”

Developmental Changes in the Late Larva of Calliphora Stygia Iv. Uptake of Plasma Protein by the Fat Body

“…Locke and Collins (1965, 1966 demonstrated that both sequestration of haemolymph protein and lysis of cytoplasmic organelles contribute to the development of protein granules in Calpodes. Exogenous proteins, such as horseradish peroxidases, were taken up from the haemolymph into the granules at a time when the blood protein level was decreasing.…”

An Electronmicroscopic Investigation of the Young Gametophyte of the FernBlechnum Spicant(L.) Roth.

“…That thcsc vesiclcs which lack ribosomes cnter into the proximal pole of the Golgi apparatus, is a fact known from other plant cells (Grovc et al, 1966;1970), from arthropods (Lockc. 8: Collins, 1965;Ncwstead & Dornfcld, 1965;Phillips & Swift, 1965;Bcams C% Sckhon, 1966;Kcssel, 1966 a), from echinoderms (Kesscl, 1966b), from aniphibia (Pcrry 6; Waddington, 1966) and from mammals (Essncr & …”