Synthesis and deposition of oocyte envelopes in the Colorado beetle, Leptinotarsa decemlineata Say

Venom gland of Pachycondyla striata worker ants (Hymenoptera: Ponerinae). Ultrastructural characterization

Morphological data concerning the venom gland of worker ants of Pachycondyla striata revealed that this gland consists of three distinct regions: an external secretory portion, composed by a secretory filament that bifurcates in order to give rise to other two filaments; an internal secretory portion, represented by the convoluted gland; and a storage portion, represented by a sac-shaped reservoir. The ultrastructural analysis showed that the reservoir is enveloped by a simple pavementous epithelium, coated internally with a cuticle. The external secretory portion is composed by cells forming a simple cubic epithelium, in which the apical portion presents numerous microvilli while the basal portion of the cells shows infoldings of the plasma membrane containing numerous mitochondria. The convoluted gland possesses cells of irregular morphology with nuclei containing condensed chromatin, suggesting inactivity. However, these cells are in fact undergoing secretory activity, which is probably added to the final secretion produced by the gland. The cytoplasm of these cells contains several elements distributed therein, such as ribosomes and polyribosomes, lipid droplets, and protein inclusions in the form of crystals, thus suggestive of protein storage, which would be used by the insect when metabolically required.

Structural and biochemical analysis of the Leptinotarsa decemlineata (Coleoptera; Chrysomeloidea) crystalline chorionic layer

The developmental aspects of the Leptinotarsa decemlineata crystalline chorionic layer (CCL) morphogenesis, its composition and its supramolecular structure were studied. The mature Leptinotarsa decemlineata eggshell consists of the vitelline membrane and the CCL, while the follicle cell remnants following their degeneration after oogenesis completion constitute the outer chorionic layer. The vitelline membrane and the CCL layers are formed through continuous material deposition from the follicular epithelium, whereas the main morphogenic factor during most insect eggshell formation, namely the follicle cell and oocyte microvilli, are seemingly involved only in vitelline membrane formation. Analysis of the CCL morphogenesis showed that this layer is assembled from a fiber-like pre-crystalline material, which accumulates at the vitelline membrane-follicle cell interface. The mature CCL is about 1 microm thick and exhibits a periodicity of approximately 10 nm, while computer image analysis studies of thin-sectioned CCL revealed the existence of crystalline layers parallel to the CCL surface. Finally, SDS-PAGE-electrophoresis of purified CCLs showed that this crystalline layer is of a proteinaceous nature and is most likely composed of 3-5 polypeptides with a molecular weight ranging in between 28-60 kDa. Overall, these data exemplify for the first time the nature and supramolecular arrangement of a crystalline layer and its constituent molecules in Coleoptera.

Developmental studies of vitellogenesis in a dipteran insect, Chironomus thummi

Vitellogenesis of developing oocytes of a Dipteran insect Chironomus thummi has been investigated. The onset of yolk deposition is marked by the differentiation of the oolemma including the formation of microvilli and endocytosis. These changes are accompanied by the appearance of small electron dense granules, similar in density to the yolk platelets, arising through the sequential accumulation of material into the matrices of the multivesicular bodies (MVBs). These latter structures are produced in the previtellogenic oocytes of the pharate pupae and early pharate adults. Often the limiting membrane of the MVBs bears bristle coats resembling those of the coated vesicles of pinocytotic origin, suggesting that it is through the fusion with the pinocytotic vesicles that the accumulation of dense material in the MVBs results. That the Mvbs transform into structures resembling yolk granules is supported by statistical analysis which indicates that the decrease in the number of electron-dense MVBs coincides with the increase in the occurrence of small dense yolk granules. In the late pharate adult stage the yolk granules are considerably larger than those of earlier stages. It is during this period that at least one type of electron-dense granule occurs at the oocyte follicle cell border, and that these apparently contribute to the formation of the vitelline envelope. The results of the present study indicate that preformed oocytic elements, the MVBs, play a strategic role in the formation and arrangement of the yolk granules in Chironomus. Since these structures account for the bulk of the ooplasm, it appears that the MVBs are at least partly responsible for the correct ordering of the cytoplasmic constituents of the oocytes, which is critical for the proper development and differentiation of the embryo.