[The post-ecdysis development of female fat tissue Locusta migratoria and its endocrine control]

The characterization of the fat bodies and oenocytes in the adult females of the sand fly vectors Lutzomyia longipalpis and Phlebotomus papatasi

The fat body (FB) is responsible for the storage and synthesis of the majority of proteins and metabolites secreted into the hemolymph. Oenocytes are responsible for lipid processing and detoxification. The FB is distributed throughout the insect body cavity and organized as peripheral and perivisceral portions in the abdomen, with trophocytes and oenocytes attached to the peripheral portion. Here, we investigated the morphology and the subcellular changes in the peripheral and perivisceral FBs and in oenocytes of the sand flies Lutzomyia longipalpis and Phlebotomus papatasi after blood feeding. In L. longipalpis two-sized oenocytes (small and large) were identified, with both cell types displaying well-developed reticular system and smooth endoplasmic reticulum, whereas in P. papatasi, only small cells were observed. Detailed features of FBs of L. longipalpis and P. papatasi are shared either prior to or after blood feeding. The peripheral and perivisceral FBs responded to blood feeding with the development of glycogen zones and rough endoplasmic reticulum. This study provides the first detailed description of the FBs and oenocytes in sand flies, contributing significantly towards are better understanding of the biology of such important disease vectors.

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.

Juvenile hormone controls previtellogenic proliferation of ribosomal RNA in the mosquito fat body

During the previtellogenic development of mosquito fat body cells, the nucleolus, the organelle responsible for producing ribosomes, enlarges threefold, reaching maximal size between 2 and 3 days after eclosion. The granular component of the nucleolus containing ribosomal precursors increases considerably as well. These signs of nucleolar activation correlate with the synthetic rate and accumulation of poly(A)- RNA (predominantly ribosomal RNA) in the fat body cells. The amount of poly(A)- RNA in fat body cells increases during the first 2 days after eclosion and then declines gradually. The rate of RNA synthesis exhibits similar kinetics, but both the rise and the decline are sharper than for the accumulation of RNA. All the characteristics of nucleolar activation, its enlargement, accumulation of poly(A)- RNA, and the increased rate of RNA synthesis, are blocked by removal of the corpora allata (CA) in newly eclosed adult females but could be restored by either implantation of CA or topical application of juvenile hormone III or its analog, 7-S-methoprene, to allatectomized females. Thus, previtellogenic activation of fat body nucleoli for ribosomal RNA production is controlled by juvenile hormone from the corpora allata.

Nuclear development in locust fat body: the influence of juvenile hormone on inclusion bodies and the nuclear matrix

The hormonal induction of vitellogenesis in insects and in oviparous vertebrates are prime models of gene regulation in eukaryotes. In vertebrates the process is under estrogenic control and normally confined to females, although males can be artificially induced. In locust in contrast, juvenile hormone (JH) is central to fat body development in both males and females, yet the response is strongly sex limited not only for vitellogenin production but also in terms of total protein, DNA and RNA synthesis and nuclear ploidy levels. To differentiate further possible sex and/or JH related developmental aspects in locusts, large-scale nuclear events were examined during normal adult maturation and in animals treated with antiallatropins and JH analogs. Fat body nuclei undergo extensive restructuring during normal development in both sexes. This included progressive nuclear enlargement, accompanied by extensive proliferation of nuclear matrix components and elaboration of complex inclusion bodies (NB). The isolated protein matrix was unusually complex relative to similar structures from vertebrates and the NB were firmly anchored to it. Although matrix proteins were qualitatively similar to those from other sources, as assessed by SDS polyacrylamide gel electrophoresis, several major matrix polypeptides, including lamins A and B, and components greater than 150 kD, fluctuated quantitatively during development and in concert with nuclear enlargement. The number and morphology of the NB were unrelated to sex, but increased in direct proportion to absolute nuclear volumes. All changes were more pronounced in females, where higher ploidy levels, larger nuclei and correspondingly more internal matrix elements occurred. Suppression of JH production by precocene prevented all foregoing nuclear changes, but re-exposure to methoprene rapidly induced normal development. The results are compared to analogous nuclear changes in steroid responsive vertebrate tissues.

Previtellogenic development and vitellogenin synthesis in the fat body of a mosquito: an ultrastructural and immunocytochemical study

We describe two phases, previtellogenic and vitellogenic, in the activity of the trophocytes in the fat body of the mosquito Aedes aegypti. The previtellogenic phase, leading to trophocyte competence to synthesize vitellogenin (Vg), occurred during the first 3 days after eclosion. This phase was characterized by enlargement and activation of the nucleoli, proliferation of ribosomes and rough endoplasmic reticulum (RER), development of Golgi complexes, and extensive invaginations of the plasma membrane. During the vitellogenic phase, initiated by a blood meal, Vg was first detected, by immunofluorescence, 1 hr after feeding. The intensity of the immunoreaction increased for the next 24 hr, was declining at 30 hr, and had disappeared by 48 hr. Vg synthesis was characterized ultrastructurally by the enlargement of the RER and the formation of dense secretion granules in Golgi complexes. These secretion granules were two to three times larger at the peak of Vg synthesis than at the beginning. The granules discharged their contents by exocytosis. Two electron microscopical immunocytochemical methods, immunoferritin and peroxidase-antiperoxidase, confirmed this pathway of Vg processing. For the first 12 hr after feeding. Vg synthetic organelles proliferated and the active nucleoli were multilobed; thereafter, while Vg synthesis continued, the nucleoli began to regress into compact bodies. Termination of Vg synthesis was marked by autophagical degradation of Vg synthetic and processing organelles.

Origin and formation of the royal fat body of the higher termite queens

The formation of the royal fat body was studied by electron microscopy in three species of higher termites (Macrotermes bellicosus, Macrotermes subhyalinus, and Cubitermes fungifaber). The swarming alate imago has a storage fat body typical of most insects. In non-physogastric young queens, during the fasting period, the adipocytes deplete their reserves and then, along with the increased vitellogenesis, acquire protein-synthesizing structures (R.E.R.). During the development of physogastry they progressively specialize in protein synthesis and secretion and undergo many cell divisions. The cytological change is paralleled by a spatial reorganization of the fat body. Observations on the transformation of imaginal adipocytes into royal adipocytes show that the royal fat body is derived from the imaginal fat body and not from the tracheal cells as previously claimed.