Histochemical and ultramorphological visualization for storage molecules in trophocytes at postembryonic developmental stages of Bombyx mori (Lepidoptera: Bombycidae).

The fat body originates from mesoderm during embryogenesis and it exists through the developmental stages in insects. It is equivalent to vertebrate adipose tissue and liver because it has multiple metabolic and storage functions. The fat body controls the synthesis, storage and metabolism of glycogen, lipid and protein, and it plays a major role in immune and endocrine systems and detoxification processes. Main cells of fat body, which accomplish these vital functions are trophocytes. In this study, we aimed to determine the reserve molecules like glycogen, lipid, protein and uric acid accumulated in the fat body at postembryonic developmental stages of Bombyx mori. For this purpose, we used specific histochemical techniques to determine glycogen, lipid, protein and uric acid molecules. We determined that glycogen contents are stored from the 3rd larval stage while proteins and uric acids are stored from the 4th larval stage. We also detected that the amount of glycogen, lipid, protein and uric acid increase gradually throughout the larval stage and then these molecules decrease gradually as they are used in the pupal stage. Fat body biology may require further investigations on the underlying function of the fat body formation throughout the developmental stages. It can also be used as a model in research of metabolic disorders and immune diseases.

Demonstrating the general structure and cell types of the fat body in Blatta orientalis (Oriental Cockroach).

The fat body is a tissue that originates from mesoderm in insects. It consists of several cell types. The basic cell of the fat body is trophocyte. Glycogen, protein and lipid which are required for energy are stored in these cells. Mycetocyte, urocyte, chromotocyte and haemoglobin cells are the other cell types which originate from differentiated trophocytes. Of the cells found in cockroaches, mycetocytes contain an endosymbiont species of bacteria while urocytes are specialized cells for storing and discharging uric acid. Oenocyte, which is not the fat body cell type but associated with epidermis and the fat body cells, is also found in cockroaches. In this research, the fat body distribution was shown for the first time in three selected sections (thorax, beginning and end of abdomen) in all stages of Blatta orientalis (Linnaeus, 1758). In addition, the fat body cell types and distribution were determined by histological, histochemical and ultrastructural studies. As a result, trophocytes, mycetocytes, urocytes of the fat body and oenocytes which are related to the fat body were determined in B. orientalis. Also, it was revealed that the fat body content increased in the selected regions of the stages depending on the development. We hope that these findings will contribute to data about the fat body and give some directions to insecticide studies.

Characterization of fat body cells at different developmental stages of Culex pipiens.

The fat body, originates from mesoderm, has many metabolic functions which changes as the embryonic development of the insect progresses. It plays an important role in the intermediate metabolism and in the metabolism of proteins, lipids and carbohydrates. It has roles in synthesis, absorption and storage of nutrients from hemolymph. It is also responsible for the production of immunological system components, antibacterial compounds and blood clotting proteins. The most common type of fat body cells are trophocytes (the basic cells of the fat body) and oenocytes are found associated with the fat body. In this study, it is aimed at determining the cell types contained in the fat body of Culex pipiens at different developmental stages as well as identifying the molecules such as carbohydrate, protein and lipid contained in each of these cells. Knowing the regional distribution of the fat body cells and the concentration of its content at each developmental stage is important in understanding the process related to its physiology and it may help in fighting against the pest C. pipiens, which is a vector species for many contagious diseases observed in humans and other species. To achieve our goal, we have employed different histochemical techniques (fixatives and staining methods) for staining C. pipiens preparates of different developmental stages and analyzed the structure of the fat body, its distribution, its cell types and the macromolecular contents of the cells. We only observed trophocytes and oenocytes as fat body components in C. pipiens. The trophocytes had all the three macromolecules (lipids, proteins, carbohydrates) in the cytoplasm varying in concentration between the different regions and different stages. The oenocytes were observed below the integument as well as between the muscles in the larvae of Culex pipiens. They were present either as single cells or in clusters and also varied in size. Their cytoplasm was stained strongly for proteins when bromophenol blue staining was applied, but it was rather heterogeneous due to the lipid inclusions. On the contrary, oenocytes were not observed among the adult C. pipiens preparations.