Structure and energy pathways of spermatozoa of the rove beetle Aleochara bilineata (Coleoptera, Staphylinidae).

The morphology of mature spermatozoa of the rove beetle Aleochara bilineata was examined by using scanning and transmission electron microscopy. They are about 1000 mum long and filiform. The acrosome and the nucleus are elongate and each about 20 mum long. A well-developed centriole adjunct region connects the nucleus with the sperm tail. The axoneme reveals the 9 + 9 + 2 pattern of the pterygote sperm flagellum. Two accessory bodies and two mitochondrial derivatives with paracrystalline inclusions are present. Cristae are reduced to the cortical zone of the derivatives. Cytochrome-c oxidase activity was detected within the cristae by DAB-reaction. The energy metabolism of the spermatozoa was investigated by using different inhibitors affecting the mitochondrial and cytoplasmic metabolic pathways. Sperm movement was used as an indicator for the utilization of ATP by the axoneme. In control experiments, the duration of motility was longer than 45 min. In the presence of atractyloside or potassium cyanide the motility duration was not affected. On the other hand, iodoacetic acid in the medium stopped sperm motility within 15 min. This indicates that sperm energy metabolism mainly depends on the glycolytic pathway.

Glycogen stores in mature ovarian follicles and young embryos of Drosophila: ultrastructural changes and some biochemical correlates.

During the last phase of oogenesis in Drosophila, large amounts of carbohydrates are taken up by the oocyte and become stored in the so-called beta-spheres whose ultrastructure and histochemical properties indicate that glycogen is the predominant storage form. The ultrastructure of the beta-spheres changes at the onset of embryogenesis: they become irregular in shape and the spacing of the granular substructures (beta-particles) increases. During the first 2 h of embryonic development, the total carbohydrate content decreases sharply while at the same time the protein content increases. Presumably the carbohydrate store is used to generate energy at this phase of development. Using monoclonal antibodies against an ecdysteroid-related antigen we showed that this antigen is mostly located in the beta-spheres. The asymmetrical distribution of the antigen in the egg (more concentrated near the posterior end) correlates with the same asymmetrical distribution of the beta-spheres in the mature follicle.

Oogenesis in the honeybee Apis mellifera: cytological observations on the formation and differentiation of previtellogenic ovarian follicles.

Oogenesis is known to be important for embryonic pattern formation. For this reason we have studied the early differentiation of the honeybee ovariole histologically, ultrastructurally, and by staining F-actin with rhodaminyl-phalloidin. At the anterior tip of the ovariole, stem cells are lined up in a single file; they are organelle-poor but contain characteristic electrondense bodies with lysosomal properties. The presence of these bodies in cystocytes as well as prefollicle cells indicates that both cell types may be derived from the apical stem cells. During later stages of oogenesis, the follicle cells differentiate cytologically in different regions of the follicle. The organization of the intercellular bridges between cystocytes derived from a single cystoblast has been studied in detail. The polyfusomes in the intercellular bridges of cystocyte clusters stain with rhodaminyl-phalloidin and hence contain F-actin. Later, when the polyfusomes begin to desintegrate, F-actin rings form which line the rims of the intercellular bridges. Actin might be recruited from conspicuous F-actin stores which were detected in the germ-line cells. The F-actin rings are dissembled some time before the onset of vitellogenesis when the nurse chamber has grown to a length of about 200 µm. At the basal side of the follicle cells (close to the basement membrane facing the haemocdele) parallel microfilament bundles encircle the ovariole. The microfilament bundles which are oriented mostly perpendicular to the long axis of the ovariole were first observed around the zone where the cystocyte divisions occur; after this phase the micro-filament bundles become organized differently in the follicle cells associated with the nurse cells and in the follicular epithelium of the oocyte.

From egg to pole cells: ultrastructural aspects of early cleavage and germ cell determination in insects.

Insect eggs are giant and very complex cells covered by an extremely resistant shell. Both the egg cell and surrounding eggshell express anteroposterior and ventrodorsal polarity. The molecular and cytoplasmic organization of both axes originates during oogenesis and leads to the production of an ooplasmic system which consists of euplasm and deutoplasm (yolk) and contains a nucleus as well as extranuclear determinants of maternal origin. Both are part of the store of information for early embryogenesis. In addition, the deutoplasm serves as raw material and early nutrient supply for building the embryo. The insect egg cell, which is arrested in the first maturation division when released from the ovary during oviposition, will be activated by different stimuli among different species to complete meiosis and start embryogenesis. The zygote nucleus undergoes a number of synchronous mitotic divisions leading to cleavage energids which initially form a syncytial blastoderm and subsequently the cellular blastoderm. In many insects, prior to blastoderm formation, polar granules (or oosome material) are incorporated in a single cell or a small number of cells which bud off at the posterior pole. These so called pole cells give rise to the primordial germ cells. Therefore, polar granules or the oosome material mark the germ line, and while structural counterparts of determinants of body pattern formation have so far not been found, the polar granules or oosome serve as an autonomous ooplasmic determinant for the pole or germ cells. Anteroposterior body polarity can arise independent of the germ plasm.

The cytoplasmic architecture of the egg cell ofSmittia spec. (Diptera, Chironomidae) : II. Periplasm and yolk-endoplasm.

1. Eggs of the midgeSmittia were investigated by light microscopy and transmission electron microscopy. This paper describes elements and architecture of periplasm and yolk endoplasm before the formation of pole cells. 2. The periplasm is coated externally by the oolemma and a multilayered egg shell. The periplasm consists of a cytoplasmic matrix rich in ribosomes; it contains mitochondria and ER cisternae, some annulate lamellae and an occasional Golgi complex. Microtubuli were demonstrated only rarely. Accumulations of a dense granulated substance resembling in its structure the oosome material were frequently observed. 3. The yolk endoplasm is a cytoplasmic network embodying proteid yolk particles, lipid droplets and accumulations of glycogen. The endoplasm is continuous with the periplasm and shows the same cell constituents. It may form between 3 and 7 cytoplasmic islands free of yolk particles. Rosette-shaped membranous structures in the yolk endoplasm are interpreted as nuclear envelope organizing centres. 4. Three carefully analysed eggs contained 2 nuclei each. both nuclei were situated in the posterior egg half. 5. Periplasm and yolk endoplasm are characterized by random distribution of cell elements. No zonation or special accumulations could be recognized. 6. The spatial distribution of the egg components studied did not indicate that any of these components could function as a determinant in embryonic pattern formation.

The cytoplasmic architecture of the egg cell ofSmittia spec. (Diptera, Chironomidae) : I. Anterior and posterior pole regions.

1. The egg of the Chironomid midgeSmittia spec. has been studied by light and electron microscopy. The present paper describes the fine structure of the anterior and posterior pole regions before pole cell formation. These regions were selected because of their functional involvement in body pattern determination and pole cell formation. 2. In the anterior cytoplasm (region I), 3 subregions can be recognized. A thin outer layer (Ia) which resembles the more equatorial periplasm (region II) but contains fewer organelles, covers a layer rich in mitochondria (Ib). This in turn borders a central cone of cytoplasm (Ic) which protrudes into the anterior face of the yolk endoplasm and frequently contains a cytaster-like structure but no chromatin. 3. The posterior cytoplasm (region III) includes a germ plasm or oosome similar to the type found in other lower dipterans. It is lens-shaped and contains a 3-dimensional network of electron-dense material. This material is probably granular, but may appear fibrous due to the spatial arrangement of the granules. 4. A series of organelles of multivesicular or lysosome-like appearance is described. These may be involved in the formation or utilization of proteid yolk. 5. Special structures or organelles restricted to the anterior pole region were not found. This might indicate that the role of this region in the switch from head formation to tail formation after UV irradiation could be due rather to differences in quantity or arrangement of ubiquitous structures than to qualitative differences between this and other egg regions. However, qualitative singularities cannot be excluded. They are obvious in the posterior pole region which contains the oosome.