Erwin Huebner

The Cell Biology of Vitellogenic Follicles in Hyalophora and Rhodnius

Insect oocytes assemble their protein yolk bodies by receptor-mediated endocytosis of specific extracellular proteins (Telfer, 1961; Anderson, 1964; Roth and Porter, 1964; other papers reviewed by Telfer, 1965; Engelmann, 1979; Hagedorn and Kunkel, 1979). The major constituent incorporated is the sex-limited hemolymph protein, vitellogenin, but smaller amounts of lipophorin and many other hemolymph proteins are also internalized (Telfer, 1960; Telfer et al., 1981a). In special cases, several apparent modifications of this general pattern have been described: In Drosophila melanogaster and related species a fraction of the total vitellogenin accumulated is apparently synthesized within the ovary (Bownes, 1980); in Hyalophora cecropia a secretory product of the follicle cells, now termed paravitellogenin, supplements the hemolymphderived proteins (Anderson and Telfer, 1969; Bast and Telfer, 1976; Rubenstein, 1979); the fine structure of Glossina austeni suggests that yolk in this species may be assembled primarily from follicle cell products (Huebner et al., 1975); and in some apterygotes fine structure implies that some yolk may be synthesized within the oocyte itself (Bilinski, 1977). While yolk formation in insects has thus evolved a certain amount of diversity, it is nevertheless clear that in most species vitellogenin synthesized by the fat body and transported through the hemolymph is the primary source of the protein that is amassed in the oocyte (reviewed by Engelmann, 1979; Hagedorn and Kunkel, 1979).

Dexrazoxane (ICRF-187) protects cardiac myocytes against doxorubicin by preventing damage to mitochondria

The clinically approved antioxidant cardioprotective agent dexrazoxane (ICRF-187) was examined for its ability to protect neonatal rat cardiac myocytes from doxorubicin-induced damage. Doxorubicin is thought to induce oxidative stress on the heart muscle, both through reductive activation to its semiquinone form, and by the production of hydroxyl radicals mediated by its complex with iron. Hydrolyzed dexrazoxane metabolites prevent site-specific iron-based oxygen radical damage by displacing iron from doxorubicin and chelating free and loosely bound iron. The mitochondrial stain Mito Tracker Green GM and doxorubicin were shown by epifluorescence microscopy to accumulate in the myocyte mitochondria. An epifluorescence microscopic image analysis method to measure mitochondrial damage was developed using the mitochondrial membrane potential sensing ratiometric dye JC-1. This method was used to show that dexrazoxane protected against doxorubicin-induced depolarization of the myocyte mitochondrial membrane. Dexrazoxane also attenuated doxorubichin-induced oxidation of intracellular dichlorofluorescin. Annexin V-FITC/propidium iodide staining of myocytes was used to demonstrate that, depending on the concentration, doxorubicin caused both apoptotic and necrotic damage. These results suggest that doxorubicin may be cardiotoxic by damaging the mitochondria and dexrazoxane may be protective by preventing iron-based oxidative damage.

Nurse cell-oocyte interaction in the telotrophic ovarioles of an insect, Rhodnius prolixus

Microinjection of intracellular tracers fluorescein, Procion Yellow, Lucifer Yellow and horseradish peroxidase unequivocally showed the syncytial structure of the tropharium and its interaction with the oocytes. The tropharium tip is a separate isolated compartment. Finger-like nurse cell projections comprising the syncytial tropharium interact via gap junctions along their abutting membranes and also via large cytoplasmic continuities at the central trophic core. The trophic cords connecting the tropharium to oocyte vary in diameter relative to oocyte stage. Continuity of the tropharium with the oocytes is lost at approximately 1000 micron oocyte length and the severed cords then regress from the oocyte to the tropharium base. Variation in cord diameters and timing of cord closure may account for the highly regulated sequential oocyte growth.

Comparative Spiralian Oogenesis—Structural Aspects: An Overview

Considerable variety exists in ovarian structure and cellular interaction in spiralians. During their development the eggs of Dwpatra cuprea , are associated with nurse cells; there are no follicle cells in this species. The nurse cells have prominent nuclei and connect to oocytes via cytoplasmic bridges through which ribosomes, mitochondria and other inclusions pass. More commonly, follicle cells surround a portion of, or entire, oocytes in many species of spiralians. Usually, as in Ilyanassa , they have a well developed compliment of organelles. The structure and distribution of organelles within follicle cells implies that they are functionally active, but precisely in what manner during oogenesis is poorly understood. Other cell types, such as Leydig and interstitial cells also seem to play a role in oogenesis. Within the oocyte, a host of components including yolk, lipid, mitochondria, ribosomes, membranous cisternae, cortical granules, etc. are accumulated. Autosynthetic yolk formation is prevalent among spiralians. Surface differentiation includes microvillar development. This may be uniform in some eggs or restricted to certain regions ( e.g. , the animal hemisphere) in other oocytes. Oocyte-follicle cell interactions change during oogenesis. The topographical association of the oocyte with other ovarian cells influences subsequent animal-vegetal polarity and other ooplasmic differences. Examples of ooplasmic localizations are discussed. Conventional EM has revealed no unusual cortical structure in many oocytes although occasionally microtubules and microfilaments are present.

Oocyte—follicle cell interaction during normal oogenesis and atresia in an insect

Analysis of the oocyte-follicle interface during an oogenesis cycle revealed the development of a complex cell-to-cell interaction. A variety of ultrastructural methods revealed the presence of numerous gap junctions between oocyte microvilli and follicle cell processes during previtellogenesis and vitellogenesis. Junctions were not present during atresia of chorion formation. Fluorescent dyes, fluorescein, Procion yellow, and Lucifer yellow, passed from injected oocytes into follicle cells at all stages except chorion formation and during atresia. The numerous gap junctions presumably play important roles in coordination of oocyte-follicle cell differentiation.

The Ultrastructure and Development of the Telotrophic Ovary

The production of a viable insect oocyte is achieved by an intimate interaction between the oocyte and various cell types during differentiation within the ovary. Functions such as organelle production, transport of cytoplasmic constituents, transport of yolk precursors, regulation of oocyte growth, production of egg envelopes, and others are carried out by these accessory cells. Meroistic ovaries exemplify the most complex forms of interaction within the insects (Gross, 1901; Telfer, 1975). Gross (1903) subdivided the meroistic into the polytrophic and telotrophic (sometimes referred to as acrotrophic) types.

Follicular modulation during oocyte development in an insect: Formation and modification of septate and gap junctions

Alterations of follicle cell contacts and shape play a key role in the regulation of the flow of yolk precursors to the oolemma during oogenesis. Detailed study of an oogenesis cycle showed the formation, location, and modification of junctions in closely apposed previtellogenic follicle cells through to the widely separated vitellogenic follicle cells that retain contacts via arm-like extensions. Analysis with light and electron microscopy, lanthanum tracing, and freezeetch methods revealed that elaborate pleated septate junctions are formed during previtellogenesis. During early vitellogenesis these junctions disassemble and reassemble in localized contact areas during mid-to late vitellogenesis. Numerous E-type gap junctions of varying size also form between follicle cells. With altered cell contacts, these also dissemble. By mid-to late vitellogenesis, gap junctions, septate junctions, and desmosomes are localized to the hihgly folded interdigitating contact areas between the arm-like follicle cell extensions. The modulation of follicle cell junctions is an essential prerequisite for patency which is necessary for vitellogenesis.

Activation of lobster hemocytes for phagocytosis

Abstract Activation of lobster (Homarus americanus) hemocytes for phagocytosis of sheep erythrocytes (SRBC) was demonstrated in vitro by incubation with lipopolysaccharide and by prolonged adherence to glass coverslips. Morphological changes, which preceded phagocytic activation, were detected by phase microscopy and Nomarski interference microscopy. These included spreading, the formation of filopodia and pseudopodia, granular darkening and dispersion, and vacuolation. Hemolymph serum opsonin greatly enhanced the recognition and phagocytosis of SRBC by activated hemocytes. Increases of 15 to 20 times background levels were observed both in the proportion of hemocytes which were actively phagocytic, and the percent of rosette-forming hemocytes. This suggested that the enhanced phagocytosis was the result of both the recruitment of a quiescent precursor population during activation, and an increase in the availability of opsonin binding sites on hemocyte membranes.

The ultrastructure of the female accessory gland, the cement gland, in the insect Rhodnius prolixus

The cement gland of Rhodnius prolixus is an epidermally derived tubular gland consisting of a distal synthetic region and a proximal muscular duct region. The synthetic region consists of numerous secretory units joined to a central chitinous duct via cuticular ductules. Proteinaceous secretion, synthesized by the goblet-shaped secretory cell, passess through the delicate cuticular lattice of a ductule-end apparatus and out through fine ductules to the central duct. Secretory cells are rich in rough endoplasmic reticulum and mitochondria. Light microscopy, SEM and TEM reveal the delicate lattice-like end apparatus structure, its formation and relationship to the secretory cell. The secretory cell associates via septate junctions with a tubular ductule cell that encloses a cuticle-lined ductule by forming an elaborate septate junction with itself. The ductules are continuous with the cuticle lining of the large central duct that conveys secretion to the proximal area. The proximal muscular duct has a corrugated cuticular lining, a thin epithelium rich in microtubules and thick longitudinal, striated muscles which contrast during oviposition, forcing the secretion out. Histochemistry and electrophoresis reveal the secretion as proteinaceous.

Histological and ultrastructural specialization of the digestive tract of the intestinal air breather hoplosternum thoracatum (teleost)

The digestive tract of Hoplosternum thoracatum consists of an esophagus, gastric area, anterior digestive intestine with elaborate folds, digestive intestine with decreasing folds and thin, smooth‐surfaced respiratory intestine. The upper tract has a mucoid columnar lining which is gently folded, whereas the gastric area has numerous pits opening into the tubular secretory glands. Striated muscle comprises the anterior muscularis but is replaced by inner circular and outer longitudinal smooth muscle layers in the gastric region. The digestive intestinal mucosa is elaborately folded, consisting of columnar cells with prominent brush borders. Mucosa, submucosa, circular and longitudinal muscularis and serosa layers are present throughout the tract. Goblet cells occur in both the digestive and respiratory intestine. Major changes that appear in the respiratory intestine are a drastic reduction in mucosa epithelial thickness and the penetration of an elaborate capillary bed into the epithelium. The other basic layers are not significantly reduced in thickness. The air‐blood barrier consists of the thin epithelium, basement lamina and very thin capillary endothelium. Regional cellular composition and ultrastructural features are correlated with respective digestive and respiratory functions.