On the origin of Z-band material and myofilaments in myoblasts from the human atrial wall

Summary The origin of cardiac myofibrils in cells from the atrial wall in human embryos was studied. Z-band substance appears throughout the cytoplasm as irregular electron dense patches in a network of thin filaments. The thin and thick filaments are synthesized as separate units in the sarcoplasm and are later aggregated into myofibrils. Complexes of Z substance and thin filaments occur numerously at different stages of myofibrillar organisation. Thick filaments are formed in close proximity to free ribosomes and are later incorporated in an hexagonal pattern into the Z-band/thin filament complex.This work was supported by grants from The Norwegian Council on Cardiovascular Disease and from The Norwegian Research Council for Science and the Humanities     

Nuclear ultrastructure: Condensed chromatin in plants is species-specific (karyotypical), but not tissue-specific (functional)

Summary In contrast to mammalian cell nuclei those of plants display nearly an identical ultrastructure in all developmental stages and tissues. This indicates that the gross organization of chromatin is species-specific, but not tissue-specific and function-dependent. The species-specific nuclear ultrastructure is determined by the basic nuclear DNA content (2 C value). The higher the DNA content, the more the euchromatin remains in the condensed state during interphase, but to a lower coiling order than the heterochromatin.Some difficulties in the interpretation of electron micrographs of cell nuclei, and the possible role of repetitive DNA sequences in the karyotypical condensation of euchromatin in plants are discussed.     

The spermatogenesis of crustaceans. VII. Review of spermatozoon of the crayfish Astacus astacus (Malacostraca,Decapoda, Macrura,Reptantia)

The star-like spermatozoon of Astacus astacus consists of a spheroidal central body around which various prolongations of same, denominated spines, are arranged. In the interior of the gamete the following parts may be distinguished: (1) The acrosomic region, formed by a complex vesicle, or thick-walled, helmetshaped body, whose opening is orientated towards the nuclear region. In the interior of the vesicle different structures can be appreciated. (2) The nuclear region, which is formed by a large cupuliform nucleus limited by a double membrane. In the nucleoplasm numerous bundles of microtubules, mixed with noncondensated chromatin fibers, are found. (3) The laminar region, present in other Decapoda, is practically nonexistent. Within the spines of these spermatozoa, only microtubules can be observed. The morphology of this crayfish is similar to that presented by Brachiura, another group of Reptantia.     

Fine structure and metabolism of multiply innervated fast muscle fibres in teleost fish

Summary Both the fast and slow muscle fibres of advanced teleost fish are multiply innervated. The fraction of slow-fibre volume occupied by mitochondria is 31.3%, 25.5% and 24.6%, respectively, for the myotomal muscles of brook trout (Salvelinus fontinalis), crucian carp (Carassius carassius), and plaice (Pleuronectes platessa), respectively. The corresponding figures for the fast muscles of these species are 9.3%, 4.6% and 2.0%, respectively. Cytochrome-oxidase and citrate-synthetase activities in the fast muscles of 9 species of teleost range from 0.20–0.93 moles substrate utilised, g wet weight muscle^-1 min^-1 (at 15° C) or around 4–17% of that of the corresponding slow fibres. Ultrastructural analyses reveal a marked heterogeneity within the fast-fibre population. For example, the fraction of fibres with <1% or >10% mitochondria is 0,4,42% and 36, 12 and 0%, respectively, for trout, carp and plaice. In general, small fibres (<500 m²) have the highest and large fibres (>1,500 m²) the lowest mitochondrial densities. The complexity of mitochondrial cristae is reduced in fast compared to slow fibres.Hexokinase activities range from 0.4–2.5 in slow and from 0.08–0.7 moles, g wet weight^-1 min^-1 in fast muscles, indicating a wide variation in their capacity for aerobic glucose utilisation. Phosphofructokinase activities are 1.2 to 3.6 times higher in fast than slow muscles indicating a greater glycolytic potential. Lactate dehydrogenase activities are not correlated with either the predicted anaerobic scopes for activity or the anoxic tolerances of the species studied. The results indicate a considerable variation in the aerobic capacities and principal fuels supporting activity among the fast muscles of different species. Brook trout and crucian carp are known to recruit fast fibres at low swimming speeds. For these species the aerobic potential of the fast muscle is probably sufficient to meet the energy requirements of slow swimming.     

Diurnal changes in the fine structure of photoreceptors in an abalone,Nordotis discus

Summary The ultrastructure of the synapses in the brain of the monogenean Gastrocotyle trachuri (Platyhelminthes) is described. The synapses consist of one presynaptic terminal separated by a uniformly wide synaptic cleft, from one or more postsynaptic elements. The presynaptic terminals are characterized by the presence of paramembranous dense projections and associated synaptic vesicles. The postsynaptic elements while possessing membrane densities, are usually devoid of vesicles.The structure of the synapses in the brain of Gastrocotyle is compared to synapses from other platyhelminths.     

Effect of aging on the morphology and function of the thyroid gland of the cream hamster

Summary The effect of aging on the morphology and function of the thyroid gland of the cream hamster was studied by light and electron microscopy coupled with autoradiography or histochemistry.Morphologically, aging induces an accumulation of lysosomal dense bodies and a loss of the phagocytosis of colloid droplets after stimulation with TSH. Iodine uptake and organification occur normally and thyroglobulin synthesis, estimated by autoradiography with ³H-leucine, is not different from that observed in young animals. The basal T₄ and T₃ plasma levels are lower in the old animals. A low iodine diet administered for several months prevents the age related accumulation of lysosomal dense bodies. Hormone secretion seems to proceed by two different mechanisms; phagocytosis of colloid droplets, the classical mechanism that decreases with age, and an additional mechanism, probably micropinocytosis, that is maintained during the whole lifespan.Presented at the First French Congress of Endocrinology, Montpellier, September 1980Work was performed under contracts n 3.4523.79 and n 3.4512.80 of the Fonds de la Recherche Scientifique Médicale, thanks to a grant of the Ministère Belge de la Politique Scientifique (Action concertée) and with the help of the Fondation Interuniversitaire pour la Recherche du Processus du Vieillissement, Belgium     

DNA Throughout the Single Mitochondrion of a Kinetoplastid Flagellate: Observations on the Ultrastructure of Cryptobia vaginalis (Hesse, 1910)

SYNOPSIS. Cryptobia vaginalis (Hesse 1910) occurs as long thin and short broad forms in the vagina of the gnathobdelliform leeches Haemopis sanguisuga (Linnaeus) and Hirudo medicinalis Linnaeus. Cytochemical staining for DNA and transmission electron microscopy of sectioned material indicate that in the thin forms the kinetoplast DNA (kDNA) is dispersed irregularly through the mitochondrial network ( pankinetoplastic condition) rather than concentrated in the adbasal region of the mitochondrion ( eukinetoplastic condition) as in trypanosomatids and most other kinetoplastid flagellates. Light-microscopic studies on the rare broad forms, however, suggest that these have conventional adbasal location of the kinetoplast. Binary fission appears to occur in the thin forms, suggesting that the dispersed kinetoplast is either highly polyenergid or lacks a genetic function. In other features of its microanatomy, C. vaginalis is a conventional kinetoplastid. The flagellate has an incomplete corset of pellicular microtubules which may have a role in the cortical contractility characteristic of the genus Cryptobia . Feeding is by pinocytosis of vaginal colloids through a microtubule-lined cytopharynx, possibly after binding to a prominent filament-coated preoral ridge. A pulsatile (contractile) vacuole is present and appears to be responsible for defecation as well as osmoregulation. Some individuals have elongate bacterial epibionts attached to the body in parallel with the cortical microtubules. All individuals have 2–8 spheroplast-like endobiotic bacteria in the prenuclear cytoplasm.     

Fetal mouse lung in circumfusion system cultures

Summary Fetal mouse lungs were cultivated, using the dual-rotary circumfusion system for tissue culture, and their histotypic development was surveyed for 75 days by phase-contrast and electron microscopy. Alveoli, terminal bronchioles and alveolar macrophages were photographed periodically with still and time-lapse phase-contrast microscopy. Their histotypic appearance was confirmed by electron micrographs of the 1- and 2 1/2-month-old specimens. These revealed typical alveoli surrounded by a basal lamina and composed of types I and II pneumocytes containing various lamellar-body forms within the type II cells, the alveolar lumen, and the alveolar macrophages. There was a shift from almost all type II cells in the 1-month-old alveoli to the presence of frequent type I cells as constituents of the alveoli in the 2 1/2-month-old cultures. The terminal bronchioles were tubules consisting of ciliated cells with Clara cells interspersed between them. The ciliated cells contained as many as 30 cilia or basal bodies per section and numerous microvilli. They were attached to each other and to the Clara cells by junctional complexes and accessory desmosomes which were generally in the apical ends of the cells. The Clara cells typically had glycogen granules interspersed between lamellae of the endoplasmic reticulum, contained numerous well dispersed mitochondria, occasional lysosome-like granules and crystalloid bodies which appeared to be tubular. Some Clara cells presented a moderately dense secretory granule in the center of the whorl of the endoplasmic reticulum. This work supported by Grant HL19684 from the National Heart and Lung Institute, National Institutes of Health. Pregnant Strong A mice were kindly supplied by Dr. Henry Browning of the Department of Anatomy.     

Fine structure of the spermatozoa of Chiton marginatus (mollusca: Amphineura), with special reference to nucleus maturation

The spermatozoon of Chiton marginatus is a long uniflagellate cell displaying structural features of “modified sperm.” The nucleus presents a conical shape with a long apical cylindrical extension. The chromatin is homogeneously dense. Scattered inside the condensed nucleus, a few nuclear lacunae are visible. The acrosomal complex is lacking. Some mitochondria are located in a laterofrontal structure side by side with the nucleus. The typical midpiece is absent. The cytoplasm forms a thin layer around the nucleus and the mitochondria. The proximal centriole is in a basal nuclear indent. The distal centriole serves to form the axoneme tail with the usual microtubular pattern. During nuclear maturation, the early spermatid nucleus is spherical and contains fine granular chromatin patches. The nuclear envelope shows a deposit of dense material at the base of the nucleus, forming a semicircular invagination occupied by a flocculent mass. In middle spermatid stage, the chromatin gets organized in filaments, coiled as a hank, attached over the inner surface of the basal thickening of the nuclear envelope. The nucleus starts to elongate anteroposteriorly. At the pointed apical portion of the spermatid, a group of microtubules is observed seeming to impose external pressure to the nucleus giving rise to the long apical nuclear point. The mitochondria have a basal position. Late spermatids have an elongated conical nucleus. The chromatin filaments are further condensed, and lacunae appear inside the nucleus. Some mitochondria migrate to a lateral position.     

Structural changes in bovine oocytes during final maturation in vivo

On the basis of structural observations bovine oocytes were grouped into four successive classed: 0, those before the luteinizing hormone (LH) surge; 1, those up to 8 h following the LH peak level; 2, those between 8 and 19 h after the LH peak level; and 3, those between 19 h after the LH peak level and ovulation. Oocytes in class 0 had mitochondria located in a generally peripheral position. Interior to the mitochondria were elements of rough endoplasmic reticulum (RER) and numerous membrane-bound vesicles which bore ribosome-like particles on their outer surface. The first visible changesater the LH peak level as seen in class 1 were the formation of the periviteline space with loss of contact between the cumulus cells and the oocyte, and ruffing of the nuclear envelope. These changes were followed b the resumption of meiosis as defined by germinal-vesicle breakdown (GVBD), the disappearance of RER, and the formation fo clusters of mitochondria in association with lipid droplets and elementrs of smooth endolasmic reticulum (SER). The period between 8 and 19 h following LH peak level (class 2) was characterized by intensive clustering of mitochoncria in association with lipid droplets and elements of SER, conversion of lipid, fusion of vesicles, and the appearance of ribosomes in the cytoplasm. During the final stage (class 3), the polar body was extruded, the mitochondria dispersed, and the majority of the organelles became located toward the center of the cell. The relatively organelle-free cortical region contained cortical granules immediately adjacent to the plasma membrane together with aggregates of tubular SER. The structural changes are discussed in the context of follicular steroidogenesis and oocyte developmental competence.