Reproductive role of attaching filaments on the egg envelope in Xenopoecilus sarasinorum (Adrianichthidae, teleostei)

Eggs of Xenopoecilus sarasinorum possess two distinct types of filaments on the surface of the egg envelope (chorion), long, attaching filaments restricted to the vegetal pole and weak, nonattaching filaments around the animal pole (micropyle). Both types are formed during oogenesis. After mature eggs were spawned through the urogenital pore, they were fertilized and hung in an abdominal concavity of the female. Oviposition never took place in the presence of embryos in the concavity because of the retardation of oogenesis. The loosely tangled tips of the attaching filaments that are retained within the ovarian cavity plug the urogenital pore by forming a hard complex with the epithelial cells. Into this plug structure that fuses with the inner wall of the urogenital pore, capillaries are provided. Within 5 days after the initiation of hatching, this plug degenerates and is released from the urogenital pore. Thus, in female X. sarasinorum, the reproductive cycle seems to be regulated by the physiological function ofthe plug structure formed by the attaching filaments in response to the presence of developing embryos.     

Egg structure of Zorotypus caudelli Karny (Insecta, Zoraptera, Zorotypidae)

The structural features of eggs of Zorotypus caudelli Karny are described in detail. The egg is elliptic with long and short diameters of 0.6 and 0.3 mm respectively, and creamy white. The egg shows a honeycomb pattern on its surface, without any specialized structures for hatching such as an operculum or a hatching line. The fringe formed by a fibrillar substance secreted after the completion of the chorion encircles the lateral surface. The egg layer is composed of an exochorion, an endochorion, and a vitelline envelope. The exochorion and endochorion are electron-dense and homogeneous in structure. The exochorion shows a perforation of numerous branching aeropyles. The exo- and endochorion are connected by numerous small columnar structures derived from the latter. The vitelline envelope is very thin and more electron-dense than the chorion. A pair of micropyles is present at the equator on the dorsal side of the egg. Originating at the micropyle, the micropylar canal runs through the chorion obliquely. The structural features of the eggs of Zoraptera were compared with those of other polyneopteran and paraneopteran orders.     

Fine Structure of Cardiac Sarcomeres in the Black Widow Spider Latrodectus mactans

Fine structural characteristics of the cardiac muscle and its sarcomere organization in the black widow spider, Latrodectus mactans were examined using transmission electron microscopy. The arrangement of cardiac muscle fibers was quite similar to that of skeletal muscle fibers, but they branched off at the ends and formed multiple connections with adjacent cells. Each cell contained multiple myofibrils and an extensive dyadic sarcotubular system consisting of sarcoplasmic reticulum and T‐tubules. Thin and thick myofilaments were highly organized in regular repetitive arrays and formed contractile sarcomeres. Each repeating band unit of the sarcomere had three apparent striations, but the H‐zone and M‐lines were not prominent. Myofilaments were arranged into distinct sarcomeres defined by adjacent Z‐lines with relatively short lengths of 2.0 μm to 3.3 μm. Cross sections of the A‐band showed hexagon‐like arrangement of thick filaments, but the orbit of thin filaments around each thick filament was different from that seen in other vertebrates. Although each thick filament was surrounded by 12 thin filaments, the filament ratio of thin and thick myofilaments varied from 3:1 to 5:1 because thin filaments were shared by adjacent thick filaments.     

Scanning electron microscopy of the eggs of Palingenia longicauda (Olivier) (Ephemeroptera : Palingeniidae)

The eggs of Palingenia longicauda (Ephemeroptera : Palingeniidae) were studied by scanning electron microscopy (SEM), and showed a biconvex shape with the 2 aspects joined along a thick peripheral border. The eggs were completely wrapped by an exochorion that differs in thickness and organization according to the region of the chorionic surface. The thickest part of the exochorion formed a plaque, which also covered part of the peripheral border, and was constituted of a network of filaments. The remaining part of the exochorion was composed of a thin wrinkled sheet. The micropyle, hitherto unknown in Palingeniidae, appeared as a round opening penetrating into the plaque. The fibrillar network surrounding the micropyle dove-tailed with the egg chorion, forming a differentiated raised process. This peculiar interconnection facilitates egg anchoring to the substratum, and is an adaptation of the fibrous coat to the aquatic environment.     

ULTRASTRUCTURAL STUDY ON THE ATTACHING FILAMENTS AND VILLI OF THE OOCYTE OF ORYZIAS LATIPES DURING OOGENESIS

The formation of the attaching filaments and villi on the surface of the oocyte of Oryzias latipes were studied electron-microscopically. The oocyte at the early stage has almost smooth surface with a few tufts of microvilli. Some parts of the surface of the oocyte are in contact with the follicle cell, and these parts subsequently become protrusions. As maturation proceeds, a mass of fine granules appears in the space between the protrusion and the follicle cell. Similar granules begin to appear also in the space between the microvilli. These granules later become the outer layer of the chorion. The protrusions are reduced in height, and consequently become almost flat. At the same time, there appears some amorphous material of high electron density on the above-mentioned granules on the flat part. A bundle of parallel microtubules is formed in the material. The tubule is 180–200 A in diameter, and its wall consists of 12 or 13 subunits. The bundle increases in volume, and becomes the attaching filament or villus.     

Oviposition cycle in the oviparous fish Xenopoecilus sarasinorum

To clarify the reproduction of the oviparous teleost Xenopoecilus sarasinorum, changes in oocyte composition and oviposition cycle were investigated. After release, a batch of spawned eggs hung from the urogenital pore by attaching filaments (36.3+/-0.8 in number, n=31; about 4.3-7.8 mm in length, 5-8 microm in diameter) on the chorion (egg envelope) in the vegetal pole region. Females accommodated a cluster of fertilized eggs in a belly concavity until the embryos hatched. Hatching of embryos took place from 18-19 days after oviposition (25 degrees C). Between 0-2 days following hatching, the attaching filaments disappeared from the urogenital pore. Between 3 and 4 days following hatching, most of the females spawned again. The growth of oocytes proceeded slowly throughout the period when the egg cluster was carried in the belly, and no ovulation occurred during this period. If the current brood was accidentally lost, the day of the next oviposition was sooner. This might imply that carrying embryos in the belly affects endocrine activity, as in viviparous reproduction.     

Thin filaments are not of uniform length in rat skeletal muscle

The variation in thin filament length was investigated in slow and fast muscle from adult and neonatal rats. Soleus (slow) muscle from adult, 3- , 7-, and 9-d-old rats, and extensor digitorum longus (EDL; fast) muscle from adult rats were serially cross-sectioned. The number of thin filaments per 0.06 microns2 (TF#) was counted for individual myofibrils followed from the H zone of one sarcomere, through the I-Z-I region, to the H zone of an adjacent sarcomere TF# was pooled by distance from the Z band or AI junction. In both adult muscles, thin filament length varied from 0.18 to 1.20 microns, with approximately 25% of the thin filaments less than 0.7 microns in length. In 7- and 9- d soleus, thin filament length ranged from 0.18 to 1.08 microns; except for the longest (0.18 to 1.20 microns) filaments, the distribution of thin filament lengths was similar to that in adult muscle. In 3-d soleus, thin filament length was more uniform, with less than 5% of the filaments shorter than 0.7 microns. In all neonatal muscles, there were approximately 15% fewer thin filaments per unit area as compared to adult muscles. We conclude: (a) In rat skeletal muscle, thin filaments are not of uniform length, ranging in length from 0.18 to 1.20 microns. (b) There may be two stages of thin filament assembly in neonatal muscle: between 3 and 7 d when short thin filaments may be preferentially or synthesized or inserted near the Z-band, and between 9 d and adult when thin filaments of all lengths may be synthesized or inserted into the myofibril.     

The eggshell of the almond wasp Eurytoma amygdali (Hymenoptera, Eurytomidae) - 1. Morphogenesis and fine structure of the eggshell layers

The almond wasp Eurytoma amvgdali (Hymenoptera: Eurytomidac) feeds and oviposits exclusively in almonds and therefore is characterized as an insect of economic importance. Its meroistic polytrophic ovaries include follicles with a tri-partitc configuration. The mature follicles exhibit two filaments occupying the two poles of the egg. One is the micropylar filament while the other might serve for respiration since it is likely that its flattened end layers remain outside the almond fruit. The eggshell is formed by aposition and the follicle cells, which surround the follicle until the end of oogenesis, may be responsible for protein synthesis and secretion which finally lead to the assembly of the eggshell. The eggshell comprises the thin vitelline membrane, possibly a 'wax' layer of waterproofing function, a transluscent layer which appears amorphous even at the end of choriogenesis, a granular layer, including large and small electron-dense granules, and finally a columnar layer very similar to layers found in other insect species of the same or different orders. Peroxidase is histochemicalLY found for the first time in an eggshell of the Hymenoptera order: the tranluscent layer in particular is positively stained (electron-dense). Two possible roles of this peroxidatic activity are discussed, first, in comparison to other fruit-infesting insects, we assume that elastic chorion is produced through the function of peroxidase induced bonds (resilin-type bonds), very important for avoiding premature breaking, while being oviposited through a narrow ovipositor. Second, referring to other studies, this layer can play a bactericidal role for additional embryonic itprotection.     

Endothelial cell connecting filaments anchor endothelial cells to the subjacent elastic lamina in the developing aortic intima of the mouse

The ultrastructural association of endothelial cells with the subjacent elastic lamina was investigated in the developing mouse aorta by electron microscopy. In the 5-day postnatal aorta, extensive filament bundles extend along the subendothelial matrix connecting the endothelial cells to the underlying elastic lamina. The connecting filaments form lateral associations with the abluminal surface of the endothelial cells in regions of membrane occupied by membrane-associated dense plaques. On the intracellular face of each plaque, the termini of stress fibers penetrate and anchor to the cell membrane in alignment with the extracellular connecting filaments. Both the stress fibers and the connecting filaments are oriented parallel to the longitudinal axis of the vessel. High magnification electron micrographs of individual endothelial cell connecting filaments reveal features similar to those of elastin-associated microfibrils. Each connecting filament consists of a 9–10 nm linear core with an electron-lucent center and peripheral spike-like projections. From the filaments, small thread-like extensions span laterally, linking the filaments into a loose bundle and anchoring them to the endothelial cell membrane and the surface of the elastic lamina. The filaments also appear heavily coated with electron-dense material; often with some degree of periodicity along the filament length. During development, the number of endothelial cell connecting filaments decreases as the elastic lamina expands and the subendothelial matrix is reduced. In the aortic intima of mature mice, the elastic lamina is closely apposed to the abluminal surface of the endothelial cell and no connecting filaments are seen. These observations suggest that endothelial cell connecting filaments are developmental features of the aortic intima which, together with the intracellular stress fibers, aid to maintain the structural integrity of the endothelial cell layer during development by providing the cells with protection from intraluminal shear forces.     

THE MYOFILAMENT ARRANGEMENT IN THE FEMORAL MUSCLE OF THE COCKROACH, LEUCOPHAEA MADERAE FABRICIUS

The structure of the femoral muscle of the cockroach, Leucophaea maderae, was investigated by light and electron microscopy. The several hundred fibers of either the extensor or flexor muscle are 20 to 40 µ in diameter in transverse sections and are subdivided into closely packed myofibrils. In glutaraldehyde-fixed and epoxy resin-embedded material of stretched fibers, the A band is about 4.5 µ long, the thin filaments are about 2.3 µ in length, the H zone and I band vary with the amount of stretch, and the M band is absent. The transverse sections of the filaments reveal in the area of a single overlap of thick and thin filaments an array of 10 to 12 thin filaments encircling each thick filament; whereas, in the area of double overlap in which the thin filaments interdigitate from opposite ends of the A band, the thin filaments show a twofold increase in number. The thick filament is approximately 205 to 185 A in diameter along most of its length, but at about 0.2 µ from the end it tapers to a point. Furthermore, some well oriented, very thin transverse sections show these filaments to have electron-transparent cores. The diameter of the thin filament is about 70 A. Transverse sections exhibit the sarcolemma invaginating clearly at regular intervals into the lateral regions of the A band. Three distinct types of mitochondria are associated with the muscle: an oval, an elongate, and a type with three processes. It is evident, in this muscle, that the sliding filament hypothesis is valid, and that perhaps the function of the extra thin filaments is to increase the tensile strength of the fiber and to create additional reactive sites between the thick and thin filaments. These sites are probably required for the functioning of the long sarcomeres.     

Cytoskeletal F-actin patterns in whole-mounted insect Malpighian tubules.

The distribution of actin filaments in Malpighian tubules of the fleshfly Sarcophaga bullata (Parker) was investigated before and after metamorphosis by means of the rhodamine phalloidin staining method. The numerous primary cells show a pattern of thick basal actin bundles resembling stress fibres of cultured cells, while the apical microvillar zone shows a bright and homogeneous labelling. The less abundant stellate cells contain no such basal actin bundles and their apical microvillar zone gets only faintly stained. Late larval stages display fingerlike infoldings and an increased actin filament concentration at the apical membrane of the stellate cells. During metamorphosis the Malpighian tubules dedifferentiate and eventually redifferentiate to give rise to adult tubules resembling larval ones. The different types of actin filament organisation in the primary and stellate cells of the Malpighian tubules are discussed.     

Morphological aspects of fertilization in Phallusia (Ascidia) nigra (Ascidiacea,Tunicata)

The spermatozoa of Phallusia (Ascidia) nigra have an elongated head (approximately 5 m in length) in which a nucleus and a single mitochondrion are located side by side. There is no midpiece. The apex of the head is wedge-shaped. Acrosomal vesicles (approximately 55–65 nm in diameter) and moderately electron-dense material (MEDM) are present between the plasmalemma and the nuclear membranes in the anterior tip of the head. The MEDM occupies a central position and three or four acrosomal vesicles are seen in a line alongside it. The acrosomal vesicles disappear as the sperm makes contact with the surface of the chorion. Gamete fusion most likely occurs between a small process extending from the peripheral margin of the sperm apex and the egg surface, resulting in incorporation of the sperm into the egg from the anterior region of its head.     

Heterocyst differentiation in the cyanobacterium Mastigocladus laminosus.

The morphological and ultrastructural aspects of heterocyst differentiation in the branching, filamentous cyanobacterium Mastigocladus laminosus were examined with light and electron microscopy. The earliest differentiation stages involved cytoplasmic changes, including (i) rapid degradation of carboxysomes, (ii) degradation of polysaccharide granules, and (iii) accumulation of electron-dense ribosomal or protein material (or both). Intermediate differentiation stages involved synthesis of a homogeneous extra wall layer, development of necks leading to adjacent cells, and elaboration of a complex system of intracytoplasmic membranes. Late differentiation stages included further development of necks and continued elaboration of membranes. Mature heterocysts possessed a uniformly electron-dense cytoplasm that contained large numbers of closely packed membranes, some of which were arranged in lamellar stacks. Mature heterocysts lacked all of the inclusion bodies present in undifferentiated vegetative cells, but contained a number of unusual spherical inclusions of variable electron density. Cells in both narrow and wide filaments were capable of differentiating. No regular heterocyst spacing pattern was observed in the narrow filaments; the number of vegetative cells between consecutive heterocysts of any given filament varied by a factor of 10. Heterocysts developed at a variety of locations in the wide, branching filaments, although the majority of them were situated adjacent to branch points. M. laminosus displayed a marked tendency to produce sets of adjacent heterocysts or proheterocysts (or both) that were not separated from each other by vegetative cells. Groups of four or more adjacent heterocysts or proheterocysts occurred frequently in wide filaments, and in some of these filaments virtually all of the cells appeared to be capable of differentiating into heterocysts.     

Cross-bridge action: present views, prospects, and unknowns

When the sliding filament hypothesis was proposed in 1953-1954, existing evidence showed that (1) contributions to tension were given by active sites uniformly distributed within each zone of filament overlap and (2) each site functioned cyclically. These sites were identified by electron microscopy as cross-bridges between the two filaments, formed of the heads of myosin molecules projecting from a thick filament and attaching to a thin filament. The angle of these cross-bridges was found to be different at rest and in rigor, suggesting that the event causing relative motion of the filaments was a change of the angle of the cross-bridges. At first, it seemed likely that the whole cross-bridge rotated about its attachment to actin, but when the atomic structures of actin and myosin were obtained by X-ray crystallography, a possible hinge was found between the "catalytic domain" which attaches to the actin filament and the "light-chain domain" which appears to act as a lever arm. Two attitudes of the lever arm are now well established, the transition between them being driven by a conformational change coupled to some step in the hydrolysis of ATP, but several recent observations suggest that this is not the whole story: a third attitude has been shown by X-ray crystallography; a non-muscle myosin has been shown to produce its working stroke in two steps; and there are suggestions that an additional displacement of the filaments is produced by a change in the attitude of the catalytic domain on the thin filament.     

Oviducal Contribution to Alteration of the Vitelline Coat in the Frog, Rana japonica. An Electron Microscopic Study

The vitelline coat (VC) surrounding coelomic eggs of the frog, Rana japonica , comprises bundles of filaments running both parallel and perpendicular to the egg surface. The coat gives little or no staining reaction with PA-CrA-Silver methenamine. In contrast, in the VC of uterine eggs the filament bundles are less conspicuous. and the interstices between the filament bundles stain strongly for carbohydrate. This alteration occurs during passage of the eggs down the first 1/20 th of the oviduct, the pars recta. The epithelium of the p. recta contains secretory cells, which contain electron-dense granules distinct from those in the jelly-secreting cells in more caudal portions of the oviduct. Treatment of coelomic eggs with an extract of p. recta followed by exposure to a sperm suspension resulted in marked swelling and softening of the VC. These results indicate that the contents of the granules secreted from the epithelial cells in the p. recta are deposited in the VC to increase its susceptibility to a fertilizing sperm.     

Fertilization cone formation in starfish oocytes: The role of the egg cortex actin microfilaments in sperm incorporation

The process of sperm incorporation into starfish (Asterias amurensis) oocytes was examined by electron and fluorescence microscopy. The fertilization cone began to form at the place where the acrosomal process fused with the egg surface and developed into an inverted conical mass containing a small amount of electron-dense cytoplasm. Microfilaments, which stained with NBD-phallacidin, were detected in the fertilization cone. Microvillar protrusions from the fully grown fertilization cone engulfed the sperm head outside the fertilization membrane. The sperm organelles were incorporated into the egg cortex with the absorption of the protrusions. Cytochalasin B inhibited sperm incorporation, fertilization cone formation, and actin filament organization. It is suggested that the development and reduction of the fertilization cone, which depend on the functioning of microfilaments, are necessary for sperm incorporation in starfish.     

NS-4 (nervous system antigen-4), a cell surface antigen of developing and adult mouse brain and sperm.

Morphological changes in the chorion of the Medaka, Oryzias latipes, brought about by the hatching enzyme were examined by transmission as well as scanning electron microscopy. The structure of the intact chorion, especially its thick multilamellar inner layer, does not change during development until about 1 hr before the onset of hatching. As choriolysis proceeds, the inner layer of the chorion is digested to yield soluble proteins of relatively high molecular weight. During this process it appears that each lamella is successively solubilized from the inner surface of the chorion. Finally, a thin outer layer with accompanying villi and attaching filaments remains.Under the experimental conditions used, the enzyme was in direct contact with both the inner and outer layers of the chorion. Because of this, the enzyme could penetrate the outer layer and act on some peripheral parts of the underlying inner layer. Based on these morphological changes, a mechanism is proposed to account for the solubilization of the chorion by the hatching enzyme.     

Program of F-actin in the follicular epithelium during oogenesis of the german cockroach, Blattella germanica

Extensive programmed structural and functional changes of insect follicular epithelium during oogenesis provide a model to study modulation of cytoskeletal organization during morphogenesis in a non-dividing cell population. Rhodamine-phalloidin staining of whole mounted and cryosectioned oogenic follicles reveal changing F-actin filament organization from pre- to post-vitellogenic stages consistent with the presumptive dorsal-ventral orientation of the future embryo. Filaments are not abundant in pre-vitellogenic follicle cells up to day 2. Differences between dorsal and ventral follicle cells appear first on day 3. Obviously patent follicle cells are seen only on the ventral follicle surface which exhibits stronger F-actin fluorescence than the dorsal non-patent epithelium. On the presumptive ventral side of midvitellogenic follicles morphologically distinct bundles of actin filaments orient peripherally into projections connecting adjacent follicle cells and from the center of follicle cells apically into macrovillar projections extending toward the oocyte surface. The mid-vitellogenic dorsal follicle cell layer also possesses macrovillar extensions containing F-actin which reach and appear to penetrate the oolema. During chorion deposition major reorganization of actin of follicle cells takes place. After chorion deposition all F-actin filaments within a given follicle cell are arranged into large parallel bundles with semi-regular cross-striations which exclude fluorescent label. The parallel orientation of actin striated filament bundles within each follicle cell appears to be random with respect to the orientation of bundles in neighboring follicle cells over much of the mid-latitude of the follicle epithelium. At anterior and posterior follicle poles a more axial orientation of striated bundles is evident. This muscle-like tissue arrangement is appropriate for cooperation in ovulating the chorionated oocyte from the follicle into the oviduct.     

小鼠精母细胞联会复合体RNA组分的电镜研究

本文运用常规染色和Bernhard染色方法对切片标本中小鼠粗线期精母细胞联会复合体(SC)的超微结构和电镜细胞化学特点进行了研究。经常规染色后,可见SC由侧生组分(LE)、中央组分(CE)和L-C纤维组成;SC宽约210nm,LE宽约60nm,中央间隔区宽约90nm。在Bernhard染色标本中,SC的LE、CE和L-C纤维着色较深,说明其中含有RNA;SC各结构组分的宽度和形态特点与常规染色标本中的基本一致。本文讨论了SC中存在有RNA等问题。     

Changes in cytoskeletal actin patterns in the Malpighian tubules of the fleshfly,Sarcophaga bullata (Parker) (Diptera : Calliphoridae), during metamorphosis

Using the rhodamine-labelled phalloidin staining method in combination with detergent extraction, metamorphic changes in actin filament patterns were investigated in the Malpighian tubules of the fleshfly, Sarcophaga bullata (Parker) (Diptera : Calliphoridae). Metamorphosis in this organ implies a process of dedifferentiation, followed by a process of redifferentiation. During dedifferentiation, the large basal actin bundles of the primary cells disappear and the microvillar membrane surface of these cells decreases. Concomitantly, several vesicles are pinched off from infoldings of the brush border. In older pupae, the Malpighian tubules redifferentiate to give rise to adult tubules with actin patterns similar to those of larvae. During redifferentiation of the tubules, the secondary cells display a marked increase in the number of actin filaments in their protrusions. The primary cells in the distal part of the anterior Malpighian tubules of late pupae display a well-developed basal pattern of thick parallel actin bundles. In most cases, major changes in actin filament patterns are found simultaneously with major changes in cell shape, indicating a close relationship between these actin filaments and the process of cellular remodelling.