The Origin and Fate of Annulate Lamellae in Maturing Sand Dollar Eggs

Electron micrograph evidence is presented that the nuclear envelope of the mature ovum of Dendraster excentricus is implicated in a proliferation of what appear as nuclear envelope replicas in the cytoplasm. The proliferation is associated with intranuclear vesicles which apparently coalesce to form comparatively simple replicas of the nuclear envelope closely applied to the inside of the nuclear envelope. The envelope itself may become disorganized at the time when fully formed annulate lamellae appear on the cytoplasmic side and parallel with it. The concept of interconvertibility of general cytoplasmic vesicles with most of the membrane systems of the cytoplasm is presented. The structure of the annuli in the annulate lamellae is shown to include small spheres or vesicles of variable size embedded in a dense matrix. Dense particles which are about 150 A in diameter are often found closely associated with annulate lamellae in the cytoplasm. Similar structures in other echinoderm eggs are basophilic. In this species, unlike other published examples, the association apparently takes place in the cytoplasm only after the lamellae have separated from the nucleus. If 150 A particles are synthesized by annulate lamellae, as their close physical relationship suggests, then in this species at least the necessary synthetic mechanisms and specificity must reside in the structure of annulate lamellae.     

The origin and fate of annulate lamellae in maturing sand dollar eggs

Electron micrograph evidence is presented that the nuclear envelope of the mature ovum of Dendraster excentricus is implicated in a proliferation of what appear as nuclear envelope replicas in the cytoplasm. The proliferation is associated with intranuclear vesicles which apparently coalesce to form comparatively simple replicas of the nuclear envelope closely applied to the inside of the nuclear envelope. The envelope itself may become disorganized at the time when fully formed annulate lamellae appear on the cytoplasmic side and parallel with it. The concept of interconvertibility of general cytoplasmic vesicles with most of the membrane systems of the cytoplasm is presented. The structure of the annuli in the annulate lamellae is shown to include small spheres or vesicles of variable size embedded in a dense matrix. Dense particles which are about 150 A in diameter are often found closely associated with annulate lamellae in the cytoplasm. Similar structures in other echinoderm eggs are basophilic. In this species, unlike other published examples, the association apparently takes place in the cytoplasm only after the lamellae have separated from the nucleus. If 150 A particles are synthesized by annulate lamellae, as their close physical relationship suggests, then in this species at least the necessary synthetic mechanisms and specificity must reside in the structure of annulate lamellae.     

Meiotic chromosome pairing and synaptonemal complex transformation in Culex pipiens oocytes

The synaptonemal complexes of the oocytes of the mosquito Culex pipiens quinquefasciatus have been reconstructed from serial sections. A diffuse structure, probably a chromocenter composed of centromeric heterochromatin, was present during pachytene. As no synaptonemal complexes were visible inside the chromocenter the continuity of the 2 arms of a bivalent was lost. The telomeric ends were clustered in a small area of the nuclear membrane in a bouquet arrangement; they were associated in pairs, and sometimes joined through a special structure. One pair was composed of the 2 telomeres of the shortest bivalent and a ring configuration was thus formed. The other 2 chromosomes may form one or two rings. During a short transitional stage, after the disappearence of the synaptonemal complexes, several thousand annuli, 1200–1500 A in diameter, were present in the nuclei. The annuli disappeared as material originating mainly from the transverse filaments of the synaptonemal complexes formed a capsule around the chromosomes during diplotene.     

The development,structure and function of modified synaptonemal complexes in mosquito oocytes

The nucleus of the maturing oocytes expands to a large thin body of 400×140×3 m but the chromosomes remain together in a small sphere, 15 m in diameter. In Aedes aegypti this sphere becomes surrounded by one to several layers of polycomplexes, annulated polycomplexes, and related annulated pseudomembranes. Just prior to egg laying the expanded nucleus disintegrates while the sphere of chromosomes is surrounded by several layers of membranes. In Culex pipiens the elements which normally connect the lateral elements of the synaptonemal complexes become extended so that all bivalents become interconnected by a framework of pseudomembranes. The continuity between the modified synaptonemal complexes and various membranes associated with the karyosphere suggest that a relationship exists, by origin or by specialization, between the synaptic structures and nuclear envelope.     

THE FINE STRUCTURE OF ANNULATE LAMELLAE

Certain lamellar structures have been described from snail (Otala) and clam (Spisula) oocytes, the acinar cells of amphibian (Ambystoma) pancreas, and from rat spermatids. These structures are alike in possessing numerous rings or annuli, resembling those in the nuclear membrane. Thus the name "annulate lamellae" has been proposed for them. It is suggested that they may function in the transfer of specificities from nucleus to cytoplasm.     

The origin of annulate lamellae in the oocyte of the ascidian,Boltenia villosa stimpson

Summary The formation of the extranuclear annulate lamellae has been revealed to be connected with a process of nuclear emission which is very active during the previtellogenetic stages of the Boltenia oocyte development. This process involves both of the nuclear membranes. At many spots on the surface of the nuclear envelope, the outer membrane pulls away from the inner membrane, thus forming what has been designated as blisters of various sizes and shapes. Masses of nuclear content, apparently not from the nucleolus, are pushed into the blisters. These blisters may become detached from the nuclear envelope and lie free in the cytoplasm. But in many cases, the detachment seems delayed, and in each blister many emission masses are squeezed tightly together and flat one on top of the other. These masses, in sections, may present the appearance of a stack of elongated outlines. The membrane, limiting any two adjacent masses in close contact, develop annuli. It is thus that an annulate lamella is formed. Whether an annulate lamella is formed between a pair of neighboring masses depends on their proximity. So the production of the annulate lamellae is incidental to, but not a necessary part of the process of nuclear emission. After the original outer nuclear membrane forming the blister has disintegrated, the annulate lamellae are left exposed in the cytoplasm.It is clear that, 1. both membranes of an annulate lamella are of inner nuclear membrane origin, 2. they hold between them some of the content of the enlarged perinuclear space resulting from the raising of the outer nuclear membrane when the blister is formed, and 3. the material held between any two lamellae is from the nucleus.The intranuclear annulate lamellae simply arise from the narrow pouches formed by the inner nuclear membrane towards the interior of the nucleus, and on these narrow pouches annuli are developed. So the intranuclear annulate lamellae is also composed of two membranes of an inner nuclear membrane origin holding between them a quantity of the content of the perinuclear space.Supported by Grant GM-11858 of National Institute of Health. The author is indebted to Dr. Richard Cloney of the Department of Zoology, University of Washington, for the use of the electron microscope.     

SMALL GRANULES IN THE AMPHIBIAN OOCYTE NUCLEUS AND THEIR RELATIONSHIP TO RNA

Small particles (100 to 300 A in diameter) are seen in sections of nucleoli, the loops of the amphibian lampbrush chromosomes, and the Balbiani-ring regions of dipteran salivary-gland chromosomes. All of these structures contain cytochemically demonstrable RNA. Furthermore, the annuli seen on the nuclear envelope are composed of small particles which are similar to or identical with those commonly associated with the endoplasmic reticulum. It seems likely that ribonucleoproteins are organized as small particulates in the nucleus as well as in the cytoplasm.     

Nuclear origin of the mitotic spindle in the oogenesis of Oligotrophus schmidti (Cecidomyiidae; Diptera)

In the oogenesis of the gall midge Oligotrophus schmidti, a material assumed to be precursor material of the first maturation division spindle appears in the middle area of the early diplotene nucleus in close association with the chromosomes. At the beginning of the growth stage of the oocyte this material together with the chromosomes is transported as a characteristic ring-shaped body toward the nuclear membrane. Having approached the nuclear membrane the ring material spreads all over its inner surface. Next, it differentiates into a continuous cortical layer of a non-chromosomal material and the chromosomal vesicles. The cortical layer, about 1, thick, is appressed tightly to the inner surface of the nuclear membrane, being delimited against the nuclear sap by a membrane-like boundary. At the end of diakinesis the chromosomes congregate in the middle area of the nucleus, and at the same time the spindle organizing activity of kinetochores begins. At the early stages of its development the spindle is a compound structure, consisting of a number of individual spindles, each of them being organized by a separate group of chromosomes. Changes in the structure of the cortical layer before and during prometaphase spindle formation are interpreted to indicate that the precursor material of the spindle is dissolved and diffuses into the nuclear sap. The nuclear membrane and the remnants of the cortical layer do not disappear until late prometaphase when the process of spindle formation is nearly completed.Dedicated to Professor Jakob Seiler on the occasion of his eightieth birthday.     

Ultrastructure of Oogenesis in Dryopteris crassirhizoma Nakai

The ultrastructure of oogenesis in Dryopteris crassirhizoma Nakai has been investigated using transmission electron microscopy. The nucleus in the young egg is rounded with an uneven outline. As it develops, it becomes amoeboid and extends nuclear protrusions that are not only sac-like nuclear evaginations like those often seen in the oogenesis of other ferns, but also mushroom-like and finger-like, with an opening at their end allowing the nucleolus material to flow out from the openings. This has not been observed previously. The nuclear protrusions differ from Dryopteris filix-mas (L.) Schott. in the absence of sheets of nuclear membrane in the form of a closed ring. As the egg matures, the nucleus transforms into a tuber-like structure with a smooth surface, lying transversely in the egg cell. In the immature egg, vesicles almost encircle the nucleus twice and are most remarkable. In the maturing egg, the vesicles are distributed at the periphery, except for at the top of the egg, and affect the formation of the separation cavity and extra egg membrane. Simultaneously, vesicles from the venter canal cell move to the egg and take part in the formation of separation cavity and extra egg membrane. In the mature egg, a large number of small vesicles containing fragments of lamellae or osmiophilic material emerge from the cytoplasm. The origin of these vesicles is obscure. Irregular plastids containing a cylindrical starch grain dedifferentiated progressively.Mitochondria seem to have been undeveloped during the process, but return to normal at later stages of oogenesis. There is a high frequency of ribosomes in the mature egg. Microtubules, rarely seen in the eggs ofD. filix-mas (L.) Schott. and Pteridium aquilinum (L.) Kuhn, have been observed inside the plasmalemma of the maturing egg in D. crassirhizoma.     

Ultrastructure of Oogenesis in Dryopteris crassirhizoma Nakai

The ultrastructure ofoogenesis in Dryopteris crassirhizoma Nakai has been investigated using transmission electron microscopy. The nucleus in the young egg is rounded with an uneven outline. As it develops, it becomes amoeboid and extends nuclear protrusions that are not only sac-like nuclear evaginations like those often seen in the oogenesis of other ferns, but also mushroom-like and finger-like, with an opening at their end allowing the nucleolus material to flow out from the openings. This has not been observed previously. The nuclear protrusions differ from Dryopterisfilix-mas (L.) Schott. in the absence of sheets of nuclear membrane in the form of a closed ring. As the egg matures, the nucleus transforms into a tuber-like structure with a smooth surface, lying transversely in the egg cell. In the immature egg, vesicles almost encircle the nucleus twice and are most remarkable. In the maturing egg, the vesicles are distributed at the periphery, except for at the top of the egg, and affect the formation of the separation cavity and extra egg membrane. Simultaneously, vesicles from the venter canal cell move to the egg and take part in the formation of separation cavity and extra egg membrane. In the mature egg, a large number of small vesicles containing fragments of lamellae or osmiophilic material emerge from the cytoplasm. The origin of these vesicles is obscure. Irregular plastids containing a cylindrical starch grain dedifferentiated progressively.Mitochondria seem to have been undeveloped during the process, but return to normal at later stages of oogenesis. There is a high frequency of ribosomes in the mature egg. Microtubules, rarely seen in the eggs of D.filix-mas (L.) Schott. and Pteridium aquilinum (L.) Kuhn, have been observed inside the plasmalemma of the maturing egg in D. crassirhizoma.     

Mitosis-like macronuclear division in a ciliate

The macronucleus of a small marine ciliate of the genus Protocrucia consists of a cluster of ten vesicles which give rise to 20 distinct chromosomal elements in the course of prophase-like condensation stages. Size differences of vesicles and chromosomes are cytological indications of their genetic individuality. In an anaphase-like stage, the chromosomal elements are separated in two daughter groups which re-form 10 vesicles each. The micronucleus divides simultaneously. The existence of a precisely functioning mode of chromosome distribution is also indicated by DNA measurements. Since the macronucleus contains much more DNA than the micronucleus, the macronuclear chromosomes are thought to be oligotenic. This hypothesis is supported by the much larger size of the macronuclear chromosomes. In contrast to other modes of macronuclear division known so far, this ciliate has retained some essential features of mitosis.     

A transmission electron microscopy investigation: the membrane complex in spermatogenesis of <Emphasis Type="Italic">Fenneropenaeus chinensis</Emphasis>

The transforming characteristics of the membrane complex in spermatogenesis of Fenneropenaeus chinensis have been studied by using transmission electron microscopy. Two types of membrane complex have been investigated based on their sources: one originating from nucleus and the other from cytoplasm. The first one, consisted of annular structures, monolayer membrane blebs, and double or multi-lamellar membrane vesicles, emerges in the primary spermatocyte, then diffuses with the nuclear membrane and finally enters the cytoplasm. This type of membrane complex seems to play an important role in the materials transfusion from nucleus to cytoplasm, and it mainly exists inside the primary spermatocyte with some inside the secondary spermatocyte. The latter, originated from cytoplasm, is formed during the anaphase of spermiogenesis. It also exists in mature sperm, locating at both sides of the nucleus under the acrosomal cap. This type of membrane complex mainly comprises rings of convoluted membrane pouches, together with mitochondria, annular lamina bodies, fragments of endoplasmic reticulum, nuclear membrane and some nuclear particles. It releases vesicles and particles into the acrosomal area during the formation of the perforatorium, suggesting a combined function of the endoplasmic reticulum, mitochondria and Golgi’s mechanism.     

Multiple Pathways for Apoptotic Nuclear Fragmentation

We analyzed the ultrastructure of apoptotic nuclear fragmentation in U937 cells treated with many different apoptogenic agents. We found that this characteristic apoptotic feature can be achieved through multiple alternative pathways, depending on the apoptogenic inducer, leading to slightly different final nuclear morphologies. In most instances, the irregularly shaped nucleus of U937 rounds up; then, chromatin condenses at the nuclear periphery. Condensed chromatin can form protruding patches, which eventually bud from the nucleus in sealed vesicles through a process which is actin-dependent, since it could be blocked by cytochalasins. Alternatively, chromatin condenses in tiny, nonprotruding crescents, and a cleavage in the nuclear sap forms, beginning from the inner nuclear membrane and growing inward, thus splitting the nucleus. In U937 induced to apoptosis by hydrogen peroxide in the presence of ADP-ribosylation inhibitors, the nuclei fragment in many vesicles before chromatin even begins to condense: chromatin condensation probably occurs as a consequence. While all the apoptotic morphologies described above evolve from interphase cells, a peculiar apoptotic morphology, possibly deriving from mitotic cells, is detected upon oxidative stress, recalling the formation of micronuclei by clastogenic treatments; it shows partially membrane-bound chromatin patches, which look midway between condensed chromosomes and apoptotic condensed chromatin. The existence of these multiple pathways for nuclear fragmentation may indicate an evolutionary convergence, suggesting that this event may play an important physiological role in apoptosis.     

DIVISION IN THE DINOFLAGELLATE GYRODINIUM COHNII (SCHILLER) : A New Type of Nuclear Reproduction

Dinoflagellates are of interest because their chromosomes resemble the nucleoplasm of prokaryotes both chemically and ultrastructurally. We have studied nuclear division in the dinoflagellate Gyrodinium cohnii (Schiller), using cells obtained from cultures undergoing phasic growth. Electron micrographs of serial sections were used to prepare three-dimensional reconstructions of nuclei and chromosomes at various stages of nuclear division. During division, a complex process of invagination of the intact nuclear envelope takes place at one side of the nucleus and results in the formation of parallel cylindrical cytoplasmic channels through the nucleus. These invaginations contain bundles of microtubules, and each of the bundles comes to lie in the cytoplasm of a cylindrical channel. Nuclear constriction occurs perpendicular to these channels without displacement of the microtubules. There are no associations between chromosomes and the cytoplasmic microtubules. In dividing cells most chromosomes become V-shaped, and the apices of the V's make contact with the membrane surrounding cytoplasmic channels. It is proposed that the membrane surrounding cytoplasmic channels in the dividing nucleus may be involved in the separation of daughter chromosomes. Thus, dinoflagellates may resemble prokaryotes in the manner of genophore separation as well as in genophore chemistry and ultrastructure.     

The Fine Structure of the Mature Gametes of Haemoproteus columbae Kruse*

SYNOPSIS. The filiform microgamete of Haemoproteus columbae consists of an elongate double-walled nucleus paralleled by 2 axonemes embedded in a homogeneous matrix. At one end of the gamete, the axonemes are sharply flexed back on themselves, but no conventional kinetosome has been recognized. No mitochondria have been seen. Single-walled vesicles occur in the matrix, and the entire gamete is surrounded by a single membrane. The large round macrogamete has a conspicuous central nucleus with its outer membrane drawn out into anastomosing evaginations which extend to the periphery of the cell. A moderately electron dense material fills the space between the 2 nuclear membranes and the lumina of the evaginations. Nucleolar material may occur in scattered masses within the nucleus. One or 2 axonemes appear to arise endogenously next to the nuclear membrane. The cytoplasm is filled with ribosomes and perhaps glycogen granules. Typical protozoan mitochondria and vesicles containing pigment retained from the erythrocytic stage are found in the peripheral cytoplasm. Accumulations of dense-walled vesicles occur in the cytoplasm in conjunction with evaginations of the nuclear membrane. Amid these vesicles triple-ringed discs resembling the cytostomes of merozoites are frequently seen. Several distinct layers of dense material surround the micro-gamete.     

Fine structure of the unistellate sperm of the shrimp, Sicyonia ingentis (Natantia)

Sperm of the prawn Sicyonia ingentis were studied cytochemically and ultrastructurally. Striking cytological differences were noted between these natantian sperm and previously studied reptantian sperm. In general, the S. ingentis sperm are composed of a spherical main body that is partially encompassed by a morphologically diverse cap region, from which extends a single appendage or spike. The main body houses an uncondensed, Feulgen-positive nuclear region that is partially surrounded by a cytoplasmic band. A single layer of small, 600 Å, vesicles lines the periphery of the cytoplasmic band. Large membranous vesicles extend from the inner surface of the cytoplasmic band into the nuclear region. The nucleus is separated from the cap or acrosomal complex by a dense plate and a highly organized crystalline lattice, which is composed of geometric squares that are approximately 350 Å in dimension. The cap region also contains convoluted membrane pouches; a central granular core; spherical bodies; an electron-dense, saucer-shaped plate; and a large anterior granule. The convoluted membrane pouches and anterior granule are periodic acid-Schiff (PAS) positive. The anterior granule also demonstrates RNAase-stable red fluorescence with acridine orange staining. A spiralled spike, approximately 6 μm long, extends from the anterior end of the cap. The cap and spike are bound by a double membrane, which results from the fusion of the plasma membrane and the convoluted pouch membrane. The sperm's acrosome is thought to be composed of the two PAS-positive cap components and the spike.     

Ultrastructure of mitosis inAmoeba proteus

Summary The fine structure ofAmoeba proteus nuclei has been studied during interphase and mitosis. The interphase nucleus is discoidal, the nuclear envelope is provided with a honeycomb layer on the inside. There are numerous nucleoli at the periphery and many chromatin filaments and nuclear helices in the central part of nucleus.In prophase the nucleus becomes spherical, the numerous chromosomes are condensed, and the number of nucleoli decreases. The mitotic apparatus forms inside the nucleus in form of an acentric spindle. In metaphase the nuclear envelope loses its pore complexes and transforms into a system of rough endoplasmic reticulum cisternae (ERC) which separates the mitotic apparatus from the surrounding cytoplasm; the nucleoli and the honeycomb layer disappear completely. In anaphase the half-spindles become conical, and the system of ERC around the mitotic spindle persists. Electron dense material (possibly microtubule organizing centers—MTOCs) appears at the spindle pole regions during this stage. The spindle includes kinetochore microtubules attached to the chromosomes, and non-kinetochore ones which pierce the anaphase plate. In telophase the spindle disappears, the chromosomes decondense, and the nuclear envelope becomes reconstructed from the ERC. At this stage, nucleoli can already be revealed with the light microscope by silver staining; they are visible in ultrathin sections as numerous electron dense bodies at the periphery of the nucleus.The mitotic chromosomes consist of 10 nm fibers and have threelayered kinetochores. Single nuclear helices still occur at early stages of mitosis in the spindle region.