Ultrastructure and development of single-walled sensilla placodea and basiconica on the antennae of the Sphecoidea (Hymenoptera : aculeata)

While the pore plates of some species of the Sphecoidea (Hymenoptera) rise above the antennal surface, those of other species are flush with it. Not all species possess pore plates. On the antennae of those species, which lack pore plates, small sensilla basiconica are found. The pore plates of Psenulus concolor were studied in detail. The cuticular apparatus rises above the antennal surface. Cuticular features are the encircling ledge and delicate cuticular ledges reinforcing the perforated plate, as well as a joint-like membrane that anchors the plate into the antennal cuticle. Each pore plate is associated with 9–23 sense cells and 4 envelope cells, the second of which is doubled. In very early developmental stages, however, supernumerary envelope cells are observed; they degenerate before the cuticulin layer is secreted. Envelope cell 1 secretes a temporary dendrite sheath, while the envelope cells 2–4 are responsible for the secretion of the cuticular apparatus.The morphology and the development of the small sensilla basiconica are described in Trypoxylon attenuatum. The curved sensillum pointing to the tip of the antenna is anchored by a joint-like membrane. About 15 sense cells innervate the sensillum. The number and the arrangement of the envelope cells resemble that of the sensilla placodea. During very early developmental stages, supernumerary envelope cells are also observed. They degenerate before the cuticle of the cone is secreted by the surviving envelope cells 2–4.     

The microanatomy of the compound eye of Munida irrasa (Decapoda: Galatheidae)

The compound eye of Munida irrasa differs in several respects from the typical decapod eye. The proximal pigment is found only in retinula cells. The eccentric cell is extremely large and expanded to fill the interstices of the crystalline tract area; thus, a typical "clear-zone" is absent. Six retinula cells course distally to screen two sides of the crystalline cone. There are approximately 12,500 ommatidia in each compound eye. There are several similarities to the typical decapod eye. Each ommatidium is composed of a typical cornea, corneagenous cells, crystalline cone cells, crystalline cone, crystalline cone tract and eight retinula cells. Distal pigment cells are present and surround the crystalline cone. The distal processes of the retinula cells also contain pigment. The retinula cell processes penetrate the basement membrane as fascicles composed of processes from adjacent retinulae.     

Formation of cone mosaic of zebrafish retina.

In the zebrafish retina, four types of cone photoreceptor cells (or cones) with different sensitive frequencies are arranged in a regular pattern, named "cone mosaic". A pair of small cones, one sensitive to red and the other sensitive to green, is in close contact and forms a "double cone". In addition, there are two kinds of single cones, sensitive to blue and to UV, respectively. We study characteristics of cell-differentiation rules that realize stable formation of cone mosaic. Assumptions are: undifferentiated cells are arranged in a regular square lattice, and they are one of the three types (B, U, and D cells). A D cell has two parts (G and R-parts) and takes one of the four directions. The cells change their cell type and orientation following a continuous-time Markovian chain. The state transtion occurs faster if it increases the stabilities of the focal cell, in which the stability is the sum of affinities with neighboring cells. After the transient period, the system may reach a stable pattern (pre-pattern). The pattern becomes fixed later when the cells are fully differentiated in which B cells, U cells, and D cells become blue-sensitive, UV-sensitive, and double cones, respectively. We search for the combinations of affinities between cell states that can generate the same cone mosaic patterns as in zerbrafish retina. Successful transition rules give (1) zero or small affinity with the pairs of cell states that are absent in the zebrafish cone mosaic (lambda(UR), lambda(BG)and the contact of two cells of the same type); (2) a large affinity between a part of D cells and a non-D cell (lambda(UG)and lambda(BR)); and (3) a positive affinity of an intermediate magnitude between two non-D cells (lambda(BU)) and between two parts of D cells (lambda(GR)). The latter should be of a magnitude of about 60-90% of the former. The time needed to form a regular pattern increases with the lattice size if all the cells start pre-pattern formation simultaneously. However, the convergence time is shortened considerably if the pre-pattern formation occurs only in a narrow band of morphogenetic cell layer that sweeps from one end of the lattice to the other.     

Events associated with the initiation of mitosis in fused multinucleate HeLa cells

Large multinucleate (LMN) HeLa cells with more than 10–50 nuclei were produced by random fusion with polyethylene glycol. The number of nuclei in a particular stage of the cell cycle at the time of fusion was proportionate to the duration of the phase relative to the total cell cycle. The fused cells did not gain generation time. Interaction of various nuclei in these cells has been observed. The nuclei initially belonging to the G1-or S-phase required a much longer time to complete DNA synthesis than in mononucleate cells. Some of the cells reached mitosis 15 h after fusion, whereas others required 24 h. The cells dividing early, contained a larger number of initially early G1-phase nuclei than those cells dividing late. The former very often showed prematurely condensed chromosome (PCC) groups. In cells with a large number of advanced nuclei the few less advanced nuclei could enter mitosis prematurely. On the other hand, the cells having a large number of nuclei belonging initially to late S-or G2-phase took longer to reach mitosis. These nuclei have been taken out of the normal sequence and therefore failed to synthesize the mitotic factors and depended on others to supply them. Therefore the cells as a whole required a longer period to enter mitosis. Although the nuclei became synchronized at metaphase, the cells revealed a gradation in prophase progression in the different nuclei. At the ultrastructural level the effect of advanced nuclei on the less advanced ones was evident with respect to chromosome condensation and nuclear envelope breakdown. Less advanced nuclei trapped among advanced nuclei showed PCC and nuclear envelope breakdown prematurely, whereas mitotic nuclei near interphase or early prophase nuclei retained their nuclear envelopes for a much longer time. PCC is closely related to premature breakdown of the nuclear envelope. Our observations clearly indicate that chromosome condensation and nuclear envelope breakdown are two distinct events. Kinetochores with attached microtubules could be observed on prematurely condensed chromosomes. Kinetochores of fully condensed chromosomes often failed to become connected to spindle elements. This indicates that the formation of a functional spindle is distinct from the other events and may depend on different factors.     

Ultrastructural studies of the formation of the egg capsule in the hermaphroditic species, Isohypsibius granulifer granulifer Thulin, 1928 (Eutardigrada: Hypsibiidae)

The egg capsule of Isohypsibius granulifer granulifer Thulin 1928 (Eutardigrada: Hypsibiidae) is composed of two shells: the thin vitelline envelope and the multilayered chorion. The process of the formation of the egg shell begins in middle vitellogenesis. The I. g. granulifer vitelline envelope is of the primary type (secreted by the oocyte), but the chorion should be regarded as a mixed type: primary (secreted by the oocyte), and secondary (produced by the cells of gonad wall). During early choriogenesis, the parts of the chorion are produced and then connected into a permanent layer. The completely developed chorion consists of three layers: (1) the inner, medium electron dense layer; (2) the middle labyrinthine layer; (3) the outer, medium electron dense layer. After the formation of the chorion, a vitelline envelope is secreted by the oocyte.     

太白红杉小孢子的发生和雄配子体的发育

太白红杉(Larix chinensis Beissn)的雄球花7月初开始分化。小孢子囊壁一般包括5～6层细胞：表皮、药室内壁、2～3层中层和绒毡层。绒毡层属于周原质团型。造孢细胞在7月下旬形成,8月上旬形成小孢子母细胞,8月下旬开始减数分裂,于10月上旬进入双线期,并以双线期渡过休眠。翌年3月下旬解除休眠继续进行减数分裂,4月中旬形成四分体,4月下旬到5月初小孢子从四分体内释放出来,小孢子经过连续4次有丝分裂后,于5月中旬形成5-细胞型的成熟花粉粒（雄配子体）并开始散粉。小孢子母细胞发育表现出不同步现象,部分小孢子母细胞在发育过程中出现退化,在小孢子囊内形成空腔。     

Proliferating ability,morphological development and acetylcholinesterase activity of the neural tube cells in early chick embryos

Summary Using ³H-thymidine autoradiography and AChE histochemistry at the electron microscopic level on the same sections, the interrelationships between loss of proliferating ability, morphological development and increase of AChE activity during the course of differentiation of the neural tube cells were investigated in early chick embryos. The neural tube wall consisted of spindle-shaped cells with no AChE activity, weakly positive spindle-shaped cells showing AChE activity in the cisternae of the nuclear envelope and in a few short profiles of r-ER, moderately positive spindle-shaped cells showing AChE activity in the nuclear envelope and in a moderate number of r-ER profiles and intensely positive large round cells showing AChE activity in the nuclear envelope and in a large number of r-ER profiles. Nuclei of the AChE-negative, weakly positive and moderately positive cells were located in the ependymal layer (matrix). The AChE-intensely positive cells were in the mantle layer. The AChE-negative and weakly positive cells were capable of proliferation and were regarded as undifferentiated neuroepithelial cells. In contrast, the moderately positive and intensely positive cells were no longer capable of proliferation and were considered to be neurons. These findings indicate that the r-ER increases rapidly in amount and volume in newly formed neurons soon after their final cell division, and that AChE increases in the neurons in parallel to the development of the r-ER.     

Nuclear Pore Complex Number and Distribution throughout the Saccharomyces cerevisiae Cell Cycle by Three-Dimensional Reconstruction from Electron Micrographs of Nuclear Envelopes

The number of nuclear pore complexes (NPCs) in individual nuclei of the yeast Saccharomyces cerevisiae was determined by computer-aided reconstruction of entire nuclei from electron micrographs of serially sectioned cells. Nuclei of 32 haploid cells at various points in the cell cycle were modeled and found to contain between 65 and 182 NPCs. Morphological markers, such as cell shape and nuclear shape, were used to determine the cell cycle stage of the cell being examined. NPC number was correlated with cell cycle stage to reveal that the number of NPCs increases steadily, beginning in G₁-phase, suggesting that NPC assembly occurs continuously throughout the cell cycle. However, the accumulation of nuclear envelope observed during the cell cycle, indicated by nuclear surface area, is not continuous at the same rate, such that the density of NPCs per unit area of nuclear envelope peaks in apparent S-phase cells. Analysis of the nuclear envelope reconstructions also revealed no preferred NPC-to-NPC distance. However, NPCs were found in large clusters over regions of the nuclear envelope. Interestingly, clusters of NPCs were most pronounced in early mitotic nuclei and were found to be associated with the spindle pole bodies, but the functional significance of this association is unknown.     

Fine structure of the compound eyes of the midwater amphipod Phronima in relation to behavior and habitat

Pelagic amphipods belonging to the genus Phronima have four compound eyes; two lateral eyes and two large transparent medial eyes which comprise the entire top of the head. The eyes are structurally similar but the crystalline cones of the medial eyes are more than twenty times as long as those of the lateral eyes, reaching 5 mm in a large animal. The dioptric system of each ommatidium consists of an unfaceted cornea, a layer of hypodermal cells, two rudimentary cone cells, two cells which surround and form the crystalline cone, and the cone itself. The cone and its surrounding cells penetrate the layer of accessory pigment cells which surrounds the retina. The fused rhabdom is formed by the five retinula cells but is separated from them by an extracellular palisade which is crossed by bridges. The retinula cell nuclei lie proximal to the basement membrane. Further proximally the bundle of retinula cell axons is crossed by a second basement membrane, which surrounds each axon with a collar. Medial and lateral eyes on each side of the head share a common lamina. The medial eyes of Phronima appear to be a solution to the problem of remaining inconspicuous to predators while still maintaining sensitivity and resolution.     

Distinctive properties of the hepatitis B virus envelope proteins.

Using recombinant adenoviral vectors, we expressed and characterized the large, middle, and major envelope proteins of hepatitis B virus (HBV). Cells infected with the recombinant adenovirus which contained the large envelope gene (HS1.HP) expressed predominantly large envelope and small but detectable quantities of middle (4%) and major (6%) envelope proteins in the cell lysate. No HBV envelope proteins were detected in the culture medium from HS1.HP-infected cells. Cells infected with recombinant adenovirus which contained the middle envelope gene (HS2.HP) expressed and secreted the middle and major envelope proteins in a molar ratio of 3:1. Cells infected with the recombinant adenovirus which contained the major envelope gene (HS.HP) expressed and secreted major envelope proteins. The HBV envelope proteins secreted by cells infected with either HS2.HP or HS.HP were assembled in 22-nm particles, as shown by velocity sedimentation rate determination, buoyant densities, and electron microscopy. Cells coinfected with a recombinant adenovirus which contained the large envelope gene and with either HS2.HP or HS.HP expressed similar quantities of the large, middle, and major envelope proteins in the cell lysates. Secretion of the major and middle envelope proteins was inhibited more than 95% by the presence of the large envelope proteins. These results suggest that differential biosynthesis, transport, and processing of the envelope proteins occur during HBV infection, allowing efficient assembly and secretion of virions and hepatitis B surface antigen particles.     

Envelope lipid-packing as a critical factor for the biological activity and stability of alphavirus particles isolated from mammalian and mosquito cells

Alphaviruses are enveloped arboviruses. The viral envelope is derived from the host cell and is positioned between two icosahedral protein shells (T = 4). Because the viral envelope contains glycoproteins involved in cell recognition and entry, the integrity of the envelope is critical for the success of the early events of infection. Differing levels of cholesterol in different hosts leads to the production of alphaviruses with distinct levels of this sterol loaded in the envelope. Using Mayaro virus, a New World alphavirus, we investigated the role of cholesterol on the envelope of alphavirus particles assembled in either mammalian or mosquito cells. Our results show that although quite different in their cholesterol content, Mayaro virus particles obtained from both cells share a similar high level of lateral organization in their envelopes. This organization, as well as viral stability and infectivity, is severely compromised when cholesterol is depleted from the envelope of virus particles isolated from mammalian cells, but virus particles isolated from mosquito cells are relatively unaffected by cholesterol depletion. We suggest that it is not cholesterol itself, but rather the organization of the viral envelope, that is critical for the biological activity of alphaviruses.     

南方鲶卵巢滤泡细胞和卵膜生成的组织学研究

南方鲶的卵巢滤泡细胞源于卵巢基质细胞,从发生到退化分为零散卵泡膜细胞期、单层扁平泡膜细胞期、多层扁平卵泡膜细胞期、立方形颗粒细胞期柱状颗粒细胞期、颗粒细胞分泌期和颗粒细胞退化期。精孔细胞中发育中滤泡细胞分化形成。初级卵精源于卵母细胞,次级卵膜由晚期滤泡细胞分泌形成。本文还对滤泡细胞和卵膜的作用进行了阐述。     

An ultrastructural investigation of the early stages of oocyte differentiation in Actinia fragacea (Cnidaria; Anthozoa)

Individuals from a population of the intertidal sea anemone Actinia fragacea (Tugwell) were collected at approximately monthly intervals over an 18 month period. Samples of gonad were removed from each anemone and examined by light and electron microscopy. During late spring and early summer, large numbers of small cells were seen in the endoderm of the female gonads, lying close to the mesoglea. For convenience, these cells were classified into three types. Type I cells are 6–9 μm in diameter, with relatively very large nuclei, which may contain synaptinemal complexes, and scant cytoplasm containing few organelles. Type II cells are larger, reaching 15 μ m in diameter, with more abundant cytoplasm containing more organelles and inclusions. The nucleus is more dense, but may also contain synaptinemal complexes. Type III cells are less common. They are similar in size to Type II cells, but their nuclei contain irregular dense chromatin masses, and the nuclear envelope is incomplete or absent. The possible significance of the various cell types is discussed. It is suggested that Type I cells are oocytes at a very early stage of differentiation and that Type II cells are rather later oocytes. The status of the Type III cells is uncertain.     

Spatiotemporal pattern of rod degeneration in the S334ter-line-3 rat model of retinitis pigmentosa

We have recently described the surviving cones and Müller-glia process remodeling in retinitis pigmentosa (RP) and shown that rod degeneration triggers the reorganization of the cone mosaic into an orderly array of rings. Within these rings, remodeled Müller-glia processes envelope cones. Here, we report the spatiotemporal pattern of healthy rods, their relationship with dying rods and the way that rod death stimulates the modification of cone spatial-distribution patterns and Müller-glia processes in the S334ter-line-3 rat, a transgenic model expressing a rhodopsin mutation that causes RP. The spatial patterns of rods, cones, microglial and Müller cells were labeled by immunocytochemistry with cell-type-specific markers at various stages of deveopment in rat whole-mount retinas. Spatial patterns of dying cells were examined by TUNEL staining. The S334ter rod mosaic began to develop small holes around postnatal day 10. These hot-spots of cell death progressively increased in size, leaving larger rod-less holes behind. The holes were temporarily occupied by active microglial cells, before being replaced by remodeled Müller-cell processes. Our data suggest that the hot spots of rod death create holes in the rod mosaic early in retinal degeneration and that the resulting pattern triggers the modification of the spatial-distribution patterns of cones and glia cells.     

An ultrastructural investigation of the testes and spermiogenesis in Myobia murismusculi (Schrank) (Acari,Actinedida: Myobiidae)

Summary

The stages of spermiogenesis in Myobia murismusculi were investigated on the basis of ultrastructural analysis of both the testes and the female organs: receptaculum seminis and seminal duct. The walls of the testes consist of a thin epithelial layer. Germ and secretory cells lie free in the lumen of the testes. In the early stages of differentiation, both cell types represent clusters of sister cells joined by intercellular bridges. Each secretory cell contains prominent RER and Golgi complex, which produce single dense granule. Growing gradually the granule fills the whole volume of the cell's cytoplasm. Mature secretory cells disintegrate and the secretory product discharges into the testicular lumen. The germ cells are represented by the early, the intermediate and the late spermatids as well as the immature sperm (prospermia). Neither spermatogonia nor meiotic figures were observed in adult males. As spermiogenesis starts, numerous narrow invaginations of the outer membrane (peripheral channels) develop on the cell surface. They form a wide circumferential network connected to pinocytotic vesicles. Owing to the secretory activity of the Golgi complex, a large acrosomal granule is formed in the early spermatids. A long acrosomal filament runs along the intranuclear canal. Nuclear material condenses and forms two spherical bodies of different electron density. The lighter one can be observed until the stage of the late spermatids, when the nuclear envelope almost completely disappears. The electron-dense nuclear body transforms into a definite chromatin body, which is observed in the mature sperm as a cup-shaped structure. The late spermatids are characterized by the presence of a large electronlucent vacuole, which seems to be unique for the process of spermiogenesis in Actinedida. After the spermia enter the female genital tract, the peripheral channels disappear as well as the vacuole. The cells form long amoeboid arms with a special microtubular layer underneath the plasma membrane. The chromatin body is encircled by a large acrosomal granule of complex shape provided by long extensions running deep into the cytoplasm. The cytoplasm contains no organelles except for a group of unmodified mitochondria in the post-nuclear region. The main characteristics of the Myobia spermiogenesis are discussed with regard to other actinedid mites.     

Notch 1 inhibits photoreceptor production in the developing mammalian retina

The transmembrane receptor Notch1 plays a role in development and homeostasis in vertebrates and invertebrates. The mammalian retina is an excellent tissue in which to dissect the precise role of Notch signaling in regulating cell fate and proliferation. However, a systematic analysis has been limited by the early embryonic lethality of Notch1-null mice. Here, Notch1 was conditionally removed from the murine retina either early or late in development. Removal of Notch1 early led to a reduction in the size of the retina as well as aberrant morphology. A decrease in the number of progenitor cells and premature neurogenesis accounted for the reduction in size. Unexpectedly, ablation of Notch1 in early progenitor cells led to enhanced cone photoreceptor production, and ablation of Notch1 at later points led to an almost exclusive production of rod photoreceptor cells. These data suggest that Notch1 not only maintains the progenitor state, but is required to inhibit the photoreceptor fate. These cone enriched mutant mice should prove to be a valuable resource for the study of this relatively rare mammalian photoreceptor cell type.     

Cell degeneration during early development of hymenopteran olfactory sensilla

The imaginal pore plates of Hymenoptera apocrita so far examined embody five or six envelope cells respectively. In early developmental stages, however, supernumerary envelope cells have been found. The results are discussed in the context of cell death as a developmental phenomenon.     

Early oogenesis in the ascidian Ciona savignyi

Summary

Morphology of the germinal epithelium and the early follicular oocyte in the ascidian Ciona savignyi as examined by electron microscopy. The oogenetic part of the germinal epithelium contains oocytes at two different stages and the dark and clear cells. The smaller oocyte contains synaptonemal complexes. The larger oocyte in the initial phase of growth has a conspicuous nucleolus, electron-dense materials and some mitochondria close to the nuclear envelope. The nucleus of the larger oocyte is round and has the smooth contour. The dark cell contains a relatively large nucleus and is sometimes connected to each other by an intercellular bridge. Therefore, the dark cell, which has been suggested to be the progenitor cell of two kinds of accessory cells, may be also the oogonium. The early follicular oocyte just after migration from the germinal epithelium retains most of cytological features similar to those of the larger oocyte. However, the nuclear contour of the early follicular oocyte is uneven. This difference in the nuclear contour probably indicates that such a follicular oocyte is in the second phase of growth.     

Regular arrangements of mitochondria and plastids during sporogenesis inEquisetum

Summary Plastids and mitochondria in premeiotic cells ofEquisetum were situated at random. By early prophase I all these organelles aggregated for a short period into one group at the nuclear envelope, but subsequently the organelles became again scattered. By late prophase I they aggregated into two groups at opposite sides of the nucleus, then moved towards the equator of the cell. By interphase plastids and mitochondria aggregated into a layer which divided each dyad into two parts. After telophase II the reorganized layer divided the tetrad into four parts. The organelle layer underwent differentiation into three strata. The cell plate was formed in the middle one which was constituted of mitochondria.     

The structure of the rectal papilla in a parasitoid hymenopteran Nasonia vitripennis (Walker) (Hymenoptera Pteromalidae)

Summary The ultrastructure of the rectal papillae of the parasitoid hymenopteran, Nasonia vitripennis (Walk), is described. These organs in this insect consist of four distinct cell types arranged as a closed, hollow cone. The majority of the cells are present in the raised cone, and are characterised by large numbers of mitochondria arranged in a membranous labyrinth. A series of cells form a collar around the base of the cone. Junction cells have been identified which are present at the point of insertion of the cone into the rectal epithelium. The base of the cone consists of cells with elaborately folded plasma membranes facing both the central cavity of the cone, and the haemolymph. The structure of this rectal papilla is compared with those found in other insects.We are indebted to Professor E. W. Knight-Jones in whose department the work was carried out, and to the Science Research Council for support for one of us (I.D.).