The structure and function of annulate lamellae: porous cytoplasmic and intranuclear membranes

Cytoplasmic nucleoporin assemblage: the cellular artwork in physiology and disease

Nucleoporins, essential proteins building the nuclear pore, are pivotal for ensuring nucleocytoplasmic transport. While traditionally confined to the nuclear envelope, emerging evidence indicates their presence in various cytoplasmic structures, suggesting potential non-transport-related roles. This review consolidates findings on cytoplasmic nucleoporin assemblies across different states, including normal physiological conditions, stress, and pathology, exploring their structural organization, formation dynamics, and functional implications. We summarize the current knowledge and the latest concepts on the regulation of nucleoporin homeostasis, aiming to enhance our understanding of their unexpected roles in physiological and pathological processes.

Defining the EM-signature of successful cell-transfection

In this report, we describe the architecture of Lipofectamine 2000 and 3000 transfection- reagents, as they appear inside of transfected cells, using classical transmission electron microscopy (EM). We also demonstrate that they provoke consistent structural changes after they have entered cells, changes that not only provide new insights into the mechanism of action of these particular transfection-reagents, but also provide a convenient and robust method for identifying by EM which cells in any culture have been successfully transfected. This also provides clues to the mechanism(s) of their toxic effects, when they are applied in excess. We demonstrate that after being bulk-endocytosed by cells, the cationic spheroids of Lipofectamine remain intact throughout the entire time of culturing, but escape from their endosomes and penetrate directly into the cytoplasm of the cell. In so doing, they provoke a stereotypical recruitment and rearrangement of endoplasmic reticulum (ER), and they ultimately end up escaping into the cytoplasm and forming unique 'inclusion-bodies.' Once free in the cytoplasm, they also invariably develop dense and uniform coatings of cytoplasmic ribosomes on their surfaces, and finally, they become surrounded by 'annulate' lamellae' of the ER. In the end, these annulate-lamellar enclosures become the ultrastructural 'signatures' of these inclusion-bodies, and serve to positively and definitively identify all cells that have been effectively transfected. Importantly, these new EM-observations define several new and unique properties of these classical Lipofectamines, and allow them to be discriminated from other lipoidal or particulate transfection-reagents, which we find do not physically break out of endosomes or end up in inclusion bodies, and in fact, provoke absolutely none of these 'signature' cytoplasmic reactions.

Exogenous chelating agents influence growth, physiological characteristics and cell ultrastructure of Robinia pseudoacacia seedlings under lead-cadmium stress

Heavy metal pollution of soil, especially by lead (Pb) and cadmium (Cd), is a serious problem worldwide. The application of safe chelating agents, combined with the growing of tolerant trees, constitutes an approach for phytoremediation of heavy-metal-contaminated soil. This study aimed to determine whether the two safe chelators, tetrasodium glutamate diacetate (GLDA) and citric acid (CA), could improve the phytoremediation capacity of black locust (Robinia pseudoacacia L.) in a Pb-Cd-contaminated soil and to find the key factors affecting the biomass accumulation of stressed black locust. In Pb- and Cd-stressed black locust plants, medium- and high-concentration GLDA treatment inhibited the growth, chlorophyll synthesis and maximum photochemical efficiency (Fv/Fm), promoted the absorption of Pb and Cd ions and resulted in the shrinkage of chloroplasts and starch grains when compared with those in Pb- and Cd-stressed plants that were not treated with GLDA. The effects of CA on plant growth, ion absorption, chlorophyll content, chlorophyll fluorescence and organelle size were significantly weaker than those of GLDA. The effect of both agents on Cd absorption was greater than that on Pb absorption in all treatments. The levels of chlorophyll a and plant tissue Cd and rates of starch metabolism were identified as the key factors affecting plant biomass accumulation in GLDA and CA treatments. In the future, GLDA can be combined with functional bacteria and/or growth promoters to promote the growth of Pb- and Cd-stressed plants and to further improve the soil restoration efficiency following pollution by heavy metals. Application of CA combined with the growing of black locust plants has great potential for restoring the Cd-polluted soil. These findings also provide insights into the practical use of GLDA and CA in phytoremediation by R. pseudoacacia and the tolerant mechanisms of R. pseudoacacia to Pb-Cd-contaminated soil.

Puzzling out nuclear pore complex assembly

Nuclear pore complexes (NPCs) are sophisticated multiprotein assemblies embedded within the nuclear envelope and controlling the exchanges of molecules between the cytoplasm and the nucleus. In this review, we summarize the mechanisms by which these elaborate complexes are built from their subunits, the nucleoporins, based on our ever-growing knowledge of NPC structural organization and on the recent identification of additional features of this process. We present the constraints faced during the production of nucleoporins, their gathering into oligomeric complexes, and the formation of NPCs within nuclear envelopes, and review the cellular strategies at play, from co-translational assembly to the enrolment of a panel of cofactors. Remarkably, the study of NPCs can inform our perception of the biogenesis of multiprotein complexes in general - and vice versa.

Loss of C9orf72 perturbs the Ran-GTPase gradient and nucleocytoplasmic transport, generating compositionally diverse Importin β-1 granules

A hexanucleotide (GGGGCC)_n repeat expansion in C9orf72 causes amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), eliciting toxic effects through generation of RNA foci, dipeptide repeat proteins, and/or loss of C9orf72 protein. Defects in nucleocytoplasmic transport (NCT) have been implicated as a pathogenic mechanism underlying repeat expansion toxicity. Here, we show that loss of C9orf72 disrupts the Ran-GTPase gradient and NCT in vitro and in vivo. NCT disruption in vivo is enhanced by the presence of compositionally different types of cytoplasmic Importin β-1 granule that exhibit neuronal subtype-specific properties. We show that the abundance of Importin β-1 granules is increased in the context of C9orf72 deficiency, disrupting interactions with nuclear pore complex proteins. These granules appear to associate with the nuclear envelope and are co-immunoreactive for G3BP1 and K63-ubiquitin. These findings link loss of C9orf72 protein to gain-of-function mechanisms and defects in NCT.

The chaperone DNAJB6 surveils FG-nucleoporins and is required for interphase nuclear pore complex biogenesis

Biogenesis of nuclear pore complexes (NPCs) includes the formation of the permeability barrier composed of phenylalanine-glycine-rich nucleoporins (FG-Nups) that regulate the selective passage of biomolecules across the nuclear envelope. The FG-Nups are intrinsically disordered and prone to liquid-liquid phase separation and aggregation when isolated. How FG-Nups are protected from making inappropriate interactions during NPC biogenesis is not fully understood. Here we find that DNAJB6, a molecular chaperone of the heat shock protein network, forms foci in close proximity to NPCs. The number of these foci decreases upon removal of proteins involved in the early steps of interphase NPC biogenesis. Conversely, when this process is stalled in the last steps, the number of DNAJB6-containing foci increases and these foci are identified as herniations at the nuclear envelope. Immunoelectron tomography shows that DNAJB6 localizes inside the lumen of the herniations arising at NPC biogenesis intermediates. Loss of DNAJB6 results in the accumulation of cytosolic annulate lamellae, which are structures containing partly assembled NPCs, a feature associated with disturbances in NPC biogenesis. We find that DNAJB6 binds to FG-Nups and can prevent the aggregation of the FG region of several FG-Nups in cells and in vitro. Together, our data show that the molecular chaperone DNAJB6 provides quality control during NPC biogenesis and is involved in the surveillance of native intrinsically disordered FG-Nups.

Annulate lamellae and intracellular pathogens

Annulate lamellae (AL) have been observed many times over the years on electron micrographs of rapidly dividing cells, but little is known about these unusual organelles consisting of stacked sheets of endoplasmic reticulum-derived membranes with nuclear pore complexes (NPCs). Evidence is growing for a role of AL in viral infection. AL have been observed early in the life cycles of the hepatitis C virus (HCV) and, more recently, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), suggesting a specific induction of mechanisms potentially useful to these pathogens. Like other positive-strand RNA viruses, these viruses induce host cells membranes rearrangements. The NPCs of AL could potentially mediate exchanges between these partially sealed compartments and the cytoplasm. AL may also be involved in regulating Ca²⁺ homeostasis or cell cycle control. They were recently observed in cells infected with Theileria annulata, an intracellular protozoan parasite inducing cell proliferation. Further studies are required to clarify their role in intracellular pathogen/host-cell interactions.

Nuclear Pores Assemble from Nucleoporin Condensates During Oogenesis

The molecular events that direct nuclear pore complex (NPC) assembly toward nuclear envelopes have been conceptualized in two pathways that occur during mitosis or interphase, respectively. In gametes and embryonic cells, NPCs also occur within stacked cytoplasmic membrane sheets, termed annulate lamellae (AL), which serve as NPC storage for early development. The mechanism of NPC biogenesis at cytoplasmic membranes remains unknown. Here, we show that during Drosophila oogenesis, Nucleoporins condense into different precursor granules that interact and progress into NPCs. Nup358 is a key player that condenses into NPC assembly platforms while its mRNA localizes to their surface in a translation-dependent manner. In concert, Microtubule-dependent transport, the small GTPase Ran and nuclear transport receptors regulate NPC biogenesis in oocytes. We delineate a non-canonical NPC assembly mechanism that relies on Nucleoporin condensates and occurs away from the nucleus under conditions of cell cycle arrest.

Ultrastructural investigations on spermatogenesis and spermatozoan morphology in the endangered Adriatic sturgeon, Acipenser naccarii (Chondrostei, Acipenseriformes)

Spermatogenesis was investigated in the Adriatic sturgeon, Acipenser naccarii, by light and electron microscopy. The testis of the unrestricted type had a germinal compartment composed of lobules containing germ cells and Sertoli cells, and separated by a basal lamina from the interstitial compartment, in which Leydig and myoid cells were detected for the first time in Acipenseridae. Spermatogenesis occurred in spermatocysts produced when Sertoli cells became associated with type A spermatogonia of subsequent generations, which produced a clone of synchronized aligned spermatogonia. In primary spermatocytes at zygo-pachytene stage, the large spherical nucleus contained synaptonemal complexes. The smaller secondary spermatocytes were ovoid with a central round nucleus and scarce cytoplasm. Spermatids were interconnected by cytoplasmic bridges until early spermiogenesis. Chromatin initially condensed as long, twisted, and nonhomogeneous fibers and finally as a compact structure made of thick filaments. Early spermatids showed the flagellum, the primordia of centriole complex and of "implantation fossa," followed by the acrosomal vesicle formed by Golgi complexes and a fibrous body associated to centriole complex. The spermatozoan head had 10 postero-lateral projections and a trapezoidal nucleus, a cylindrical midpiece with six to eight mitochondria, the centriole complex, and a "9 + 2" flagellum with a pair of lateral fins. Three helical endonuclear canals crossed the nucleus from the acrosome base to the implantation fossa; their spiralization and that of chromatin fibers suggest a spiral twisting of the nucleus during spermiogenesis. The Sertoli cells performed phagocytosis of degenerating spermatids and spermatozoa. Significant interindividual differences were detected in most morphological parameters of spermatozoa. Data on spermatogenesis in A. naccarii and morphometric measurements on mature spermatozoa provide information about the reproductive biology of the species useful not only for phylogenetic studies but also for evaluation of sperm quality for artificial reproduction projects and restocking of this and other critically endangered sturgeon species.

Pre-assembled Nuclear Pores Insert into the Nuclear Envelope during Early Development

Nuclear pore complexes (NPCs) span the nuclear envelope (NE) and mediate nucleocytoplasmic transport. In metazoan oocytes and early embryos, NPCs reside not only within the NE, but also at some endoplasmic reticulum (ER) membrane sheets, termed annulate lamellae (AL). Although a role for AL as NPC storage pools has been discussed, it remains controversial whether and how they contribute to the NPC density at the NE. Here, we show that AL insert into the NE as the ER feeds rapid nuclear expansion in Drosophila blastoderm embryos. We demonstrate that NPCs within AL resemble pore scaffolds that mature only upon insertion into the NE. We delineate a topological model in which NE openings are critical for AL uptake that nevertheless occurs without compromising the permeability barrier of the NE. We finally show that this unanticipated mode of pore insertion is developmentally regulated and operates prior to gastrulation.

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Annulate lamellae (AL) NPCs insert into the nuclear envelope during interphase

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AL-NPCs are pore scaffolds devoid of most transport channel nucleoporins

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NE-openings enable AL insertion, yet the permeability barrier remains unperturbed

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AL-NPC insertion operates only before gastrulation

M, Tyrrell DLJ, Wozniak RW. The Hepatitis C Virus-Induced Membranous Web and Associated Nuclear Transport Machinery Limit Access of Pattern Recognition Receptors to Viral Replication Sites

Hepatitis C virus (HCV) is a positive-strand RNA virus of the Flaviviridae family and a major cause of liver disease worldwide. HCV replicates in the cytoplasm, and the synthesis of viral proteins induces extensive rearrangements of host cell membranes producing structures, collectively termed the membranous web (MW). The MW contains the sites of viral replication and assembly, and we have identified distinct membrane fractions derived from HCV-infected cells that contain replication and assembly complexes enriched for viral RNA and infectious virus, respectively. The complex membrane structure of the MW is thought to protect the viral genome limiting its interactions with cytoplasmic pattern recognition receptors (PRRs) and thereby preventing activation of cellular innate immune responses. Here we show that PRRs, including RIG-I and MDA5, and ribosomes are excluded from viral replication and assembly centers within the MW. Furthermore, we present evidence that components of the nuclear transport machinery regulate access of proteins to MW compartments. We show that the restricted assess of RIG-I to the MW can be overcome by the addition of a nuclear localization signal sequence, and that expression of a NLS-RIG-I construct leads to increased immune activation and the inhibition of viral replication.

Hepatitis C virus (HCV) is a positive-strand RNA virus and it is a major cause of liver disease worldwide affecting more than 170 million individuals. Infection of cells with HCV leads to rearrangement of cytoplasmic host cell membranes and the formation of the membranous web (MW) containing viral replication and assembly complexes. The MW is thought to function in concentrating viral components, regulating virus replication, and immune evasion. Our analysis has provided new insight into the organization of the MW and the mechanisms that contribute to the formation and maintenance of distinct compartments within the MW. We show that the MW limits access of host cell innate immune receptors to sites of viral replication and assembly. Moreover, we show that components of the nuclear transport machinery, normally involved in regulating traffic between the cytoplasm and the nucleus, have a role in limiting immune receptor access to compartments within the MW. These findings provide important insights in how HCV, and likely other positive-strand RNA viruses, organize their replication factories and evaded recognition by host cell immune receptors.

Hepatitis C virus-induced cytoplasmic organelles use the nuclear transport machinery to establish an environment conducive to virus replication

Hepatitis C virus (HCV) infection induces formation of a membranous web structure in the host cell cytoplasm where the viral genome replicates and virions assemble. The membranous web is thought to concentrate viral components and hide viral RNA from pattern recognition receptors. We have uncovered a role for nuclear pore complex proteins (Nups) and nuclear transport factors (NTFs) in the membranous web. We show that HCV infection leads to increased levels of cytoplasmic Nups that accumulate at sites enriched for HCV proteins. Moreover, we detected interactions between specific HCV proteins and both Nups and NTFs. We hypothesize that cytoplasmically positioned Nups facilitate formation of the membranous web and contribute to the compartmentalization of viral replication. Accordingly, we show that transport cargo proteins normally targeted to the nucleus are capable of entering regions of the membranous web, and that depletion of specific Nups or Kaps inhibits HCV replication and assembly.

Adult neural stem cells from the subventricular zone: a review of the neurosphere assay

The possibility of obtaining large numbers of cells with potential to become functional neurons implies a great advance in regenerative medicine. A source of cells for therapy is the subventricular zone (SVZ) where adult neural stem cells (NSCs) retain the ability to proliferate, self-renew, and differentiate into several mature cell types. The neurosphere assay, a method to isolate, maintain, and expand these cells has been extensively utilized by research groups to analyze the biological properties of aNSCs and to graft into injured brains from animal models. In this review we briefly describe the neurosphere assay and its limitations, the methods to optimize culture conditions, the identity and the morphology of aNSC-derived neurospheres (including new ultrastructural data). The controversy regarding the identity and "stemness" of cells within the neurosphere is revised. The fine morphology of neurospheres, described thoroughly, allows for phenotypical characterization of cells in the neurospheres and may reveal slight changes that indirectly inform about cell integrity, cell damage, or oncogenic transformation. Along this review we largely highlight the critical points that researchers have to keep in mind before extrapolating results or translating experimental transplantation of neurosphere-derived cells to the clinical setting.

Nuclear structures in Tribolium castaneum oocytes

The first ultrastructural and immunomorphological characteristics of the karyosphere (karyosome) and extrachromosomal nuclear bodies in the red flour beetle, Tribolium castaneum, are presented. The karyosphere forms early in the diplotene stage of meiotic prophase by the gathering of all oocyte chromosomes in a limited nuclear volume. Using the BrUTP assay, T. castaneum oocyte chromosomes united in the karyosphere maintain their transcriptional activity until the end of oocyte growth. Hyperphosphorylated RNA polymerase II and basal transcription factors (TFIID and TFIIH) were detected in the perichromatin region of the karyosphere. The T. castaneum karyosphere has an extrachromosomal capsule that separates chromosomes from the rest of the nucleoplasm. Certain structural proteins (F-actin, lamin B) were found in the capsule. Unexpectedly, the karyosphere capsule in T. castaneum oocytes was found to be enriched in TMG-capped snRNAs, which suggests that the capsule is not only a structural support for the karyosphere, but may be involved in biogenesis of snRNPs. We also identified the counterparts of 'universal' extrachromosomal nuclear domains, Cajal bodies (CBs) and interchromatin granule clusters (IGCs). Nuclear bodies containing IGC marker protein SC35 display some features unusual for typical IGCs. SC35 domains in T. castaneum oocytes are predominantly fibrillar complex bodies that do not contain trimethyl guanosine (TMG)-capped small nuclear (sn) RNAs. Microinjections of 2'-O-methyl (U)22 probes into the oocytes allowed revealing poly(A)+ RNAs in these nuclear domains. Several proteins related to mRNA export (heterogeneous ribonucleoprotein core protein A1, export adapters Y14 and Aly and export receptor NXF1) were also detected there. We believe that unusual SC35 nuclear domains of T. castaneum oocytes are possibly involved in mRNP but not snRNP biogenesis.

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 2: changes in spermatid organelles associated with development of spermatozoa

Spermiogenesis is a long process whereby haploid spermatids derived from the meiotic divisions of spermatocytes undergo metamorphosis into spermatozoa. It is subdivided into distinct steps with 19 being identified in rats, 16 in mouse and 8 in humans. Spermiogenesis extends over 22.7 days in rats and 21.6 days in humans. In this part, we review several key events that take place during the development of spermatids from a structural and functional point of view. During early spermiogenesis, the Golgi apparatus forms the acrosome, a lysosome-like membrane bound organelle involved in fertilization. The endoplasmic reticulum undergoes several topographical and structural modifications including the formation of the radial body and annulate lamellae. The chromatoid body is fully developed and undergoes structural and functional modifications at this time. It is suspected to be involved in RNA storing and processing. The shape of the spermatid head undergoes extensive structural changes that are species-specific, and the nuclear chromatin becomes compacted to accommodate the stream-lined appearance of the sperm head. Microtubules become organized to form a curtain or manchette that associates with spermatids at specific steps of their development. It is involved in maintenance of the sperm head shape and trafficking of proteins in the spermatid cytoplasm. During spermiogenesis, many genes/proteins have been implicated in the diverse dynamic events occurring at this time of development of germ cells and the absence of some of these have been shown to result in subfertility or infertility.

An unusual membrane system in the oocyte of the ascidian Botryllus schlosseri

During vitellogenesis, oocytes of Botryllus schlosseri always exhibit an unusual system scattered in the cytoplasm. It consists of an association between a single fenestrated endoplasmic reticulum cisterna and one or a few smooth vesicles (cisterna vesicle association: CVA) containing a dense core facing the cisterna itself. The latter is smooth and perforated by numerous small pores (about 25 nm in diameter) in the area of association; towards the periphery, it extends into several branches with ribosomes bound to their membranes. In the vesicles, fibrillar material radiates from the dense core and is sometimes organized into a long, dense lamina. The membranes of both cisterna and vesicles appear to be coupled, but are in fact separated by a constant narrow space occupied by short densities. The presence in B. schlosseri of this unusual fenestrated membrane system contrasts with the absence of a typical porous cytoplasmic organelle, the annulate lamellae (ALs), which is widely distributed in female gametes. However, as in other animals, B. schlosseri oocytes possess intranuclear annulate lamellae (IALs) and vesicles. Comparative observations extended to the oocytes of the ascidian Ciona intestinalis have shown that the latter species exhibits typical ALs and IALs, but not the CVA. The morphology of the CVA is analysed here in detail, and similarities and differences with ALs are pointed out. Hypotheses regarding CVA function are discussed in terms of possible relations with ALs.

Chapter 6: cubic membranes the missing dimension of cell membrane organization

Biological membranes are among the most fascinating assemblies of biomolecules: a bilayer less than 10 nm thick, composed of rather small lipid molecules that are held together simply by noncovalent forces, defines the cell and discriminates between “inside” and “outside”, survival, and death. Intracellular compartmentalization—governed by biomembranes as well—is a characteristic feature of eukaryotic cells, which allows them to fulfill multiple and highly specialized anabolic and catabolic functions in strictly controlled environments. Although cellular membranes are generally visualized as flat sheets or closely folded isolated objects, multiple observations also demonstrate that membranes may fold into “unusual”, highly organized structures with 2D or 3D periodicity. The obvious correlation of highly convoluted membrane organizations with pathological cellular states, for example, as a consequence of viral infection, deserves close consideration. However, knowledge about formation and function of these highly organized 3D periodic membrane structures is scarce, primarily due to the lack of appropriate techniques for their analysis in vivo. Currently, the only direct way to characterize cellular membrane architecture is by transmission electron microscopy (TEM). However, deciphering the spatial architecture solely based on two-dimensionally projected TEM images is a challenging task and prone to artifacts. In this review, we will provide an update on the current progress in identifying and analyzing 3D membrane architectures in biological systems, with a special focus on membranes with cubic symmetry, and their potential role in physiological and pathophysiological conditions. Proteomics and lipidomics approaches in defined experimental cell systems may prove instrumental to understand formation and function of 3D membrane morphologies.

Gonadal development and sex differentiation in the cichlid fishCichlasoma dimerus (Teleostei, perciformes): A light- and electron-microscopic study

Although the overall pattern and timing of gonadal sex differentiation have been established in a considerable number of teleosts, the ultrastructure of early stages of gonadal development is not well documented. In this study, gonads from larval and juvenile stages of laboratory-reared Cichlasoma dimerus were examined at the light-microscopic and ultrastructural levels. This freshwater species adapts easily to captivity and spawns with high frequency during 8 months of the year, providing an appropriate model for developmental studies. Larvae and juveniles were kept at a water temperature of 26.5 +/- 1 degrees C and a 12:12 hour photoperiod. Gonadal development was documented from 14-100 days postfertilization, covering the period of histologically discernible sex differentiation. Gonadal tissue was processed according to standard techniques for light and electron microscopy. C. dimerus, a perciform teleost, is classified as a differentiated gonochorist, in which an indifferent gonad develops directly into a testis or ovary. On day 14, the gonadal primordium consists of a few germ cells surrounded by enveloping somatic cells. Ovarian differentiation precedes testicular differentiation, as usual in teleost fishes. The earliest signs of differentiation, detected from day 42 onward, include the onset of meiotic activity in newly formed oocytes, which is soon accompanied by increased oogonial mitotic proliferation and the somatic reorganization of the presumptive ovary. The ovarian cavity is completely formed by day 65. Numerous follicles containing perinucleolar oocytes are observed by day 100. In contrast, signs of morphological differentiation in the presumptive testis are not observed until day 72. By day 100, the unrestricted lobular organization of the testis is evident. The latest stage of spermatogenesis observed by this time of testicular development is spermatocyte II.

Nup88 (karyoporin) in human malignant neoplasms and dysplasias: correlations of immunostaining of tissue sections, cytologic smears, and immunoblot analysis

Nuclear pore complexes (NPCs) are elaborate macromolecular structures that regulate the bidirectional nucleocytoplasmic traffic system. In vertebrate cells, NPCs include a family of 50 to 100 proteins termed nucleoporins (Nups). The 88-kD Nup has been found to be linked in a dynamic subcomplex with the oncogenic CAN/Nup214. Applying a polyclonal antiserum to Nup88 on paraffin sections, we found that it immunoreacts with numerous malignant neoplasms. All carcinomas reacted irrespective of site, type, or degree of differentiation; often, high-grade carcinomas stained more strongly and extensively. Some sarcomas (e.g., fibrosarcomas, leiomyosarcomas, liposarcomas, and rhabdomyosarcomas) reacted intensely; melanomas, gliomas, mesotheliomas, and malignant lymphomas also stained. In situ carcinomas of the colon, stomach, breast, and prostate stained convincingly, as did in situ melanomas; some samples of fetal tissues also reacted. Cytologic smears of some of the aforementioned tumors also stained. In selected samples, enhanced immunostaining of tissue sections and cytologic smears correlated strongly and consistently with immunoblot data. Immunoblots of the same tumors with antibodies to 2 other Nups (Nup214 and Nup153) showed no comparable enhancement. Therefore, it seems that in some malignant tumors, Nup88 overexpression is not parallelled by an overexpression of other Nups. Benign tumors, hyperplasias, and normal tissues showed weak and sporadic staining or absence of staining; immunoblots of the same samples yielded weak signals. Occasional highly proliferative hyperplastic-reactive processes showed focal staining. Thus, our correlative histologic, cytologic, and molecular data indicate that Nup88 may be viewed as a potentially useful, broadly based histodiagnostic and molecular marker of many malignancies and premalignant dysplasias, and further suggest that in some malignant tumors, Nup88 may be selectively overexpressed as compared with other Nups. Thus, we propose that Nup88 be designated as karyoporin.

A novel, nuclear pore-associated, widely distributed molecule overexpressed in oncogenesis and development

Nuclear pore complexes are large, elaborate macromolecular structures that mediate the bidirectional nucleocytoplasmic traffic. In vertebrates, nuclear pore complexes comprise 50 to 100 proteins termed nucleoporins (Nup). An 88-kd nucleoporin (Nup88) has been recently cloned and characterized, and found to be associated in a dynamic subcomplex with the oncogenic nucleoporin CAN/Nup 214. We have produced a polyclonal antiserum to Nup88, and found that it immunoreacts convincingly in conventional tissue sections of 214 samples of malignant tumors of many types. All carcinomas were stained irrespective of site or line of differentiation; the majority of cases reacted strongly and extensively. In situ carcinomas and highly dysplastic epithelia were similarly reactive. Samples of malignant mesotheliomas, gliomas, sarcomas, and lymphoreticular tumors were also stained. Substantial reactions were also found in certain fetal tissues. Focal reactions were noted in some reactive-proliferative processes. Most benign epithelial and mesenchymal tumors and hyperplasias, and normal adult tissues reacted weakly and sporadically or not at all. Immunoblot analysis of selected samples strongly corroborated those findings. If further substantiated, our findings indicate that Nup88 could be regarded as a selective yet broadly based proliferation marker of potential significance in the histological evaluation and diagnosis of malignant transformation. Its ready applicability on conventional paraffin sections and on cytological preparations may broaden its clinical and investigative significance.

Ultrastructural and cytochemical studies on cell death of osteoclasts induced by bisphosphonate treatment

The process of apoptosis and fate of osteoclasts are not well elucidated because dying osteoclasts are rarely seen in normal bone. Histological, cytochemical, and ultrastructural features of osteoclasts undergoing apoptosis were studied in the femur and tibia of rats treated with a third-generation bisphosphonate (disodium dihydrogen (cycloheptylamino)-methylene-1, 1-bisphosphonate). After the bisphosphonate administration, osteoclasts decreased significantly in number. Initially, they became devoid of ruffled borders and detached from the bone surface. In such osteoclasts, the Golgi apparatus was degraded, or dispersed in the cytoplasm. Later, osteoclasts revealed typical features of apoptosis, with pyknotic nuclei showing condensation and margination of heterochromatins and DNA fragmentation. They were often convoluted to give rise to apoptotic bodies. In addition, enlargement and fusion of nuclear envelopes and subsequent disruption leading to leakage of nuclear contents into the cytoplasm were observed in osteoclasts in the late stage of apoptosis. These osteoclasts as well as apoptotic bodies were surrounded by cytoplasmic processes of macrophages, which often contained degenerated cytoplasmic fragments of osteoclasts. Apoptotic osteoclasts migrating into or present in capillaries were also observed in some areas. In conclusion, bisphosphonate induces apoptosis of osteoclasts, which was characterized by ultrastructural changes of the nucleus typical of apoptosis accompanied by degradation of cell organelles. The majority of them are eliminated by macrophages, but there are some that escape into blood vessels.

Characterization of zebrafish primordial germ cells: morphology and early distribution of vasa RNA

Research into germ line development is of conceptual and biotechnologic importance. In this study, we used morphology at the level of light and electron microscope to characterize the primordial germ cells (PGCs) of the zebrafish throughout embryonic and larval development. The study was complemented by the detailed analysis of mRNA expression of a putative germ line marker vasa. By morphology alone PGCs were identified at the earliest at the 5-somite stage in the peripheral endoderm in contact with the yolk syncytial layer. Subsequently, they move from lateral to medial positions into the median mesoderm and from there by means of the dorsal mesentery into the gonadal anlage at day 5 postfertilization (pf), to establish gonads with mesenchymal cells by day 9 pf. Ultrastructural analysis of the 4-day-old zebrafish larvae demonstrates the presence of the germ line-specific structures, nuage, and annulate lamellae. vasa RNA-positive cells can be followed during zebrafish embryogenesis from the 32-cell stage onward (Yoon et al., 1997). Upon completion of gastrulation, the RNA is exclusively present in the cells of the hypoblast, which as a consequence of convergence and extension movements first arrange themselves in a V-shaped string-like conformation to end up, by late somitogenesis, as a string of cells on each side of the midline. We show that the localization of maternal vasa RNA in the ovary changes from cytoplasmic, in the previtellogenic oocytes, to cortical in the vitellogenic oocytes, to concentrate at the boundary of the yolk and cytoplasm in the one cell stage zygote. These results demonstrate that the cortical vasa RNA localization precedes its cleavage furrow-associated localization in the embryos and is presumably cytoskeleton dependent. vasa RNA localization changes from asymmetric subcellular at the sphere stage, to become entirely cytoplasmic at the dome stage. These data suggest a close resemblance in modes of segregation of the germ plasma in the frog and vasa mRNA in the fish during cleavage stages. Based on the significantly larger size and the stereotype and similar position of morphologically distinct cells, presumed to be PGCs, and their vasa RNA-positive counterparts, we conclude that vasa RNA-positive cells are the PGCs and vasa RNA represents a definitive germ line marker in the fish. Dev Dyn 1999;216:153-167.

Assembly of nuclear pore complexes and annulate lamellae promotes normal pronuclear development in fertilized mammalian oocytes

In addition to functional nuclear pore complexes engaged in nucleo-cytoplasmic transport, the cytoplasmic stacks of pore complexes, called annulate lamellae, exist in numerous cell types. Although both annulate lamellae and nuclear pore complexes are present in fertilized mammalian oocytes, their relative roles in the process of fertilization and preimplantation development are not known. Using epifluorescence and electron microscopy, we explored their fate during bovine fertilization. The assembly of annulate lamellae in bovine oocytes was triggered by sperm-oocyte binding and continued concomitantly with the incorporation of the nuclear pores in the nuclear envelopes of the developing male and female pronuclei. This process was also induced by the parthenogenetic activation of metaphase-II-arrested oocytes. Depletion of Ca2+, previously implicated in oocyte activation and in the insertion of pore complexes into the nuclear envelope, prevented the formation of nuclear pore complexes, but not the assembly of annulate lamellae in oocyte cytoplasm. Injection of the nuclear pore antagonist, wheat germ agglutinin, into the cytoplasm of mature oocytes that were subsequently fertilized caused the arrest of pronuclear development, indicating the requirement of nuclear pore complexes for normal pronuclear development. Treatment of the fertilized oocytes with the microtubule inhibitor, nocodazole, prevented gathering of annulate lamellae around the developing pronuclei, insertion of nuclear pores into their nuclear envelopes, and further pronuclear development. The formation of the male pronuclei was reconstituted in Xenopus egg extracts and reflected the behavior of nuclear pores during natural fertilization. These data suggest that nuclear pore complexes are required for normal pronuclear development from its beginning up until pronuclear apposition. Annulate lamellae may be involved in the turnover of nuclear pore complexes during fertilization, which is in turn facilitated by the reorganization of oocyte microtubules and influx of Ca2+ into oocyte cytoplasm.

In vivo dynamics of nuclear pore complexes in yeast

While much is known about the role of nuclear pore complexes (NPCs) in nucleocytoplasmic transport, the mechanism of NPC assembly into pores formed through the double lipid bilayer of the nuclear envelope is not well defined. To investigate the dynamics of NPCs, we developed a live-cell assay in the yeast Saccharomyces cerevisiae. The nucleoporin Nup49p was fused to the green fluorescent protein (GFP) of Aequorea victoria and expressed in nup49 null haploid yeast cells. When the GFP-Nup49p donor cell was mated with a recipient cell harboring only unlabeled Nup49p, the nuclei fused as a consequence of the normal mating process. By monitoring the distribution of the GFP-Nup49p, we could assess whether NPCs were able to move from the donor section of the nuclear envelope to that of the recipient nucleus. We observed that fluorescent NPCs moved and encircled the entire nucleus within 25 min after fusion. When assays were done in mutant kar1-1 strains, where nuclear fusion does not occur, GFP-Nup49p appearance in the recipient nucleus occurred at a very slow rate, presumably due to new NPC biogenesis or to exchange of GFP-Nup49p into existing recipient NPCs. Interestingly, in a number of existing mutant strains, NPCs are clustered together at permissive growth temperatures. This has been explained with two different hypotheses: by movement of NPCs through the double nuclear membranes with subsequent clustering at a central location; or, alternatively, by assembly of all NPCs at a central location (such as the spindle pole body) with NPCs in mutant cells unable to move away from this point. Using the GFP-Nup49p system with a mutant in the NPC-associated factor Gle2p that exhibits formation of NPC clusters only at 37 degrees C, it was possible to distinguish between these two models for NPC dynamics. GFP-Nup49p-labeled NPCs, assembled at 23 degrees C, moved into clusters when the cells were shifted to growth at 37 degrees C. These results indicate that NPCs can move through the double nuclear membranes and, moreover, can do so to form NPC clusters in mutant strains. Such clusters may result by releasing NPCs from a nuclear tether, or by disappearance of a protein that normally prevents pore aggregation. This system represents a novel approach for identifying regulators of NPC assembly and movement in the future.

Nuclear pore complex assembly studied with a biochemical assay for annulate lamellae formation

Formation of the nuclear pore is an intricate process involving membrane fusion and the ordered assembly of up to 1,000 pore proteins. As such, the study of pore assembly is not a simple one. Interestingly, annulate lamellae, a cytoplasmic organelle consisting of stacks of flattened membrane cisternae perforated by numerous pore complexes, have been found to form spontaneously in a reconstitution system derived from Xenopus egg extracts, as determined by electron microscopy (Dabauvalle et al., 1991). In this work, a biochemical assay for annulate lamellae (AL) formation was developed and used to study the mechanism of AL assembly in general and the assembly of individual nucleoporins into pore complexes in particular. Upon incubation of Xenopus egg cytosol and membrane vesicles, the nucleoporins nup58, nup60, nup97, nup153, and nup200 initially present in a disassembled form in the cytosol became associated with membranes and were pelletable. The association was time and temperature dependent and could be measured by immunoblotting. Thin-section electron microscopy as well as negative staining confirmed that annulate lamellae were forming coincident with the incorporation of pore proteins into membranes. Homogenization and subsequent flotation of the membrane fraction allowed us to separate a population of dense membranes, containing the integral membrane pore protein gp210 and all other nucleoporins tested, from the bulk of cellular membranes. Electron microscopy indicated that annulate lamellae were enriched in this dense, pore protein-containing fraction. GTP gamma S prevented incorporation of the soluble pore proteins into membranes. To address whether AL form in the absence of N-acetylglucosaminylated pore proteins, AL assembly was carried out in WGA-sepharose-depleted cytosol. Under these conditions, annulate lamellae formed but were altered in appearance. When the membrane fraction containing this altered AL was homogenized and subjected to flotation, the pore protein-containing membranes still sedimented in a distinct peak but were less dense than control annulate lamellae.

NUP145 encodes a novel yeast glycine-leucine-phenylalanine-glycine (GLFG) nucleoporin required for nuclear envelope structure

We have isolated and characterized the gene encoding a fourth yeast glycine-leucine-phenylalanine-glycine (GLFG) repeat nucleoporin with a calculated molecular mass of 145.3 kD, and therefore termed NUP145. The amino-terminal half of Nup145p is similar to two previously identified GLFG nucleoporins, Nup116p and Nup100p (Wente, S. R., M. P. Rout, and G. Blobel. 1992. J. Cell Biol. 119:705-723). A deletion/disruption in the amino-terminal half of NUP145 (nup145 delta N) had only a slight effect on cell growth at temperatures between 17 and 37 degrees C. However, immunofluorescence microscopy of nup145 delta N cells with antinucleoporin antibodies showed that the characteristic punctate nuclear staining normally seen in wild-type yeast cells was reduced, with the majority of the signal located in one or two intense spots at the nuclear periphery. Thin section electron microscopy analysis revealed the presence of what appeared to be successive herniations of the nuclear envelope forming grape-like structures at primarily one site on the nup145 delta N nuclei. These successive herniations contained numerous NPC-like structures, correlating to the limited bright patches of anti-nucleoporin immunofluorescence signal. In some cases the successive herniations were small. Occasionally, however, multi-lobulated nuclei were seen. We suggest that the ultrastructural phenotype of nup145 delta N cells is due to a defective interaction of nup145 delta N NPCs with the surrounding pore membrane domain of the nuclear envelope. We have also analyzed the synthetic lethal phenotypes among GLFG nucleoporin mutant alleles, and found that strains harboring nup116 and either nup100 or nup145 mutations were not viable. This, in combination with the morphological analysis, may reflect overlapping yet distinct roles for these three GLFG nucleoporins in NPC-nuclear envelope interactions.

Ultrastructure of the ootype of the lung fluke Paragonimus ohirai (Digenea, Troglotrematidae) in mated and single-infection worms

The ootype of Paragonimus ohirai was studied by both scanning and transmission electron microscopy. The ootype wall in 20-week-old worms from single infections was similar in its epithelial cell architecture and components to that of mated worms at 10 weeks postinfection. The lining epithelium consisted of a single layer of nucleated cells. The cytoplasm displayed a variety of organelles such as occasional Golgi complexes, well-developed annulate lamellae, frequent lysosomes, abundant mitochondria, and numerous ribosomes, suggesting high activities of intracellular synthesis and digestion. The former three organelles were generally located in the apical cytoplasm protruding into the lumen and may be significant in participating in regulation of egg formation. The present comparative studies suggest that the ootype epithelium can mature even by single infections and that the organized intracellular activities remain developed in single worms even after prolonged infection.

Intranuclear filaments containing a nuclear pore complex protein

Nuclear pore complexes (NPCs) are anchoring sites of intranuclear filaments of 3-6 nm diameter that are coaxially arranged on the perimeter of a cylinder and project into the nuclear interior for lengths varying in different kinds of cells. Using a specific monoclonal antibody we have found that a polypeptide of approximately 190 kD on SDS-PAGE, which appears to be identical to the recently described NPC protein "nup 153," is a general constituent of these intranuclear NPC-attached filaments in different types of cells from diverse species, including amphibian oocytes where these filaments are abundant and can be relatively long. We have further observed that during mitosis this filament protein transiently disassembles, resulting in a distinct soluble molecular entity of approximately 12.5 S, and then disperses over most of the cytoplasm. Similarly, the amphibian oocyte protein appears in a soluble form of approximately 16 S during meiotic metaphase and can be immunoprecipitated from egg cytoplasmic supernatants. We conclude that this NPC protein can assemble into a filamentous form at considerable distance from the nuclear envelope and discuss possible functions of these NPC-attached filaments, from a role as guidance structure involved in nucleocytoplasmic transport to a form of excess storage of NPC proteins in oocytes.

A temperature-sensitive NUP116 null mutant forms a nuclear envelope seal over the yeast nuclear pore complex thereby blocking nucleocytoplasmic traffic

NUP116 encodes a 116-kD yeast nuclear pore complex (NPC) protein that is not essential but its deletion (nup116 delta) slows cell growth at 23 degrees C and is lethal at 37 degrees C (Wente, S. R., M. P. Rout, and G. Blobel. 1992. J. Cell Biol. 119:705-723). Electron microscopic analysis of nup116 delta cells shifted to growth at 37 degrees C revealed striking perturbations of the nuclear envelope: a double membrane seal that was continuous with the inner and outer nuclear membranes had formed over the cytoplasmic face of the NPCs. Electron-dense material was observed accumulating between the cytoplasmic face of these NPCs and the membrane seal, resulting in "herniations" of the nuclear envelope around individual NPCs. In situ hybridization with poly(dT) probes showed the accumulation of polyadenylated RNA in the nuclei of arrested nup116 delta cells, sometimes in the form of punctate patches at the nuclear periphery. This is consistent with the electron microscopically observed accumulation of electron-dense material within the nuclear envelope herniations. We propose that nup116 delta NPCs remain competent for export, but that the formation of the membrane seals over the NPCs blocks nucleocytoplasmic traffic.

The single transmembrane segment of gp210 is sufficient for sorting to the pore membrane domain of the nuclear envelope

The glycoprotein gp210 is located in the "pore membrane," a specialized domain of the nuclear envelope to which the nuclear pore complex (NPC) is anchored. gp210 contains a large cisternal domain, a single transmembrane segment (TM), and a COOH-terminal, 58-amino acid residue cytoplasmic tail (CT) (Wozniak, R. W., E. Bartnik, and G. Blobel. 1989. J. Cell Biol. 108:2083-2092; Greber, U. F., A. Senior, and L. Gerace. 1990. EMBO (Eur. Mol. Biol. Organ.) J. 9:1495-1502). To locate determinants for sorting of gp210 to the pore membrane, we constructed various cDNAs coding for wild-type, mutant, and chimeric gp210, and monitored localization of the expressed protein in 3T3 cells by immunofluorescence microscopy using appropriate antibodies. The large cisternal domain of gp210 (95% of its mass) did not reveal any sorting determinants. Surprisingly, the TM of gp210 is sufficient for sorting to the pore membrane. The CT also contains a sorting determinant, but it is weaker than that of the TM. We propose specific lateral association of the transmembrane helices of two proteins to yield either a gp210 homodimer or a heterodimer of gp210 and another protein. The cytoplasmically oriented tails of these dimers may bind cooperatively to the adjacent NPCs. In addition, we demonstrate that gp210 co-localizes with cytoplasmically dispersed nucleoporins, suggesting a cytoplasmic association of these components.

Nuclear membrane modifications in polytene nuclei of Drosophila melanogaster: serial reconstruction and cytochemistry

The nuclear envelope of polytene nuclei of salivary glands of Drosophila melanogaster displays modifications consisting of nuclear envelope invaginations (NEI) and evaginations (NEE). Ultrastructural analyses combined with three-dimensional reconstruction and cytochemistry show that NEI are bounded by a single membrane and that they may arise as invaginations of the inner nuclear membrane. NEI extend deeply into the nucleus. The lumens of NEI may collapse resulting in membranous sheets which may combine with those arising from adjacent NEI to form intranuclear structures resembling annulate lamellae. All NEI are associated with NEE. In contrast to NEI, NEE are enclosed in a double membrane morphologically identical to the nuclear envelope. While NEI and NEE share wheat germ agglutinin binding properties with the nuclear envelope, they differ in their ability to localize lanthanum. Pore annuli of NEI display complete lack of lanthanum binding, while those of NEE exhibit minor deposition of this cation. In contrast, pore annuli of the nuclear envelope are specifically and significantly decorated by lanthanum. A conceptual model based on the results obtained suggests that NEI are formed by invaginations of the inner nuclear membrane, together with accompanying modifications of pore complexes.

Nuclear pore structure and function

Nuclear pores are huge macromolecular assemblies, approximately 120 nm in diameter, that perforate the nuclear membrane and mediate nucleocytoplasmic transport. Nuclear pores are constructed from a cylindrical spoke-plug complex sandwiched between nucleoplasmic and cytoplasmic rings. The spoke-plug complex has pronounced 8-fold rotational symmetry, which is also present in the rings. Nucleocytoplasmic transport is an energy-requiring process that takes place through the centre of the pores and can accommodate particles up to about 25 nm diameter. Translocation is preceded by a separate binding step which does not require energy. Several nuclear pore proteins have been isolated and characterized. Many of these proteins contain O-linked N-acetyl glucosamine residues and may have similar modular domain structures.

Cytoplasmic distribution of poly(A)-containing RNA in developing Necturus maculosus oocytes with reference to annulate lamellae

The cytoplasmic distribution of poly(A)+ mRNA and its relationship to annulate lamellae were examined in developing Necturus maculosus oocytes by in situ hybridization with [3H]poly(U). The specificity of [3H]poly(U) binding was tested by incubating control ovarian sections with either KOH or RNase A before in situ hybridization. In both experiments, the silver grain densities were markedly reduced. Poly(A)+ RNA is uniformly distributed in the cytoplasm until the mid-growth phase and then later in vitellogenesis becomes localized in the subcortical ooplasm. The silver grain density in the cytoplasm varied during oogenesis and was greatest in previtellogenic oocytes. Annulate lamellae commonly are observed with the light microscope in oocytes prior to vitellogenesis. In such oocytes, the labeled mRNA probe is observed over cytoplasmic regions of annulate lamellae. The results suggests that a differential localization of messenger RNA occurs during oogenesis in Necturus maculosus. Furthermore, poly(A)+ RNA is present in cytoplasmic regions of annulate lamellae.

The influence of LH and/or FSH on Leydig and Sertoli cell morphology after testicular involution in the Djungarian hamster, Phodopus sungorus, induced by hypophysectomy or short photoperiods

In the Djungarian hamster, Phodopus sungorus, the morphological alterations of Sertoli and Leydig cells were investigated under the influence of gonadotropins (LH and/or FSH) after testicular regression induced either by hypophysectomy or photoinhibition. Stimulation with LH or LH/FSH lead to a redifferentiation of morphological features of Leydig cells such as nuclear structure, smooth endoplasmic reticulum and size of cell and nucleus area within 7 days of hormone treatment. Similarly, stimulation with FSH or LH/FSH caused redifferentiation of Sertoli cell nuclear structure, rough endoplasmic reticulum and nuclear size within 7 days. Incomplete restoration of Leydig and Sertoli cell morphology was observed under FSH and LH treatment respectively. In both Leydig and Sertoli cells combined LH and FSH application resulted in an increased response in respect to morphological redifferentiation, possibly indicating paracrine regulatory mechanisms. In all groups treated an intact blood-testis barrier (BTB) was reestablished after a minimum of 7 days, indicating that the existence of the blood-testis barrier is not dependent on specific gonadotropin supply but on the developmental stage of the seminiferous epithelium. Sham-operated animals showed increased cell and nucleus area of Leydig cells in comparison to photostimulated animals. After testicular involution as well as after LH or FSH treatment there were no significant morphological differences between hypophysectomized and photoinhibited animals in respect to the documented ultrastructural and morphometrical characteristics.(ABSTRACT TRUNCATED AT 250 WORDS)

A lamin-independent pathway for nuclear envelope assembly

The nuclear envelope is composed of membranes, nuclear pores, and a nuclear lamina. Using a cell-free nuclear assembly extract derived from Xenopus eggs, we have investigated how these three components interact during nuclear assembly. We find that the Xenopus embryonic lamin protein LIII cannot bind directly to chromatin or membranes when each is present alone, but is readily incorporated into nuclei when both of the components are present together in an assembly extract. We find that depleting lamin LIII from an extract does not prevent formation of an envelope consisting of membranes and nuclear pores. However, these lamin-depleted envelopes are extremely fragile and fail to grow beyond a limited extent. This suggests that lamin assembly is not required during the initial steps of nuclear envelope formation, but is required for later growth and for maintaining the structural integrity of the envelope. We also present results showing that lamins may only be incorporated into nuclei after DNA has been encapsulated within an envelope and nuclear transport has been activated. With respect to nuclear function, our results show that the presence of a nuclear lamina is required for DNA synthesis to occur within assembled nuclei.

Structural and ultrastructural study of the ovary in childhood leukemia after successful treatment

Ovarian biopsy specimens from ten girls (three postmenarcheal) who had undergone antiblastic treatment for acute lymphoblastic leukemia (ALL) and were in complete remission were examined by light microscope. The biopsy specimens from four of these patients (three postmenarcheal) were also observed by electron microscope. The structural and ultrastructural analysis showed a reduction in the number of follicles which were otherwise normal. No follicles were found in the thin sections from two of the three postmenarcheal girls, whereas normal follicles were observed in the third. The cortical stroma showed moderate to severe signs of fibrosis and changes of capillaries. All of these alterations were more evident in patients where ALL was diagnosed at an older age and this finding suggests that they are at a higher risk for low fertility or early menopause.

A review of echinoderm oogenesis

This review of the anatomical, histological, biochemical, and molecular biological literature on echinoderm oogenesis includes the entire developmental history of oocytes; from their inception to the time they become ova. This is done from a comparative perspective, with reference to members of the five extant echinoderm classes; crinoids, holothurians, asteroids, ophiuroids, and echinoids. I describe the anatomy and fine structure of the echinoderm ovary, with emphasis on both the cellular relationships of the germ line cells to the somatic cells of the inner epithelium, and on the neuromuscular systems. I review the literature on the growth of oogonia into fully formed oocytes, including the process of vitellogenesis, presenting an ultrastructural analysis of the organelles and extracellular structures found in fully formed echinoderm oocytes. Echinoderm oocyte maturation is reviewed and a description of the ultrastructural, biochemical and molecular biological changes thought to occur during this process is presented. Finally, I discuss oocyte ovulation, the severing of cellular connections between the oocyte and its surrounding somatic epithelial cells.

Synapses formed by olivocochlear axon branches in the mouse cochlear nucleus

Cochlear nucleus branches of thick olivocochlear axons were labeled by injections of horseradish peroxidase into the spiral ganglion of the cochlear basal turn in mice. Six labeled axons were traced by light microscopy, and selected portions of seven branches were sectioned serially for electron microscopic examination. Axonal branches most frequently terminated near certain granule cell regions of the ventral cochlear nucleus. This article describes terminals, synapses, and postsynaptic elements of these olivocochlear branches. The olivocochlear branches had both terminal and en passant boutons that contained round vesicles and made asymmetric synapses with other neuronal processes. About a quarter of the synapses also possessed additional specializations, postsynaptic, or subjunctional bodies. Mossy terminals, a multisynaptic type of terminal commonly found in granule cell regions, were not found arising from any of the labeled branches. No somatic synapses were found, although contacts with cell bodies were occasionally observed. The predominant synaptic target of olivocochlear branches were what appeared to be dendrites of large diameter. At least some of these large dendrites received multiple synapses from a single labeled olivocochlear branch. The morphological characteristics of reconstructed dendrites suggest that multipolar cells might be predominant targets for the medial olivocochlear system in the cochlear nucleus. This was demonstrated in one case in which a large dendrite was followed to its cell body of origin.