Freeze-fracture studies of annulate lamellae in zebrafish oocytes

Summary The zebrafish oocyte contains prominent stacks of annulate lamellae (AL) located primarily in a subcortical position of the ooplasm. Many lamellae comprising a stack eventually exhibit continuity with the rough-surfaced endoplasmic reticulum which is present in abundance in larger oocytes. Pore structure of both AL and nuclear envelope (NE) was studied and compared by use of freeze-fracture electron microscopy. In freeze-fracture replicas, the NE and AL pores were easily distinguished, and a variety of fracture planes with respect to the stacked AL were generated. The pore diameter of NE and AL is similar (100nm). The number of nuclear pores varied from an average of 40 pores/m² in early stage oocytes to nearly double this number in later stage oocytes. For AL, the center-to-center spacing (120–130 nm) and the number of pores per square micrometer (56–67) did not change markedly regardless of oocyte developmental stage examined. Hexagonal packing of AL pores is a common feature. The AL pores have an angular margin with octagonal symmetry suggested in some cases. The AL pore interior contains fibrillar and particulate components and, depending upon the fracture plane, may appear to be filled with a plug of material. Both P- and E-membrane fracture faces of AL have a relative scarcity of intramembranous particles. The non-porous membranes that extend from the AL, however, have a higher concentration of intramembranous particles.     

Ribosomal bodies and annulate lamellae in the oocytes of the lizardPodarcis sicula

Summary Ultrastructural studies suggest that, in the oocytes of the lizardPodarcis sicula, ribosomal bodies are structurally continuous with annulate lamellae during their organization and disaggregation. This observation may indicate the dynamic transformation of the cytomembranes of one structure into those of the other, and vice versa. Moreover, the presence of annulate lamellae has been detected for the first time in lizard oocytes. The hypothesis is advanced that ribosomal bodies and annulate lamellae, in spite of some different structural characteristics, may play a similar role during the oocyte growth.     

Intranuclear annulate lamellae in oocytes of the tunicate,Styela partita

Summary Intranuclear annulate lamellae have been observed with the electron microscope in oocytes of the tunicate, Styela partita. Morphological evidence suggests that the annulate lamellae may arise by a specialized fusion process of individual vesicles. Intranuclear vesicles appear to be formed, in time, before differentiated annulate lamellae. It is also suggested that the position and structure of an annulus is in large part determined by the fusion of the vesicles. An annulus may be present as soon as two vesicles have completed their fusion process. Finally, it is again suggested on the basis of morphological evidence that the intranuclear vesicles are derived by the blebbing activity of the inner layer of the nuclear envelope.This investigation was supported by grants (RG-9229, 9230) from the National Institutes of Health, Public Health Service. The electron microscope facilities used were also supported by a grant (GM-05479) from the National Institutes of Health to Professor H. W. Beams.     

Pre-M phase-promoting factor associates with annulate lamellae in Xenopus oocytes and egg extracts

We have used complementary biochemical and in vivo approaches to study the compartmentalization of M phase-promoting factor (MPF) in prophase Xenopus eggs and oocytes. We first examined the distribution of MPF (Cdc2/CyclinB2) and membranous organelles in high-speed extracts of Xenopus eggs made during mitotic prophase. These extracts were found to lack mitochondria, Golgi membranes, and most endoplasmic reticulum (ER) but to contain the bulk of the pre-MPF pool. This pre-MPF could be pelleted by further centrifugation along with components necessary to activate it. On activation, Cdc2/CyclinB2 moved into the soluble fraction. Electron microscopy and Western blot analysis showed that the pre-MPF pellet contained a specific ER subdomain comprising "annulate lamellae" (AL): stacked ER membranes highly enriched in nuclear pores. Colocalization of pre-MPF with AL was demonstrated by anti-CyclinB2 immunofluorescence in prophase oocytes, in which AL are positioned close to the vegetal surface. Green fluorescent protein-CyclinB2 expressed in oocytes also localized at AL. These data suggest that inactive MPF associates with nuclear envelope components just before activation. This association may explain why nuclei and centrosomes stimulate MPF activation and provide a mechanism for targeting of MPF to some of its key substrates.     

Structural organization and possible functional role of annulate lamellae containing cytoplasmic pores

This review is devoted to annulate lamellae, a specific compartment of endoplasmic reticulum that occurs, presumably, in actively growing and rapidly dividing cells (oocytes, embryonic and tumor cells). We summarized both earlier and recent data on the dustribution of annulate lamellae in various cell types, on their morphology, and the distribution of interaction with intracellular structures at various treatments. As the annulate lamellae contain cytoplasmic pore complexes, a special attention was paid to their relation with nuclear pores. Possible functions of the annulate lamellae in intracellular processes and, particularly, in nuclear envelope assembly, are discussed.     

Differentiation and distribution of annulate lamellae in growing oocytes in the newt, Cynops pyrrhogaster

Stages of oocyte development in Cynops pyrrogaster are defined, and changes of annulate lamellae in their fine structure, number, sizes and locations during oogenesis are described. The results show that two different types of annulate lamellae occur during oogenesis. One type differentiates in or at the periphery of vesicle-rich cytoplasm at the early stages of vitellogenesis and increases in number and size. The maximum number of about 40 stacks per median section of oocyte is reached at the stage of complete differentiation of the animal and the vegetal hemispheres. In these growing oocytes, all the stacks show elongate appearances and tetragonal arrangements of annuli as common characteristics. A second type of stacks of annulate lamellae is added anew in full-grown oocytes, increasing the number of stacks per median section of the oocyte to about 90. The new stacks occur in close contact with electron-dense bodies in the cytoplasm and have a massive appearance and hexagonal array of annuli. It is suggested that they appear coincidentally with the onset of oocyte maturation. The possible significance of the observed results is discussed.     

Relationships between annulate lamellae and filament bundles in oocytes of the zebrafish,Brachydanio rerio

Summary Bundles of filaments have been observed in the vitellogenic oocyte of the zebrafish, Brachydanio rerio; and these filaments illustrate a close spatial and structural relationship to annulate lamellae. The filaments range from 6–8 nm in diameter, and the annulate lamellae may cap both rounded ends of the bundle as well as extend parallel to the surface of the filament bundles. The ends of the filaments can be observed to exhibit an apparent termination in close relation to pore margins of the annulate lamellae, the membrane of the interpore regions of the annulate lamellae, as well as many nearby polyribosomes. The possible functional significance of this unique relationship is discussed in reference to a recent hypothesis regarding the function of annulate lamellae.     

The effect of glutaraldehyde fixation on the elucidation of the morphogenesis of annulate lamellae in oocytes ofRana pipiens

Summary Primary fixation of the frog oocyte with glutaraldehyde, compared to osmium tetroxide, alters the appearance of components involved in the morphogenesis of annulate lamellae. With glutaraldehyde, the outer layer of the nuclear envelope is connected with membranous laminae of variable length. Rounded blebs of the outer layer of the nuclear envelope are infrequently observed. Further, rather than clusters or rows of cytoplasmic vesicles as are observed in osmium tetroxide-fixed cells; numerous and long, smooth-surfaced lamellae are present in the ooplasm after glutaraldehyde fixation. The long membranous laminae then become concentrated in several ooplasmic packets. This is followed by the progressive alignment or orientation of the laminae within the packet. Eventually, those aligned and formerly smooth-surfaced lamellae are converted into annulate lamellae.This study was supported by research grants (HD-00699, GM-09229) and a Career Development Award from the National Institutes of Health, U.S. Public Health Service.     

Dynamics of annulate lamellae in Drosophila syncytial embryos

The mitotic events in eukaryotic cells are controlled by a family of evolutionary conserved cyclin-dependent kinases (cdk) that phosphorylate cell proteins, which results in the structural reorganization of the entire cell. Our recent studies of Drosophila syncytial embryos have demonstrated that changes in cdk1 activity controlling the assembly and disassembly of nuclear pore complexes also affect the structure of cytoplasmic pores in annulate lamellae. Here, we report a comparative electron microscopic analysis of the dynamics of these organelles during mitosis throughout the development of a Drosophila syncytial embryo. We presume that the distribution of annulate lamellae containing mature cytoplasmic pores across the cytoplasm reflects local reductions in the mitotic kinase cdk1 activity during the development of Drosophila syncytial embryos.     

Annulate lamellae: comparison of antigenic epitopes of annulate lamellae membranes with the nuclear envelope

Laminin derived from the Engelbreth-Holm-Swarm (EHS) tumor and a lamininlike molecule synthesized by RN22 Schwannoma cells both stimulate rapid neurite outgrowth, consistent with a common neurite-promoting site. However, antilaminin antisera can only inhibit the activity of the EHS laminin. The blocking antibodies in such sera are directed against the terminal heparin-binding domain of the laminin long arm (Edgar, D., R. Timpl, and H. Thoenen. 1984. EMBO [Eur. Mol. Biol. Organ.] J. 3: 1463-1468). These epitopes are demonstrated by immunoblotting to be part of the A chain and to be absent in RN22 laminin, showing (through metabolic labeling) that the cells synthesized little if any 440-kD A chain. This indicates that the antibody inhibition was probably due to steric hindrance, a common neurite-promoting site, apparently not being antigenic in native molecules. Antibodies raised against a 25-kD proteolytic fragment derived from the long arm of laminin were then used as probes to identify other potential neurite-promoting structures. Although these antibodies do not cross-react with native laminin, they recognized the B chains of denatured EHS and RN22 molecules on immunoblots. The antibodies also bound to the large proteolytic fragment, derived from the long arm of laminin that contains the neurite-promoting site, thus inhibiting its activity. Taken together, these results point to the localization of normally nonantigenic, defined, B chain sequences within or close to the neurite-promoting site of laminin.     

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.     

Unusual circular annulate lamellae in hepatocytes of Torpedo marmorata

This report describes an unusual morphology of annulate lamellae (AL) in the hepatocytes of Torpedo marmorata Risso. These Als and fragments are detected amidst the main glycogen and lipid deposits. AL cisterns are circumscribed by parts of the smooth endoplasmic reticulum. Based on the finding of these unusual annular ALs, accompanied by other subcellular lesions such as a number of membranous whorls and altered mitochondria. These findings can concur and support other authors' observations suggesting that these adult hepatocytes transient changes reflect that this species could be exposed to local, natural or likely human coastal seabed pollutants.     

Dynamics of the annulate lamellae in Drosophila syncytial embryos

In eukaryotic cells, mitotic events are controlled by evolutionarily conserved cyclin-dependent kinases (cdk): these kinases phosphorylate cell proteins, which causes structural reorganization of the entire cell. Our recent studies of Drosophila syncytial embryos have demonstrated that cdk1 activity is a key factor that controls nuclear pore complex assembly/disassembly and affects the structure of cytoplasmic pores in the annulate. In this paper, we report a comparative analysis of these cytoplasmic organelles throughout the cell-cycle and throughout the development of Drosophila syncytial embryos. Based on the results obtained, it was presupposed that distribution of annulate lamellae containing cytoplasmic pores could reflect the inactivation of the mitotic kinase cdk1 in Drosophila syncytial embryos.     

The dependence of annulate lamellae formation on the nucleus in parthenogenetic rabbit eggs

Previously it has been shown that, in the rabbit, although annulate lamellae (AL) are absent in the follicular oocytes, they appear in the fertilized eggs after the formation of the pronuclei. Furthermore, neither pronuclei nor AL appear when unfertilized eggs are aged in vivo or in vitro. This study was undertaken to determine whether AL formation requires presence of an intact nucleus, or whether the sperm alone contains the stimulatory factors essential to AL synthesis. Rabbit eggs were exposed to 10 degrees C, then incubated for 24 hours. Control eggs were incubated without cold-treatment. Electron microscopic observations indicated that two-thirds of the eggs formed one to two 'pronuclei', or subnuclei. The remainder one-third of the cold-treated eggs and the control eggs failed to form 'pronuclei'. AL were present in large amounts only in those activated eggs (parthenogenones) which formed 'pronuceli.' AL were absent in the control and the non-activated experimental eggs, both of which failed to form a 'pronucleus.' A few small AL were observed in eggs with subnuclei. Condensed fine textured nucleoli appeared precociously during cold-treatment in some eggs and they were present in the 'pronuclei' of activated eggs. It was concluded that the sperm is not necessary for AL formation, but the presence of an intact nucleus is mandatory.