Nuclear pores in the spermatozoon of the rat

Summary The paper describes a hexagonal array of nuclear pores in a non-redundant region of the nuclear envelope underlying the basal surface of the rat spermatozoon head. It is concluded that intranuclear material protruding through these pores is the cause of the characteristic rows of circular bumps found in surface replicas of this region.     

Functions of nuclear bodies as revealed by ultrastructural autoradiography and cytochemistry

Summary The simple nuclear body containing a few RNA particles appears through the nuclear pores in the cytoplasm, originating from the nucleolus. The complex nuclear body consisting mainly of RNA components is highly active in the incorporation of RNA precursors. Accordingly, the appearance of nuclear bodies may be related either to transport to the cytoplasm of nucleolar components or to the enhancement of rRNA synthesis.     

Many mechanisms, one entrance: membrane protein translocation into the nucleus

The inner nuclear membrane harbors a unique set of membrane proteins, many of which interact with nuclear intermediate filaments and chromatin components and thus play an important role in nuclear organization and gene expression regulation. These membrane proteins have to be constantly transported into the nucleus from their sites of synthesis in the ER to match the growth of the nuclear membrane during interphase. Many mechanisms have evolved to enable translocation of these proteins to the nucleus. The full range of mechanisms goes from rare autophagy events to regulated translocation using the nuclear pore complexes. Though mechanisms involving nuclear pores are predominant, within this group an enormous mechanistic range is observed from free diffusion through the peripheral channels to many distinct mechanisms involving different nucleoporins and other components of the soluble protein transport machinery in the central channels. This review aims to provide a comprehensive insight into this mechanistic diversity.     

Elektronenmikroskopisch-cytochemische Untersuchungen an der Kernmembran vonStreptotheca thamesis

Summary The nuclear envelope and nuclear pores of the diatomStreptotheca thamesis are described, concerning some ultrastructural and functional features. Treatment with DNAse or pepsine results in a partial breakdown of these organelles.     

Pyk2 cytonuclear localization: mechanisms and regulation by serine dephosphorylation

Cytonuclear signaling is essential for long-term alterations of cellular properties. Several pathways involving regulated nuclear accumulation of Ser/Thr kinases have been described but little is known about cytonuclear trafficking of tyrosine kinases. Proline-rich tyrosine kinase 2 (Pyk2) is a cytoplasmic non-receptor tyrosine kinase enriched in neurons and involved in functions ranging from synaptic plasticity to bone resorption, as well as in cancer. We previously showed the Ca²⁺-induced, calcineurin-dependent, nuclear localization of Pyk2. Here, we characterize the molecular mechanisms of Pyk2 cytonuclear localization in transfected PC12 cells. The 700–841 linker region of Pyk2 recapitulates its depolarization-induced nuclear accumulation. This region includes a nuclear export motif regulated by phosphorylation at residue S778, a substrate of cAMP-dependent protein kinase and calcineurin. Nuclear import is controlled by a previously identified sequence in the N-terminal domain and by a novel nuclear targeting signal in the linker region. Regulation of cytonuclear trafficking is independent of Pyk2 activity. The region regulating nuclear localization is absent from the non-neuronal shorter splice isoform of Pyk2. Our results elucidate the mechanisms of Ca²⁺-induced nuclear accumulation of Pyk2. They also suggest that Pyk2 nuclear accumulation is a novel type of signaling response that may contribute to specific long-term adaptations in neurons.     

Kinetics of chemo-attraction of polymorphonuclear leukocytes towards N-formyl peptide studied with a novel polycarbonate (Nucleopore) membrane in the Boyden chamber

The motile responses of human polymorphonuclear leukocytes (PMN) to N-formyl-methionyl-leucyl-phenylalanine (FMLP) in the Boyden chamber using a new sparse-pore polycarbonate membrane (pores 3 micron in diameter and occupying 0.1% of surface area) were compared with those demonstrated by using a standard polycarbonate (Nuclepore) filtration membrane (pores 3 micron in diameter and occupying 5% of surface area). Motility of PMN in gradients of FMLP using the new membrane was not influenced by chemokinetic effects of the factor, and the 'background' migration of the cells was minimal. However, motility of PMN in gradients of FMLP using the standard membrane was found to be influenced by chemokinetic effects of the chemotactic factor, and the 'background' or 'control' migration (in the absence of chemotactic factor) of the cells was substantial. Greater directional migration of PMN according to steepness of the gradient of chemotactic factor was demonstrated with the use of the new membrane. The new membrane may be of considerable value in the further study of the chemotactic responses of PMN.     

A novel exocrine gland inside the thoracic appendages (‘gemmae’) of the queenless antDiacamma australe

Summary In the queenless antDiacamma australe, all workers eclose with a pair of tiny thoracic appendages (gemmae). These are sac-like and exhibit a distinct cuticular sculpturing, with minute pores opening on the outer surface. These pores are connected to glandular cells which completely fill the appendages, and thus an exocrine stignal is likely to be released. We discuss the social context of this signal: only one worker in each colony retains the gemmae.     

Electron microscopical observation of the contact between ribosomes and detergent-resistant cytofilaments

Summary The contact of cytofilaments with ribosome-like particles in Triton X-100-treated cells of Zajdela ascites hepatoma was revealed. It is suggested that cytofilaments are engaged in the transport of ribosomes from the nuclear surface into definite areas of cytoplasm.     

Electron microscopical observation of the contact between ribosomes and detergent-resistant cytofilaments

The contact of cytofilaments with ribosome-like particles in Triton X-100-treated cells of Zajdela ascites hepatoma was revealed. It is suggested that cytofilaments are engaged in the transport of ribosomes from the nuclear surface into definite areas of cytoplasm.     

Scanning electron microscopy of antibody-dependent cell-mediated cytotoxicity of Friend leukemia virus-infected spleen cells.

Friend leukemia virus (FLV) infected splenocytes treated with rabbit anti-FLV serum and subsequently incubated with splenic lymphocytes from non-immune Balb/c mice were examined by scanning electron microscopy. Villous-covered lymphocytes adherred to the tumor cells and induced surface blebs, numerous membrane pores and eventual tumor cell lysis.     

Scanning electron microscopy of antibody-dependent cell-mediated cytotoxicity of Friend leukemia virus-infected spleen cells

Summary Friend leukemia virus (FLV) infected splenocytes treated with rabbit anti-FLV serum and subsequently incubated with splenic lymphocytes from non-immune Balb/c mice were examined by scanning electron microscopy. Villous-covered lymphocytes adherred to the tumor cells and induced surface blebs, numerous membrane pores and eventual tumor cell lysis.     

Possible mechanisms and function of nuclear trafficking of the colony-stimulating factor-1 receptor

Receptor tyrosine kinases (RTK) have long being studied with respect to the “canonical” signaling. This includes ligand-induced activation of a receptor tyrosine kinase at the cell surface that leads to receptor dimerization, followed by its phosphorylation in the intracellular domain and activation. The activated receptor then recruits cytoplasmic signaling molecules including other kinases. Activation of the downstream signaling cascade frequently leads to changes in gene expression following nuclear translocation of downstream targets. However, RTK themselves may localize within the nucleus, as either full-length molecules or cleaved fragments, with or without their ligands. Significant differences in this mechanism have been reported depending on the individual RTK, cellular context or disease. Accumulating evidences indicate that the colony-stimulating factor-1 receptor (CSF-1R) may localize within the nucleus. To date, however, little is known about the mechanism of CSF-1R nuclear shuttling, as well as the functional role of nuclear CSF-1R.     

Position of the nucleolus within the nuclei of pachytene spermatocytes of Dromiciops australis and Marmosa elegans (Didelphoidea-Marsupialia).

The location of the nucleoli within the nuclei of pachytene spermatocytes, and their relation with the position of the nucleolar organizer region (NOR) was studied. It appears that a terminal NOR determines a peripheral location of the nucleolus, due to the position of the NOR over the synaptonemal complex and to the attachment of the nucleolar chromosome telomeres at the nuclear membrane.     

Microtubules, interkinetic nuclear migration and neurulation.

The hypotheses dealing with mechanisms of neurulation are reviewed briefly. The phenomenon of interkinetic nuclear migration is thought to be an important factor to be considered in the invagination of the neuroepithelium in the chick embryo. Evidence is presented that implicates cytoplasmic microtubules in this phenomenon. It is suggested that microtubules not only participate in cell elongation but also that they are involved, through interkinetic nuclear migration, in the broadening of the basal region of the cells; this widening progressively creates the strain that ensures the invagination of the neuroepithelium.     

常温、常压、常态的大气环境下黏性土微观孔隙的缓慢变异特征

作为建筑材料和地基的土体处于常温、常压、常态的大气环境下,大气氧化过程是缓慢的、不易察觉的,但对土质长期劣化效果不容忽视.本文以此命题为出发点,以大气氧化过程中微观孔隙变化特征为突破口,联合扫描电镜测试、压汞法及氮吸附法研究大气环境作用对湛江黏土的微观结构改造作用及其对土性影响机理.研究表明,大气氧化后土色由青灰色、绿灰色变为淡黄棕、黄棕色,颗粒团聚程度增强,塑性降低,膨胀性与收缩性减弱,灵敏性与结构屈服强度明显降低.大气环境作用对d0.1?m孔隙组产生"缩合"效果,对d1?m孔隙组产生"胀散"效果,表现为氧化土的总孔隙体积减小,但d1?m的孔隙体积明显增大,局部出现断裂孔隙,"墨水瓶"型孔隙减少,开放性孔隙向封闭性孔隙转化.湛江黏土在大气影响下土性发生异变并不是土的矿物本性变化所引起,而是水-土-电解质-大气间的化学反应与运动导致颗粒联结形式更改进而重塑微观结构所导致,土的超微观结构形态变化是发生这一现象的根本因素.鉴于大气氧化过程导致的结构强度的减损效果对土体稳定性的影响是长期的且潜在危害较大,应加强监测环境物化因素变化对岩土工程的影响.     

The subcommissural organ of the lizardLacerta s. sicula raf. ultrastructure during the winter

Summary The secretory activity of the SCO cells ofLacerta s.sicula Raf. is strongly reduced during the winter. Such reduction is documented by the decrease of the number of secretory granules type A and B described in previous papers in the summer SCO cells. Also the sacks of RER filled with electron-dense material (type C secretion) are very few; in their place there are, in the basal region of the cells, large vacuoles. In the distal region of the cells, at the free cell surface, a pronounced increase in the number of microvilli is noticed.     

Ovulation and the role of the ovarian surface epithelium.

Epon sections from all tissue layers of the rabbit ovary, including the often neglected surface or germinal epithelium, were studied to elucidate the mechanism of follicle rupture. Scanning electron microscopy showed cells covering preovulatory follicles increased clearly in size up to 8 hours after human chorionic gonadotropin (HCG) injection. These showed an increasing number of large, intracellular structures with prominent rounded contours. Transmission electron microscopy showed large, electron dense, lysosomelike bodies in some cells 4 hours after HCG. These membrane-surrounded structures increased in size up to 8 hours after HCG, then decreased markedly. These obviously corresponded to the bodies found by light microscopy and scanning electron microscopy. Histochemistry revealed many represent lysosomes. During the last 2 hours before rupture, the dense bodies of the surface epithelium considerably decrease, signs of material emptying into vacuoles is found, and sometimes there is open communication from vacuoles towards the unerlying tunica albuginea. An extracellular edema appeared under the epithelium with degenerated fibroblasts and disintegrated collagen; these changes gradually proceeded inwards. Blood capillaries close to the membrana granulosa gradually showed small pores and close to ovulation the endothelial cells had gaps up to 3 mcm in diameter. The preovulatory follicles grew rapidly and an augmenting edema occupied the whole ovary. In the last hours before ovulation the membrana granulosa gradually dissociated. Whatever the net effect of the prostaglandins, prostaglandin F2alpha appears to be essential for follicle rupture since intrafollicular injections of antiserum blocked ovulation. Prostaglandin E1 promotes vascular permeability and lysosommal enzymes released extracellularly may be coupled to collagen degration. The enzyme synthesis and lysosomal growth in the surface epithelium of preovulatory follicles may be due to the high local concentration of sex steroids.     

A stereoscan analysis of cell surface characteristics during the interkinetic nuclear migration in normal and colchicine-treated developing chick retina

Summary The cell surface and shape changes taking place during the interkinetic nuclear migration are reported in normal neuroepithelial cells of chick retina, and after metaphase-arrest induced by colchicine. Persistence of the apical junctions and loss of basal connections during the preparation for mitosis have been demonstrated in these cells.