Interplay of the nuclear envelope with chromatin in physiology and pathology

The nuclear envelope compartmentalizes chromatin in eukaryotic cells. The main nuclear envelope components are lamins that associate with a panoply of factors, including the LEM domain proteins. The nuclear envelope of mammalian cells opens up during cell division. It is reassembled and associated with chromatin at the end of mitosis when telomeres tether to the nuclear periphery. Lamins, LEM domain proteins, and DNA binding factors, as BAF, contribute to the reorganization of chromatin. In this context, an emerging role is that of the ESCRT complex, a machinery operating in multiple membrane assembly pathways, including nuclear envelope reformation. Research in this area is unraveling how, mechanistically, ESCRTs link to nuclear envelope associated factors as LEM domain proteins. Importantly, ESCRTs work also during interphase for repairing nuclear envelope ruptures. Altogether the advances in this field are giving new clues for the interpretation of diseases implicating nuclear envelope fragility, as laminopathies and cancer.

ABBREVIATIONS

na, not analyzed; ko, knockout; kd, knockdown; NE, nuclear envelope; LEM, LAP2-emerin-MAN1 (LEM)-domain containing proteins; LINC, linker of nucleoskeleton and cytoskeleton complexes; Cyt, cytoplasm; Chr, chromatin; MB, midbody; End, endosomes; Tel, telomeres; INM, inner nuclear membrane; NP, nucleoplasm; NPC, Nuclear Pore Complex; ER, Endoplasmic Reticulum; SPB, spindle pole body.

A bacterium belonging to the Rickettsiaceae family inhabits the cytoplasm of the marine ciliate Diophrys appendiculata (Ciliophora, Hypotrichia)

Bacteria of the family Rickettsiaceae (order Rickettsiales, alpha-Proteobacteria) are mainly known to be endosymbionts of arthropods with the capability to infect also vertebrate cells. Recently, they have also been found as leech endocytobionts. In the present paper, we report the first finding of a bacterium belonging to the family Rickettsiaceae in a natural population of a marine ciliate protozoan, namely Diophrys appendiculata, collected in the Baltic Sea. Bacteria were unambiguously identified through morphological characterization and the "full-cycle rRNA approach" (i.e., 16S rRNA gene characterization and use of specifically designed oligonucleotide probes for in situ detection). Symbionts are rod-shaped bacteria that grow freely in the cytoplasm of the host cell. They present two different morphotypes, similar in size, but different in cytoplasmic density. These are typical morphological features of members of the family Rickettsiaceae. 16S rRNA gene sequence showed that Diophrys symbionts share a high similarity value (>92%) with bacteria belonging to the genus Rickettsia. Phylogenetic analysis revealed that these new endosymbionts are clearly included in the clade of the family Rickettsiaceae, but they occupy an independent phylogenetic position with respect to members of the genus Rickettsia. This is the first report of a member of this family from a host protozoan and from a marine habitat. This result shows that this bacterial group is more diversified and widespread than supposed so far, and that its ecological relevance could until now have been underestimated. In light of these considerations, the two 16S rRNA oligonucleotide probes here presented, specific for members of the Rickettsiaceae, can represent useful tools for further researches on the presence and the spread of these microorganisms in the natural environment.

In situ identification by fluorescently labeled oligonucleotide probes of morphologically similar, closely related ciliate species

Ciliate protozoa are important members of microbial communities in which they play specific ecological roles. The determination of single species distribution is fundamental for food web analysis, but species recognition, which is mainly based on morphological characters, is often difficult between closely related species. The use of species-specific, purposely designed, fluorescently labeled probes for in situ hybridization is here presented as an easy and fast identification method for three closely related species belonging to the widespread genus Euplotes, namely E. crassus, E. vannus, and E. minuta, that in spite of their remarkable morphological similarity have significant metabolic and ecological differences. These three species can be detected simultaneously, provided the probes employed are bound to different fluorescent dyes: in this way their relative abundance and their population dynamics in the natural environment can be evaluated. As more ciliate sequences become available in databases, species-specific probes can be designed for other ciliates, thus rendering the application of the method of more general importance. The probes used in this study may also provide a tool to prevent erroneous species identification in future studies.

Defensive extrusive ectosymbionts of Euplotidium (Ciliophora) that contain microtubule-like structures are bacteria related to Verrucomicrobia

Epixenosomes, ectosymbionts on hypotrich ciliates (genus Euplotidium) defend their host against the ciliate predator Litonotus lamella. Although here only Euplotidium itoi and Euplotidium arenarium from tide pools along a rocky shore near Leghorn (Ligurian sea) were studied in detail, these epibionts are certainly present on specimens of E. itoi and on other Euplotidium species in similar north coastal habitats. The complex life history of epixenosomes has two main stages. In stage I, cells with typical prokaryotic structure divide by binary fission. Stage II cells show complex organization with different cytoplasmic compartments where an extrusive apparatus within a proteinaceous matrix, although not membrane-bounded, differs from the remaining cytoplasm. The ejection process is involved in defense; extrusive apparatus is surrounded by a basket consisting of bundles of tubules. These tubules, 22 +/- 3 nm in diameter, delimited by a wall made up of globular structures, are sensitive to inhibitor of tubulin polymerization (nocodazole/4 degrees C temperature) and react positively with different antitubulin antibodies, two of which are monoclonal. The prokaryotic vs. eukaryotic nature of epixenosomes was resolved by comparative sequence analysis of amplified small subunit rRNA genes and in situ hybridization with fluorescently labeled rRNA-targeted polynucleotide probes. These unique ectosymbionts are phylogenetically related to Verrucomicrobia. Epixenosomes represent marine symbionts in this recently discovered division of the Bacteria.

Mutations in twinstar, a Drosophila gene encoding a cofilin/ADF homologue, result in defects in centrosome migration and cytokinesis

We describe the phenotypic and molecular characterization of twinstar (tsr), an essential gene in Drosophila melanogaster. Two P-element induced alleles of tsr (tsr1 and tsr2) result in late larval or pupal lethality. Cytological examination of actively dividing tissues in these mutants reveals defects in cytokinesis in both mitotic (larval neuroblast) and meiotic (larval testis) cells. In addition, mutant spermatocytes show defects in aster migration and separation during prophase/prometaphase of both meiotic divisions. We have cloned the gene affected by these mutations and shown that it codes for a 17-kD protein in the cofilin/ADF family of small actin severing proteins. A cDNA for this gene has previously been described by Edwards et al. (1994). Northern analysis shows that the tsr gene is expressed throughout development, and that the tsr1 and tsr2 alleles are hypomorphs that accumulate decreased levels of tsr mRNA. These findings prompted us to examine actin behavior during male meiosis to visualize the effects of decreased twinstar protein activity on actin dynamics in vivo. Strikingly, both mutants exhibit abnormal accumulations of F-actin. Large actin aggregates are seen in association with centrosomes in mature primary spermatocytes. Later, during ana/telophase of both meiotic divisions, aberrantly large and misshaped structures appear at the site of contractile ring formation and fail to disassemble at the end of telophase, in contrast with wild-type. We discuss these results in terms of possible roles of the actin-based cytoskeleton in centrosome movement and in cytokinesis.

Chromatin and microtubule organization during premeiotic, meiotic and early postmeiotic stages of Drosophila melanogaster spermatogenesis

Larval and pupal testes of Drosophila melanogaster were fixed with a methanol/acetone fixation procedure that results in good preservation of cell morphology; fixed cells viewed by phase-contrast optics exhibit most of the structural details that can be seen in live material. Fixed testis preparations were treated with anti-tubulin antibodies and Hoechst 33258 to selectively stain microtubules and DNA. The combined analysis of cell morphology, chromatin and microtubule organization allowed a fine cytological dissection of gonial cell multiplication, spermatocyte development, meiosis and the early stages of spermatid differentiation. We placed special emphasis on the spermatocyte growth phase and the meiotic divisions, providing a description of these processes that is much more detailed than those previously reported. In addition, by means of bromo-deoxyuridine incorporation experiments, we were able to demonstrate that premeiotic DNA synthesis occurs very early during spermatocyte growth.

A comparative study of digestion in a raptorial ciliate and in the facultative carnivorous form of a filter feeding ciliate

Digestion in the carnivorous form (giant) of the filter feeding ciliateOxytricha bifaria and in the obligatory carnivorous, raptorial feeding ciliateLitonotus lamella were studied and compared at the ultrastructural level. It was found that whenO. bifaria, shifts from the normal, bacterivorous to the gigantic carnivorous form, it modifies its morphology, acquiring new and more effective feeding devices but maintaining unaltered the digestion pattern and mode of food absorption. This takes place through pinocytotic activity at the food vacuolar membrane. The digestive process inLitonotus is far more rapid: within 10 min the vacuolar membrane disappears; in this way the cytoplasm of the prey, not yet completely digested, is mixed with that of the predator and a pinocytotic mechanism does not seem to he necessary for nutrient assimilation. In general, results demonstrate that filter feeders and raptorial ciliates differ not only in their food intake mechanism, but also in the pattern and the timing of their digestive process, even when they ingest similar kinds of food.

Pyrolytic carbon coating enhances Teflon and Dacron fabric compatibility with endothelial cell growth

Compatibility with endothelial cell attachment and growth appears to be an important requisite of vascular prosthetic materials, possibly influencing thrombosis, pseudointimal hyperplasia, and accelerated atherosclerosis at the site of blood-material interaction. Since deposition of pyrolytic carbon (PC) on prosthetic surfaces has been associated with enhanced hemocompatibility, in the present study we assessed whether a thin layer (0.5 microns) of PC deposited onto materials such as knitted Teflon and Dacron enhanced endothelial cell attachment and growth. Cultured human umbilical vein endothelial cells (HUVEC) were seeded at a density of 4.5 x 10(4) cells/cm2 on PC-coated and uncoated grafts. In order to quantify endothelial cell attachment on the fabrics, the area of Teflon and Dacron fabrics covered by endothelial cells was estimated on day 2 after seeding using the point counting method in scanning electron micrographs. Subsequently, on days 2 and 4 after seeding, endothelial cell proliferation was measured both as number of endothelial cells and as total proteins of the endothelial cells covering the fabrics. On day 2 endothelial cell growth on PC-coated fabrics was greater (mean +/- SE; area 42.3 +/- 9.9 mm2, n = 6; cell number 3.9 x 10(4) +/- 3.03 x 10(3) cells, n = 4; total proteins 14.9 +/- 1.2 micrograms, n = 4) than on uncoated fabrics (area 10.6 +/- 4.6 mm2, n = 6; cell number 2.9 x 10(4) +/- 4.3 x 10(3) cells, n = 4; total proteins 11.3 +/- 1.7 micrograms, n = 4; P less than 0.001, less than 0.05 and less than 0.05, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Ultrastructure of the apical zone of Euglena gracilis: photoreceptors and motor apparatus

Euglena is an organism that every student of biology has observed; its morphology has been a subject of interest since the early microscopic literature for its enigmatic role of "plant-like" or "animal-like" organism. Therefore, this review has no pretensions to absolute novelty, but, like a journey to the centre of the earth, will attempt to arouse the reader's curiosity by taking him inside the cell Euglena, through the canal opening into the reservoir chamber. In light of the most recent knowledge, though much remains to be clarified, the aim is to provide information from ultramicroscopical studies on the apical zone of Euglena and possible functional meanings of the structures present therein. The survey of these structures is carried on as a study in correlation: TEM of cells after various treatments is correlated with SEM of cells fixed by means of different techniques. Notes on locomotion and other features of cytological and biological interest are added to assist with the comprehension of this microorganism.

Motor and predatory behavior of Litonotus lamella (Protozoa, Ciliata)

The ethogram of Litonotus lamella is described and discussed. Individuals of the species creep on the substrate at a velocity of 189 ± 40 μm/s, moving toward the right along geometrically perfect arcs with different radii, lengths, and amplitudes. The arcs are connected by four types of reaction: the continuous trajectory change, the smooth trajectory change, the rough trajectory change, and the side-stepping reaction. Litonotus lamella swims along a helicoid, keeping its ciliated surface outwards. Under appropriate conditions, L. lamella kills, engulfs, and eats the ciliate Euplotes crassus. This predatory behavior consists of two different sets of behavioral patterns; the first is part of the normal motor behavior, while the second comprises behavioral patterns performed characteristically and exclusively during the predatory activity.