Ultrastructural analysis of the nucleolar aspects at spermiogenesis in triatomines (Heteroptera,Triatominae)

In this study the ultrastructural technique was used to analyze seminiferous tubule cells of the triatomine species Panstrongylus megistus, Rhodnius pallescens and Triatoma infestans. The data obtained provided evidence of the phenomenon known as persistence of the nucleolar material in initial spermatids at early differentiation. Our results confirmed the presence of the nucleolus and its products during spermiogenesis up to the formation of the axoneme and during spermatid elongation in all three species studied, similar to the process that takes place during cell division. In early spermatids, the nucleoli had a reticulate appearance and a well defined nucleolonema in P. megistus; showed a clear distinction between the fibrillar and the granular component in T. infestans; and had a compact aspect in R. pallescens. In this study, ultrastructural analyses at spermiogenesis indicated that these nucleolar products may represent RNP complexes that will probably be needed at early spermiogenesis when important changes such as chromatin condensation and acrosome and flagellum formation take place. Therefore, it was concluded from the ultrastructural analysis that the triatomine nucleolus does not totally disappear but remains as corpuscles that gather to form the next nucleolar cycle that in the case of meiosis, will be completed if fertilization occurs and a zygote is formed.     

Study of the nucleolar cycle and ribosomal RNA distribution during meiosis in triatomines (Triatominae, Heteroptera)

Aspects of nucleolar activity during spermatogenesis were assessed in three triatomine species (Panstrongylus megistus, Rhodnius pallescens and Triatoma infestans) using cytochemical and fluorescent staining techniques. Toluidine blue and a variant of critical electrolytic concentration (CEC) allowed the discrimination of rRNA providing structural details of the nucleolus and RNA distribution during meiotic cell division. Acridine orange fluorochrome staining permitted the differentiation of nucleic acids, and silver-ion impregnation made possible the observation of pre-nucleolar bodies (PNBs). Our results support the phenomenon known as "persistence of the nucleolar material", and the hypothesis of post-meiotic reactivation of rRNA genes. Nucleolar organizer regions (NORs) were observed in some metaphasic spermatogonial chromosomes in P. megistus and T. infestans. In P. megistus at diplotene-diakinesis, NORs were also detected in one of the sex chromosomes and in an autosome. Therefore, it may be inferred that, in triatomines, the nucleolus does not completely disappear, but persists in the form of small bodies that get together to form the next nucleolar cycle which, in the case of meiosis, will be completed if fertilization occurs and a new zygote is formed.     

Chromatoid body: remnants of nucleolar proteins during spermatogenesis in triatomine (Heteroptera, Triatominae)

In this study, we analyzed fibrillarin nucleolar protein expression in CBs of spermatogenic cells from testicular follicles of Triatoma sordida and Triatoma infestans. In the structural and ultrastructural analysis, it was used impregnation by silver ions, immunocytochemistry, immunofluorescence and transmission electron microscopy using antibodies against fibrillarin. Regarding the results, the fibrillarin nucleolar protein marked the nucleus and some cytoplasmic spots of germ cells during spermatogenesis in triatomines. These data suggest that fibrillarin could be a constituent of the CB that was most likely derived from nucleolar fragmentation. This is the first time that fibrillarin protein expression has been shown in the CB during spermatogenesis progression in triatomines. The knowledge regarding CB constituents may help to expand the understanding of the physiological role of this structure and the role that it plays in the reproductive biology of triatomines, which are vectors of Chagas Disease.     

Ultrasound production by the long haired rat of Australia (Rattus Villosissimus)

The ultrasonic vocalizations produced by the long haired Australian rat Rattus villosissimus, during agonistic behaviour were investigated using a commercial ultrasonic receiver with earphones, a microphone and storage oscilloscope, and a tape recorder and sonograph. The rats were found to produce one audible call with ultrasonic components up to 64 kHz, the limit of the detecting apparatus used, and one pure ultrasound. Suggestions are made as to their behavioural significance.     

Dynamic changes of nucleolar DNA configuration and distribution during the cell cycle in Allium sativum cells

To investigate the correlation between subnucleolar structure and function, the precise distribution and configuration of nucleolar DNA during the cell cycle of Allium sativum were determined using the NAMA-Ur DNA-specific staining technique. We showed that nucleolar DNA is present in two forms: compacted chromatin clumps and a decondensed DNA cloud. The form of the DNA within the nucleolus varied greatly as the cell cycle progressed. During telophase, chromosomes extended into the prenucleolar body. In early G1 phase, DNA was only located in the fibrillar centers in the form of the condensed chromatin clump, while in mid-G1, S and G2 phases, the two forms of DNA were distributed in the fibrillar centers (FC) and dense fibrillar component (DFC). In prophase of mitosis, nucleolar DNA, along with FC and DFC, was linked into a network structure and condensed into a large chromatin clump. The area of the DNA cloud in the dense fibrillar component changed during different phases of the cell cycle. Our results demonstrated that the configuration of nucleolar DNA undergoes a series of decondensations and condensations during the cell cycle to fulfill the function of the nucleoli during the different phases.     

Morphology of the male reproductive system and spermiogenesis in Hypanthidium foveolatum (Alfken, 1930) (Hymenoptera: Apidae: Megachilinae)

The morphological aspects of male reproductive tract, spermiogenesis and spermatozoa are typical for each species and reflect its evolution, establishing a unique source of characters, which has been used to help solve phylogenetic problems. In Hypanthidium foveolatum the reproductive tract is composed of the testes comprising 28 testicular tubules, deferent ducts, seminal vesicles, accessory glands and an ejaculatory duct. The differentiation of spermatids occurs within cysts of up to 128 germ line cells each one. During the early spermatid phase, the nucleus resembles that of somatic cells. There follows a gradual chromatin condensation with an increase in nuclear electron density. In the spermatozoon, the nucleus contains heterogeneous chromatin with a loose appearance. The acrosome, shaped with the active participation of the Golgi complex, shows an electron-dense perforatorium involved by four electron-lucent acrosomal vesicle projections. The sperm tail presents an axoneme with a 9 + 9 + 2 microtubule pattern and two mitochondrial derivatives, which appear with different sizes. A dense crystalloid is formed initially in the mitochondrial matrix of the large derivative. The mitochondrial derivatives’ differentiation occurs concomitantly with an axoneme outgrowth. The centriolar adjunct is observed near the axoneme, anterior to the smaller mithocondrial derivative and exhibits an approximately triangular shape in cross-sections. Microtubules were observed around the head region and flagellar components during spermiogenesis.     

Iron(III) species formed during iron(II) oxidation and iron-core formation in the bacterioferritin of Escherichia coli

Summary This paper describes a preliminary investigation of the mechanisms of Fe(II) oxidation and storage of Fe(III) in the bacterioferritin ofEscherichia coli (EcBFR). Using M?ssbauer spectroscopy to examine the initial oxidation of iron by EcBFR we have confirmed that this ferritin exhibits ?ferroxidase? activity and have shown that dimeric and monomeric iron species are produced as intermediates. We compare the characteristics of ferroxidase activity in EcBFR with those of human H-chain ferritin (HuHF) and discuss the different M?ssbauer parameters of their dimeric iron with reference to the structures of their di-metal sites. In addition, we present preliminary findings suggesting that after an initial ?burst?, the rate of oxidation is greatly reduced, possibly due to blockage of the ferroxidase centre by bound iron. A new component, not found in HuHF and probably representing a small cluster of Fe(III) atoms, is reported. Paper presented at the ICAME-95, Rimini, 10–16 September 1995.     

Chemistry and formation process of Ga(Al)As oxide during local anodic oxidation nanolithography

We present our investigation on the early stage of the photon induced desorption of oxide nanostructures grown on GaAs/AlAs/GaAs heterostructures. The oxide structures were fabricated by local anodic oxidation performed by means of an atomic force microscope. We observed that after a first rapid evolution in which a thick layer of heterogeneous material is removed, the oxide composition remains almost constant. These results support our model in which the oxidation process on a layered material resembles a melting process and produces a mixed material whose composition is the average of the initial one.     

Cellular organisation of the mature testes and stages of spermiogenesis in Danio rerio (Cyprinidae; Teleostei)--structural and ultrastructural studies

The male gonads of Danio rerio occupy a position typical of the Teleostei species. The structure of the testes corresponds to the anastomosing tubular type with unrestricted spermatogonia and represents a cystic type of spermatogenesis. The results of this study indicate that four distinct stages of cell differentiation can be identified during spermiogenesis. These stages are characterised by chromatin condensation, the development of flagellum, nuclear rotation, the formation of nuclear fossa and the elimination of excess cytoplasm. A round head and the absence of an acrosome characterise the differentiated sperm. The midpiece is short and large, and C-shaped mitochondria form a ring surrounding the initial region of the flagellum. The axoneme shows a 9 + 2 pattern. In the D. rerio spermatozoa the flagellar axis is at an angle of 110° to the nucleus diameter running through the centriole.     

Stochastic aspects of pattern formation during the catalytic oxidation of CO on Pd(111) surfaces

We present experimental results on rare transitions between two states due to intrinsic noise between two states in a bistable surface reaction, namely the catalytic oxidation of CO on Pd(111) surfaces. The mean time scales involved are typically of order 10⁴ s and the probability distribution shows two peaks over a large part of the bistable regime of this surface reaction. We use measurements of the resulting CO₂ rate as well as photoelectron emission microscopy (PEEM) to characterize these rare transitions. From our dynamic data we can extract probability distributions for the CO₂ rate. We use x-t plots from PEEM measurements to describe the transitions, which are-as we demonstrate-characterized by one wall moving through the field of view in PEEM measurements. The resulting probability distributions for the CO₂ rate are shown to depend strongly on the value, Y, of the CO fraction in the reactant flux inside the bistable regime. We find that the probability distribution is strongly asymmetric indicating that the two basins of attraction are rather different in depth and width. This is also concluded from the PEEM measurements, which show in one case a rather sharp and narrow domain wall going one way, while it is rather wide and diffuse for the motion in the opposite direction. To have two basins of attraction in the bistable regime, which are rather different in nature is reminiscent of other bistable systems such as, for example, optical bistability, although the time scales involved in the present system are entirely different.     

STM observation of pit formation and evolution during the epitaxial growth of Si on Si(001) surface

Pit formation and surface morphological evolution in Si(001) homoepitaxy are investigated by using scanning tunneling microscopy. Anti-phase boundary is found to give rise to initial generation of pits bound by bunched D B steps. The terraces break up and are reduced to a critical nucleus size with pit formation. Due to anisotropic kinetics, a downhill bias diffusion current, which is larger along the dimer rows through the centre area of the terrace than through the area close to the edge, leads to the prevalence of pits bound by {101} facets. Subsequent annealing results in a shape transition from {101}-faceted pits to multi-faceted pits.     

Acetate formation during the ethanol oxidation on Rh(1 1 1)

The catalytic cracking of ethanol on clean and oxygen precovered Rh(1 1 1) surfaces has been studied by a combination of synchrotron based high-resolution core level spectroscopy and surface infrared spectroscopy. On the clean surface the decomposition of ethanol occurs without any formation of atomic oxygen. The presence of oxygen on the surface changes the reactivity significantly and acetate (CH₃COO) was identified as an important surface intermediate in the ethanol oxidation.     

Inelastic changes during the formation of multilayers of C2H6 on Ag(110)

Adsorption of C₂H₆ on Ag(110) has been studied using inelastic He atom scattering. Changes in the inelastic spectrum have been observed for the first time during adsorption up to three monolayers. No changes occurred as a fourth layer was added. The spectrum moves to lesser energy values. The ratio of the energy gain and loss events varies from layer to layer (at constant surface temperature). The (00) peak also reflects some changes in intensity during adsorption.     

Transformation of a Si(111) stepped surface during the formation of a Si(3 × 1)Ca superstructure

The morphological changes of a Si(111) stepped surface during the formation of a Si(3 × 1)Ca surface structure have been studied using ultra high vacuum reflection electron microscopy (UHV REM). Monoatomic step clustering during surface reconstruction and an influence of adatom electromigration on step clustering have been found. The mechanism and conditions of step cluster formation during superstructural transitions are discussed.     

Acoustic characteristics of the low-frequency nest call of discomfort of the house mouse (<Emphasis Type="Italic">Mus musculus</Emphasis>) early ontogenesis

Acoustic characteristics of the low-frequency nest call signaling discomfort of mouse pups are considered. The spectral temporal analysis of the call is realized for house mouse pups. In the structure of some calls, the frequency modulation and components of the noise are established. Signal duration varies from 20 to 170 ms. A statistically significant decrease of call duration and its fundamental frequency is shown from the 6th to 29th day of the mouse pups’ lives. The most stable parameters of the call-the harmonic structure, low-frequency range (up to 20 kHz), and location of the fundamental frequency between 4 and 8 kHz are recognized.     

Lateral mobility of plasma membrane proteins in dividing eggs of the loach (Misgurnus fossilis): Regional differences and changes during the cell cycle

Regional differences in lateral diffusion rates of fluorescence-labeled proteins have been studied in the plasma membrane of dividing eggs of the loach (Misgurnus fossilis) by fluorescence recovery after photobleaching (FRAP). Apparent animal-vegetal differences in fluorescence intensity, lateral diffusion coefficients, and fractions of mobile proteins have been found, with all these quantities being higher in the animal pole region than in the yolk region. Cyclic changes in protein diffusion coefficients and mobile fractions during the first few cell cycles have also been recorded. Soon after the end of a cleavage, the diffusion coefficient reaches its minimal value and increases rapidly before the next cleavage.     

Effects of adsorbates on the formation of doubly excited He atoms during impact of He2+ ions on Fe(110) and Ni(110) surfaces

The formation of doubly excited states of He atoms during collisions of He²⁺ ions with projectile energies between 74 eV and 124 eV with an Fe(110) and a Ni(110) surface is studied via Auger electron spectroscopy. We observe that the electron spectra from autoionization of doubly excited states of 2s², 2s2p, 2p² configurations show a pronounced dependence on the coverage with oxygen for both surfaces. For a controlled O₂ adsorption on the Fe(110) and Ni(110) surfaces we can explain the resulting changes in the electron spectra by the modification of the measured work functions of the target surfaces. In terms of thermal desorption and dissolution into the bulk of surface contaminations at elevated temperatures, we present an alternative interpretation of similar previous studies by another group, where the local electron spin polarization of Fe(110) and Ni(110) surfaces was deduced from changes in the electron spectra as function of target temperature.     

Chemistry of thin film formation and stability during praseodymium oxide deposition on Si(111) under oxygen-deficient conditions

The growth of thin praseodymium oxide films on silicon (111) using small deposition rates under oxygen-deficient conditions was investigated in the range from submonolayer up to six monolayers coverage by transmission electron microscopy (TEM) and photoemission spectroscopy (PES). A detailed analysis of the silicon 2p and oxygen 1 s core level and valence band spectra reveals chemical reactions between deposited species, substrate, and the growing film. Silicate, silicide and oxide species are coexisting over the entire range of coverages investigated. Cross sectional TEM shows silicide inclusions extending from the surface several nanometers into the substrate and affecting the substrate band bending at the interface. The reactivity of the praseodymia overlayer leads to reactions in the as-deposited film even at room temperature and render it unstable. The article aims at providing a coherent picture of the chemistry proceeding during interface formation and film growth at low rates of deposition (0.06 nm/min). The results will be discussed in comparison to studies using higher rates, emphasizing the possibility of growth rate dependent reactions between substrate and deposited material and, consequently, distinctly different film compositions and structures for different rates of deposition.