bluuebunny/crossref_metadata_2025 huggingface dataset:
Persistence of corners in free boundaries in Hele-Shaw flow
Authors: King J. R. , Lacey A. A. , Vazquez J. L.
Published: September 2008

In this paper we investigate the movement of free boundaries in the two-dimensional Hele-Shaw problem. By means of the construction of special solutions of self-similar type we can describe the evolution of free boundary corners in terms of the angle at the corner. In particular, we prove that, in the injection case, while obtuse-angled corners move and smooth out instantaneously, acute-angled corners persist until a (finite) waiting time at which, at least for the special solutions, they suddenly jump into an obtuse angle, precisely the supplement of the original one. The critical values of the angle π and π/2 are also considered.
Bounds on solutions of one-phase Stefan problems
Authors: Lacey A. A.
Published: September 2008

The reformulation of one-phase Stefan problems, by use of a Baiocchi-type transformation, as ‘oxygen-diffusion’ problems, makes it possible to compare different solutions. The comparison extends to ‘zero-specific-heat’ cases, which are better known, in two dimensions, as Hele-Shaw problems. Known solutions of Hele-Shaw problems can be used to bound and estimate asymptotic behaviour of solutions to Stefan problems. The use of similar techniques gives rise to some exact solutions of ‘squeeze-film’ problems and some limited results concerning continuity.
Diffractive optics in nonlinear media with periodic structure
Authors: Bao Gang , Dobson David C.
Published: September 2008

The diffraction of time-harmonic waves in a nonlinear medium with periodic structure is studied in this paper. In particular second harmonic generation – an important phenomenon in nonlinear optics-is modelled. The model, derived from a general nonlinear system of Maxwell's equations, is shown to have a unique solution for all but a discrete number of frequencies. The problem is solved numerically by combining a method of finite elements and a fixed-point iteration scheme. Numerical experiments for some simple grating structures are presented and discussed.
Functional series and Hashin–Shtrikman type bounds on the effective conductivity of random media
Authors: Markov K. Z. , Zvyatkov Kr. D.
Published: September 2008

A general method of placing variational bounds on the effective scalar conductivity of random heterogeneous solids is proposed. The method utilizes the Hashin-Shtrikman variational principle and trial fields which are obtained upon truncating the functional series expansion for the polarization field in the medium. It is shown how the earlier variational procedures due to Hashin and Shtrikman, Milton and Phan-Thien and Willis find natural places in the proposed general scheme. The new results reported include, for example, the fact of nonexistence of certain Gaussian-like random media and, for dispersions of spheres with volume fraction c, an exact O(c2) relation for the effective conductivity which contains absolutely convergent integrals only.
A differential constraints approach to partial invariance
Authors: Ondich Jeffrey
Published: September 2008

Ovsiannikov's method of partially invariant solutions of differential equations can be considered to be a special case of the method of differential constraints introduced by Yanenko and by Olver and Rosenau. Differential constraints are used to construct non-reducible partially invariant solutions of the boundary layer or Prandtl equations.
On long-wave morphological instabilities in directional solidification
Authors: Skeldon A. C. , McFadden G. B. , Impey M. D. , Riley D. S. , Cliffe K. A. , Wheeler A. A. , Davis S. H.
Published: September 2008

A binary liquid that undergoes directional solidification is susceptible to morphological instabilities which cause the solid/liquid interface to change from a planar to a cellular state. This paper presents a numerical study of a class of long-wave equations that describe the evolution of interface morphology. We find new bifurcation points, new solution branches, and the existence of inverted hexagonal nodes and cells.
Singularity formation in the one-dimensional supercooled Stefan problem
Authors: Herrero Miguel A. , Velázquez Juan J. L.
Published: September 2008

It is well-known that solutions to the one-dimensional supercooled Stefan problem (SSP) may exhibit blow-up in finite time. If we consider (SSP) in a half-line with zero flux conditions att= 0, blow-up occurs if there existsT< ∞ such that limt↑Ts(t) > 0 and lim inft↑T⋅(t) = – ∞,s(t) being the interface of the problem under consideration. In this paper, we derive the asymptotics of solutions and interfaces near blow-up. We shall also use these results to discuss the possible continuation of solutions beyond blow-up.
Sonic shocks governed by the modified Burgers' equation
Authors: Harris S. E.
Published: September 2008

In this paper, we investigate the evolution of N-waves in a medium governed by the modified Burgers' equation. It is shown that the general behaviour when the nonlinearity is of arbitrary odd integer order is the same as for the cubic case. For an N-wave of zero mean displacement, a shock is formed immediately to prevent a multi-valued solution and a second shock is formed at later times. At a finite time, the second shock satisfies a sonic condition and this state persists. The Taylor-type shock structure ceases to be the appropriate description, and instead we have a shock which matches only algebraically to the outer wave on one side. At a larger time still, the other shock is affected but the two shocks remain distinct until the wave dies under linear mechanisms. The behaviour of N-waves of non-zero mean is also examined and it is shown that in some cases, a purely one-signed profile remains.
On the Bean critical-state model in superconductivity
Authors: Prigozhin L.
Published: September 2008

We consider two-dimensional and axially symmetric critical-state problems in type-II superconductivity, and show that these problems are equivalent to evolutionary quasi-variational inequalities. In a special case, where the inequalities become variational, the existence and uniqueness of the solution are proved.
The Cahn–Hilliard equation with a concentration dependent mobility: motion by minus the Laplacian of the mean curvature
Authors: Cahn J. W. , Elliott C. M. , Novick-Cohen A.
Published: September 2008

We show by using formal asymptotics that the zero level set of the solution to the Cahn–Hilliard equation with a concentration dependent mobility approximates to lowest order in ɛ. an interface evolving according to the geometric motion,

(whereVis the normal velocity, Δ8is the surface Laplacian and κ is the mean curvature of the interface), both in the deep quench limit and when the temperature θ iswhere є2is the coefficient of gradient energy. Equation (0.1) may be viewed as motion by surface diffusion, and as a higher-order analogue of motion by mean curvature predicted by the bistable reaction-diffusion equation.
Hydrodynamic stability of a polymerization front
Authors: Volpert Vit. A. , Volpert Vl. A. , Pojman J. A. , Solovyov S. E.
Published: September 2008

We consider the propagation of an exothermic reaction wave which converts liquid reactants into a solid product. Such reaction waves are observed, for example in addition polymerization, where there is a propagating localized polymerization zone, in which monomer is converted to polymer. We study uniformly propagating travelling waves and their linear stability. We show that, though this problem is similar to the problem of gaseous combustion, which exhibits a hydrodynamic instability, here there is no such hydrodynamic instability. This theoretical result is consistent with experimental observations in the case when the polymerization process occurs under high external pressure conditions.
Hele–Shaw flows with free boundaries driven along infinite strips by a pressure difference
Authors: Richardson S.
Published: September 2008

Consider the classical Hele–Shaw situation with two parallel planes separated by a narrow gap, and suppose the plan-view of the region occupied by fluid to be confined to an infinite strip by barriers in the form of two infinite parallel lines. With the fluid initially occupying a bounded, simply-connected region that touches both barriers along a single line segment, we seek to predict the evolution of the plan-view as the blob of fluid is driven along the strip by a pressure difference between its two free boundaries. Supposing the relevant free boundary condition to be one of constant pressure (but a different constant pressure on each free boundary), we show that the motion is characterized by (a) the existence of two functions, analytic in disjoint half-planes, that are invariants of the motion and (b) the centre of area of the plan-view of the blob has a component of velocity down the infinite strip that is simply related to the imposed pressure difference. These features allow explicit analytic solutions to be found; generically, the mathematical solution breaks down when cusps appear in the retreating free boundary. A rectangular blob, of course, moves down the strip unchanged, with no breakdown, but if it encounters stationary blobs of fluid placed within the strip then, modulo multiply-connected complications, these are first absorbed into the advancing front of the rectangular blob and then disgorged from its retreating rear, leaving behind stationary blobs of exactly the same form in exactly the same place as those originally present, but consisting of different fluid particles. This soliton-like interaction involves no phase change: with a given pressure difference driving the motion, the rectangular blob is in the same position at a given time after the interaction as it would have been had no intervening blobs been present.
On p-harmonic functions, convex duality and an asymptotic formula for injection mould filling
Authors: Aronsson Gunnar
Published: September 2008

This work treats the injection of certain thermoplastics into a planar mould cavity. The problem is to determine the filling pattern. It is assumed that the thermoplastic can be modelled as a non-Newtonian fluid of power-law type whose power-law exponent is relatively small (the pseudo-plastic case). The dependence of the viscosity on thermal variations is neglected. The mathematical description leads to a moving boundary problem, for which an asymptotic solution is found. According to this solution, the expansion of the polymer melt follows the level sets of an interior distance function, which is determined by the geometry of the mould, and the position of the injection point. The solution is easily computed and results of numerical experiments are given.
Heavy traffic asymptotics of the queue length in the GI/M/l – K queue
Authors: Yang Yongzhi , Knessl Charles
Published: September 2008

We consider the GI/M/1 – K queue which has a capacity of K customers. Using singular perturbation methods, we construct asymptotic approximations to the stationary queue length distribution. We assume that K is large and treat several different parameter regimes. Extensive numerical comparisons are used to show the quality of the proposed approximations.
Oscillatory flow over a cylinder resting on a plane boundary
Authors: Wybrow M. F. , Riley N.
Published: September 2008

Oscillatory flow over a circular cylinder, or part-cylinder, placed on a plane boundary, when the Strouhal and streaming Reynolds numbers are large, is considered. The solution is developed in matching inner and outer boundary layers. A steady streaming motion in the outer layer can lead to a net flow away from the cylinder along the plane boundary. A simple experiment substantiates this prediction, and the implications for bed-scouring are examined.
A sharp interface limit of the phase field equations: one-dimensional and axisymmetric
Authors: Stoth Barbara E. E.
Published: September 2008

We study the singular limit of the dimensionless phase-field equations

We consider two cases: either the space dimension is 1 and then ɛ tends to zero; or the solutions are radially symmetric and then both ɛ and α tend to zero. It turns out that, in the first case, the limiting functions solve the Stefan problem with kinetic undercooling, provided the initial temperature is small compared to the surface tension and the latent heat. In the second case, the limiting functions satisfy the Stefan problem coupled with the Gibbs–Thomson law for the melting temperature. We show, in addition, that the multiplicity of the interface is always one, in a sense to be explained at the end of § 1. As main tool we use energy type estimates, and prove that the formal first-order asymptotic expansion with respect to ɛ in fact gives an approximation of the exact solution. Our results hold without smoothness assumptions on the limiting Stefan problem.
Behaviour of hamster and mouse round spermatid nuclei incorporated into mature oocytes by electrofusion
Authors: Ogura Atsuo , Yanagimachi Ryuzo , Usui Noriko
Published: September 2008

summary

Round spermatids of the hamster and mouse were electrofused with homologous mature oocytes to examine the behaviour of their nuclei within the ooplasm. A single spermatid was inserted in the perivitelline space of a mature oocyte and an electric fusion pulse given. In the hamster, the best spermatid-oocyte fusion took place when the oocytes were pretreated with neuraminidase, subjected to 30 s AC (2 MHz, 20 V/cm) followed by a single fusion DC pulse (3000 V-cm, 10 μs) and another 30 s AC current. Inclusion of micromolar Ca2+and Mg2+in the fusion medium was essential for oocyte activation. Under these conditions all oocytes were activated and 20–40% fused with spermatids. Of these fused oocytes only 5–10% had fully developed spermatid (male) and oocyte (female) pronuclei. In the rest the spermatid-derived pronuclei remained small throughout the pronuclear stage. However, nucleolus-like structures appearedde novoand DNA synthesis occurred in these small pronuclei. Regardless of the size of male pronuclei, chromosomes from the spermatid and oocyte appeared to mingle and participate in the first cleavage. About 70% of the fused oocytes developed into the 2-cell stage. Electrofusion of mouse oocytes with spermatids was less efficient. Even under the best conditions tested, less than 10% of the oocytes fused with spermatids. Here again, most spermatid nuclei remained small throughout the pronuclear stage.
Microinjection of FITC-dextran into mouse blastomeres to assess topical effects of zona photoablation
Authors: Li Leyi , Munne Santiago , Licciardi Frederick , Neev Joseph , Tadir Yona , Berns Michael , Godke Robert , Cohen Jacques
Published: September 2008

The objective of the current experiments was to investigate whether all or only some blastomeres from precompacted mouse embryos were affected by zona photoablation. The microbeam of xenon chloride excimer laser (308 nm) was guided through an inverted microscope (non-contact system). Topical effects of lasing were determined by microinjection of a vital fluorescent dye of high molecular weight (fluorescein isothiocyanate [FITC] dextran) into the cell immediately adjacent to the site of zona photoablation. This dye is only passed onto daughter blastomeres and therefore allows study of specific cell lines. Embryonic growth was assessed following cell separation at the morula and blastocyst stage. Four-cell embryos treated with the laser had significantly fewer cells 12 h after zona photoablation than control embryos. A similar effect was noted after 24 h between dye injected embryos and those injected and lased simultaneously, indicating potential toxic effects of the laser treatment on the embryo. Effects on the blastomere closest to the site of ablation were evaluated by calculating the ratio of dyed cells to the total number of cells at specific time intervals. The ratios were similar in the dye and laser + dye groups of treated 4-cell embryos 36 h after treatment (0.22 and 0.23, respectively), indicating that the dye was still present in approximately 25% of the cells and that the negative effect of photoablation was evenly distributed among the blastomeres. It is concluded that zona photoablation may have long-term detrimental effects of a non-topical nature on precompacted mouse embryos in spite of the apparent precision of the laser spot size.
Evaluation of the antifertility activity of the broomSpartium junceumin the mammalian male
Authors: Baccetti B. , Burrini A.G. , Chen J.S. , Collodel G. , Giachetti D. , Matteucci F. , Menesini-Chen M.G. , Moretti E. , Piomboni P. , Sensini C.
Published: September 2008

Male adult rabbits and rats treated withSpartium junceumshowed a significant decrease in fertility, demonstrated by a lower number of pregnancies. The target of the drug seems to be the acrosomal protease system, the activity of which appears greatly reduced, while the morphology of testicular cells and epididymal spermatozoa is only partially affected. The antifertility effect is completely reversible.
Activation currents, sperm entry and surface contractions in ascidian eggs
Authors: Pecorella C. , Tosti E. , Kyozuka K. , Dale B.
Published: September 2008

Spermatozoa from the mollusc Ostrea edulis are capable of fusing to and entering de-chorionated ascidian eggs. During interaction they generate activation currents, comparable to the fertilisation currents induced by homologous spermatozoa. Activation currents are inward at − 80 mV, with a mean initial slope of 111 ± 124 pA/s for Ciona intestinalis eggs and 47 ± 25 pA/s for Phallusia mammillata eggs, while the mean peak currents are 2782 ± 1132 pA and 1523 ± 1668 pA, respectively. The fertilisation and activation currents reverse at a holding potential of 0 mV to + 20 mV, suggesting that oyster sperm and ascidian sperm gate the same channel precursor, a non-specific, large conductance channel described previously (Dale & DeFelice, 1984). In contrast to homologous fertilisation, the activation current is not followed by a polarised contraction of the egg surface, nor other signs of egg activation. Staining eggs with Hoechst 33342 after insemination shows the female nucleus and a single oyster sperm nucleus at the antipode. This suggests a specialised predetermined site at the vegetal pole for sperm entry. Homologous and heterologous spermatozoa delivered, in a large pipette, to localised areas of the egg surface generate fast inward currents of 200–2000 pA, but do not induce contraction of the egg surface. This shows that although channel precursors are located globally over the egg surface, channel activation does not necessarily trigger the contraction wave. Subsequent induction of both a fertilisation current and a contraction by homologous sperm added to the bath, implies a regionalised activation site with an accumulation of channel precursors and a ‘pacemaker’ for the initiation of the contraction wave.
Changes in protein association with intracellular membranes ofXenopus laevisoocytes during maturation and activation
Authors: Duesbery N.S. , Masui Y.
Published: September 2008

Intracellular membranes isolated from fully grown immature oocytes, mature oocytes (eggs) and activated eggs ofXenopus laeviswere fractionated through a discontinuous sucrose density gradient into light, intermediate and heavy fractions. Electron microscopy showed that the light and intermediate fractions consisted mainly of smooth membranes, while the heavy fraction consisted mainly of rough membranes and mitochondria. Variations in the proteins associate with samples taken at different stages were observed by SDS-PAGE. The following differences were consistently observed: a 200 kDa protein was present only in the intermediate fraction of activated eggs, 29 and 44 kDa proteins were present only in the intermediate fractions of immature oocytes and activated eggs, and 120 and 145 kDa proteins were present only in the heavy fractions of mature oocytes and activated eggs. Examination of Western blots showed that cyclins A and B2did not associate with membrane fractions at any stage of meiosis. Instead, cyclin A was present in the cytosols of mature oocytes and cyclin B2 was present in the cytosols of immature and mature oocytes.c-mosprotein was detected in the cytosols and occasionally in the light fractions of mature oocytes and activated eggs. While α- and β-tubulins were detected in the light and intermediate fractions at all the stages of meiosis examined, only β-tubulin was present in the heavy fraction. βtubulin present in the heavy fraction was detected only at interphase, i.e. in immature oocutes and activated eggs, and not in mature oocytes. Using immunogold labelling we confirmed these results and found evidence to suggest that β-tubulin associates with the rough endoplasmic reticulum of interphase cells by a linking protein.
Retention of hamster oolemma fusibility with spermatozoa after various enzyme treatments: a search for the molecules involved in sperm-egg fusion
Authors: Ponce Ruben H. , Yanagimachi Ryuzo , Urch Umbert A , Yamagata Tatsuya , lto Makoto
Published: September 2008

The plasma membrane (oolemma) of the hamster egg retains the ability to fuse with spermatozoa even after exhaustive treatment with proteases and glycosidases. In contrast, when mouse oolemma is treated with proteases, the ability of eggs to fuse with spermatozoa is reduced. In the present study, similar treatments effective in reducing fusibility in the mouse were reexamined in the hamster. Of the several enzymes and treatments tested, only trypsin in Ca2+-free medium significantly reduced the hamster oolemma's ability to fuse with spermatozoa. This is suggestive of a cadherin-like system of binding and fusion. When hamster oolemmae were treated with the same protease regimen that reduced fusibility of mouse oolemma for mouse spermatozoa, heterologous fusion of hamster oolemmae with mouse spermatozoa was reduced, without affecting the fusion of these oolemmae with hamster spermatozoa. These data suggest that a protease-sensitive oolemma molecule is of critical importance for mouse sperm-oolemma fusion but not for hamster sperm-oolemma fusion.
An ankryin-like protein in ascidian eggs and its role in the evolution of direct development
Authors: Jeffery William R. , Swalla Billie J.
Published: September 2008

An erythrochyte anti-ankryin antibody was used to investigate the presence and distribution of ankryin in eggs and embryos of ascidian species with different modes of development. In eggs of the indirect developerAscidia ceratodesanti-ankryin reacted with a 210 kDa polypeptide which has an electrophoretic mobility similar to the vertebrate ankryins. Immunofluorescence microscopy showed that the ankryin-like protein is co-distributed with the myoplasm throughout development. It is restricted to a thin layer under the plasma membrane in unfertilised eggs, undergoes ooplasmic segregation to the posterior pole of the zygote after fertilisation, and is distributed to the tail muscle cells during cleavage and embryogenesis. After gastrulation and neurulation, lower levels of the ankryin-like protein, presumably of zygotic origin, were observed in brain cells and in the apical margin of epidermal cells. The ankryin-like protein was also localised in the myoplasm in eggs and embryos of another indirect developing species,Halocynthia roretzi. The ankryin-like protein may link the cytoskeleton with the plasma membrane in ascidian eggs, as it does in vertebrate erythrocytes. In contrast toA. ceratodesandH. rorefzi, which are members of the families Ascidiidae and Pyuridae respectively, the pattern of ankryin-like protein expression was changed in five species in the family Molgulidae. These molgulid ascidians exhibit either indirect or direct development, and eggs of the direct developing species have lost or modified the myoplasm. The ankryir like protein was present in young oocytes but failed to persist during oogenesis and disappeared in mature eggs and embryos of these molgulid species. The change in ankryin-like protein expression may be a preadaptation for loss of the myoplasm and the evolution of direct development.
Non-plasmalemmal localisation of the major ganglioside in sea urchin eggs
Authors: Shogomori Hidehiko , Chiba Kazuyoshi , Kubo Hideo , Hoshi Motonori
Published: September 2008

M5 ganglioside (NeuGcα2–6Glcβl-' Cer) is the predominant glycosphingolipid in sea urchin eggs. Distribution of M5 ganglioside was studied in unfertilised and fertilised eggs of the sea urchinHemicentrotus pulcherrimusby indirect immunofluorescence microscopy. In the cortices of unfertilised eggs, anti-M5 antibody strongly stained the submembranous, polygonal and tubular network of endoplasmic reticulum that was revealed by a membrane-staining dye, DiIC18(3). In addition to the cortical network of endoplasmic reticulum, at least two morphologically distinct vesicles were positive to the antibody. In the cortices isolated from fertilised eggs 30 min after insemination, the antibody stained only a similar network of endoplasmic reticulum, presumably the one reconstructed 5–10 min after fertilisation. During mitosis the endoplasmic reticulum is known to aggregate within the asters of the mitotic apparatus. Indeed, the antibody stained the asters and (more strongly) the vesicular components attaching to the periphery of the mitotic apparatus.
Effect of zinc and copper on preimplantation mouse embryo developmentin vitroand metallothionein levels
Authors: Vidal Francesca , Hidalgo Juan
Published: September 2008

The effect of zinc and copper on thein vitrodevelopment of mouse preimplantation embryos and on metallothionein (MT) levels was studied by exposing the embryos to 100 μM concentrations of the metals for 24 h at the 1-cell,2-cell, 6-8-cell, morula and blastocyst stages. Zinc affected embryo development in the early but not in the late stages, whereas copper affected it more generally. The combined presence of both metals caused a stronger embryotoxicity. MT levels were measured by radioimmunoassay and were found to be similar at all developmental stages, though possibly higher at the blastocyst stage. The exposure of embryos to zinc and copper increased MT levels significantly only at the blastocyst stage, supporting previously published results on MT mRNA levels.
In vivo parthenogenetic activation of ovulated oocytes in a marsupial, Sminthopsis crassicaudata
Authors: Anderson Rebecca , Breed William G.
Published: September 2008

The occurrence of in vivo parthenogenesis is documented for laboratory-bred individuals of the Australian dasyurid marsupial, Sminthopsis crassicaudata. About 30% of females that had been isolated from males for a greater period of time than the length of pregnancy were found, on dissection of their uteri, to have embryos present. The embryos were surrounded by a mucoid coat and shell membrane and at least the first two cleavage divisions occurred normally. After this time, however, unequal cleavage divisions appeared to result. The parthenogenesis that takes place may be initiated as a result of activation of ageing ovulated oocytes. Its frequent occurrence may prove useful in a study of maternal and paternal contributions to early embryonic development in this species.
Sperm penetration in parthenogenetic mouse embryos triggers a plasma membrane block to polyspermy
Authors: Maleszewski Marek , Bielak Anna
Published: September 2008

Mouse oocytes activated parthenogenetically do not generate a plasma membrane block against spermatozoa over the first three cell cycles. We show that they lose this fusibility spontaneously at the 8-cell stage. Insemination of 1-cell parthenogenetic embryos induces loss of fusibility earlier, at the 2-cell stage. This observation suggests that incorporation of the sperm cell membrane components into the oolemma may be responsible for the development of the membrane block.
A molecular screen for polar-localised maternal RNAs in the early embryo ofDrosophila
Authors: Ding Dali , Lipshitz Howard D.
Published: September 2008

Localised, maternally synthesised RNAs and proteins play an important role in an early animal embryogenesis. InDrosophila, genetic screens have recovered a number of maternal effect loci that encode localised products in the embryo. However, only a third ofDrosophila'sgenes have been genetically mutated. Consequently, we conducted a molecular screen for polar-localised RNAs in the earlyDrosophilaembryo in order to identify additional maternal molecules that carry out spatially restricted functions during early embryogenesis. Total RNA was purified from anterior or posterior poles cut off earlyDrosophilaembryos. These RNAs were used to construct directionally cloned anterior and posterior cDNA libraries which were used in a differential screen for cDNAs representing maternal RNAs localised to one or other pole of the embryo. Five such clones were identified, representingcyclinB RNA, Hsp83 RNA, 28SribosomalRNA,mitochondrial cytochrome c oxidase subunit oneRNA andmitochondrial 16S large ribosomalRNA. Mutations in the loci encoding these RNAs have not been recovered in genetic screens, confirming that our molecular approach complements genetic strategies for identifying maternal molecules that carry out spatially restricted functions in the early embryo. We consider the possible biological significance of localisation of each of these species of transcripts as well as the mechanism of their localisation, and discuss the potential use of our cDNA libraries in screens for rarer localised RNAs.
Correlation between male fertility and acrosin-like protease activity in rats treated withspartium junceum
Authors: Chen J.S. , Menesini-Chen M.G. , Giachetti D. , Matteucci F. , Barbetti M. , Sensini C. , Baccetti B.
Published: September 2008

Intraperitoneal injections of extracts ofSpartium junceumin adult male rats were shown to reduce the rate of fertility and acrosin enzyme activity. For the latter the drug effects could be divided into two phases: in the first stage a significant increase in proteolytic activity was observed in all experimental animals examined; and in the second stage, there was a general decrease of up to 50% in enzyme hydrolytic properties. There is a notable difficulty in correlating the acrosin activity and the data obtained from mating tests. The effect of drugs on the activity of another acrosomal protease, benzamidine-resistant protease, was assayed. A significant decrease in this enyme was noted though the modality was different from that of acrosin. Extrapolating the data of the two co-extracted acrosomal proteases, the ratio of acrosin-like protease [E] and benzamidine-resistant protease [E]x, it was possible to correlate the value expressed to the rate of pregnancy. The implications of this finding is discussed although the exact molecular basis of the phenomenon is uncertain.
Fertilistion in sea urchins: how many different molecules are involved in gamete interaction and fusion?
Authors: Lennarz William J.
Published: September 2008

It has been established that fertilisation in the sea urchin involves binding of acrosome-reacted sperm to an egg cell surface receptor. The structure and function of receptor, as well as the possible involvement of other cell surface molecules in the binding, fusion and activation events, is discussed.
Confocal image analysis of spatial variations in immunocytochemically identified calmodulin during pollen hydration, germination and pollen tube tip growth inNicotiana tabacumL.
Authors: Tirlapur Uday K. , Scali Monica , Moscatelli Alessandra , Casino Cecilia Del , Cai Gianpiero , Tiezzi Antonio , Cresti Mauro
Published: September 2008

Using monoclonal anti-calmodulin antibodies in conjunction with confocal scanning laser microscopy we have analysed the spatial variations in the distribution pattern of calmodulin (CaM) during the sequential events of pollen hydration, germination and tube growth inNicotiana tabacum. These immunocytochemical observations have been complemented by immunochemical studies wherein the anti-calmodulin antibody raised against pea CaM recognises a polypeptide ofc.18 kDa in the pollen extracts. Digitisation of confocally acquired optical sections of immunofluorescence images reveals that in hydrated pollen a high level of CaM is consistently present in the region of the germinal apertures. Subsequently, with the onset of germination a high CaM concentration was found associated with the plasma membrane of the germination bubble and in the cytoplasm in its vicinity, while in the vegetative cytoplasm a weak diffuse and intense punctate signal was registered. CaM immunostain was also detected in association with the plasma membrane of the tube tips in both short and long pollen tubes. Furthermore, the cytosol of the tubes invariably manifested an apically focused CaM gradient. We were, however, unable to detect any vacuolar association of CaM in the older regions of the pollen tubes. Although punctate immunostain was obvious across the pollen tube numerous punctate structures were invariably present in the extreme tip. The possible implications of these findings in development of cell polarity, polarised growth, maintenance of calcium homeostasis and CaM interactions with other mechanochemical motor proteins in effecting propulsion of organelles during pollen hydration, germination and pollen tube growth are discussed.
In vitro fertilisation of maize by single egg and sperm cell protoplast fusion mediated by high calcium and high pH
Authors: Kranz Erhard , Lörz Horst
Published: September 2008

We present evidence for the fusion of isolated single maize egg and sperm cell protoplasts in a mannitol solution (400–430 mosmol/kg H2O) containing 0.05 M CaCl2 at pH 11.0, followed by cell division of the fusion products. These findings allow the performance of in vitro fertilisation of higher plants by combining single gametes as in lower plant and animal systems. Further, our findings open new avenues for investigating the basic mechanisms of adhesion and fusion of higher plant gametes and eventually for examining processes that inhibit polyspermy in higher plants.
Sperm-egg interaction in an Australian dasyurid marsupial with special refernce to changes in acrosomal morphology
Authors: Breed W.G
Published: September 2008

The morphology of the acrosome of spermatozoa an Australian daysyurid marsupial during in vivo fertilisation, as seen with the tranamission electron microscope, is described. In some spermatozoa close to the outer zona surface with largely intact acrosomes, eletron-demse struts between the inner and outer acrosomal membranes could be seen; in addition fusion between the outer acrosomal and overlying plasma membranes was sometimes evident. The zona matrix close to the acrosomal region of spermatozoa with heads party embedded within the zona pellucida was less electron-dense and more filamentous than elsewhere; perhaps indicative of local lytic activety. Nevertheless some of these spermatozoa at least had partly intact acrosomes with local regions of electron-dense bridges between the two acrosomal membranes. Spermatozoa with condensed chomatin were also observed within the egg cytoplsam some of which had membranes, vacuoles or close to the dorsal nuclear surface which could, in part, be acrosomal in orgin. These observations lend some support to the recent view, based on findings from an American species, that acrosomal changes of spermatozoa of some marsupials at the of fertillsation may be somewhat similar to those of eutherian mamals in spite of the considerable differences in gamete structure and design. How generally applicable these findings are to all marsupials remains, however, to be determined.
Oocyte reaction to penetrating sperm
Authors: Galeati G.
Published: September 2008

Before fertilisation the egg is metabolically quiescent and its nucleus is arrested at metaphase of the second meiosis. After sperm-egg fusion, the arrested nucleus resumes meiosis, and then changes into the female pronucleus. Such a sequence of morphological and biochemical events is called “activation”. The inital responses of the egg to activation by the sperm include cortical granule exocytosis and resumption of meiosis.
Stability of the mammalian sperm nucleus
Authors: Yanagimachi R.
Published: September 2008

The nuclei of spermatozoa leaving the testies are transcritionally inactivated and are structurally stabilised by extensive association of sperm DNA with protamines, highly basic proteins that replace somatic histones during spermiogenesis. During sperm matureation within teh epididymis, protamine–SH is oxidised to -SS-(Bedford & Calvin, 1974).
Cytogenetic studies of oocyte fusion products
Authors: Nogués Carme , Ponsà Montserrat , Egozcue Josep , Vidal Francesca
Published: September 2008

We describe for the first time the cytogenetic characteristics of mouse ‘embryos’ obtained by oocyte fusion (oocyte fusion products; OFP). Our results indicate that, after fusion, meiosis II is resumed correctly, with extrusion of two haploid polar bodies, and that metaphase synchronisation of the two haploid sets and chromosome segregation during the first cleavage are also normal.
Is the plasma membrane of the human oocyte reorganised following fertilisation and early cleavage?
Authors: Dale B. , Tosti E. , Iaccarino M.
Published: September 2008

The purpose of the present study was to determine whether the plasma membrance of the human oocyte is reorganised following fertlisation and during early cleavage. In order to characterise and localise the major sugar moieties on surface glycoporteins, oocytes and embroys were labelled with a range of flourescent lectins. Regional organisation of plasma membrane microvilli in oocytes and embryos was also studied using scanning electron microscopy (SEM). The plasma membrance of human oocytes, zygotes and early blastomeres stained strongly and homogeneously with concanavalin A andTriticum vulgarislectin (WGA), indicationg the presence of plasma membrance glycoconjugates with α-D-mannosyl residues, sialic acid and β-NAc-glucosaminyl groups. We did not observe regional domains in oocytes and zygotes, suggesting that the plasma membrane is not topographically reorganised following fertilisation. SEM shows the surface of the human zygote to be organised into short microvilli 0.2–3.0 μm in length and at a density of 5–20/μm2. In early cleavage stages the microvilli are shorter and less frequent (0.2–1.0 μm; 1–5/μm2); however, there is no evidence of polarisation at this level of organisation, at either stage of development. The surface of cell fragments, common in the human embryoin vitro, differs in having few microvilli and numerous cytoplasmic blebs. In conclusion, there are no obvious morphological signs of regionalisation in the plasma membrane of the human embryo before the 8-cell stage.
In vivostorage of XR family interspersed RNA inXenopusoocytes
Authors: Liu Chengyu , Smith L. Dennis
Published: September 2008

Interspersed RNA is an abundant class of cytoplasmic poly(A)+RNA which contains repetitive elements within mostly heterogeneous single copy sequences. In spite of its quantitative importance in oocytes or eggs (two-thirds of the total poly(A)+RNA), very little is known about its synthesis, its interaction with other molecules, and its functional significance. Here, we analysed a prevalent family of interspersed RNa (XR family) duringXenopusoogenesis. We found that XR interspersed RNA, unlike extracted interspersed RNA, did not form RNA duplexesin vivo. Im small oocytes (stage III), XR RNA interacted with proteins forming rapidly sedimenting ribonucleoprotein particles (RNPs) with a median sedimentaion constant of 80S. However, towards the end of oogenesis (stage VI), these XR RNPs changed into smaller particles with a median sedimentaion constant of 40S. By analysing the proteins associated with XR RNA sequence, we have identified a 42 kilodalton protein in small oocytes, which was replaced by a 45 kilodalton protein at stage V of oogenesis.
Capacity of mouse oocytes to become activated depends on completion of cytoplasmic but not nuclear meiotic maturation
Authors: McConnell Joise M.L. , Campbell Liz , Vincent Caroline
Published: September 2008

The ability of mouse oocytes to become activated after exposure too the calcium ionophore A23187 has been investigated at different stages of meiotic maturation. The potential to respond to ionophore has been studied in relation to the time since resumption of meiotic maturation, the chromosomal conformation of the DNA within each cell and the protein synthetic profile of the maturing oocyte. Our studies demonstrate that when maturing oocytes from an MF1 strain of mice were treated with A23187 activation occured only in oocytes which had reached second meiotic metaphase (MII). However, development of the ability to respond to ionophore was not dependent on an orderly progression through normal chromosomal rearrangements such as separation at metaphase I (MI) and subsequent polar body extrusion, since there process could be prevented and the capacity to be activated became apparent in such oocytes at a time when control cells had reached MII. These data suggest that the ability to respond to ionophore depends on the development of a cytoplasmic or complex capable of monitoring the time since initiation of germinal vesicle breakdown. Metabolic radiolabelling of oocytes which were able to respond to calcium ionophore, even though they had been prevented from undergoing normal chromosomal rearrangements, showed them to be synthesising a group of proteins known as the 35 kDa complex.
Evaluation of a simple method for measuring the cellular DNA content of mouse oocytes and embryos, human fibroblasts and parthenogenetically activated human oocytes using a computerised image analysis system(Seescan)
Authors: Taylor Alison S. , Braude Peter R.
Published: September 2008

We report the use of a simple, reproducible, photocytometric method for measuring nuclear DNA content of DAPI-stained cells, using a computerised image analysis system: Seescan. As this technique is non-destructive and uses very short exposure to ultraviolet light, it can be used for either fixed or vital material. After correcting for any background cytoplasmic staining, the intensity of nuclear stain was measured by the Seescan and compared with that of control cells of known ploidy. Fixed material was found to stain more intensely than live material initially, but demonstrated a rapid loss of nuclear intensity over the first 90 min following removal from DAPI, after which the level plateaued. In contrast, live cells showed no change in nuclear intensity with time. The system was validated by measuring the DNA content of carefully timed mouse blastomeres, human fetal lung fibroblasts and parthenogenetically activated human oocytes. The results obtained were appropriate for the developmental stage or phenotypic appearance of each of the cell types measured.
Human oocyte cytometry and fertilisation rate after subzonal insemination
Authors: Wolf Jean Philippe , Bulwa Sylvie , Rodrigues Daniel , Jouannet Pierre
Published: September 2008

The cytometry of 545 oocytes was evaluated during subzonal insemination (SUZI; 85 attempts), on day 0 (egg retrieval and SUZI), day 1 and day 2(embryo transfer). On day 0, the egg and oolemma diameters (mean ± SD) were 164.0 ± 19.6 μm and 114.2±16.8 μ5m respectively.The zona thickness was 17.8± 13.4 μm and correlated with the oolemma diameter(r= 0.24,p< 0.001). The fertilisation rate was significantly lower for the smaller oocytes (less than 108 μm diameter) compared with the larger oocytes (over 108μm) (9.8% vs 21.2% respectively; p < 0.05). These was little variation in oocyte diameter according to nuclear status. However, oocyte diameter increased significantly between day 0 and day 1 (p< 0.001) for both fertilised and unfertilised oocytes. Six different indications for SUZI were investigated in detail: three with non-specific (normal and subnormal sperm within vitrofertilization failure, oligoasthenospermia) and three with specific sperm defects (flagellar dyskinesia, absence of outer dynein arms, antisperm antibodies). Oocytes from the non-specific defect groups had significantly smaller diameters than the others (p< 0.05). The mean fertilisation rate was related to the mean oolemma diameter for the groups with non-specific sperm defects and the group lacking dynein arms (LODA) (r= 0.91,p< 0.05). Eggs from the groups of patients with LODA and those with antisperm antibodies had thicker zona pellucida than others (p< 0.05). These findings suggest that in addition to nuclear criteria of maturity, the growth of oocytes is an important factor for fertilising ability. Insufficient development of the ooplasm may contribute to fertilisation failure, particularly when sperm with functional defects are used. In contrast, a thick zona pellucida may prevent sperm with specific anomalies such as LODA or antisperm antibodies from penetrating into the perivitelline space.
Xenopusinterspersed RNA families, Ocr and XR, bind DNA-binding proteins
Authors: Guttridge Katherine Ladner , Smith L. Dennis
Published: September 2008

Interspersed RNA makes up two-thirds of cytoplasmic polyadenylated RNA inXenopusand sea urchin eggs.Although it has no known function, previous work has suggested that at least one family of interspersed RNA, XR, bindsXenopusoocyte proteins, and can influence the rate of translation. We have used twoXenopusrepeat families, Ocr and XR, to explore their protein binding abilities. Ocr RNA binds the same pattern of highly abundant oocyte proteins that XR RNA binds, which are believed to be messenger ribonucleoprotein (mRNP) particle proteins. In addition, we show that Ocr RNA binds the Oct-60 protein, a member of the POU-domain family of transcription factors found inXenopusoocytes. Using a 32 base pair sequence from the XR repeat in a DNA affinity column two proteins were isolated, 66KDa and 92KDa, that together form a complex with XR DNA. One of these proteins (92KDa) also binds XR RNA. We suggest that the role of at least a subset of interspersed RNAs in development may be to bind, and sequester in the cytoplasm, DNA-binding proteins until the end of oogenesis
Genome organisation in the murine sperm nucleus
Authors: Jennings Carol , Powell Don
Published: September 2008

The organisation of DNA sequences in the murine sperm nucleus was studied usingin situhybridisation of biotinylated DNA probes. The efficiency of this reaction was assessed using a dispersed repetitive DNA probe. Telomeric DNA was distributed around the nucleus. Centromeric and ribosomal DNA sequences occupied restricted domains in the sperm nucleus. DNA sequences for a transgene and a cluster of homeogenes occupied different, and rather less defined, domains. Together these results imply that both repetitive and protein-coding sequences are arranged in the nucleus in an ordered fashion.