bluuebunny/crossref_metadata_2025 huggingface dataset:
A singular minimization problem for droplet profiles
Authors: Novick-Cohen Amy
Published: September 2008

A minimization problem for partially wetting droplet profiles is considered, in which Van der Waal's forces have been taken into account via a singular ‘disjoining pressure’. When the singular disjoining pressure is neglected, energy minimization leads to Laplace's equation and Young's equation; once the singular disjoining pressure is included, this is no longer the case. Indeed, the free energy is no longer bounded from below. Introducing the notion of overtaking to compare the energies of configurations whose energies are arbitrarily large and negative, we demonstrate that if a configuration is not convex then it cannot be an absolute minimizer. If profiles are allowed to ‘double-over’ then there does not exist an absolute minimizer. Within the class of profiles which do not double-over, absolute minimizers are shown to exist; these minimizing profiles are not single-valued. The singular minimization problem is shown to be discontinuously dependent on the definition of the wetting profile in the neighbourhood of the contact points; the implications of this discontinuity are discussed.
Continuous and semidiscrete travelling waves for a phase relaxation model
Authors: Nochetto Ricardo H. , Paolini Maurizio , Verdi Claudio
Published: September 2008

Quite precise asymptotic estimates, in terms of the relaxation parameter and the time step, are derived for travelling wave solutions to a Stefan problem with phase relaxation and a semidiscrete counterpart. These estimates quantify the regularizing effects of phase relaxation and time discretization that give rise to thin transition layers as opposed to sharp interfaces. Layer width estimates, pointwise error estimates, and asymptotic expressions for the profile of the relevant physical variables are proved. Applications to a related nonlinear Chernoff formula are also given.
A state-dependent GI/G/1 queue
Authors: Knessl Charles , Tier Charles , Matkowsky B. J. , Schuss Z.
Published: September 2008

We consider a state-dependent GI/G/1 queueing system characterized by the unfinished work U(t) in the system at time t. We introduce state-dependence by allowing (i) the arrival process to depend on the instantaneous value of U(t), (ii) the service rate, that is, the rate at which U(t) decreases in the absence of arrivals, to depend on U(t), and (iii) the customer's service requirement to depend on U(t*) where t* denotes the instant in which that customer entered the system. We consider the limit of short inter-arrival times and small service requests and compute asymptotic approximations to the stationary density of the unfinished work, including the stationary probability of finding the system empty, using the WKB method and the method of matched asymptotic expansions.
Resolving weak internal layer interactions for the Ginzburg–Landau equation
Authors: Reyna Luis G. , Ward Michael J.
Published: September 2008

The internal layer behaviour, in one spatial dimension, associated with two classes of Ginzbug–Landau equation with double-well nonlinearities and small diffusivities is investigated. The problems that are examined are the Ginzburg–Landau equation with and without a constant mass constraint. For the constrained problem, steady-state internal layer solutions are constructed using a formal projection method. This method is also used to derive a differential-algebraic system describing the slow dynamics of the constrained internal layer motion. The dynamics of a two-layer evolution is studied in detail. For the unconstrained problem, a nonlinear WKB-type transformation is introduced that magnifies exponentially weak layer interactions and leads to well-conditioned steady problems. A conventional singular perturbation method, without the need for exponential asymptotics, is used on the resulting transformed problem as an alternative method to construct equilibrium solutions and metastable patterns. Exponentially sensitive steady-state internal layer solutions as well as a one-layer evolution are computed accurately using the transformed problem.
An asymptotic procedure and numerical study for the analysis of an elastic body with a thin sub-surface crack
Authors: Movchan A. B. , Willis J. R.
Published: September 2008

A class of three-dimensional crack problems is considered, of which a prototype example is provided by a half-space containing a long internal crack, located in a plane perpendicular to the boundary. By means of an asymptotic procedure, the original three-dimensional problem is split up into a sequence of two-dimensional formulations. Results of its numerical implementation are in good agreement with results of more computer-intensive finite-element calculations.
A mathematical model for washing a tow of fibres: Part 2
Authors: Byatt-Smith J. G. , Terrill E. L.
Published: September 2008

In Part I of this paper (Terrill & Byatt-Smith, 1993) the problem of the flow between an obstacle in the form of a wedge and a porous flexible tow was modelled using lubrication theory. In the region close to the wedge where bending is important the following equation

was derived for the non-dimensional gap width,H(X), between the tow and the wedge.
Self-similar solutions for a free boundary problem in the doping of semiconductors
Authors: Peletier L. A. , Troy W. C.
Published: September 2008

We study the development of concentration profiles in a semi-infinite slab of semi-conductor material, in which impurities have been implanted at a high concentration. When the implant is uniform throughout the slab, no impurities can pass through the face of the slab, and the vacancy concentration at the surface is kept at its equilibrium value, it is shown that the density profiles of impurities, vacancies and host atoms may have self-similar form. The analysis is constructive and yields qualitative properties of the profiles and the front.
A Stefan problem in a Bridgman crystal grower
Authors: den Decker P. , van der Hout R. , Van Duijn C. J. , Peletier L. A.
Published: September 2008

We discuss a one-dimensional model for a Bridgman crystal grower, where the removal of heat is described by an internal heat sink. A consequence is the apparent existence of mushy regions for relatively large velocities of the cooling machine; these mushy regions are an artefact of the one-dimensional approximation. We show that for some types of cooling profiles there exists a critical speed for the existence of mushy regions, whereas for different cooling profiles no such critical speed exists. The presence of a mushy region may indicate a strong curvature of the liquid/solid interface in the real situation.
A free boundary problem arising in the modelling of internal oxidation of binary alloys
Authors: Hu Bei , Zhang Jianhua
Published: September 2008

A one-dimensional free boundary problem arising in the modelling of internal oxidation of binary alloys is studied in this paper. The free boundary of this problem is determined by the equation u = 0, where u is the solution of a parabolic partial differential equation with discontinuous coefficients across the free boundary. Local existence, uniqueness and the regularity of the free boundary are established. Global existence is also studied.
On the maximum drag of a curved plate in flow with a wake
Authors: Maklakov D. V. , Uglov A. N.
Published: September 2008

In this work exact upper bounds of the drag force are found for curved plates of fixed total arc-length in flow with a wake, which forms according to the Joukowsky-Roshko-Eppler model. The shapes of maximum drag are determined in an explicit analytical form and can be interpreted as those of ideal parachutes.
Convergence of attractors for the simplified magnetic Bénard equations
Authors: Imai Hitoshi , Ishimura Naoyuki , Nakamura Masaaki
Published: September 2008

The simplified magnetic Bénard; equations (SMB) are derived from the two-dimensional magnetic Bénard system and extend the well-known Lorenz equations (L). (SMB) contains a parameter Q associated with the magnetic field. When Q = 0, the long time dynamics of (SMB) agrees with that of (L). In this paper, we investigate the long time behaviour of (SMB) as Q→0. We prove analytically that the global attractor of (SMB) converges to the one of (L) as Q→0 upper semicontinuously in the Hausdorff sense. However, numerical computation indicates that generically there is no continuity in the dimension of the attractor.
On self-similar solutions of Barenblatt's nonlinear filtration equation
Authors: Cole Julian D. , Wagner Barbara A.
Published: September 2008

We derive the asymptotic form of the self-similar solutions of the second kind of the Cauchy problem for Barenblatt's nonlinear filtration equation by perturbing the Lie group of the underlying linear problem. We also show that the decay rate, appearing in the similarity solutions, can be found by a simple inspection of the corresponding energy dissipation law.
Interfacial wave theory for oscillatory finger formation in a Hele–Shaw cell: a comparison with experiments
Authors: Xu Jian-Jun
Published: September 2008

This paper is devoted to an analysis of the formation of oscillatory viscous fingers in a Hele-Shaw cell on the basis of the interfacial wave theory, previously established for the pattern formation dynamics in dendrite growth, as well as in the classic Saffman–Taylor flow. In particular, we study the problem of selection and persistence of oscillatory fingers with a tiny bubble at the finger tip. We obtain uniformly valid asymptotic solutions for this problem, and derive the linear, global wave instability mechanism for this more complicated system. The global, neutrally stable modes are computed in a large region of parameters, which select the form of oscillatory fingers in the later stage of evolution. We have compared the theoretical predictions with the experimental data by Couder et al. (1986) and by Kopf-Sill & Homsy (1987), and found excellent quantitative agreement.
A ξ-vector formulation of anisotropic phase-field models: 3D asymptotics
Authors: Wheeler A. A. , McFadden G. B.
Published: September 2008

In this paper we present a new formulation of a large class of phase-field models, which describe solidification of a pure material and allow for both surface energy and interface kinetic anisotropy, in terms of the Hoffman–Cahn ξ-vector. The ξ-vector has previously been used in the context of sharp interface models, where it provides an elegant tool for the representation and analysis of interfaces with anisotropic surface energy. We show that the usual gradient-energy formulations of anisotropic phase-field models are expressed in a natural way in terms of the ξ-vector when appropriately interpreted. We use this new formulation of the phase-field equations to provide a concise derivation of the Gibbs–Thomson–Herring equation in the sharp-interface limit in three dimensions.
On the asymptotics of solutions of a class of linear functional-differential equations
Authors: Derfel G. , Vogl F.
Published: September 2008

A sharp estimate of the growth of solutions of the initial value problem for systems of the form

where Cj(t) are matrices with elements of power growth, is found. As a corollary of this result, it follows, for instance, that each solution of the initial value problem satisfies the estimate ‖u(t)‖ ≤ Cexp{γln2(1+|t|)} for some C > 0 and γ > 0.
The existence of multiple solutions for a Ginzburg–Landau type model of superconductivity
Authors: Hastings S. P. , Kwong M. K. , Troy W. C.
Published: September 2008

We study a system of two second-order differential equations with cubic nonlinearities which model a film of superconductor material subjected to a tangential magnetic field. We verify some recent conjectures of one of the authors about multiplicity of solutions. We show that for an appropriate range of parameter values the relevant boundary value problem has at least two symmetric solutions. It is also proved that a second range of parameters exists for which there are three symmetric solutions.
Solution of a contact lens problem
Authors: McLeod J. B.
Published: September 2008

In this paper we study the question of existence and uniqueness of solutions to the equation

which occurs in the modelling of hard contact lenses. Using ‘shooting’ arguments, we show that, depending on the parameters in the problem, there are cases where there is precisely one solution, others where there is more than one, and others where there are none.
Staurosporine advances interblastomeric flattening of the mouse embryo
Authors: O'Sullivan D. Michael , Johnson Martin H. , McConnell Josie M.L.
Published: September 2008

Staurosporine, an inhibitor of protein kinase activity, causes premature intercellular flattening of blastomeres but does not induce their premature polarisation. The flattening induced is calcium dependent, is reversed transiently at mitosis and requires the continuing presence of the drug. Staurosporine also blocks the decompacting effect of phorbol ester on 8-cell embryos.
Structural and functional differentiation of follicular and oviductal mouse oocytes visualised with FITC-protein conjugates
Authors: Kim Haekwon , Schuetz Allen W.
Published: September 2008

The fluroscence labelling characteristics of mouse oocytes were examined at various stages of periovulatory differentiation using FITC-protein conjugates. The zona pellucida perivitelline space and plasma membrane underwent visible changes which were developmentally and environmentally related. Following exposure to fluorescein isothiocyanate (FITC)-casein conjugates, the zona pellucida (ZP) of germinal vesicle stage (GV) ovarian oocytes exhibited a bright, amorphous, mesh-like staining pattern (immature type). In contrast, mature polar body stage (PB) oocytes, either ovarian or oviductal, displayed faint, spotty fluorescence labelling of the ZP (mature type). The perivitelline space (PVS) of mature ovarian oocytes (12 h post-hCG) failed to label, whereas approximately 50% of oviductal oocytes showed PVS labelling. The incidence of PVS staining increased with postovulatory age, possibly as a result of the accumulation of materials secreted by the oviduct. Followingin vivoorin vitrofertilisation of oocytes, a characteristic pattern of plasma membrane (PM) labelling was observed. Similar patterns of PM labelling were seen in oocytes parthenogenetically activated with ethanol or ionophore (A23187) but not in control oocytes. The pattern of PM labelling observed with FITC-protein conjugates was strikingly similar to that observed with FITC-labelled lectins, which are thought to interact with glycoconjugates released from cortical granules. Immature type of ZP staining also occurred when GV oocytes were treated with FITC alone or with a variety of FITC-protein conjugates. Thus, protein may not be required for labelling of the ZP by FITC-protein conjugates as previously thought. FITCconjugated proteins including casein, bovine serum albumin, peroxidase and non-immune immunoglobulin G (IgG), all labelled the PM of activated oocytes; however, FITC-IgG failed to label the PVS. Results demonstrate for the first time that various components of viable mouse oocytes exhibit and undergo characteristic structural and functional changes during periovulatory differentiation as evidenced by their interaction with one or more FITC-protein conjugates and/or FITC. On the basis of these results the intrafollicular and oviductal mechanisms mediating these changes are discussed as is the possibility that the fluorescent molecule attached to conjugates may play a role in oocyte labelling.
Isoloation of H-SF substances, the high-molecular-weight precursors of egg envelope preteins, from the ascites accumulated in the oestrogen-treated fish Oryzias latipes
Authors: Murata Kenji , Iuchi Ichiro , Yamagami Kenjiro
Published: September 2008

High- and low-molecular weight spawning-female-specific (H-SF and L-SF) substances are liver-derived putative precursors of the inner layer of egg envelope of the medaka Oryzias latipes, and are also found in the ascites which are accumulated in the male fish on prolonged treatment with oestrogen. In the present study, the H-SF substances purified from the ascites of the oestrogen-treated male medaka were found to consist of three proteins. Their molecular weights ranged from 74 000 to 76 000, which corresponds to those of ZI-1 and ZI-2, the major components of medaka egg envelope. The amino acid composition of the H-SF substances was characterised by high contents of proline (17.58 mol%) and glutamic acid/glutamine (13.34 mol%). The characteristics were almost identical to those of ZI-1 and ZI-2 but differed from those of L-SF substance, a precursor of ZI-3, another major component of the egg envelope. These results confirm our view that H-SF substances are the precursors of ZI-1 and ZI-2. The average amino acid compositions of H-SF substances and L-SF subsatance coincided with the amino acid composition of whole egg envelope. This result strongly suggests that an equal amount of H-SF substances and L-SF substance would construct the inner layer of egg envelope after a little modification.
The parental origin of the distal pronucleus in dispermic human zygotes
Authors: Tang Ya-xu , Munné Santiago , Reing Adrienne , Schattman Glenn , Grifo Jamie , Cohen Jacques
Published: September 2008

The purpose of this investigation was to determine the parental origin og the pronucleus furthest from the second polar body (the distal pronucleus) in dispermic human zygotes. Infact dispermic embryos (n = 53) and those from which the distal pronucles (n =50) was removed at the zygote stage were biopsied after cleavage. Blastomeres were sexed using either coamplification of X and Y probes using a duplex polymerase chain reaction (PCR), or simultaneous fluorescence in situ hybridisation (FISH) with directly fluorochrome-labelled probes for chromosomes X, Y and 18. The ratio X/Y was determined in both groups of embryos by assessing a minimum of two blastomeres. If the pronuclei in dispermic zygotes are topographcially in a fixed position, the X/Y ratio should change from 1:3 in dispermic embryos to 1:1 in enucleated ones. The ratio of embryos containing only an X chromosome and those with X as well as Y chromosomes in the intact dispermic zygotes was 1.0:2.3 which is similar to the theoretical ratio of 1:3. This ratio was 1.0:1.3 in dispermic zygotes from which the distal pronuclei were removed. This ratio is not significantly different from the 1:1 ratio based on a statistical analysis with a sample size of 50. These sex ratios would have been considered different if more than 200 enucleations had been performed. Although the ratio X/Y was altered following removal of distal pronuclei, suggesting frequent targeting of male pronuclei, accidental removal of the female pronucleus could not be excluded. This indicates that enucleation of dispermic zygotes could produce high yields of gynogenetic and androgenetic embryos for research purposes. Clinical application aimed at producing biparental zygotes may be hazardous, since mosaicism was common among enucleated embryos.
The spindle apparatus in early embryonic divisions ofEphestia Kuehniella Z.(Pyralidae, Lepidoptera) is formed by alignment of minispindles
Authors: Wolf Klaus Werner
Published: September 2008

Spindles were isolated from deposited eggs of the Mediterranean mealmoth,Ephestia Kuehniella. Their structure and development were studied using anti-tubulin immunofluorescence. The microtubules were labelled with three different monoclonal antibodies. These were directed against β-tubulin, tyrosinated α-tubulin and acetylated α-tubulin. Significant differences in the staining behaviour were not detected with the three antibodies. An unusual mode of spindle formation was observed during the first mitotic division after fusion of the pronuclei. Several of the ensuing embryonic divisions may show the same phenomenon. Prophase of these divisions was characterised by an irregular arrangement of microtubules in the nuclear area. The microtubule mass in the nuclear area increased concomitantly with chromosome condensation. Microtubular foci, comparable to the forming asters of canonical spindles, were not detected. The formation of an orderly pattern in the microtubule mass was signalled by the appearance of minispindles apparently developing around individual chromosomes. Several minispindles subsequently aligned and formed metaphase-like entities within the nuclear area. The metaphase-like entities, in turn, aligned with one another and gave rise to a conventional bipolar metaphase spindle with small asters. The further development of the spindle was conventional. The chromosomes migrated towards the spindle poles and finally daughter nuclei formed. The anaphase and telophase spindles possessed both a prominent array of interzone microtubules and asters. The events in prophase of early embryonic mitosis of E.kuehniellamay represent a rare case of chromosomeinduced spindle formation.
Human cumulus cell complexes studied in vitro by light microscopy and scanning electron microscopy
Authors: Kennedy Sian , England Marjorie A. , Mills Carla
Published: September 2008

Various researchers describe the morphology of cumulus cells (CC) in vitro, but few have investigated their behaviour on plastic. Knowledge concerning the behaviour of human CC could be useful in improving the success of in vitro fertilisation procedures. This study aimed to describe the morphology and behaviour of CC in vitro and to investigate movement on a collagen-coated substrate. Following collection some cumulus were mechanically dissected from those surrounding the oocyte. Cumulus aggregates were cultured over 24 h using Earle's medium supplemented with 8% albumin. Substrata were plastic coverslips coated with collagens I, IV, or mixed collagens. Cumulus cultured over corresponding time periods on uncoated coverslips served as controls. Specimens were fixed and prepared for scanning electron microscopy. Over 24 h the controls began exhibiting the morphological features associated with cell movement: cell surface protrusions changed from blebs to microridges, lamellipodia and leading lamellae; cell shape altered from rounded and upright, to flattened. Extracellularmatrix (ECM) transformed from a thick, sheet-like substance to a thin, fibrous material. By 24 h, cells contacting ECM remained rounded showing few features of movement. Collagens enhanced attachment of CC as a monolayer on the substrate. Cell morphology varied according to the collagen type used. On mixed collagens, cells attached rapidly, appearing to be predominantly non-motile. On collagen type I there was less attachment of cells but increased motility. On collagen type IV there was decreased attachment and the cells remained spherical. In conclusion, collagens enhance the settling of cumulus cells on a plastic substrate and the cells exhibit some specificity in attaching to collagens.
Gap junction communication and cell adhesion in development
Authors: DeHaan Robert L.
Published: September 2008

During the past decade growing evidence has suggested that cell-cell communication via gap junctions is crucial for early developmental processes (Warneret al., 1984; Guthrie & Gilula, 1989; Serraset al., 1989). It has been shown that embryos of mice (Kalimi & Lo, 1988), teleosts (Kimmelet al., 1984), insects (Warner & Lawrence, 1982; Ruangvoravat & Lo, 1992) and molluscs (Serraset al., 1989) become regionally organized into restricted domains of junctionally connected cells that share developmental potential. In the mouse gastrula, for example, dye-coupling experiments have demonstrated that cells within a developmental compartment have a high degree of coupling whereas cells across compartmental boundaries have reduced coupling (Kalimi & Lo, 1988). Classic experiments (Townes & Holtfretter, 1955; Steinberg, 1963) demonstrated that as cells begin to differentiate along common pathways, they develop selective adhesion properties and the ability to sort themselves from unlike neighbours (for review see Edelman 1988; Edelmanet al., 1990). More recently a multitude of specific cell adhesion molecules (CAMs) have been identified that mediate these processes and trigger the cytoplasmic events that drive further differentiation (Edelmanet al., 1990; Albelda, 1991; Geiger & Ayalon, 1992).
Provisional bilateral symmetry inXenopuseggs is estiblished during maturation
Authors: Brown E.E. , Margelot K.M. , Danilchik M.V.
Published: September 2008

Dorsal–ventral patterning in theXenopusegg becomes established midway through the first cell cycle during a 30° rotation of the subcortical yolk mass relative to the egg cortex. This rotation of symmetrisation is microtubule dependent, and its direction is thought to be cued by the usually eccentric sperm centrosome. The fact that parthenogenetically activated eggs also undergo a directed rotation, despite the absence of a sperm centrosome, suggests that an endogenous asymmetry in the unfertilised egg supports the directed polymerisation of microtubules in the vegetal cortex, in the way that an eccentric sperm centrosome would in fertilised eggs. Consistent with this idea, we noticed that the maturation spot is usually located an average of more than 15° from the geometric centre of the pigmented animal hemisphere. In parthenogenetically activated eggs, this eccentric maturation spot can be used to predict the direction of rotation. Although in most fertilised eggs the yolk mass rotates toward the sperm entry point (SEP) meridian, occasionally this relationship is perturbed significantly; in such eggs, the maturation spot is never on the same side of the egg as the SEP. In oocytes tilted 90° from upright during maturationin vitro, the maturation spot developed 15° or more from the centre of the pigmented hemisphere, always displaced towards the point on the equator that was up during maturation. This experimentally demonstrated lability is consistent with an off-axis oocyte orientation during oogenesis determining its eccentric maturation spot position, and, in turn, its endogenous rotational bias.
Pronuclear formation and cleavage of mammalian eggs after microsurgical injection of freeze-dried sperm nuclei
Authors: Hoshi Kazuhiko , Yanagida Kaoru , Katayose Haruo , Yazawa Hiroyuki
Published: September 2008

A study was conducted to evaluate the ability of mammalian oocytes to develop to the pronuclear stage and beyond if injected with freeze-dried sperm nuclei. The rate of development of hamster eggs to the pronuclear stage after microinjection of freeze-dried hamster sperm nuclei was 90%. The pronuclear formation rate of hamster eggs injected with freeze-dried human sperm nuclei was 85%. On the other hand, the rates for eggs injected with untreated sperm nuclei were 84% and 89% respectively. The survival rate of rabbit eggs microinjected with freeze-dried rabbit sperm nuclei was 64%, the fertilisation rate 56% and the cleavage rate 38%. The survival, fertilisation and cleavage rates of eggs injected with non-freeze-dried sperm nuclei were 78%, 45% and 34%, respectively. There was no difference between eggs injected with freeze-dried sperm nuclei and those injected with sperm nuclei that had not been freeze-dried. Of the viable rabbit eggs injected with freeze-dried rabbit sperm nuclei, 6% developed to the 6- to 8-cell stage 62 h after injection.
Activation of bovine oocytes penetrated after germinal vesicle breakdown
Authors: Abeydeera Lalantha R. , Okuda Kiyoshi , Niwa Koji
Published: September 2008

The present study was designed to examine the ability of bovine oocytes, after germinal vesicle breakdown (GVBD), to be activated by sperm penetration and the sequence of sperm nuclear transformation. Bovine oovytes cultured for 8 h in maturation medium (tissue culture medium TCM-199 containing 10% fetal calf serum) were inseminated in Brackett and Oilphant's medium supplemented with bovine serum albumin (10 mg/ml), caffeine (5mM) and heparin (10 μg/ml). When oocytes were transferrred to the maturation medium 8 h after insemination and additionally cultured for 5−40 h at 39°C in 5% CO2 in air, 71−76% of oocytes were penetrated and polyspermy (67–75%) was common. The proportions of penetrated oocytes that were activated significantly increased with the lapse of the additional culture time, reaching 88% and 87% by 25 and 40 h after additional culture, respectively. When compared with unpenetrated oocytes, signifcantly higher proportions of penetrated oocytes, reached metaphase II or beyond 15 and 25 h after additional culture. After penetration, sperm nuclei were transformed into metaphase chromosomes and then to telophase chromomes before the formation of male pronuclei. These results provide evidence that bovine oocytes acquire the ability to respond to sperm-mediated activation soon after GVBD.
Interactions in glycine and methionine uptake, conversion and incorporation into proteins in the preimplantation mouse embryo
Authors: Khatchadourian Chaqué , Guillaud Josette , Menezo Yves
Published: September 2008

Glycine is the most concentrated amino acid in the female genital tract. In this study, we report its conversion and incorporation into proteins in the presence or absence of methionine, in borth 1-cell and blastocyst mouse embryos. The uptake, incorporation and conversion of radiolabelled glycine were studied in the presence or absence of unlabelled methionine. For control purposes, the reciprocal experiment was performed with labelled methionine in the presence or absence of unlabelled glycine. At the 1-cell stage neither glycine uptake nor its incorporation into proteins is inhibited by methionine. Glycine is, however, highly used as an oxidisable energy substrate, via glycolate. At the blastocyst stage, glycine conversion into other amino acids is high and mainly utilised in the formation of glutamic acid. Glycine is highly incorporated into proteins, resulting in a poor exchange of glycine from the preloaded embryos. Methionine competes for glycine uptake and consequently reduces its overall incorporation into proteins. For methionine, neither its uptake nor its incorporation into proteins is reduced in the presence of glycine for the two embryonic stages tested here. The embryo has different mechanisms for incorporation and utilisation of methionine and glycine. Glycine, which has an important function in the embryo, has an inefficient transport system compared with methionine. We were unable to demonstrate the presence of methyiglycine since SAM-glycine-methyltransferase (EC 2.1.1.20) was not detected. The same results were obtained when exogenous methionine was added. We therefore concluded that glycine does not compete in transmethylation within the embryo.
Stages leading to and following fusion of sperm and egg plasma membranes
Authors: Longo Frank J. , Cook Susan , McCulloh David H. , Ivonnet Pedro I. , Chambers Edward L.
Published: September 2008

The site of gamete interaction of electrophysiologically recordedLytechinus variegatuseggs, fixed with osmium tetroxide (O5O4) and/or glutaraldehyde (GTA) at varying intervals after the onset of the increase in membrane conductance induced by an attached sperm, has been examined by high-voltage and conventional transmission electron microscopy. Although GTA and a GTA-O5O4mixture iduced different electrical responses, specimens prepared with the two fixatives were ultrastructurally similar. In specimens observed within 5 s of the change in conductance, the acrosomal process projected through the vitelline layer and abutted the egg plasma membrane. A conspicuous layer of bindin surrounded the acrosomal process and connected the sperm to the egg's vitelline layer. In a fortuitous specimen fixed within 4 s following the change in conductance, the area of contact between the gamete plasma membranes possessed a trilaminar structure that separated the egg's and sperm's cytoplasms. The morphology of this area of contact was consistent with previously proposed intermediates of membrane fusion. Five to six seconds after the change in conductance, the sperm was connected to the egg via a narrow cytoplasmic bridge that consisted of the former acrosomal process and a projection of the egg cortex. The region of the bridge midway between the fused gametes was encircled by dense material that marked the site of sperm-egg fusion. Gamete interactions in which the activation potential was recorded (unclamped egg) were comparable in time and ultrastructure to events taking place in voltage-clamped eggs except for one major difference. Intact cortical granules (one to three) were observed beneath the tip of the incorporating sperm in unclamped eggs fixed following the onset of the activation potential, whereas all cortical granules dehisced in clamped eggs.
Methods for the assessment of capacitation
Authors: Barboni Barbara
Published: September 2008

Enjaculated spermatozoa do not have the immediate capacity for ferilisation. Austin (1952) and Chang (1951) first realised that the sperm gain this capacity within the female genital tract. The physiogical changes that make the spermatozoon competent to fertilise were defined as ‘Capacitation’ (Austin, 1952).
Oocyte activation in invertebrates and humans
Authors: Dale Brain
Published: September 2008

Oocytes are metabolically repressed cells that, in most cases, require a signal from the fertilising spermatozoon to trigger activation. Physiological competence of the activated oocyte, a prerequisite for early embryogenesis, depends, therefore, not only on the quality of the oocyte, but also on the quality of the spermatozoon (Dale, 1983; Tosti & Dale, 1992). There are two current opinions as to how the spermatozoon triggers the oocyte into metabolic activity (Dale & DeFelice, 1990). The first hypothesis is that following gamete fusion the spermatozoon releases a soluble activating factor into the oocyte cytoplasm that is then amplified globally by second messengers in the oocyte. The second is that sperm binding to receptors spanning the oocyte plasma membrane is the signal that is transduced to the second messenger system of the oocyte (Swann, 1993; Foltz & Shilling, 1993).
Metaphase arrest in newly matured or microtubule-depleted mouse eggs after calcium stimulation
Authors: Moses Ruth M. , Masui Yoshio
Published: September 2008

In mouse eggs arrested at meiotic metaphase II, the increase in intracellular calcium that results from fertilisation induces nuclear formation in both newly ovulated and older eggs. In contrast, the calcium increase that results from exposure to the calcium ionophore A23187 induces nuclear formation in older, but not young, newly ovulated eggs. When treated with the microtubule inhibitor colcemid, and fertilised, young eggs remained at metaphase, but many older eggs formed nuclei, although older eggs treated with colcemid and A23187 remained at metaphase. However, young A23187-treated eggs, young colcemid-treated fertilised eggs, and older colcemid- and A23187-treated eggs, formed nuclei when treated, in addition, with the protein synthesis inhibitor cycloheximide, or the protein kinase inhibitor 6-dimethylaminopurine (6-DMAP). The possibility is discussed that metaphase in newly matured eggs and microtubule-depleted eggs may be maintained by similar mechanisms involving short-lived phosphorylated proteins.
Mouse sperm fertilising capacity following subzonal microinjection is dependent on sperm washing and response to solubilised zonae pellucidae
Authors: Kaplan Orly Lacham , Trounson Alan
Published: September 2008

Spermatozoa obtained from hybrid male mice were treated with solubilised zonae pellucidae after a period of capacitationin vitroto induce the acrosome reaction. Single spermatozoa were selected and microinjected into the perivitelline space of mature oocytes. A high proportion of the spermatozoa acrosome-reacted affter treatment with solubilised zonae (63%). However, the fertilisation rate (37%) after subzonal microinjection of oocytes by the treated spermatozoa was not different to the fertilisation rate (40%) of oocytes microinjected with untreated spermatozoa which had a lower rate of acrosome reaction (39%). When spermatozoa were washed by high-speed centrifugation before treatment with solubilised zonae pellucidae and subzonal microinjection, the fertilisation rate (68%) was significantly higher (p< 0.001) than that (29%) for occytes microinjected with untreated spermatozoa and was found to be correlated with a high acrosome reaction rate (74%) (r= 0.8). The washing of spermatozoa by centrifugation itself did not increase the acrosome reaction rate or fertilisation rate of oocytes after microinjection. The results of this study suggests that some modifications other than the acrosome reaction are needed to enable capacitated mouse spermatozoa to fuse with the oocyte plasma membrane. These modifications were achieved by washing spermatozoa by high-speed centrifugation and the replacement of the supernatant with fresh culture medium used for capacitation. Induction of the acrosome reaction by solubilised zonae pellucidae following this treatment leads to a high fertilisation rate of oocytes by subzonal sperm microinjection.
Characterisation of isolated egg cells,in vitrofusion products and zygotes ofZea maysL. using the technique of image analysis and confocal laser scanning microscopy
Authors: Tirlapur Uday K. , Kranz Erhard , Cresti Mauro
Published: September 2008

Changes in membrane Ca2+, calcium receptor protein calmodulin, endoplasmic reticulum (ER), mitochondria and cellulose in unfixed, living, isolated egg cells and fusion products of pairs of one egg and one sperm cell ofZea maysL. have been investigated using chlorotetracycline, fluphenazine, immunocytochemical techniques, 3,3'dihexyloxa-carbocyanine iodide (DiOC6(3)) and calcofluor white in conjuction with computer-controlled video image analysis. In addition, confocal laser scannig microscopy has been used in conjuction with ethidium bromide to detect the nature and location of the sperm cell nuclear chromatin before and after karyogamy. Digitised video images of chlorotetra cycline (CTC) fluorescence reveal that egg cells contain high levels of membrane Ca2+in organelles present around the nucleus while the cytosolic signal is relatively low. Intense CTC fluorescence is invariably present just below the plasma membrane of egg cells and a certain degree of regionalised distribution of Ca2+in cytoplasm is also discrnible. Similarly, the fluphenazine (FPZ)-detectable calmodulin (CaM) and that localised immunocytochemically using monoclonal anti-CaM antibodies reveal high levels of Cam in the vicinity of the nucleus in egg cells. Only a few ER profiles and mitochondria could be visualised in the egg cell and no calcofluor fluorescence could be detected. Followingin vitrofertilisation of single isolated eggs substantial changes in the Ca2+levels occur which include an increase in the membrane Ca2+of the fusion product, particularly in the cytosol and around the nucleus. Unlike in the eggs the fine CTC fluorescence signal below the plasma membrane is not detectable in the fusion products. Compared with isolated egg cell protolasts an increase in the CaM level in the cytoplasm was observed in the fusion products. There is a slight increase in the CaM level in the cytoplasm was observed in the fusion products. There is a slight increase in the fluorescene around the fusion product is visible after 16 h in in culture. The sperm cell chromatin in the fusion product is highly condensed, unlike that of the egg cell, and confocally imaged serial optical sections of thein vitrofusion product reveal the occurrence of karyogamy 35 min following gamete fusion. First visual evidence for intermingling of sperm nuclear chromatin in the zygotic nuclei is also provided.
Molecular structure and function of CD4 on murine egg plasma membrane
Authors: Guo Mao Wu , Watanabe Toshiki , Mori Etsuko , Mori Tsuneatsu
Published: September 2008

In the present study, the expression of the CD4 molecule on murine egg plasma membrane was confirmed by the indirect immunofluorescence (IIF) method. The full-length CD4 cDNA from murine eggs was synthesised by the reverse transcriptase-polymerase chain reaction (RT-PCR) method and its authenticity verified by Southern blot hybridisation using an end-labelled internal oligonucleotide. The results of DNA sequencing showed that the nucleotide sequence of the cDNA of CD4 from murine egg mRNA was identical to that of immune T cells. To demonstrate the direct interaction of CD4 from murine egg with murine sperm cells bearing MHC (major histocompatibility complex) class II molecule, we employed a baculovirus expression system to generate CD4 on the surface ofSpodoptera frugiperda(Sf9) cells. Expression of CD4 on Sf9 cells infected with autographa californica nuclear polyhedrosis virus (AcNPV)-CD4 was demonstrated by IIF and immunoblotting. The CD4-expressing Sf9 cells adhered to MHC class II-bearing sperm cells since the adhension was specifically blocked by anti-CD4 monoclonal antibody (mAb) or anti-monomorphic region of MHC class II mAb. Taking our previous and present experimental results together, they strongly suggest that intercellular membrane adhesion between two gametes at the fusion step in fertilisation is mediated by the MHC class II molecule located on the posterior region of the sperm head and the CD4 molecule on egg plasma membrane.
Sulphydryl reagent iodoacetamide inhibits progression of meiosis and sperm transformation in mouse oocytes fertilisedin vitro
Authors: Maleszewski Marek
Published: September 2008

The effect of iodoacetamide (IA), a sulphydryl blocking agent, on fertilisation in the mouse was examined by transferring zona-free oocytes into IA (500 μM)-containing medium at various times after insemination. When inseminated oocytes were transferred into IA medium 10 min after insemination, the oocyte chromosomes remained aggregated in one or two masses and the sperm nucleus failed to decondense. When oocytes were transferred during the second meiosis, oocytes meiosis was more or less arrested. The sperm nucleus decondensed but remained blocked at an early stage of decondensation. These observations suggest that thiol groups in the oocyte's cytoplasm and perhaps microtubules of the meiotic spindle play crucial roles in the completion of meiosis and the transformation of sperm nucleus into pronucleus.
Cortical changes in starfish (Asterina pectinifera) oocytes during 1-methyladenine-induced maturation and fertilisation/activation
Authors: Longo Frank J. , Woerner Mark , Chiba Kazuyoshi , Hoshi Motonori
Published: September 2008

Maturation of the starfish oocyte cortex to produce an effective cortical granule reaction and fertilisation envelope is believed to develop in three phases: (1) pre-methyladenine (1-MA) stimulation; (2) post-1-MA stimulation, pregerminal vesicle breakdown; and (3) post-germinal vesicle breakdown. The present study was initiated to identify what each of these phases may encompass, specifically with respect to structures associated with the oocyte cortex, including cortical granules, microvilli and vitelline layer. 1-MA treatment brought about an orientation of cortical granules such that they became positioned perpendicular to the oocyte surface, and an ∼ 4-fold decrease in microvillar length. A-23187 activation of immature oocytes treated with (10 min; pregerminal vesicle breakdown) or without 1-MA resulted in a reduction in cortical granule number of 21% and 41%, respectively (mature oocytes underwent a 96% reduction in cortical granules). Elevation of the fertilisation envelope in both cases was significantly retarded compared with activated mature oocytes. In activated mature oocytes, the vitelline layer elevated 20.0 ± 5.4 μm from the egg's surface, whereas in immature oocytes treated with just A-23187 or with 1-MA (10 min) and A-23187, it lifted 0.35 ± 0.1 and 0.17 ± 0.04 μm, respectively. The fertilisation envelopes of activated (or fertilised) immature oocytes also differed morphologically from those of mature oocytes. In activated, immature oocytes, the fertilisation envelope was not uniform in its thickness and possessed thick and thin regions as well as fenestrations. Additionally, it lacked a complete electron-dense stratum that characterised the fertilisation envelopes of mature oocytes. The nascent perivitelline space of immature oocytes was also distinguished by the presence of numerous vesicles which appeared to be derived from microvilli. Differences in the morphology of cortices from activated (fertilised) and non-activated, immature and mature oocytes substantiate previous investigations demonstrating three phases of cortical maturation, and are consistent with physiological changes that occur during oocyte maturation, involving ionic conductance of the plasma membrane, establishment of slow and fast blocks to polyspermy and elevation of a fertilisation envelope.
Mast cell-Leydig cell relationships in the testis of the lizard podarcis s. sicula Raf: thermal manipulation, ethane 1,2-dimethane sulphonate (EDS) and sex hormone treatment
Authors: Minucci Sergio , Vitiello Italia Izzo , Marmorino Concetta , Di Matteo Loredana , Baccari Gabriella Chieffi
Published: September 2008

Mast cells of connective tissue type are scattered in the interstitial compartment of the lizard Podarcis s. sicula. Their number varies during the year, showing peaks in spring and in winter, respectively.Thermal manipulation affects mast cell number (MCN): high temperature decreased MCN in both January and May, while low temperature increased MCN only in January. Ethane dimethane sulphonate, a toxin which specifically destroys Leydig cells, induced an increase in MCN on days 3 and 7 of treatment. Oestradiol treatment provoked a strong increase in MCN that was blocked by tamoxifen. Blocking androgen receptors with cyproterone acetate resulted in an increase in MCN, while testosterone injection provoked a strong decrease. These results suggest a relationship between the presence of mature Leydig cells and mast cell proliferation and/or differentiation.
The role of microtubules and inositol triphosphate induced Ca2+release in the tyrosine phosphorylation of mitogen-activated protein kinase in extracts ofXenopus laevisoocytes
Authors: Duesbery N.S. , Masui Y.
Published: September 2008

Microsomal fractions ofXenopusoocytes release preloaded45Ca2+when treated with inositol triphosphate (InsP3). The effective concentration of InsP3required for half-maximal release (EC50) is 59 nM and maximal release occurs at ∼ 2 μM InsP3. Uptake and release of45Ca2+are not altered by the catalytic subunit of protein kinase A, dibutyrl cyclic adenosine monophosphate, protein kinase A peptide inhibitor or nocodazole. In contrast, taxol decreases the sensitivity of the microsomal fraction to InsP3, shifting the EC50for InsP3-induced Ca2+release from 59 to 259 nM. In lysates of oocytes, InsP3-induced Ca2+release causes the tyrosine phorphorylation of a 42000 (Mr42k) protein identified as 42k mitogen-activated protein (MAP) kinase. InsP3-induced tyrosine phosphorylation of MAP kinase is prevented by BAPTA and taxol, but not by nocodazole. Thus, microtubule polymerisation modifies InsP3-induced Ca2+release, thereby inhibiting phosphorylation of MAP kinase.