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Oceanic core complexes provide an accessible window into deep processes occurring at slow and ultra-slow-spreading mid-ocean ridges. We analyse samples from IODP ocean drilling of core complexes at the Atlantis Bank, Atlantis Massif, and near the Kane Transform at the South West Indian and Mid-Atlantic ridges. We correlate secondary minerals, including oxides, with sites of melt migration. We interpret changes to mineral assemblage and microchemistry, reaction textures and melt-pseudomorph microstructures as fingerprints of open-system melt-mediated processes. This micro-scale information is combined with a macro-scale review of legacy mineral chemistry data to show that melt-fluxed rocks share remarkably similar characteristics across the three core complexes investigated. These are rich in oxides and have olivine, orthopyroxene and clinopyroxene grains that are chemically distinct from oxide-poor gabbros. We propose that oceanic crust fluxed with external melt can be recognised by the following key features: (1) high modes of secondary minerals, such as oxides and olivine, (2) microstructural evidence for the former presence of melt, and (3) mineral chemistry differences between primary and secondary olivine, orthopyroxene, clinopyroxene and plagioclase. Importantly, olivine has previously only been reported as primary, that is, having crystallised from magma. However, our results show that gabbros with secondary olivine are reliable indictors of melt–rock interaction during deformation-assisted diffuse melt migration through the gabbroic oceanic crust. Finally, we propose a new model for the formation of oceanic core complexes where deformation-assisted melt migration plays a critical role in strain localisation, exhumation and evolution of the core complex. Secondary mineral microstructures indicate the former presence of melt. Olivine, plagioclase and pyroxene chemistry fingerprint melt-fluxed oceanic crust. Evidence of multiple fluxes of external melt associated with strain localisation. High oxide mode and secondary minerals are fingerprints of melt-fluxed zones in oceanic core complexes. [ABSTRACT FROM AUTHOR]

The flow properties of middle crustal rocks are commonly represented by viscous flow. Examples of pinch and swell structures found in a high strain zone at St. Anne Point (Fiordland, New Zealand) and Wongwibinda (N.S.W., Australia) suggest pinch and swell structures may be initiated by brittle failure of the more competent layer in conjunction with subsequent material softening. On this basis we develop a numerical model where Mohr--Coulomb constitutive strain localising behaviour is utilised to initiate pinch and swell structure development. Results show that pinch and swell structures develop in a competent layer in both Newtonian and non-Newtonian flow, provided the competent layer has sufficient viscosity contrast and can localise strain to form shear bands. The flow regime and strain localising characteristics of the surrounding country rock appear not to impact pinch and swell structure formation. The degree of material softening after the initial strain localising behaviour is shown to impact pinch and swell characteristics, while extensive material softening causes the formation of thick necks between swells by limiting the focused localisation of strain into shear bands. To aid analysis of the structures and help derive the flow properties of rocks in the field, we define three stages of pinch and swell development and offer suggestions for measurements to be made in the field. Our study suggests that Mohr--Coulomb strain localising behaviour combined with viscous flow is a viable alternative representation of the heterogeneous rheological behaviour of rocks seen in the middle crust. This type of mid-crustal rheological behaviour can have significant influence on the localisation of strain at all scales. For example, inclusion of Mohr-- Coulomb strain localising behaviour with viscous flow in just some mid-crustal layers within a crustal-scale model can result in significant strain localisation, extending from the upper crust into the middle crust. This localisation also influences the development of near-surface structures. [ABSTRACT FROM AUTHOR]

Serious weaknesses are exposed regarding recent claims to have demonstrated that there is no prepatterning of axes in the mouse. That the orientation of the axis of polarity of the blastocyst is dictated by the shape of the zona pellucida is contradicted by systematic observations on living conceptuses. Moreover, this "mechanical constraint' hypothesis fails to account for key findings on which the case for prepatterning is based. [ABSTRACT FROM AUTHOR]

Discusses issues on a study which established a patterning role for the spermatozoa by demonstrating that the sperm entry point consistently maps to the plane of first cleavage. Reason for the difficulty of showing unequivocally that any marker retains its position in zygotes; Information on the fertilization cone.

The preimplantation mammalian conceptus shows an impressive ability to develop normally following the loss, gain or rearrangement of cells. This has prompted the view that, unlike in other species, patterning in mammals cannot depend on information that is already present in the zygote before it begins to cleave. However, various findings are hard to reconcile with this conclusion, including evidence that the incidence of monozygotic twinning is sensitive to the conditions to which eggs or very early concepti are exposed. Possible causes of early twinning are discussed, and it is argued that partial hatching of the conceptus through a hernia in the zona pellucida cannot account for all cases. Moreover, it remains questionable whether studies on aggregated morulae and isolated blastomeres really provide compelling evidence against the existence of indispensible patterning information in the egg. Finally, regularities in axial relationships between the blastocyst and zygote have been revealed employing strictly non-invasive techniques. These show that, at least in normal development, patterning begins before cleavage. [ABSTRACT FROM AUTHOR]

During growth of the blastocyst there is a net flow of cells from the polar to the mural trophectoderm which is presumed to be radially symmetrical. However, such a pattern of cell movement is inconsistent with findings from a recent clonal analysis. To visualize the overall flow of cells directly, the polar trophectoderm of expanding blastocysts was labelled globally with fluorescent microspheres. Following further growth, the great majority of blastocysts that remained labelled throughout the polar trophectoderm exhibited a polarized rather than radial spread of label into the mural region. This was the case regardless of the labelling technique, whether the blastocysts were grown in utero or in vitro, or had the zona pellucida removed or left on. Intriguingly, where there were two foci of spread of label into the mural trophectoderm rather than one, these were diametrically opposite each other. In further experiments, fluorescent lineage labels were used to distinguish junctional trophectoderm cells with and without an extension onto the blastocoelic surface of the inner cell mass. The location of clones formed following further blastocyst growth provided no evidence that egress of cells from the polar trophectoderm is restricted circumferentially by the presence of junctional cells having an extension. [ABSTRACT FROM AUTHOR]

A numerical model for a lightning channel that includes a multigroup treatment of radiative transport was used to calculate the optical output corresponding to an assumed current waveform. The calculation compares well with the experimental data that are available. The time development of the temperature, pressure, density, and electrical conductivity profiles across the channel were investigated, as was the energy balance for the process. [ABSTRACT FROM AUTHOR]

We have previously developed a technique of trophectoderm biopsy to obtain cells from human blastocysts for preimplantation genetic diagnosis. To determine whether this technique affects the subsequent development of the blastocyst, 45 manipulated blastocysts were observed from days 3 to 14 in culture, the amount of human chorionic gonadotrophin (HCG) secreted by each embryo was measured and these results were compared with those of 26 non-manipulated controls documented in a previous study. A slit was made in the zona pellucida opposite the inner cell mass in 18 of the 45 blastocysts. This increased the rate of hatching but the other morphological changes up to day 14 were similar to those seen in the non-manipulated controls. There was no difference in the mean cumulative HCG secretion by these zona-slit controls (149.8 +/- 45.7 mIU/ml) compared to the non-manipulated controls (146.2 +/- 23.7 mIU/ml). A slit was also made in the zona pellicida of the other 27 blastocysts. Approximately 12-18 h later, in 18 blastocysts a biopsy of the herniating trophectoderm cells (5-30) was performed. The rate of hatching and adherence to the culture dish was similar to the non-manipulated controls. The mean cumulative HCG secretion decreased significantly (57.5 +/- 16.2 mIU/ml, P less than 0.01) after the biopsy procedure. However, if a small biopsy was performed (less than 10 cells removed) the decrease in HCG secretion (87.6 +/- 24.8 mIU/ml) was not significant, whereas when a large biopsy was performed (greater than 10 cells), HCG levels fell to 19.9 +/- 9.1 mIU/ml.(ABSTRACT TRUNCATED AT 250 WORDS) [ABSTRACT FROM AUTHOR]

Micromanipulation of human oocytes and embryos has provided new opportunities for both the treatment of infertility and the preimplantation diagnosis of genetic disease. It is important to determine whether manipulated embryos develop normally in vitro, as an indication of their suitability for transfer. However, at present there is little information on the development of non-manipulated embryos in vitro for comparison. We have therefore monitored morphological changes and human chorionic gonadotrophin (HCG) secretion in 36 non-manipulated human embryos, including 26 blastocysts and 10 cavitating morulae, daily from day 3 to day 14 of culture. Hatching was observed in 10 (38.5%) blastocysts and five of these adhered to the culture dish and appeared viable until day 14. The secretion of HCG was first detected on day 8, peaked at day 10 (51.11 +/- 8.7 mIU/ml) and then declined but was still detectable in four blastocysts on day 14. There was no overall difference in HCG secretion by hatched blastocysts and those which remained within the zona. However, those hatched blastocysts which showed adherence had significantly increased (P less than 0.05) HCG secretion. For individual blastocysts, the pattern of HCG secretion correlated well with the assessment of morphology. These data provide the basis for comparative studies of morphological changes and HCG secretion in manipulated embryos. [ABSTRACT FROM AUTHOR]

Trophectoderm biopsy was carried out on 47 human blastocysts. A slit was made in the zona pellucida opposite the inner cell mass by micromanipulative techniques. The human blastocyst zona offered more resistance to slitting compared to that of the mouse. After 18-24 h, controlled herniation of the trophectoderm cells was observed. These cells were biopsied when the diameter of the herniation was approximately equal to that of the blastocyst. The size of the slit and the stage of embryonic development at which slitting was performed were important for successful herniation to occur. After slitting, 76% of day 5-6 blastocysts showed herniation whilst only 42% of day 7-8 blastocysts herniated. Further development of the manipulated embryos was not apparently impaired, as hatching occurred in 44% of the former and 20% of the latter, compared with 18.1% in non-manipulated controls. The biopsied cells (approximately 10-30) usually remained in a clump but 14% formed vesicles on the day after biopsy. There was, however, no evidence of adherence to the dish or formation of monolayers. These results demonstrate the feasibility of trophectoderm biopsy in human blastocysts and that sufficient extra-embryonic material can be obtained by this technique for preimplantation diagnosis of genetic disorders. [ABSTRACT FROM AUTHOR]

Mammals are generally held to be exceptions to the rule that organization of the egg plays a role in specifying the differentiation of cells, axes, or other aspects of patterning in the early embryo. However, there are several grounds for questioning this conclusion. Not only do certain experimental findings remain unexplained but, more importantly, nearly all have been interpreted specifically in terms of the differentiation of trophectoderm versus inner cell mass. The possibility that egg organization is instrumental in patterning of the early embryo in mammals has so far been almost entirely neglected, notwithstanding evidence that the mouse blastocyst becomes bilaterally symmetrical before it implants. Difficulties confronting attempts to tackle the issue of the significance of egg organization in mammals are discussed with respect to polarity and cytoplasmic differentiation in the oocyte and zygote. Evidence for an enduring influence of the maternal genome during early development is reviewed and weaknesses in the case against a role for egg organization are exposed. Finally, consideration is given to what needs to be done if this issue is to be resolved. [ABSTRACT FROM PUBLISHER]

The results of experiments in which horseradish peroxidase (HRP) was used to mark single trophectoderm or inner cell mass (ICM) cells in situ in mouse blastocysts have led to the proposal that growth of the trophectoderm depends on stem cells located in the inner cell mass. Thus, the finding that the visual centre of clones formed following labelling of the central polar trophectoderm cell in early or expanding blastocysts was consistently shifted towards or into the mural trophectoderm was attributed to their displacement by ICM-derived cells. However, the frequency with which central polar cells were displaced is likely to have been overestimated by using the visual centre of descendant clones as the index of their location. Also, the possibility that displacement of central polar cells was an artefact of the marked temporary interruption of their cycling that resulted from labelling was not discounted. Furthermore, no attempt was made to ascertain whether cells located elsewhere in the polar trophectoderm also moved murally, as expected if there is a general displacement of such cells. In the present study, labelling of either the central or a peripheral polar trophectoderm cell with HRP was achieved without obviously perturbing their subsequent proliferation. Moreover, displacement was assessed by recording the location of the proximal boundary rather than the visual centre of the resulting clones. Even by this conservative criterion, the majority of labelled central cells moved towards or into the mural trophectoderm. In marked contrast, however, labelled peripheral polar cells moved murally in only a minority of cases. The remainder either retained their original position or moved towards rather than away from the central polar region. Such an anisotropic pattern of growth of the polar trophectoderm is not readily explicable in terms of recruitment of cells from the ICM. Rather, it accords with the view that the polar trophectoderm is a proliferative centre, and suggests that movement murally of its surplus cells may be restricted circumferentially, possibly through anchorage of the junctional trophectoderm cells that extend processes over the free surface of the ICM. [ABSTRACT FROM AUTHOR]

A recent paper in Zygote criticizes the 'theory of origins' of the various classes of monozygotic twins originally proposed and developed by Corner. It does so on the basis of recent observations on human IVF embryos. Here, the validity of one of the evidential sources is upheld, but an alternative explanation is proposed that is more plausibly based on evidence than the explanation offered in Zygote. [ABSTRACT FROM AUTHOR]