Showing papers by "Andrew J. Watson published in 2001"

Regulation of blastocyst formation.

Abstract: Preimplantation or pre-attachment development encompasses the "free"-living period of mammalian embryogenesis, which directs development of the zygote through to the blastocyst stage. Blastocyst formation is essential for implantation, establishment of pregnancy and is a principal determinant of embryo quality prior to embryo transfer. Cavitation (blastocyst formation) is driven by the expression of specific sets of gene products that direct the acquisition of cell polarity within the trophectoderm, which is both the first epithelium of development and the outer cell layer encircling the inner cell mass of the blastocyst. Critical gene families controlling these events include: the E-cadherin-catenin cell adhesion family, the tight junction gene family, the Na/K-ATPase gene family and perhaps the aquaporin gene family. This review will update the roles of each of these gene families in trophectoderm differentiation and blastocyst formation. The current principal hypothesis under investigation is that blastocyst formation is mediated by a trans-trophectoderm ion gradient(s) established, in part, by Na/K-ATPase, which drives the movement of water through aquaporins (AQPs) across the epithelium into the extracellular space of the blastocyst to form the fluid-filled blastocoel. The trophectoderm tight junctional permeability seal regulates the leakage of blastocoel fluid, and also assists in the maintenance of a polarized Na/K-ATPase distribution to the basolateral plasma membrane domain of the mural trophectoderm. The cell-to-cell adhesion provided by the E-cadherin-catenin gene families is required for the establishment of the tight junction seal and the maintenance of the polarized Na/K-ATPase distribution. Blastocyst formation is therefore directly linked with trophectoderm cell differentiation, which arises through fundamental cell biological processes that are associated with the establishment of cell polarity.

A Lagrangian SF6 tracer study of an anticyclonic eddy in the North Atlantic: patch evolution, vertical mixing and nutrient supply to the mixed layer

Abstract: Biological and biogeochemical change in the surface mixed layer of an anticyclonic eddy at 60°N in the North Atlantic were monitored within a Lagrangian time-series study using the tracer sulphur hexafluoride (SF6). Four ARGOS buoys initially released at the patch centre remained closely associated with the SF6 patch over a 10-day period, with the near-circular eddy streamlines contributing to the stability and coherence of the patch. Progressive deepening of the surface mixed layer was temporarily interrupted by a storm, which increased mixed-layer nitrate and accelerated the transfer of SF6 to the atmosphere. Diapycnal exchange of SF6 was relatively rapid due to the shallow pycnocline gradient, and a vertical eddy diffusivity (Kz) of 1.95 cm2 s?1 at the base of the mixed layer was estimated from vertical SF6 profiles at the patch centre. Application of Kz to the nutrient gradients inferred vertical nitrate and phosphate fluxes of 1.8 and 1.25 mmol m?2 d?1, respectively, for the pre-storm period, which accounted for 33% and 20% of the reported in vivo uptake rates. Integration of the vertical nitrate flux and decline in surface layer nitrate suggest a total loss of 0.54 mmol N m?3 d?1 during the 5-day pre-storm period, of which in vivo nitrate consumption only accounted for 49%. Vertical transport of ammonium regenerated in the pycnocline accounted for up to 25% of in vivo phytoplankton uptake. The results suggest that the contribution of vertical turbulence to the mixed-layer nutrient pool was less important than that recorded in other regions of the open ocean, inferring that advective processes are more significant in an eddy. This study also emphasises the potential of SF6 for oceanic Lagrangian time series studies, particularly in dynamic regions, and in constraining estimates of new production.

Cyclooxygenase-2 and prostaglandin E(2)(PGE(2)) receptor messenger RNAs are affected by bovine oocyte maturation time and cumulus-oocyte complex quality, and PGE(2) induces moderate expansion of the bovine cumulus in vitro.

Abstract: Expression of cyclooxygenase-2 (COX-2) and prostaglandin E(2) (PGE(2)) receptor 2 (EP2) are necessary for rodent cumulus expansion in vivo. Prostaglandin E(2) receptor 3 (EP3) has been detected in bovine preovulatory follicles and corpora lutea. The current experiments examined the effect of PGE(2) on bovine cumulus expansion in vitro and expression of COX-2, EP1, EP2, EP3, and EP4 mRNAs in bovine cumulus-oocyte complexes (COCs) at 0, 6, 12, 18, and 24 h time points during maturation in vitro. Concentrations of PGE(2) above 50 ng/ml resulted in moderate cumulus expansion of bovine COCs, but expansion did not occur in the absence of serum. COX-2 mRNA expression increased in bovine COCs at 6 h and 12 h of maturation, then decreased. EP2 mRNA was detectable by reverse transcription-polymerase chain reaction at all time points. EP3 mRNA expression increased in COCs from 0 to 6 h and remained at this higher level through the culture period. Very low levels of EP4 mRNA expression were detectable, but EP1 was not detected in bovine COCs. Because EP receptor mRNAs and COX-2 mRNA are expressed in bovine COCs, there exists the potential for a prostaglandin autocrine/paracrine regulatory pathway during oocyte maturation. Differential expression of the EP3 mRNA among varying COC classes indicates that this gene product may be a useful marker of oocyte competence. Although the PGE(2) pathway is involved in cumulus expansion, serum factors are required to mediate PGE(2)-induced expansion.

Southern Ocean iron enrichment promotes inorganic carbon drawdown

Abstract: The effect of iron supply on phytoplankton growth and the marine carbon cycle was tested in situ at 61°S 141°E in the Southern Ocean Iron Release Experiment (SOIREE). On 9 February 1999 iron and the tracer sulphur hexafluoride (SF6) were added to the mixed layer with additional iron infusions after 3, 5 and 7 days. A small decrease of the fugacity of carbon dioxide (fCO2) and dissolved inorganic carbon (DIC) by iron-induced algal growth was observed 4–5 days after the first infusion. From then onwards fCO2 and DIC steadily decreased, and the iron-enriched waters became a sink for atmospheric CO2. The region with surface-water fCO2 drawdown closely matched the shape of the patch, as indicated by SF6. Surface-water fCO2 and DIC drawdown were relatively constant across the patch, whereas SF6 decreased from the patch centre outwards. This pointed to uniform algal carbon uptake, not limited by iron, in the patch. After 13 days surface-water fCO2 and DIC in the patch centre had decreased by 32–38 μatm and 15–18 μmol kg−1, respectively. Surface-water fCO2 outside the patch had increased by 8 μatm, partly as a result of surface-water warming. The iron-induced fCO2 change exceeded seasonal fCO2 variability in this region by a factor of two. From the surface-water fCO2 distribution we estimate a net DIC drawdown of 1353 t of carbon (±14%) (1 t=106 g) across the patch after 12 days, assuming uniform drawdown in the upper 50 m. Correction for vertical diffusion and air–sea exchange results in a gross DIC drawdown of 1408 t of carbon. The decrease of fCO2 and DIC, integrated over the mixed layer, was remarkably similar in size after 13 days of SOIREE as changes observed after 6–9 days during IronEx II, if we consider the 4–5 days lag in algal carbon uptake at the Southern Ocean site. SOIREE has demonstrated in situ the occurrence of algal iron limitation and of iron-induced carbon uptake in these Southern Ocean waters. The subsequent fate of the fixed inorganic carbon can only be speculated upon.

Sensitivity of bovine blastocyst gene expression patterns to culture environments assessed by differential display RT-PCR.

Abstract: The use of culture media to support the development of preimplantation embryos to the blastocyst stage is often associated with detrimental effects on normal development. These effects have been uncovered largely by investigating the phenotypic abnormalities displayed by fetuses and newborns derived from cultured preimplantation embryos. Research to understand the impact of culture on the embryonic developmental programme has focused on embryo metabolism, gene expression and genomic imprinting. We have used differential display RT-PCR to examine culture influences on global transcript pools in bovine embryos. Others have examined culture influences on candidate "marker genes" in cultured murine, ovine and bovine embryos. These studies have demonstrated that culture conditions influence the amount of marker gene transcripts and downregulate or induce the expression of novel genes during early development. Optimized defined culture media maintain embryonic gene expression patterns closely resembling those displayed by embryos derived in vivo. Preimplantation mammalian embryos display an impressive capacity to respond to the pressures that suboptimal culture environments place upon them. However, this plasticity operates within a defined range of tolerances. Continued research using molecular techniques will lead to increased understanding of developmental mechanisms causing culture-related phenotypic abnormalities in post-implantation embryos.

A piece in the CO2 jigsaw

Abstract: A study of the year-to-year variation in net CO2 uptake by the oceans helps in assessing the mechanisms of global climate change.

Determination of Persian Gulf Water Transport and oxygen utilisation rates using SF6 as a novel transient tracer

Abstract: Sulphur hexafluoride (SF6) has potential as a transient tracer of recently ventilated water masses, as its atmospheric burden continues to increase. Northern Arabian Sea hydrography was examined using measurements of atmospheric and dissolved SF6, CFC-11, CFC-12 and CFC-113. Persian Gulf Water (PGW) was characterised by its SF6 signal, and the time elapsed since its formation was evaluated by two approaches. Four ventilation age estimates were derived from SF6/CFC-11, SF6/CFC-12, CFC-113/CFC-11 and CFC-113/CFC-12, and their agreement at the oceanic stations confirms the validity of SF6 as a transient tracer. A second approach, of correcting SF6 partial pressure for PGW dilution by an optimal mixing model and referencing to the atmospheric SF6 chronology, provided a relative tracer age. This indicated a PGW flow of 0.016 (+/−0.003) m/s across the northern Arabian Sea, with an associated oxygen consumption of 10.1 µmol/l p.a. that exceeds tracer-derived estimates but confirms rates derived from export flux.

Chlorofluorocarbon‐derived formation rates of the deep and bottom waters of the Weddell Sea

Abstract: The spreading and mixing of deep and bottom waters from the Weddell Sea (originating with potential temperature <0°C) are investigated through analysis of new and historical CFC measurements. We investigate the component that enters the southern Indian Ocean with a simple one-dimensional advection-diffusion model of the deep boundary current. This model does not require a condition of mixing solely with tracer-free water to be imposed. As boundary conditions, we derive time histories for the CFC concentrations of newly formed Weddell Sea deep and bottom waters. A range of best fit velocities is obtained by determining which model velocities produce model tracer concentrations closest to measured concentrations. From this, we derive a formation rate of 3.2±1.5 Sv for the waters originating with temperatures lower than 0°C that subsequently enter the southern Indian Ocean. This compares to an upper limit for these waters of 5.7 Sv derived from the CFC-11/CFC-12 ratio. Whilst the former value is dependent on the highly idealized concepts of the model used, the latter is a more robust upper limit. Using the CFC-11/CFC-12 ratio measured at Vema Channel during the World Ocean Circulation Experiment cruise A23, an upper limit of 0.9 Sv is derived for the formation rate of waters colder than 0°C that enter the South Atlantic. Overall, an upper limit of 6.6 Sv is derived for the rate of formation of the deep and bottom waters of the Weddell Sea. A better representation is obtained by combining the upper limit to the South Atlantic component with the model-derived southern Indian Ocean estimate; we thus estimate the formation rate of the deep and bottom waters in the Weddell Sea to be 3.7±1.6 Sv. Whilst the range obtained is large and the assumptions implicit in the calculations are potentially significant, we believe this more realistically represents the true formation rate than estimates derived using an imposed condition of tracer-free mixing. The range can be narrowed in future as more data become available.

Abrupt climate change and the stability of the thermohaline circulation.

Abstract: Ocean-atmosphere interactions in the North Atlantic are responsible for heat transports that keep the UK 5-10°C warmer than it would otherwise be. This is caused by the ocean’s thermohaline circulation (THC), driven by temperature and salinity differences. However, existing THC patterns might not continue: climate models suggest that the increasing atmospheric greenhouse-gas burden could dramatically weaken the THC and associated circulation systems within a few decades. Furthermore, palaeo-data indicate large and rapid variability in North Atlantic THC strength during the past 20,000 years, and recent observations on the extent and thickness of Arctic sea-ice show that a new regime shift may already be underway. This observation-based programme will investigate the dynamics and sensitivity of the North Atlantic THC, and the climatic consequences of potential changes. It will focus on delivering: (i) the establishment of efficient and cost-effective systems for detecting and quantifying THC change; (ii) the identification of the main northern high-latitude drivers of the THC; (iii) an improved fundamental understanding of interactions of THC dynamics with the atmosphere and cryosphere; (iv) quantitative palaeo-estimates of past THC changes; (v) advances in conceptual understanding of the THC. Models are essential to the programme: they will be used to investigate mechanisms controlling the strength of the THC; to provide scenarios for risk assessment of the impact of THC changes on climate; to synthesise field data; and to assist the design of programme field work and longer-term observational strategies. The proposed programme builds on the existing strengths of the UK community in oceanographic research and climate modelling, and will be tied closely to related international efforts. In particular, it will provide the main UK contribution to a collaboration with Norway on high-latitude ocean and climate research encouraged by the Prime Ministers of both countries (Wadhams and Nicholls, 1999). NERC support required is £16.9m over 5 years. A key overall deliverable would be the identification of the critical observations that would eventually need to be part of a quasi-operational observing system. Moreover, this programme would produce recommendations for future climate model development, to increase confidence in projections of THC and climate change.

Expression of PTHrP and PTHR (PTH/PTHrP-r) mRNAs and polypeptides in bovine ovary and stimulation of bovine blastocyst development in vitro following PTHrP treatment during oocyte maturation.

Abstract: Parathyroid hormone related protein (PTHrP) and its receptor have well-established roles in the development and regulation of many tissues, including bone and mammary gland. The objectives of this study were: (1) to characterize the distribution of mRNAs encoding parathyroid hormone (PTH)-related protein (PTHrP) and receptor (PTHR) in bovine ovary; (2) to characterize the distribution of PTHrP and PTHR polypeptides in bovine ovary; (3) to examine the influences of PTHrP (1-141) treatment during bovine oocyte maturation in vitro on blastocyst development. mRNAs encoding PTHrP and PTHR were detected by in situ hybridization methods in oocytes, and granulosa cells in all follicles from primordial to large antral. PTHrP and PTHR polypeptides displayed distinct distribution patterns with PTHrP polypeptides primarily confined to oocytes from primordial to large antral follicles. PTHrP polypeptides were detectable but at a reduced level in ovarian stroma and in granulosa and thecal layers. PTHR polypeptides were detected in oocytes of all follicular stages but were predominantly found in ovarian stroma, granulosa and theca follicular layers. Supplementation of serum-free cSOFMaa oocyte maturation medium with PTHrP (1-141) resulted in a concentration-dependent increase in development to the blastocyst stage in vitro. The results suggest that granulosa cells may be a primary site of PTHrP production and release. Oocytes from all follicular stages stained strongly for PTHrP polypeptides and PTHrP enhanced development to the blastocyst stage in vitro.

U.K. research funding. Universities raise their game, but the money doesn't flow.

Abstract: U.K. RESEARCH FUNDINGNORWICH, U.K.-- British researchers won warm praise last week for their talent, but it came with a splash of fiscal cold water. According to a mammoth review carried out every 5 years or so to allocate funding for research infrastructure, U.K. researchers are currently performing better than those of any country in the world. Unfortunately, these hardworking researchers have raised the level of their game so fast that they have stripped bare the government fund designed to support them.

Rubbery Liquid Crystal Gives Lasers a Stretch

Abstract: Artificial rubber with the light-altering properties of a liquid crystal has been turned into a new type of laser--one that emits light without mirrors or a cavity and that changes its wavelength when pulled like taffy. Researchers call the work a significant step that might lead to the development of a low-cost, tunable laser.

Star-Cluster Census Shows Surprises

Abstract: ASTROPHYSICSAstrophysicists studying the cores of the ancient balls of stars known as globular clusters have a new weapon: the Chandra X-ray Observatory, uniquely equipped to spot the x-rays emitted by many of the core's inhabitants. As reported online by Science this week ([www.sciencexpress.org][1]), a team at the Harvard-Smithsonian Center for Astrophysics has used Chandra to produce a sharp, color-coded x-ray map of a core, resolve individual x-ray sources and their energies for the first time. [1]: http://www.sciencemag.org/cgi/content/abstract/1061135

Post-buckling of single and multi-bay panels using strut, strip and fe methods

Abstract: A compressively-loaded stiffened panel has been designed with post-buckling reserve of strength in its skins using the strip program VICONOPT. Comparisons are made with Finite Element single and double bay models. The panel has been shown by VICONOPT to have a stiffener buckling failure mode when an overall sinusoidal imperfection causing increased stiffener compression is present. Such a failure is not seen in a typical single-bay Finite Element model of such panels. However, the failure is confirmed by a double-bay Finite Element model, which is a closer representation of an aerospace application, such as a wing box. A new strut model, following a Shanley type approach has been developed to emphasise the difference between the single and multi-bay responses. The strut model shows good agreement with single bay Finite Element results. It also indicates the presence of an imperfection in the double bay Finite Element model, which may be represented by offsetting the load towards the skin in the strut model. The VICONOPT code is able to design an aerospace panel of realistic dimensions and loading but only when considering linear elastic material properties.