Ethnic differences in cross-sectional associations between impaired glucose regulation, identified by oral glucose tolerance test or HbA1c values, and cardiovascular disease in a cohort of European and South Asian origin.

AIMS: We contrasted impaired glucose regulation (prediabetes) prevalence, defined according to oral glucose tolerance test or HbA1c values, and studied cross-sectional associations between prediabetes and subclinical/clinical cardiovascular disease (CVD) in a cohort of European and South Asian origin. METHODS: For 682 European and 520 South Asian men and women, aged 58-85 years, glycaemic status was determined by oral glucose tolerance test or HbA1c thresholds. Questionnaires, record review, coronary artery calcification scores and cerebral magnetic resonance imaging established clinical plus subclinical coronary heart and cerebrovascular disease. RESULTS: Prediabetes was more prevalent in South Asian participants when defined by HbA1c rather than by oral glucose tolerance test criteria. Accounting for age, sex, smoking, systolic blood pressure, triglycerides and waist-hip ratio, prediabetes was associated with coronary heart disease and cerebrovascular disease in European participants, most obviously when defined by HbA1c rather than by oral glucose tolerance test [odds ratios for HbA1c -defined prediabetes 1.60 (95% CI 1.07, 2.39) for coronary heart disease and 1.57 (95% CI 1.00, 2.51) for cerebrovascular disease]. By contrast, non-significant associations were present between oral glucose tolerance test-defined prediabetes only and coronary heart disease [odds ratio 1.41 (95% CI 0.84, 2.36)] and HbA1c -defined prediabetes only and cerebrovascular disease [odds ratio 1.39 (95% CI 0.69, 2.78)] in South Asian participants. Prediabetes defined by HbA1c or oral glucose tolerance test criteria was associated with cardiovascular disease (defined as coronary heart and/or cerebrovascular disease) in Europeans [odds ratio 1.95 (95% CI 1.31, 2.91) for HbA1c prediabetes criteria] but not in South Asian participants [odds ratio 1.00 (95% CI 0.62, 2.66); ethnicity interaction P = 0.04]. CONCLUSIONS: Prediabetes appeared to be less associated with cardiovascular disease in the South Asian than in the European group. These findings have implications for screening, and early cardiovascular prevention strategies in South Asian populations.

What my mother told me: Examining the roles of maternal gene products in a vertebrate.

In Xenopus, mRNAs synthesized during oocyte differentiation are inherited by the egg and direct all protein synthesis until the late-blastula stage. This provides an opportunity to study the roles of maternally expressed genes in embryonic development of a vertebrate. Oocytes can be depleted of specific mRNAs by the injection of antisense deoxyoligonucleotides and then fertilized to assay for developmental abnormalities. The ease of experimental manipulation of early Xenopus embryos in culture gives considerable opportunity for the analysis of the abnormalities seen.

Meiotic maturation in Xenopus oocytes: a link between the cessation of protein secretion and the polarized disappearance of Golgi apparati.

We have studied the relationship between the timing of the late meiotic events that occur during progesterone-induced oocyte maturation, and intracellular protein transport. We have monitored the secretion of chick oviduct proteins from Xenopus laevis oocytes microinjected with polyadenylated mRNA and found that chick ovalbumin and lysozyme are not secreted during the second meiotic metaphase, in contrast to the earlier prophase stage. Maturation had no detectable effect on the glycosylation of ovalbumin, whereas it affected the glycosylation of chick ovomucoid. As maturation proceeded, the Golgi apparati disappeared in a polarized fashion, beginning in the vegetal half. This disappearance coincided temporally and spatially with that of the nuclear envelope. We speculate that Golgi apparatus disappearance and the block in secretion are causally related.

Interactions between germ cells and extracellular matrix glycoproteins during migration and gonad assembly in the mouse embryo.

Cells are known to bind to individual extracellular matrix glycoproteins in a complex and poorly understood way. Overall strength of adhesion is thought to be mediated by a combinatorial mechanism, involving adhesion of a cell to a variety of binding sites on the target glycoproteins. During migration in embryos, cells must alter their overall adhesiveness to the substrate to allow locomotion. The mechanism by which this is accomplished is not well understood. During early development, the cells destined to form the gametes, the primordial germ cells (PGCs), migrate from the developing hind gut to the site where the gonad will form. We have used whole-mount immunocytochemistry to study the changing distribution of three extracellular matrix glycoproteins, collagen IV, fibronectin, and laminin, during PGC migration and correlated this with quantitative assays of adhesiveness of PGCs to each of these. We show that PGCs change their strength of adhesion to each glycoprotein differentially during these stages. Furthermore, we show that PGCs interact with a discrete tract of laminin at the end of migration. Closer analysis of the adhesion of PGCs to laminin revealed that PGCs adhere particularly strongly to the E3 domain of laminin, and blocking experiments in vitro suggest that they adhere to this domain using a cell surface proteoglycan.

Early events in the mammalian germ line.

Germ cells represent the genetic and cellular link between generations, as well as the transmitters of inherited diseases. Despite their central importance, not much is known about the molecular mechanisms whereby a germ cell lineage becomes set aside during development, or how the germ cells, once formed, migrate to the gonads and combine with somatic cells to make a gonad. This article provides a brief review of current knowledge on these issues, with particular focus on the mammalian germ line.

The onset of germ cell migration in the mouse embryo.

Mouse primordial germ cells (PGCs) are specified between embryonic day 6.5 (E6.5) and E7.5, when they have been visualized as an alkaline phosphatase-positive (AP+) cell population in the developing allantois. By E8.5, they are embedded in the hind-gut epithelium. Previous experiments have suggested different sites for PGCs' origin, and it is unclear how they reach the gut epithelium. We have used transgenic mice expressing GFP under a truncated Oct4 promoter to visualize living PGCs. We find GFP+/AP+ cells in the posterior end of the primitive streak as a dispersed population of cells actively migrating into the allantois, and directly into the adjacent embryonic endoderm. Time-lapse analysis shows these cells to be actively migratory from the time they exit the primitive streak.

The role of cadherins during primordial germ cell migration and early gonad formation in the mouse.

Primordial germ cells (PGCs) are the founder cells of the gametes. In mammals, PGCs migrate from the hindgut to the genital ridges, where they coalesce with each other and with somatic cells to form the primary sex cords. We show here that, in both sexes, PGCs express P- and E-cadherins during and after migration, and N-cadherin at post-migratory stages. E-Cadherin is not expressed by PGCs whilst in the hindgut, but is upregulated as they leave. Blocking antibodies against E-, but not P-cadherin cause defective PGC-PGC coalescence, and in some cases, ectopic PGCs.

A Xenopus c-kit-related receptor tyrosine kinase expressed in migrating stem cells of the lateral line system.

The mammalian c-kit receptor tyrosine kinase gene is required during embryogenesis for the survival and/or proliferation of three migrating stem cell populations: primordial germ cells, haematopoietic stem cells and neural crest-derived melanoblasts. We have cloned a Xenopus gene, XKrk1, whose closest relative is c-kit. Differences in the expression pattern suggest that XKrk1 is not the Xenopus homologue of c-kit; however, it is expressed in a migrating stem cell population, the precursor cells for the mechanosensory lateral line system. XKrk1 is the first reported marker for lateral line stem cells.

Early stages in male germ cell differentiation in the mouse. Review article.

Primordial germ cells arise during gastrulation and migrate from the hindgut into the gonad primordium during early organogenesis. In this article, we discuss factors that control migration, proliferation and targeting of the PGCs. In particular we discuss how changes in adhesiveness control germ cell positioning in the gonad, and the molecules involved.

Synergistic control of stimulated pronosupination with the stimulated grasp of persons with tetraplegia.

The control of stimulated forearm pronosupination in concert with stimulated hand grasp of persons with tetraplegia has been investigated. It has been shown that hand grasp stability increased as supination was achieved. In accordance with this, a strategy of object acquisition has been proposed incorporating pronosupination and hand grasp. It has been proposed that, after object acquisition in the pronated posture, that supination be used to increase grasp stability. Three types of pronosupination control which act in synchrony with grasp were implemented incorporating this principle. The three types used were position-controlled pronator stimulation, touch-controlled pronator stimulation, and constant pronation stimulation. These controllers played a supporting role to the separate user control of hand grasp and release. The three controllers were evaluated and compared using a standardized test procedure that incorporated stimulated pronosupination control with stimulated grasp. Such methods of pronosupination control are likely to provide enhanced options for improving upper extremity function using electrical stimulation.

Control of a hand grasp neuroprosthesis using an electroencephalogram-triggered switch: demonstration of improvements in performance using wavepacket analysis.

Volitionally modulated electroencephalographic (EEG) waves were monitored for the purpose of controlling a hand neuroprosthesis in people with tetraplegia. The region of the EEG signal spectrum monitored was the occipital alpha wave (8-13 Hz), and volitional modulation was achieved with the opening and closing of the eyes. In a set of 13 trials evaluated, a subject with tetraplegia successfully completed ten trials undertaking stimulated grasp and release using the EEG-triggered switch. EEG signal data recorded during the 13 trials were also post-processed off-line using wavepacket analysis. Following this signal processing, the speed and reliability of the EEG-triggered switch, when operated by the subject with tetraplegia, was significantly improved (p < 0.002). Such improvements provide system performance that is likely to be acceptable to a neuroprosthesis user during activities of daily life.

Clinical evaluation of expanded input dynamic range in Nucleus cochlear implants.

OBJECTIVE: The aim of this study was to investigate whether expanded instantaneous input dynamic ranges (IIDRs) in the Nucleus cochlear implant system benefit speech perception in the laboratory and listening in the real world. DESIGN: Until recently, Nucleus cochlear implants have used an IIDR of approximately 30 dB. In this study, an IIDR of 31 dB was compared with 46 dB and 56 dB in the SPEAR3 research processor with nine adult implant recipients. Subjects were given two, 2-wk blocks of take-home experience with each of the three IIDRs. A single IIDR setting was used in each trial period. During the take-home experience with the expanded IIDRs, subjects used two programs: a standard program (with clinically measured electrode dynamic ranges) and a program with adjusted thresholds (decreased T levels). After each block of take-home experience, speech perception testing was conducted for CNC words in quiet (at 45 dB and 55 dB SPL) and for CUNY sentences in the presence of multi-taker babble. RESULTS: On average, CNC word recognition at low presentation levels was significantly better with the 46 dB and 56 dB IIDRs, compared with the 31 dB IIDR; however, there was no significant difference between the 46 dB and 56 dB IIDR conditions. These benefits were greater for standard programs than for reduced T level programs. For CUNY sentences in babble, group results indicated no significant difference in performance across IIDR. The three IIDRs were rated similarly in real-life listening situations, and two of the subjects expressed tolerance problems with the expanded standard IIDRs. CONCLUSIONS: IIDRs of 46 and 56 dB provided benefit in accessing low-level speech without a decrement in sentence perception in babble. Most subjects accepted the standard, wider IIDR programs in everyday life. No significant differences were found between the 46 dB and 56 dB IIDR programs.

The role of FoxC1 in early Xenopus development.

FoxC1 is an important transcription factor in vertebrate development since its mutation in humans results in Axenfeld-Rieger syndrome. In the mouse, disturbance of its function causes congenital hydrocephalus and abnormalities in the development of various mesodermal derivatives. In this report, we provide one mechanistic basis for the requirement for FoxC1 in vertebrate development. We find that, in Xenopus laevis embryos, FoxC1 expression is regulated by the maternal T-box transcription factor VegT, via the nodal sub-family of TGFbeta signaling transducers. We show that at the late neurula to early tailbud stage, FoxC1 depletion causes the down-regulation of adhesion molecules, EP and E cadherin, as well as members of the Ephrin/EphR signaling families in the mesoderm germ layer resulting in the loss of adhesion and apoptosis of mesodermal cells.

Patterning the Xenopus blastula.

This review starts from the classical standpoint that there are at least two separable processes acting with respect to axis formation and tissue specification in the early Xenopus embryo: a UV-insensitive event establishing a postgastrula embryo consisting of three concentric germ layers, ectoderm, mesoderm and endoderm, all of a ventral character; and a UV-sensitive event producing tissue of a dorsal type, including somites, notochord and neural tissue, and concomitantly establishing the dorsoventral and anteroposterior axes. The experimental evidence suggesting the molecular basis of the dorsal and ventral pathways is reviewed.

The role of intermediate filaments in early Xenopus development studied by antisense depletion of maternal mRNA.

The effects of depleting a maternal cytokeratin mRNA on the developing embryo are described. Cytokeratins are members of the intermediate filament family of cytoskeletal proteins, and are expressed in a cortical network of the superficial cytoplasm of the oocyte. After fertilisation, a new cortical network is built up, which comes to occupy only the most superficial cells of the blastula. The maternal cytokeratin mRNA is abundantly translated, both during oogenesis, and during oocyte maturation and after fertilisation. Depletion of the mRNA results in depletion of the cortical filaments at the blastula stage and leads to gastrulation abnormalities. We discuss the various possible control experiments required for antisense oligo depletion studies and the implications of these results for cytokeratin function.

Genital ridges exert long-range effects on mouse primordial germ cell numbers and direction of migration in culture.

The functional gametes of all vertebrates first arise in the early embryo as a migratory population of cells, the primordial germ cells (PGCs). These migrate to, and colonise, the genital ridges (GR) during the early organogenesis period, giving rise to the complete differentiating gonad. PGCs first become visible by alkaline phosphatase staining in the root of the developing allantois at 8.5 days post coitum (dpc). At 9.5 dpc they are found in the wall of the hind-gut and, during the following three days, they migrate along the hind-gut mesentery to the dorsal body wall, and then to the genital ridges. By 12.5 dpc, the great majority of PGCs have colonised the genital ridges. During this period the number of PGCs increases from less than 100 to approximately 4000. In a previous paper (Donovan et al. 1986), we showed that 10.5 dpc PGCs can be explanted from the hind-gut mesentery, and will spread and migrate on feeder cell layers. We showed also that the intrinsic ability of PGCs to spread and migrate changes as they colonise the genital ridges. In this paper, we examine extrinsic factors that control PGC behaviour in vitro. Using PGCs taken from 8.5 dpc embryos, at the beginning of their migratory phase, we show that culture medium conditioned by 10.5 dpc genital ridges causes an increase in the number of PGCs in these cultures. We also show that PGCs migrate towards 10.5 dpc genital ridges in preference to other explanted organs. These experiments show that genital ridges exert long-range effects on the migrating population of PGCs.(ABSTRACT TRUNCATED AT 250 WORDS)

Primordial germ cell migration.

Primordial germ cells are migratory cells. They arise very early in embryogenesis and have a similar pattern of migration in Drosophila, Xenopus, chick and mouse. In each case the primordial germ cells associate with the developing gut from which they migrate to the gonads during organogenesis. Germ cells proliferate mitotically from the time they begin to migrate to the time they colonize the genital ridges. From the study of mouse primordial germ cells, we now know of a number of agents which affect primordial germ cell proliferation, migration and adhesion in vitro. More recently, we have studied the interactions between primordial germ cells and the cells and extracellular matrix molecules on their migratory route. By labelling germ cells in whole-mount preparations with an antibody to the germ cell marker SSEA-1, we have studied the spatial distribution of germ cells in situ using confocal microscopy. This study has revealed that germ cells link up with each other forming extensive networks during migration.

Beta-catenin signaling activity dissected in the early Xenopus embryo: a novel antisense approach.

Xenopus embryos develop dorsal/ventral and anterior/posterior axes as a result of the activity of a maternal Xwnt pathway, in which beta-catenin is an essential component, acting as a transactivator of transcription of zygotic genes. However, the questions of where and when beta-catenin is required in early embryogenesis have not been addressed directly, because no loss-of-function method has been available. Here we report the use of a novel antisense approach that allows us to target depletion of protein to individual blastomeres. When a "morpholino" oligo complementary to beta-catenin mRNA is injected into early embryos, it depletes beta-catenin protein effectively through the neurula stage. By targeting the oligo to different cleavage blastomeres, we block beta-catenin activity in different areas and at different times. Dorsal vegetal injection at the 2- and 4-cell stages blocks dorsal axis formation and at the 8-cell stage blocks head formation, while A-tier injection at the 32-cell stage causes abnormal cement gland formation. This approach shows the complex involvement of Xwnt pathways in embryonic patterning and offers a rapid method for the functional analysis of both maternal and early zygotic gene products in Xenopus.

The formation of the gonadal ridge in Xenopus laevis. I. A light and transmission electron microscope study.

In Xenopus laevis tadpoles, between stages 44 and 49 (Nieuwkoop & Faber, 1956), the primordial germ cells (PGCs) migrate from the dorsal mesentery of the gut to the site of the presumptive GD gonadal ridge. This paper describes the process at the light- and electronmicroscope levels. The PGCs in the mesentery, which at first are very large and yolk-laden, seem to lie entirely within the cellular matrix of the mesentery, although this is not obvious in light micrographs. Where the PGCs bulge out into the coelomic cavity, they stretch the somatic cell covering to a thin, cytoplasmic layer. The somatic cells of the mesentery are held together around them at this stage by well-differentiated desmosomes. At this, and subsequent stages, the PGCs have cytoplasmic processes, roughly the size of microvilli, which are irregularly distributed over their surfaces, and which are inserted between surrounding somatic cells. Whether these processes play any role in locomotion or exploration of the substrate is uncertain. As the PGCs move laterally from the root of the mesentery to the presumptive gonadal ridge, the coelomic lining cells which cover them, initially with a very thin squamous layer, differentiate to form the cuboidal cells of the germinal epithelium. Several interesting ultrastructural features of these cells, and the PGCs, are described, particularly in the light of their surface interaction. In the light of the morphological data presented here, particularly of the cell surfaces involved, we conclude that both active locomotion by the PGCs and passive movement by the morphogenetic movements of the cells around them contribute to the establishment of the early gonadal ridge.