Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Mechanistic dissection of plant embryo initiation
    Radoeva, T.M. - \ 2016
    Wageningen University. Promotor(en): Dolf Weijers, co-promotor(en): Sacco de Vries. - Wageningen : Wageningen University - ISBN 9789462578135 - 183
    embryogenesis - embryos - plants - auxins - genes - genomics - arabidopsis - cell suspensions - in vivo experimentation - zygotes - monozygotic twins - embryogenese - embryo's - planten - auxinen - genen - genomica - arabidopsis - celsuspensies - in vivo experimenten - zygoten - monozygote tweelingen

    Land plants can reproduce sexually by developing an embryo from a fertilized egg cell, the zygote. After fertilization, the zygote undergoes several rounds of controlled cell divisions to generate a mature embryo. However, embryo formation can also be induced in a variety of other cell types in many plant species. These non-zygotic embryos go through analogous developmental phases and are morphologically similar to the zygotic embryo. Despite its fundamental importance and enormous application potential, the mechanisms that alter cell fate from non-embryonic to embryonic are elusive. In the past decades, a variety of different model systems have been used to identify regulators of embryo induction, but it is unclear if these act in a common network. We recently found that inhibition of auxin response in the extra-embryonic suspensor cells cell-autonomously and predictably triggers a switch towards embryo identity. In my thesis I have used the suspensor-derived embryogenesis as a uniform model system to study the crucial first reprogramming step of embryo initiation process.

    Through genome-wide transcriptional profiling upon local (suspensor-specific) auxin response inhibition (Chapter 2) and through testing the ability of fifteen known embryogenesis inducers to promote embryo formation in suspensor cells (Chapter 3), we suggest that suspensor to embryo transformation requires a defined set of genetic regulators. The results obtained in my thesis provide essential tools and basis for further research and are a step forward to understanding the first step of embryo initiation process and to unravel the mystery of totipotency in plants.

    Control of Pig Reproduction IX
    Rodriguez-Martinez, H. ; Soede, N.M. ; Flowers, W.L. - \ 2013
    Leicestershire, United Kingdom : Context Products Ltd (Society of Reproduction and Fertility volume 68) - ISBN 9781899043484 - 345
    varkens - geslachtelijke voortplanting - gameten - embryo's - kunstmatige inseminatie - embryotransplantatie - zwangerschap - partus - pasgeborenen - biggen - overleving - biotechnologie - metabolomica - eiwitexpressieanalyse - kunstmatige selectie - pigs - sexual reproduction - gametes - embryos - artificial insemination - embryo transfer - pregnancy - parturition - neonates - piglets - survival - biotechnology - metabolomics - proteomics - artificial selection
    Beoordeling van Zaadkwaliteit met behulp van Chlorofyl Fluorescentie Beelden
    Jalink, H. - \ 2010
    zaadkieming - chlorofyl - embryo's - fluorescentie - zaden - technieken - capsicum - glastuinbouw - seed germination - chlorophyll - embryos - fluorescence - seeds - techniques - capsicum - greenhouse horticulture
    Tijdens het kiemingsproces van zaden wordt o.a. chlorofyl gevormd. Dit chlorofyl wordt aangemaakt door het embryo. Het is gebleken dat de toename van chlorofyl een maat is voor het verloop van het kiemingsproces. Dit chlorofyl kan gevoelig worden gemeten met een fluorescentietechniek.
    Telers zijn bestuiving en bevruchting meestal liever kwijt dan rijk : de ontseksualisering van de tuinbouw
    Kierkels, T. ; Heuvelink, E. - \ 2010
    Onder Glas 7 (2010)1. - p. 12 - 13.
    tuinbouw - levenscyclus - chromosomen - bestuiving - bevruchting - spermatozoön - genetische parameters - embryo's - eicellen - vruchtgroenten - sierteelt - glastuinbouw - groenten - horticulture - life cycle - chromosomes - pollination - fertilization - spermatozoa - genetic parameters - embryos - ova - fruit vegetables - ornamental horticulture - greenhouse horticulture - vegetables
    Bestuiving en bevruchting zijn natuurlijke processen om nakomelingen te krijgen. In de sierteelt zijn echter steeds minder gewenst, omdat ze de bloemkwaliteit ernstig aantasten. Bevruchting is het samengaan van twee sets chromosomen. De mannelijke zaadcel moet daarvoor de vrouwelijke eicel bereiken. Een gecompliceerd proces dat op veel fronten mis kan gaan. Daarom zoeken veredelaars ook bij vruchtgroenten manieren om het te omzeilen
    Embryotemperatuur betere maat voor controleren broedproces
    Lourens, A. - \ 2009
    V-focus 6 (2009)2. - ISSN 1574-1575 - p. 42 - 43.
    pluimveehouderij - pluimvee - embryo's - broeden - eieren - poultry farming - poultry - embryos - incubation - eggs
    De embryotemperatuur in de broedeieren is een betere maat voor het controleren van het broedproces dan de machinetemperatuur. Variaties in de embryotemperatuur kunnen namelijk een groot effect hebben op de uiteindelijke resultaten. Dat blijkt uit het promotieonderzoek van ASG-onderzoeker Sander Lourens. De eischaaltemperatuur blijkt een goede graadmeter te zijn voor het bepalen van de embryotemperatuur
    Embryo temperature during incubation: practice and theory
    Lourens, A. - \ 2008
    Wageningen University. Promotor(en): Bas Kemp, co-promotor(en): Henry van den Brand; R. Meijerhof. - S.l. : S.n. - ISBN 9789085852582 - 131
    kuikens - embryo's - temperatuur - broeden - embryonale ontwikkeling - warmteproductie - warmteverlies - eierschaal - incubators - pluimveehouderij - chicks - embryos - temperature - incubation - embryonic development - heat production - heat loss - egg shell - incubators - poultry farming
    (Key words: incubation, embryo temperature, embryonic development, heat production, heat loss)

    Until recently, all incubator studies were performed using a constant machine temperature (MT). But it is embryo temperature (ET) that is of importance to the embryo, and not MT. In practice, MT is often measured at one location within the incubator, while ET can vary between eggs within an incubator. Furthermore, ET is the result of the balance between heat production (HP) and heat loss, and if HP or heat loss is affected it may have consequences for ET. Aim of this dissertation was to identify the causes of variable ET and to describe the consequences of variable ET on embryonic development, hatchability, HP and chick quality. Because the direct measurement of ET is destructive, it was chosen in this dissertation to use eggshell temperature (EST) measurements as a reflection of ET.
    Long term deviations of 1.1ºC away from a constant EST of 37.8ºC decreased embryonic growth, development, hatchability, and the ability of young chicks to maintain high body temperatures after hatching, especially under cold stress. HP was considered to be positively related to embryonic development, because when more energy is used for growth, HP during incubation will increase and chicks will subsequently hatch with a larger yolk free body and with a lower amount of energy left over in the residual yolk. Within the EST zone of 1.0ºC below and above 37.8ºC it was observed that HP increased linearly with short term EST increments, and the response of the embryos to EST variations was identical in young, mid term and late term embryos. Maximizing HP based on metabolic responses to EST fluctuations will therefore increase EST above the studied EST zone, leading to decreased embryonic growth and increased embryonic mortality. High EST increases the demand for oxygen, so oxygen availability was expected to limit HP and embryonic growth more at higher EST profiles than at EST of 37.8ºC. However, despite the fact that HP at day 18 was highest for the combination of high EST with high oxygen concentration, embryonic development did not show the same relationship. At EST above 37.8ºC, the amount of energy utilized from the egg content remained the same, but the efficiency of energy transfer (EYFB) between egg and embryo decreased. Factors as egg size, breed, and oxygen availability affected HP through changes in energy utilization, and had no effect on EYFB.
    In this thesis, the importance was shown to measure and control ET during incubation and not MT. Factors were identified that affect ET through changes in HP and heat loss. When ET is controlled and maintained at a constant level of 37.8ºC, embryonic development may be improved by measures that increase energy utilization through increments in gas exchange, which will increase HP.
    Nog even verder broeden
    Brand, H. van den; Klein Swormink, B. - \ 2007
    De Pluimveehouderij 37 (2007)32. - ISSN 0166-8250 - p. 14 - 15.
    pluimveehouderij - pluimvee - eieren - embryo's - embryonale ontwikkeling - broedeieren - poultry farming - poultry - eggs - embryos - embryonic development - hatching eggs
    Wageningen UR deed onderzoek naar het onder water bewaren van broedeieren. In de eerste fase van ontwikkeling verloopt de embryonale ontwikkeling erg goed, maar in de tweede fase moet die voorsprong weer worden prijs gegeven
    The potential of cryopreservation and reproductive technologies for animal genetic resources conservation strategies
    Hiemstra, S.J. ; Lende, T. van der; Woelders, H. - \ 2006
    In: The Role of Biotechnology in Exploring and Protecting Agricultural Genetic Resources / Ruane, J., Sonnino, A., Rome : FAO - ISBN 9789251054802 - p. 45 - 60.
    genetische bronnen van diersoorten - cryopreservering - vee - vissen - kunstmatige inseminatie - voortplanting - technologie - conservering - embryo's - embryokloneren - spermaconservering - genetische diversiteit - ex-situ conservering - animal genetic resources - cryopreservation - livestock - fishes - artificial insemination - reproduction - technology - conservation - embryos - embryo cloning - semen preservation - genetic diversity - ex situ conservation
    This chapter focuses on ex situ conservation. An overview of the state of the art cryopreservation and reproductive technology for farm animals and fish is followed by a discussion on the implications of ex situ conservation strategies. Ex situ conservation of genetic material from livestock and fish through cryopreservation is an important strategy to conserve genetic diversity in these species. Conservation strategies benefit from advances in cryopreservation and reproductive technologies. Choice of genetic material type to be preserved for different species depends highly on objectives, technical feasibility (e.g. collection, cryopreservation), costs and practical circumstances
    Molecular mechanisms governing primordial germ cell migration in zebrafish
    Doitsidou, M. - \ 2005
    Wageningen University. Promotor(en): Ton Bisseling. - [S.l.] : S.n. - 85
    danio rerio - kiemcellen - embryonale ontwikkeling - embryogenese - moleculaire biologie - embryo's - danio rerio - germ cells - embryonic development - embryogenesis - molecular biology - embryos

    In most sexually reproducing organisms primordial germ cells (pGCs) are specified early in development in places that are distinct from the region where the somatic part of the gonad develops. From their places of specification they have to migrate towards the site where they associate with somatic gonadal cells and differentiate to the gametes. The question conceming the molecular mechanisms that guide PGCs during their migration and allow them to reach their target is the focus of this work. The process was investigated in zebrafish, where the extrauterine development of the embryos their translucency allows monitoring cell migration at high resolution.
    Previous studies showed that zebrafish PGCs are specified in four different positions. From these positions the cells perform distinct migration steps until they arrive at their target by the end of the flTst day of development. During their migration the cells are guided by cues provided by somatic tissues.
    To identify the actual molecules that function as the guidance cues, a largescale antisense-oligonucleotide-based screen was carried out. In this screen, a chemokine receptor, CXCR4b and its ligand, the chemokine SDFla, were identified as proteins required for guided PGC migration. This pair of molecules had previously been shown to guide cell migration in other model organisms in a variety of developmental processes and disease. For example, SDF-l/CXCR4 signalling guides leul(Ocytes to the sites of inflarnmation or metastatic tumour ce lis to sites where they form secondary tumors.
    We found that in zebrafish embryos, the receptor CXCR4b is expressed in the migrating PGCs and its ligand, SDFla, is expressed in the tissues along which the PGCs migrate. Knocking down either CXCR4b or SDFla impairs PGC directed migration, which becomes evident by the inability of the cells to reach their target. Furthermore, when SDFla was expressed in ectopic sites in the embryos, PGCs arrived at these sites thus demonstrating the instructive role of this chemokine in PGC migration. Together, these results strongly suggest that SDFla provides the directional cue for PGC migration in zebrafish. These findings have since been generalized to mouse and chicken, where it was shown that CXCR4 and SDF-I play an essential role in PGC migration as weIl.
    Interestingly, in Drosophila a different biochemical pathway was shown to be important for providing directional cues for migrating PGCs, namely, the cholesterol/isoprenoid biosynthesis pathway. To determine whether this pathway plays a similar role in zebrafish, a 'block and rescue' pharmacogenetic approach was employed. Small chemical compounds were utilized to inhibit distinct steps in the cholesterol and isoprenoid synthesis pathway and the effect on PGC migration was examined. Using this approach, we showed that blocking HMGCoAR reductase (an enzyme that catalyses the rate limiting step in cholesterol synthesis) results in slower PGC migration. As a consequence, PGCs in treated embryos were frequently found in Abnormal locations. We then determined which components of the Cholesterol/isoprenoid biosynthetic pathway that act downstream of HMGCoAR are involved in this process. We could demonstrate that Geranylgeranyl transferase I (GGTI) activity in the isoprenoid branch of the pathway is important for optimal PGC motility.
    Oxygen diffusion in fish embryos
    Kranenbarg, S. - \ 2002
    Wageningen University. Promotor(en): J.L. van Leeuwen; J.W.M Osse; M. Muller. - S.l. : s.n. - ISBN 9789058086808 - 183
    vissen - embryo's - embryonale ontwikkeling - embryologie - zuurstof - diffusie - zuurstoftransport - zuurstofconsumptie - voedingsstoffen - beperkingen - grootte - vorm - cardiovasculair systeem - genexpressie - modellen - biofysica - fishes - embryos - embryonic development - embryology - oxygen - diffusion - oxygen transport - oxygen consumption - nutrients - constraints - size - shape - cardiovascular system - gene expression - models - biophysics - cum laude

    All vertebrate embryos pass through a developmental period of remarkably low morphological variability. This period has been called phylotypic period. During the phylotypic period, organogenesis takes place, including blood vessel development. Before the phylotypic period, the embryos rely on diffusion for the internal oxygen transport. Diffusion, however, is an efficient way of transport only over small distances. Analytical models were constructed to investigate whether physical constraints ( i.e. diffusional limitations) demand the development of an internal oxygen transport system as the embryos grow bigger. These models showed that teleost embryos are smaller than their theoretically maximum size during the phylotypic period, based on oxygen diffusion. Lack of oxygen does therefore not demand blood vessel development. Subsequently, numerical models of oxygen diffusion in a zebrafish embryo ( Danio rerio ) were developed, thereby including the realistic shape of the embryo. These models were tested and refined with oxygen micro-electrode measurements of the oxygen partial pressure profile in and around the zebrafish embryo. This numerical-experimental procedure revealed a high oxygen permeability in the yolk of the zebrafish embryo. Furthermore, lowest oxygen partial pressures were found in the head region with a gradient of posteriorly increasing oxygen partial pressures along the midline of the embryo. The three-dimensional oxygen partial pressure profile was compared with the expression pattern of the angiogenic factor ( vegf ), which is known to be expressed under hypoxic conditions. The apparent colocalization of low oxygen partial pressure and the expression of vegf suggests oxygen to play an important role in regulating blood vessel development rather than posing a direct request for its development.

    Schadelijke stoffen in scholekstereieren; responsmetingen in bioassays ter bepaling van risico's van contaminanten in eieren van scholeksters uit het Zeehavenkanaal
    Roode, D.F. de; Crum, S.J.H. ; Rouhani Rankouhi, T. ; Sanderson, T. ; Bosveld, A.T.C. - \ 2001
    Wageningen : Alterra (Alterra-rapport 402) - 37
    vogels - toxische stoffen - verontreinigende stoffen - toxiciteit - hexachloorbenzeen - biotesten - bursa van fabricius - embryo's - waadvogels - waterbodems - broedvogels - ecotoxicologie - milieuverontreiniging - scholekster - zeevogels - Groningen - Delfzijl - birds - toxic substances - pollutants - toxicity - hexachlorobenzene - bioassays - bursa fabricii - embryos - waders - water bottoms
    In het verleden zijn door het RIKZ in het Zeehavenkanaal te Delfzijl hoge hexachloorbenzeengehalten gemeten. Na sanering voldeed de onderwaterbodem voor hexachloorbenzeen echter nog steeds niet aan de normen voor het baggerbeheer. In eieren van scholeksters die foerageren in het met hexachloorbenzeen verontreinigde gebied, zijn ook verhoogde concentraties gemeten. De vraag is of deze verhoogde concentraties hexachloorbenzeen en eventuele andere verontreinigingen nadelige effecten hebben op de scholeksters. Uit het onderzoek waarvan de resultaten in dit rapport beschreven staan, blijkt dat de in de eieren aanwezige stoffen in staat zijn om effecten bij vogels te veroorzaken.
    Non-surgical embryo transfer in pigs
    Hazeleger, W. - \ 1999
    Agricultural University. Promotor(en): J.P.T.M. Noordhuizen; B. Kemp. - S.l. : Hazeleger - ISBN 9789058080721 - 128
    varkens - zeugen - uterus - resectie - embryo's - embryotransplantatie - embryosterfte - embryonale ontwikkeling - zwangerschapspercentage - biggenwerppercentage - worpgrootte - voortplantingsvermogen - superovulatie - voortplanting - pigs - sows - uterus - resection - embryos - embryo transfer - embryo mortality - embryonic development - pregnancy rate - farrowing rate - litter size - reproductive performance - superovulation - reproduction

    Embryo transfer in pigs has been performed surgically for a long time. However, a less invasive, non-surgical, procedure of embryo transfer could be a valuable tool for research (to study embryo survival and embryo-uterus interactions) and practical applications (export, prevention of disease transmission and prevention of long distance transport of animals). Therefore the aim of this study was to develop non-surgical procedures for the collection and transfer of porcine embryos which can be used for both practical and research purposes.

    The development of these procedures was expected to give insight in factors which are important for embryonic survival. Non-surgical (trans-cervical) embryo collection appeared to be possible from sows with surgically resectioned uterine horns. On average 8 embryos were collected from these sows. After superovulation induction the average but variable yield was increased to 18 embryos. Non-surgical (trans-cervical) transfer of embryos to non-sedated recipients appeared to be possible. A pregnancy rate of 60% and a litter size of 11 foetuses on Day 35 of pregnancy was realised.

    These results appeared to be dependent on the asynchrony between donor and recipient sows and on the development of the transferred embryos. Donor sows with a high preceding litter size, produced the highest number of transferable embryos. On a certain moment after ovulation the best developed embryos resulted in the highest pregnancy rates. No relations between characteristics of recipients, like age or previous litter size, with pregnancy rates were found. Also no relations between scores of the procedure of embryo transfer (like resistance in the cervix, duration of the procedure, etc.) and pregnancy results were found. Therefore factors affecting embryonic development and their survival after non-surgical transfer need further attention.

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