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author:("hajduk, Anna")
1.  The basal position of nuclei is one pre-requisite for asymmetric cell divisions in the early mouse embryo 
Developmental Biology  2014;392(2):133-140.
The early mouse embryo undertakes two types of cell division: symmetric that gives rise to the trophectoderm and then placenta or asymmetric that gives rise to inner cells that generate the embryo proper. Although cell division orientation is important, the mechanism regulating it has remained unclear. Here, we identify the relationship between the plane of cell division and the position of the nucleus and go towards identifying the mechanism behind it. We first find that as the 8-cell embryo progresses through the cell cycle, the nuclei of most – but not all – cells move from apical to more basal positions, in a microtubule- and kinesin-dependent manner. We then find that all asymmetric divisions happen when nuclei are located basally and, in contrast, all cells, in which nuclei remain apical, divide symmetrically. To understand the potential mechanism behind this, we determine the effects of modulating expression of Cdx2, a transcription factor key for trophectoderm formation and cell polarity. We find that increased expression of Cdx2 leads to an increase in a number of apical nuclei, whereas down-regulation of Cdx2 leads to more nuclei moving basally, which explains a previously identified relationship between Cdx2 and cell division orientation. Finally, we show that down-regulation of aPKC, involved in cell polarity, decreases the number of apical nuclei and doubles the number of asymmetric divisions. These results suggest a model in which the mutual interdependence of Cdx2 and cell polarity affects the cytoskeleton-dependent positioning of nuclei and, in consequence, the plane of cell division in the early mouse embryo.
•In 8-cell embryo most of the nuclei move from apical to basal positions.•The nuclear movement depends on microtubules and kinesins.•Only blastomeres with basally located nuclei can divide asymmetrically.•Blastomeres with apically located nuclei divide only symmetrically.•Position of the nucleus is regulated by interdependence of Cdx2 and cell polarity
PMCID: PMC4111899  PMID: 24855000
Mammalian embryo; Preimplantation development; Division plane; Cell polarity; Cytoskeleton
2.  Advances in embryo selection methods 
Despite many recent advances in the field of reproductive biology and medicine, the efficiency of in vitro fertilization procedures remains relatively low. There is a need for a reliable and non-invasive method of embryo selection to ensure that only embryos with the highest developmental potential are chosen for transfer to mothers-to-be. Here, we compare various methods currently used for assessing embryonic viability, such as examination of embryonic morphology, quality of the genetic material, or metabolism. Additionally, we discuss novel procedures for embryonic assessment based on advanced time-lapse imaging techniques, which show great promise and may lead to increased in vitro fertilization efficiencies.
PMCID: PMC3369238  PMID: 22685489
3.  Rhythmic actomyosin-driven contractions induced by sperm entry predict mammalian embryo viability 
Nature Communications  2011;2:417-.
Fertilization-induced cytoplasmic flows are a conserved feature of eggs in many species. However, until now the importance of cytoplasmic flows for the development of mammalian embryos has been unknown. Here, by combining a rapid imaging of the freshly fertilized mouse egg with advanced image analysis based on particle image velocimetry, we show that fertilization induces rhythmical cytoplasmic movements that coincide with pulsations of the protrusion forming above the sperm head. We find that these movements are caused by contractions of the actomyosin cytoskeleton triggered by Ca2+ oscillations induced by fertilization. Most importantly, the relationship between the movements and the events of egg activation makes it possible to use the movements alone to predict developmental potential of the zygote. In conclusion, this method offers, thus far, the earliest and fastest, non-invasive way to predict the viability of eggs fertilized in vitro and therefore can potentially improve greatly the prospects for IVF treatment.
Cytoplasmic flows—the movement of cytoplasmic material—can be detected following the fertilization of an egg by a sperm in many species. In this study, rhythmic cytoplasmic flows are shown to be induced in mice by calcium-induced cytoskeleton contractions which could be used to predict the successful outcome of fertilization.
PMCID: PMC3265380  PMID: 21829179
4.  Mouse oocytes fertilised by ICSI during in vitro maturation retain the ability to be activated after refertilisation in metaphase II and can generate Ca2+ oscillations 
At fertilisation, mammalian oocytes are activated by oscillations of intracellular Ca2+ ([Ca2+]i). Phospholipase Cζ, which is introduced by fertilising spermatozoon, triggers [Ca2+]i oscillations through the generation of inositol 1,4,5-triphosphate (IP3), which causes Ca2+ release by binding to IP3 receptors located on the endoplasmic reticulum (ER) of the oocyte. Ability to respond to this activating stimulus develops during meiotic maturation of the oocyte. Here we examine how the development of this ability is perturbed when a single spermatozoon is introduced into the oocyte prematurely, i.e. during oocyte maturation.
Mouse oocytes during maturation in vitro were fertilised by ICSI (intracytoplasmic sperm injection) 1 – 4 h after germinal vesicle break-down (GVBD) and were subsequently cultured until they reached metaphase II (MII) stage. At MII stage they were fertilised in vitro for the second time (refertilisation). We observed that refertilised oocytes underwent activation with similar frequency as control oocytes, which also went through maturation in vitro, but were fertilised only once at MII stage (87% and 93%, respectively). Refertilised MII oocytes were able to develop [Ca2+]i oscillations in response to penetration by spermatozoa. We found however, that they generated a lower number of transients than control oocytes. We also showed that the oocytes, which were fertilised during maturation had a similar level of MPF activity as control oocytes, which were not subjected to ICSI during maturation, but had reduced level of IP3 receptors.
Mouse oocytes, which were experimentally fertilised during maturation retain the ability to generate repetitive [Ca2+]i transients, and to be activated after completion of maturation.
PMCID: PMC1913504  PMID: 17584490

Results 1-4 (4)