Preferencje help
Widoczny [Schowaj] Abstrakt
Liczba wyników

Znaleziono wyników: 23

Liczba wyników na stronie
Pierwsza strona wyników Pięć stron wyników wstecz Poprzednia strona wyników Strona / 2 Następna strona wyników Pięć stron wyników wprzód Ostatnia strona wyników

Wyniki wyszukiwania

Wyszukiwano:
w słowach kluczowych:  zarodki swinskie
help Sortuj według:

help Ogranicz wyniki do:
Pierwsza strona wyników Pięć stron wyników wstecz Poprzednia strona wyników Strona / 2 Następna strona wyników Pięć stron wyników wprzód Ostatnia strona wyników
This review presents evolution and current possibilities, state of knowledge and prospects for cryopreservation of pig embryos. In the early stages the development of this technology for use in the international pig industry was slow. Initially freezing technologies utilized the stepwise method to cryopreserve swine embryos. Conventional freezing methods will not work for pigs embryos, which are extremely sensitive to slow cooling below temperatures of approximately 15°C, since, as they cool, they undergo physiological and structural changes that leave them incapable of normal development. Using a rapid cooling processes – vitrification - is thought to outpace the damaging effects of slow cooling. It allows for an increase of the cryopreserved pig embryo survival rate to more than 80% in the laboratory. At present, vitrification is regarded as an alternative to traditional slow freezing procedures which do not offer satisfactory results for the cryopreservation of porcine embryos. Recently a novel approach consisting of a minimum sample size, increased cooling rate from 2500 C/min to 20.000 C/min, and the use propyleno and ethyleno glicol in the vitrification solution have been effective for crypreservation of pig embryos. Many factors such as the stage of embryonic development, cryoprotectant toxicity, the composition of vitryfication solution, cooling and warming rates can influence the survival of pig emryos after vitrification. Peri-hatching and hatched blastocysts tolerate slow freezing without special pretreatment, while morula and early blastocysts do not survive this cryopreservation procedure. Vitrification results in higher survival rates after warming when untreated early-to-hatched-blastocysts-stage embryos are used. An increase in cooling rate decreases sensitivity to slow freezing and may permit a reduction of cryoprotectant concentration.
This review presents the evolution and current possibilities, state of knowledge and prospects for in vitro production of pig embryos. Development of this technology for use in the international pig industry remains slow. IVP systems are generally comprised of three stage-specific culture environments: in vitro oocyte maturation (IVM), in vitro fertilization (IVF), and in vitro embryo culture (IVC). Hormonal supplements, such as FSH, eCG or hCG and follicular fluid, are added to the IVM medium in order to mimic the in vivo situation and stimulate nuclear maturation of the oocyte. Important elements are the cumulus cells that play a protective and metabolic role in oocyte cytoplasmic maturation. Efficiency of cytoplasmic maturation includes the ability of the oocyte to block the penetration of more than one sperm and also to support the decondensation of the sperm head within the ooplasm of the fertilized oocyte. The main feature, widely perceived to be a distinctive trait in porcine IVF, is the high prevalence of polyspermic fertilization. In the great majority of IVP studies on the pig, oocytes are harvested from the ovaries of prepubertal gilts out of necessity, due to the relative unavailability of adult sow ovaries. In fact, penetration rates exceeding 80% are typically achieved in prepubertal gilt oocytes, but polyspermy rates rarely measure less than 40%. When using sow oocytes, polyspermy rates in the range of 10% are routinely achieved. Instead, a number of porcine IVP groups routinely obtain a blastocyst formation rate of about 30% from in vitro matured oocytes, which is on par with that achieved in other farm animal species. Parameter for evaluating the success of a given porcine IVP system are also not without their pitfalls. Parameters used to define embryo quality include blastocyst morphology, total and inner cell mass, cell number, chromosomal abnormalities, metabolism, gene expression and apoptosis. One parameter of particular interest in the pig is apoptosis. The nuclear apoptotic features can be visualized using relatively simple fluorescent DNA-labeling techniques called TUNEL.
The aim of this review was to present the role of embryonic genome activation in zygote formation and in early embryonic development. Moreover, the authors emphasize the influence of selected factors on the quality and development of embryos in preimplantation stages. In recent years, reproductive biologists have focused on such processes as the regulation of oogenesis, folliculogenesis and morphogenesis. Thanks to the development of molecular biology and reproductive bio-techniques, it was possible to demonstrate the important role that activation of the embryonic genome plays in the above processes. Embryonic genome activation is a specific process whose origins dependent on the species of the mammal. In some species, activation of the embryonic genome begins in the 2-cell-stage embryo, while in others it begins during the 5th cell division. Molecular changes associated with embryonic genome activation play a crucial role in the morphological structure of the embryo. However, most of these morphological structure changes occur in the cell nucleus following the formation of nucleolus precursor bodies (NPB). It has also been suggested that epigenetic changes, such as the methylation and demethylation of embryonic DNA or the acetylation of histones, may play an important role in embryonic genome activation. There is little literature describing the influence of sperm RNA on basic semen parameters, the ability of a spermatozoon to fertilize an oocyte, or early mammalian embryonic development. This review discusses these parameters, as well as the role of micro-engineering and microfluidic research in the assessment of embryo quality.
Pierwsza strona wyników Pięć stron wyników wstecz Poprzednia strona wyników Strona / 2 Następna strona wyników Pięć stron wyników wprzód Ostatnia strona wyników
JavaScript jest wyłączony w Twojej przeglądarce internetowej. Włącz go, a następnie odśwież stronę, aby móc w pełni z niej korzystać.