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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.
Several morphological, molecular and cellular changes lead to the differentiation of primordial germ cells (PGC) into gametes, eggs and spermatozoa. This process is followed by the migration of these cells to gonads and several cell division cycles (mitotic and meiotic) as well as cell differentiations where these cells are changed into fully mature gametes. The process of gametes maturation is composed of several stages of specific biochemical changes that include changes in the nucleus as well as the changes in oocyte’s cytoplasm. The main factor which determines the formation of the developmental competence of oocytes is the long stage of mRNA and proteins storage (cytoplasmic maturation) that plays the main role in the blastocyst formation process. In this article selected issues associated with the regulation of each of the stages of oocytes differentiation as well as their influence of selected factors such as follicular size or formation of oocyte’s transcriptome have been presented. Moreover, a new-noninvasive system of oocytes/embryos quality assessment by using microfluidic techniques was presented.
Evaluation of oocyte developmental competence has an important influence on the ability of these cells to attain maturation, successful fertilization, development of embryo to the blastocyst stage and proper implantation. Factors determining the reproductive potential of gametes included: (1) expression of important transcription factors, (2) epigenetic changes, which influence the silencing of selected genes transcription, (3) transcription regulation, and (4) post-transcriptional regulation. The epigenetic changes mainly include: DNA methylation, histones modifications and changes in chromatin structure in the oocytes. In several studies, the association between oocyte morphology (mostly determined by cumulus cell layers and granularity of cytoplasm) and the ability of these cells to attain maturation and fertilization has been described. The use of biochemical, metabolomical and molecular markers is the most frequently applied tool in the assessment of oocyte developmental competence. However, most of these methods are invasive and lead to the decreased viability of the analyzed cells. Searching for new, objective and noninvasive techniques leads to the development of a microfluidic chip system, which shows the physical (spectral) properties of oocytes and embryos in comparison to the biological parameters. In this article, selected issues associated with the genetic regulation of such processes as: maturation of oocytes, fertilization and early stages of embryonic development, have been presented. Moreover, the regulation of transcription and post-transcriptional modification during oogenesis and embryogenesis in mammals, with special relation to pigs and the possibilities of applying of microfluidics in assessment of oocyte and embryo developmental competence was shown.
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