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Is the Human Embryo an Organism?
Published in Nicholas Colgrove, Bruce P. Blackshaw, Daniel Rodger, Agency, Pregnancy and Persons, 2023
The earliest examples of integrated, organismal activity in the zygote are the immediate steps taken to prevent additional sperm from fusing to the cell surface (a condition known as polyspermy) and thereby contributing an abnormal amount of DNA to the zygotic genome. Within minutes of sperm-egg fusion, the zygote initiates a molecular cascade that will chemically modify the cell surface to block additional sperm from binding (Evans 2020). While the primary biological function of the gametes is to find each other and fuse, the zygote acts immediately and specifically to antagonize this function, clearly demonstrating it has entered into a novel pattern of behavior. Importantly, preventing polyspermy is not required for mere cellular life (many normal human body cells contain multiple copies of the genome; see Lacroix and Maddox 2012; Zybina and Zybina 2020) yet is critical for the health of the embryo, specifically. Polyspermy is a major cause of triploidy in humans, a condition that is incompatible with normal human development (Masset et al. 2021). Thus, in acting immediately to prevent additional sperm binding, the zygote acts in an integrated manner, not to preserve the health of the zygote as a cell, but rather to specifically preserve the health of a developing, multicellular organism.
The Journey of the Porcine Spermatozoa from Its Origin to the Fertilization Site: The Road In Vivo vs. In Vitro
Published in Juan Carlos Gardón, Katy Satué, Biotechnologies Applied to Animal Reproduction, 2020
Cristina Soriano-Úbeda, Francisco Alberto García-Vázquez, Carmen Matás
From the studies reviewed, major research progress has been made in reproductive physiology and technology in swine. However, attempts to improve in vitro reproduction in pigs have not been enough. Lack of knowledge of many factors involved in in vitro sperm capacitation and fertilization and its regulation could contribute to the abnormally high incidence of polyspermy in this species. The use of simple in vitro systems of pre-treatment of gametes and IVF have been well demonstrated to be valid to analyze the complex processes of fertilization and evaluate several sperm, oocyte and embryo parameters. However, they suffer from serious limitation for the in vitro production of embryos due to fact that the available capacitation media produce a large percentage of capacitated spermatozoa that ready for fertilize at the same time. The direction in which we must advance is to allow oocytes to express their natural ability to block polyspermy, with more studies on the physiology of gametes, as well as with the development of new strategies for modulation of sperm capacitation. To do this, it would seem logical to first adjust the known parameters involved in in vitro sperm capacitation and fertilization processes that are far from their counterparts in vivo and that could firmly establish the basis of these techniques in the porcine species.
Regulation of Reproduction by Dopamine
Published in Nira Ben-Jonathan, Dopamine, 2020
After digesting a hole in the ZP, the sperm head enters the egg’s parenchyma and the membranes of the two cells fuse. The next critical step is prevention of polyspermy, given that polyploidy is not compatible with life. Within seconds of contact with a sperm, Na+ channels in the egg’s membrane are activated, and a rushed entry of sodium depolarizes the egg’s resting potential of –70 mV. The fast, although transient, electrical block to polyspermy is followed within 10–15 min by the cortical reaction. The lysosome-like cortical granules are released from the egg’s membrane, destroying the oocyte’s sperm receptors, and modifying the extracellular matrix around the egg, which becomes impenetrable to additional sperm entry. Although there are several publications on DAR expression and putative functions of DA in Drosophila, Xenopus, and Zebrafish oocytes, there are no comparable records on mammalian oocytes.
Correlation between the number of oocytes and the increase of polyspermy rate in IVF cycles
Published in Gynecological Endocrinology, 2023
Polyspermy refers to the phenomenon that two or more than two sperm enter into oocytes, and form three or more pronucleus. Tt is common abnormal fertilization way in in vitro fertilization (IVF), polyspermy rate of which can reach more than 10%. The embryos from polyspermy oocytes cannot be used for transplantation. High three pro-nuclei (3PN) zygotes proportion associated with normal embryo multinucleation at the two-cell stage [1]. Previous studies had also shown that polyspermy may lead to adverse laboratory and clinical outcomes [2–6]. Therefore, polyspermy rate has become one of the quality control indexes in reproductive laboratories. Vienna Consensus in 2017 [7] recommend that the polyspermy rate in IVF should be limited to 6%. However, despite of strict laboratory standardized procedures, polyspermy rate could still exceed 6% in IVF.
Effects of three pro-nuclei (3PN) incidence on laboratory and clinical outcomes after early rescue intracytoplasmic sperm injection (rescue-ICSI): an analysis of a 5-year period
Published in Gynecological Endocrinology, 2021
Wennan Chen, Haiyan Bai, Mingzhao Li, Xia Xue, Juanzi Shi
3PN formation resulting from conventional IVF fertilization could be due to polyspermy. Some investigators suggested that 3PN incidence made negative effects on the clinical outcomes in the conventional IVF cycles [10,11]. Our previous studies also showed that 3PN incidence significantly decreased the clinical pregnancy rate for patients with lower retrieved oocytes in the fresh cleavage-stage ET cycles [12]. For ICSI, a single sperm was injected into a single oocyte which negated the potential for dispermic triploidy. Some studies also suggested that 3PN incidence might make negative effects on the clinical outcomes in the ICSI cycles [4,13]. In conclusion, 3PN incidence was not good for the clinical outcomes either in the conventional IVF and ICSI cycles. Nevertheless, it was still unknown whether or not 3PN could make negative effects on the clinical outcomes after early rescue-ICSI. In this study, we firstly investigated the effect of 3PN incidence on laboratory and clinical outcomes after early rescue-ICSI.
Cleavage-stage embryo micromanipulation in the clinical setting
Published in Systems Biology in Reproductive Medicine, 2018
Iman Halvaei, Shahin Ghazali, Stefania A. Nottola, Mohammad Ali Khalili
Micromanipulation in assisted reproductive technology (ART) has been of great help to treat infertile patients and to understand the basic fertilization and embryo development concepts. In light of the introduction of the successful human in vitro fertilization (IVF) method in 1987, many infertile patients were given hope of becoming parents. However, after several years, there remained many cases with male factor infertility that could not be treated by this standard technique. Thus, micromanipulation techniques were introduced by embryologists to overcome this problem. Micromanipulation techniques include injecting a single sperm into the oocyte to assist fertilization, zona breaching to improve blastocyst hatching, fragment or lysed cell removal to improve embryo development, and embryo biopsy to detect possible chromosomal abnormalities. The first micromanipulation technique was partial zona dissection (PZD) in which the zona pellucida (ZP) was opened by mechanical force in order to facilitate sperm access to the oocyte vestment. Subzonal insemination (SUZI) was the next procedure where sperm cells were directly deposited into the perivitellinespace (PVS). The high rate of polyspermy, due to more than one sperm entering into the oocyte, and low rate of fertilization were the drawbacks of this technique. Next was the injection of a single spermatozoon into an oocyte, called intracytoplasmic sperm injection (ICSI) (Palermo et al. 1992). Assisted zona hatching, fragment/debris/lysed cell removal, blastomere biopsy, and finally embryo splitting were introduced successively. Micromanipulation techniques are performed in every stage of development including oocytes, zygote, cleavage-stage embryos, morula, and blastocyst. This review aims to discuss the micromanipulation of the cleavage-stage human embryo in clinical ART. This review also underlines the possible role exerted by micromanipulation in inducing epigenetic alterations and the need for high quality control during micromanipulation.