Objections to the Basic Moral Status of Human Embryos
Christopher Kaczor in The Ethics of Abortion, 2023
A questionable premise of Stretton's argument is that the single-celled zygote fissions into two duplicate, identical cells, as takes place with amoebae. The first cell division in the zygote gives rise to two cells, one of which will give rise to the embryo proper; the other of which will give rise to the trophoblast (George & Tollefsen 2011, pp. 154–155). These different developmental paths may be due to differences already present in each cell rather than to external influences. It is also questionable whether this division is properly described as fission:The main reason is that when a zygote divides a very important item is retained. Both at the initial stage and at the resulting two-cell stage there is not only a complete, connected external boundary, but, more precisely, a membrane or a physical covering—the zona pellucida—surrounding the cells. This membrane does not divide or disappear. The division takes place within its boundaries .… [T]he division of an amoeba by fission is not an adequate analogue to the division of a one-cell zygote. Amoebas do not retain a common external boundary or membrane after they divide, nor do they start to specialize into amoebas with different, yet coordinated functions.(Damschen, Gómez-Lobo, & Schönecker 2006, pp. 169, 171)
Implantation and Embryonic Imaging
Mary C. Peavey, Sarah K. Dotters-Katz in Ultrasound of Mouse Fetal Development and Human Correlates, 2021
Similarly to human ovulation and fertilization, the mouse embryo after ovulation is transported through the fallopian tube, where fertilization with sperm occurs. The fertilized oocyte is known as the zygote, which will continue to divide into an embryo. As the embryo travels through the fallopian tube, it continues to undergo cell division; by the third day, the embryo is approximately eight cells and begins compaction. On its fifth day of growth, the human embryo has developed into a blastocyst and travels to the uterus where it begins the process of implantation and further growth. At this point, as in humans, the blastocyst consists of a discrete inner cell mass, within a spherical cavity lined by the trophectoderm cell layer. These preimplantation events cannot be ascertained via ultrasonographic methods in either the human or mouse. However, the non pregnant uterus, consisting of the myometrium and endometrium can be easily measured via sonographic methods. See Fig. 1.1.
Use of Time-Lapse Embryo Imaging in Assisted Reproductive Technology Practice
Botros Rizk, Yakoub Khalaf in Controversies in Assisted Reproduction, 2020
It should be noted that one particular kinetic event has attracted much attention in morphokinetic studies—the direct cleavage (DC) of zygotes. The occurrence of direct cleavage was detected in nearly 14% of the total embryonic cohort (9). More importantly, since embryos with DC were found to have much lower implantation rates, deselecting these embryos at the time of uterine transfer could improve the efficiency of the implantation process. It is generally agreed that the following morphokinetic features may be used to discard embryos with low implantation potential: (a) direct cleavage from zygote to three-blastomere embryo; (b) too short second-cell cycle, i.e., duration of two-cell stage embryo (cc2 = t3-t2 < 5 hours); and (c) too long second synchrony, i.e., duration as three-cell stage embryo (s2 = t4-t3 > 1.5 hours).
(Zebra)fishing for nephrogenesis genes
Published in Tissue Barriers, 2023
Brooke E. Chambers, Nicole E. Weaver, Caroline M. Lara, Thanh Khoa Nguyen, Rebecca A. Wingert
During vertebrate embryogenesis, the kidney is derived from the intermediate mesoderm (IM), which is a narrow bilateral band of cells situated between the paraxial and lateral plate mesoderm4,5,36,37. In mammals, the IM begins to express Pax8 and Pax2, indicating renal lineage commitment. Further, Pax8 and Pax2 have redundant functions, as doubly deficient mouse embryos are unable to form later nephric structures.163 In Xenopus and zebrafish, pax8 expression precedes pax2/pax2a in the IM. Xenopus loss of function studies indicate pax8 functions earlier to establish the pronephric anlage, and pax2 is required for tubule differentiation.164 In line with these observations, zebrafish pax2a mutants exhibit defects in tubule differentiation and cloacal morphogenesis.165 Interestingly, pax2a mutants correctly initiate pax8 transcription, but are unable to maintain this expression over the course of pronephric development, suggesting a genetic intersection of these two factors.166 Regulation of renal progenitor fate choice is also mediated by the transcription factor odd skipped related 1 (osr1) as well as antagonistic interplay between Osr1 and the bHLH transcription factor Hand2.75,167–172 Further, osr1 expression is necessary for the survival of progenitor cells and the proper establishment of the podocyte lineage.75,173
Towards the selection of embryos with the greatest implantation potential
Published in Journal of Obstetrics and Gynaecology, 2021
Dalia Khalife, Antoine Abu-Musa, Ali Khalil, Ghina Ghazeeri
Because of the few observations during the morphological assessment, several investigators have accepted the challenge to show that morphokinetic development of embryos presents a broader image of the embryo behaviour. It has been shown to be advantageous in providing more information on the timing of events such as fertilisation, the extrusion of polar bodies and the timing of cellular divisions (Fréour et al. 2013; Muñoz et al. 2013). Morphokinetic parameters used to predict the formation of a zygote into a blastocyst were based on the duration of the first cellular division, the time interval between 1 and 2 cell embryo and the synchronicity from 2 to 4 cell embryo. The development to high-grade blastocyst can be estimated in the first 2 days of embryo culture (Kirkegaard et al. 2013), as it is correlated to an early cellular division, to a shorter time of second division (3 to 4 cells) between 9.33 to 12.65 h and shorter time of third division (5 to 8 cells) between 0 to 4 h (Montag et al. 2011; Hashimoto et al. 2012; VerMilyea et al. 2014).
Current concepts on diffuse choroidal hemangioma in Sturge Weber syndrome
Published in Ophthalmic Genetics, 2021
Martina Formisano, Maria Chiara di Pippo, Luca Scuderi, Solmaz Abdolrahimzadeh
DCH is usually associated with SWS that is a rare neuro-oculo-cutaneous syndrome occurring almost entirely sporadically and with equal frequency in both sexes (6). The abnormalities of blood vessel development and function usually involve the brain as leptomeningeal angiomatosis, the ipsilateral facial skin as a naevus flammeus (Figure 1), and the eye with choroidal hemangioma (6). The clinical manifestations have been suggested to arise due to the proximity of the ectoderm destined to form the upper facial skin, the part of the neural tube that forms the parieto-occipital brain and leptomeninges, and the optic vesicle during embryogenesis (7). However, as these anomalies are localized, Happle suggested a somatic mosaic mutation during the first trimester of pregnancy with differences depending on the phase of embryonic development (8). The incidence of DCH in patients with SWS is about 50% (9) and is more common in eyes with naevus flammeus involving the upper eyelid (3).
Related Knowledge Centers
- Egg Cell
- Multicellular Organism
- Sexual Reproduction
- Sperm
- Blastomere
- Animal Embryonic Development
- Fertilisation
- Zygote
- Cleavage
- Cell