Biological Dimensions of Difference
Christopher J. Nicholls in Neurodevelopmental Disorders in Children and Adolescents, 2018
Fertilization involves the fusion of gametes into a new organism, the “zygote.” Cell division initially involves no growth, but rather cleavage of the cells into 2, 4, 16, and so on until 128 cells are reached, at which time the embryo becomes called a “blastula.” At about 7 days after fertilization, the blastula attaches itself to the uterus and becomes implanted. By day 9, two “germ” layers have become differentiated (an outer or “dorsal” ectoderm and an inner or “ventral” endoderm), and later as a result of the blastula folding inward, a third level (mesoderm) develops between the ectoderm and the endoderm. On day 18 of life, the nervous system begins to form on the dorsal surface (think of the dorsal fin on a shark) of the embryo, and in the third week of gestation, the ectodermal germ layer differentiates into a pear-shaped disk with an upper (cranial) and lower (caudal) end. This disk is called the “neural plate.” The more central cells on this plate become narrower on their inner surface, while the cells around them become narrower on their outer surface, which produces a “neural groove” which gradually deepens and eventually folds over onto itself, to become the “neural tube.” This tube closes from the middle toward each end, and gradually extends as a fluid filled tube with two open ends that eventually close by about 25 days of life. The cranial end of this tube ultimately becomes the brain, while the caudal end becomes the spinal cord. The reader is encouraged to review any of the multitude of YouTube videos showing the sequences of the above steps which are collectively termed “neurulation.”
Adult Stem Cell Plasticity
Richard K. Burt, Alberto M. Marmont in Stem Cell Therapy for Autoimmune Disease, 2019
Strictly defined, a stem cell is a cell capable of extensive self-renewal, enabling it to persist long term, and of differentiation into at least one mature cell type. However, this definition alone is imprecise. There are many different types of stem cells that can be defined by: (1) the stage of differentiation at which they are present; (2) where they are found in the organism; and (3) their differentiative potential. In the 2-4 cell stage of embryogenesis, each of the cells in the blastula is totipotent in that each is capable of differentiating into all embryonic and extraembryonic cell types necessary for development of the fetus. In contrast, stem cells in the adult are traditionally considered to have limited potential. For example, intrahepatic liver stem cells are only thought capable of differentiation into the primary cell types in the liver – hepatocytes and cholangiocytes. At the heart of the debate surrounding adult stem cell plasticity is whether predominantly tissue-specific adult stem cells are capable of differentiating into cell types outside of their primary lineage if in an appropriate microenvironment. To truly understand the debate surrounding BMSC plasticity, one must first understand the role stem cells play in ontogeny and adult physiology.
Objections to the Basic Moral Status of Human Embryos
Christopher Kaczor in The Ethics of Abortion, 2023
One difficulty with the bag of marbles analogy is there is evidence that the cells of the early human embryo are interacting with one another and becoming specialized so as to contribute to the development of a mature human body. S. Matthew Liao argues,there are thousands of cells by the time a blastula is formed around the nine-day stage, and certainly many more by the sixteen-day stage. Though by no means metaphysically impossible, it seems highly suspect that these thousands of cells would all be distinct and separate organisms; that they would not be sufficiently coordinated; and that at the sixteen-day stage, all of them would all of a sudden become sufficiently coordinated to compose a single organism.(2010b, p. 64)
Radiosensitizer effect of usnic acid on Biomphalaria glabrata embryos
Published in International Journal of Radiation Biology, 2018
F. T. J. Santos, W. N. Siqueira, M. L. O. Santos, H. A. M. F. Silva, J. L. F. Sá, T. S. Fernandes, N. H. Silva, E. J. França, E. B. Silva, A. M. M. A. Melo
Pigmented adult snails of B. glabrata were used, measuring 10–14 mm diameter, from São Lourenço da Mata, Pernambuco and maintained for successive generations in the Radiobiology Laboratory of the Department of Biophysics and Radiobiology of Federal University of Pernambuco. The snails were kept in plastic tanks of approximately 20 L filtered and dechlorinated water, pH 7 and a temperature of about 25 ± 3 °C. The snails were fed daily with fresh organic lettuce (Lactuca sativa). The animals deposited their spawn onto colorless polyethylene strips (5x5 cm) that were floated on the water surface and examined under a stereomicroscope (Tecnival SQZ-SD4, São Paulo, Brazil) for individualization and identification of embryonic stage. After identification, embryos in the blastula stage were collected and divided into groups of 100 ± 3 specimens.
Toxicity assessment of biological suspensions using the dielectric impedance spectroscopy technique
Published in International Journal of Radiation Biology, 2018
S. Muñoz, J. L. Sebastián, P. Antoranz, J. P. García-Cambero, A. Sanchis-Otero
In order to assess the capability of the setup measurement to detect possible variations of the electrical parameters, we have characterized suspensions of ZFe at three different development stages (V1, V2 and V3) and non-viable embryos (NV1, NV2 and NV3) obtained following lethal ethanol exposure of each viable suspension. Figure 4 shows microscope images of the viable and non-viable suspensions: (a) suspension V1, with embryos at earlier stage of the blastula period, between 2.5 and 3.5 h post-fertilization (hpf); (b) suspension V2, with embryos between 3.5 and 4 hpf; (c) suspension V3, with embryos between late blastula period and the onset of gastrula period, from 4.3 to 5.7 hpf and (d) coagulated embryos from any of the non-viable (NV) embryo suspensions.
Modification of late human embryo development after blastomere removal on day 3 for preimplantation genetic testing
Published in Systems Biology in Reproductive Medicine, 2021
Jenna Lammers, Arnaud Reignier, Sophie Loubersac, Sana Chtourou, Tiphaine Lefebvre, Paul Barrière, Thomas Fréour
An older study based on conventional static microscopy (without time-lapse) also evaluated the effect of blastomere biopsy on day 3 on subsequent embryo development (Tarín et al. 1992). Tarin et al. studied 129 human embryos randomized in the day 2 biopsy group on or non-biopsy group. Although the blastulation rate was similar in both groups, they observed a significantly higher proportion of embryos reaching the morula stage after day 4 in the biopsied-group as compared to the control group, suggesting acceleration to late embryo developmental stages in the biopsy group, in agreement with our findings.
Related Knowledge Centers
- Animal
- Inner Cell Mass
- Sperm
- Blastomere
- Trophoblast
- Blastocyst
- Animal Embryonic Development
- Cell
- Blastocoel
- Fertilisation