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Totipotency continuity from zygote to early blastomeres - a model under revision.

08:00 EDT 1st April 2019 | BioPortfolio

Summary of "Totipotency continuity from zygote to early blastomeres - a model under revision."

The mammalian zygote is a totipotent cell that generates all the cells of a new organism through embryonic development. However, if one asks about the totipotency of blastomeres after one or two zygotic divisions, opinions differ. As it is impossible to determine the intrinsic developmental potency of early blastomeres in an intact embryo, experiments of blastomere isolation were conducted in various species, showing that 2-cell blastomeres could give rise to a new organism when sister cells were separated. A mainstream interpretation was that each of the sibling mammalian blastomeres was equally totipotent. However, reevaluation of those experiments raised some doubts about the real prevalence of cases in which this interpretation could truly be validated. We compiled experiments that tested the intrinsic developmental potency of early mammalian blastomeres in a cell-autonomous way (i.e. excluding nuclear transfer and chimera production). We then confronted the developmental abilities with reported molecular differences between sibling blastomeres. The reevaluated observations were at odds with the mainstream view: A viable 2-cell embryo can already include one non-totipotent blastomere. We were, thus, led to propose a revised model for totipotency continuity based on the construction of the zygote as a mosaic, which accounts for differential inheritance of totipotency-relevant components between sister blastomeres. This takes place with no preordained mechanisms that would ensure a reproducible partition. This model, which is compatible with the body of data on regulative properties of mammalian early embryos, aims at tempering the rigid interpretation that discounted maternal constraints on totipotency.

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This article was published in the following journal.

Name: Reproduction (Cambridge, England)
ISSN: 1741-7899
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Medical and Biotech [MESH] Definitions

Undifferentiated cells resulting from cleavage of a fertilized egg (ZYGOTE). Inside the intact ZONA PELLUCIDA, each cleavage yields two blastomeres of about half size of the parent cell. Up to the 8-cell stage, all of the blastomeres are totipotent. The 16-cell MORULA contains outer cells and inner cells.

The earliest developmental stage of a fertilized ovum (ZYGOTE) during which there are several mitotic divisions within the ZONA PELLUCIDA. Each cleavage or segmentation yields two BLASTOMERES of about half size of the parent cell. This cleavage stage generally covers the period up to 16-cell MORULA.

An early embryo that is a compact mass of about 16 BLASTOMERES. It resembles a cluster of mulberries with two types of cells, outer cells and inner cells. Morula is the stage before BLASTULA in non-mammalian animals or a BLASTOCYST in mammals.

Statistical formulations or analyses which, when applied to data and found to fit the data, are then used to verify the assumptions and parameters used in the analysis. Examples of statistical models are the linear model, binomial model, polynomial model, two-parameter model, etc.

The occurrence in an individual of two or more cell populations of different chromosomal constitutions, derived from a single ZYGOTE, as opposed to CHIMERISM in which the different cell populations are derived from more than one zygote.

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