Early Human Zygote, with 2 pronuclei
The first diploid cell that forms following fertilization by fusion of the haploid oocyte (egg) and spermatozoa (sperm) resulting in the combination of their separate genomes. The first image shows the cell with the 2 pronuclei still present before fusion enclosed within the zona pellucida. In humans, this cell then undergoes a series of mitotic cell divisions, still enclosed within the zona pellucida, during the first few days of development to form 2 blastomeres then a solid cell mass called the morula.
- Zygote Links: Fertilization | Week 1 | Carnegie stage 1 | Morula | Blastocyst | ART | SCNT | Category:Zygote
Some Recent Findings
- Human embryos from zygote to blastocyst reveals distinct gene expression patterns relative to the mouse "Mammalian embryogenesis is controlled by mechanisms governing the balance between pluripotency and differentiation. The expression of early lineage-specific genes can vary significantly between species, with implications for developmental control and stem cell derivation. ...We observed that the pluripotency-associated transcription factor OCT4 was initiated in 8-cell embryos at 3 days post fertilization (dpf) and is restricted to the inner cell mass (ICM) in 128-256 cell blastocysts (6dpf), approximately 2 days later than the mouse. "
- cyclic AMP in the maturation of Ciona intestinalis oocytes"Immature oocytes are arrested at prophase I of the meiotic process and maturation onset is indicated by oocyte nuclear disassembly (germinal vesicle breakdown or GVBD). Signaling pathways that elevate intracellular cyclic AMP (cAMP) may either prevent or induce oocyte maturation depending on the species. "
- Number of blastomeres and distribution of microvilli in cloned mouse embryos during compaction "We concluded that: (i) the cleavage of blastomeres in cloned embryos was slow at least before compaction; (ii) the distribution of microvilli in cloned, normal, parthenogenetic, and tetraploid embryos was coherent before and after compaction; and (iii) the initiation of compaction in somatic cell nuclear transfer (SCNT) embryos was delayed compared with that of intracytoplasmic sperm injection (ICSI) embryos."
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<pubmed limit=5>Zygote Development</pubmed>
Human Zygote Size
Labeled parental genomes in an early zygote (mouse)
Animation based upon individual images of mouse maternal and paternal genomes.
Mouse zygote pronuclei
Most ribosomal DNA located around the Nucleolar-Precursor Bodies (NPBs), with some associated with pericentromeric filaments (extending from the NPBs towards the nuclear periphery) as well as rDNA signals joining two NPBs.
Formation of Zygote
- male and female pronuclei, 2 nuclei approach each other and nuclear membranes break down
- DNA replicates, first mitotic division
- sperm contributes centriole which organizes mitotic spindle
Movie - Pronuclear Fusion | Movie - Parental Genomes
Conceptus - term refers to all material derived from this fertilized zygote and includes both the embryo and the non-embryonic tissues (placenta, fetal membranes).
Zygote Protein Expression
The table above shows the pattern of protein expression (as percentages of total) in the mouse zygote according to 14 molecular function categories.
- Links: Germinal vesicle oocyte protein expression | MII oocyte protein expression | Zygote Protein Expression | Mouse Development | Oocyte Development | Zygote
Male Pronucleus Reprogramming
|Mouse zygote paternal genome reprogramming
Mouse zygotes male pronucleus contains 5-hydroxymethylcytosine (5hmC) thought to be formed by enzymatic oxidation of 5-methylcytosine (5mC).
- A - Mouse zygote double-stained with anti-5hmC antibody (green) and anti-5mC antibody (red). The smaller maternal pronucleus is closer to the polar body (pb). A bright-field image is shown on the far left.
- B - Additional zygotes double-stained with anti-5hmC antibody (green) and anti-5mC antibody (red). Merged images are shown.
- C - Zygotes obtained by in vitro fertilization were double-stained similarly. Two polyspermic zygotes (to the right) exhibit 5hmC staining in two paternal pronuclei.
- D - 5mC and 5hmC staining reveal two separate chromosome sets at metaphase of zygote division. A confocal image is shown.
- E - Individual chromosomes are largely stained for either 5mC (likely originated from the maternal pronucleus) or 5hmC (likely from the paternal pronucleus) at anaphase of zygote division. Two Z sections of the same zygote are shown.
- Links: Epigenetics
Mouse zygote mitosis
- Zygote An international journal dedicated to the rapid publication of original research in early embryology, Zygote covers interdisciplinary studies in animals and humans, from gametogenesis through fertilization to gastrulation.
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Cite this page: Hill, M.A. (2021, December 8) Embryology Zygote. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Zygote
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- © Dr Mark Hill 2021, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G