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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[1] "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[2]"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[3] "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."
More recent papers
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This table shows an automated computer PubMed search using the listed sub-heading term.

  • Therefore the list of references do not reflect any editorial selection of material based on content or relevance.
  • References appear in this list based upon the date of the actual page viewing.

References listed on the rest of the content page and the associated discussion page (listed under the publication year sub-headings) do include some editorial selection based upon both relevance and availability.

Links: References | Discussion Page | Pubmed Most Recent | Journal Searches

Search term: Zygote Development

Matheus Pereira Dos Santos, George Shigueki Yasui, Pedro Luiz Porfírio Xavier, Nadya Soares de Macedo Adamov, Nivaldo Ferreira do Nascimento, Takafumi Fujimoto, José Augusto Senhorini, Laura Satiko Okada Nakaghi Morphology of gametes, post-fertilization events and the effect of temperature on the embryonic development of Astyanax altiparanae (Teleostei, Characidae). Zygote: 2016;1-13 PubMed 27220819

Sangho Jeong, Emily Eilbert, Ahmed Bolbol, Wolfgang Lukowitz Going mainstream: how is the body axis of plants first initiated in the embryo? Dev. Biol.: 2016; PubMed 27207388

Aspasia Destouni, Masoud Zamani Esteki, Maaike Catteeuw, Olga Tšuiko, Eftychia Dimitriadou, Katrien Smits, Ants Kurg, Andres Salumets, Ann Van Soom, Thierry Voet, Joris R Vermeesch Zygotes segregate entire parental genomes in distinct blastomere lineages causing cleavage-stage chimerism and mixoploidy. Genome Res.: 2016, 26(5);567-578 PubMed 27197242

K Kishida, H Harayama, F Kimura, T Murakami Individual differences in the distribution of sperm acrosome-associated 1 proteins among male patients of infertile couples; their possible impact on outcomes of conventional in vitro fertilization. Zygote: 2016;1-8 PubMed 27185107

Kiyomasa Nishii, Yasushi Kobayashi, Yosaburo Shibata Absence of connexin43 and connexin45 does not disturb pre- and peri-implantation development. Zygote: 2016, 24(3);457-64 PubMed 27172058



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 ‎‎Human Fertilization
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 ‎‎Human Fertilization
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 ‎‎Pronuclear Fusion
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 ‎‎Mouse Fertilisation
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 ‎‎Zygote Mitosis
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 ‎‎Early Division
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 ‎‎Parental Genomes
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 ‎‎Mouse Blastocyst
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Human Zygote Size

Actual Size 5cm ruler.jpg

Enlarged Size Stage1 size with ruler.jpg

Parental Pronuclei

Parental Genomes

Labeled parental genomes in an early zygote (mouse)

Animation based upon individual images of mouse maternal and paternal genomes.

Mouse zygote pronuclei
Fluorescent image of early mouse zygote pronuclei DIC image of early mouse zygote pronuclei
Fluorescence[4] DIC Optics showing pronuclear bodies[5]

Nucleolar-Precursor Bodies

Mouse zygote pronuclei 02.jpg

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.[6]

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

Human zygote two pronuclei 22.jpg Parental genome mix 01 icon.jpg

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

Maternally inherited Yes-associated protein (Yap), a co-activator of TEAD family transcription factors, plays a key role in activating embryonic transcription following fertilization in the mouse. Lysophosphatidic acid (LPA) in the mouse tubal fluid binds to its G-protein coupled receptor at the plasma membrane, and induces the activation of YAP by inhibiting LATS1/2. [7] Developmental Signals - Hippo

Mouse- zygote protein expression.jpg

The table above shows the pattern of protein expression (as percentages of total) in the mouse zygote according to 14 molecular function categories.[8]

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[4]

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 paternal genome reprogramming 01.jpg

Mouse zygote mitosis[4]

Mouse zygote mitosis metaphase.jpg Mouse zygote mitosis anaphase.jpg


  1. Kathy K Niakan, Kevin Eggan Analysis of human embryos from zygote to blastocyst reveals distinct gene expression patterns relative to the mouse. Dev. Biol.: 2013, 375(1);54-64 PubMed 23261930
  2. Francesco Silvestre, Alessandra Gallo, Annunziata Cuomo, Tiziana Covino, Elisabetta Tosti Role of cyclic AMP in the maturation of Ciona intestinalis oocytes. Zygote: 2011, 19(4);365-71 PubMed 20810008
  3. Chao-Bo Li, Zhen-Dong Wang, Zhong Zheng, Li-Li Hu, Shu-Qi Zhong, Lei Lei Number of blastomeres and distribution of microvilli in cloned mouse embryos during compaction. Zygote: 2011, 19(3);271-6 PubMed 20735894
  4. 4.0 4.1 4.2 Khursheed Iqbal, Seung-Gi Jin, Gerd P Pfeifer, Piroska E Szabó Reprogramming of the paternal genome upon fertilization involves genome-wide oxidation of 5-methylcytosine. Proc. Natl. Acad. Sci. U.S.A.: 2011, 108(9);3642-7 PubMed 21321204 | PMC2132672 | PNAS
  5. Alison B Singer, Joseph G Gall An inducible nuclear body in the Drosophila germinal vesicle. Nucleus: 2011, 2(5);403-9 PubMed 21941118 | Nucleus
  6. Tiphaine Aguirre-Lavin, Pierre Adenot, Amélie Bonnet-Garnier, Gaétan Lehmann, Renaud Fleurot, Claire Boulesteix, Pascale Debey, Nathalie Beaujean 3D-FISH analysis of embryonic nuclei in mouse highlights several abrupt changes of nuclear organization during preimplantation development. BMC Dev. Biol.: 2012, 12;30 PubMed 23095683 | BMC Dev Biol.
  7. Chao Yu, Shu-Yan Ji, Yu-Jiao Dang, Qian-Qian Sha, Yi-Feng Yuan, Jian-Jie Zhou, Li-Ying Yan, Jie Qiao, Fuchou Tang, Heng-Yu Fan Oocyte-expressed yes-associated protein is a key activator of the early zygotic genome in mouse. Cell Res.: 2016; PubMed 26902285
  8. Shufang Wang, Zhaohui Kou, Zhiyi Jing, Yu Zhang, Xinzheng Guo, Mengqiu Dong, Ian Wilmut, Shaorong Gao Proteome of mouse oocytes at different developmental stages. Proc. Natl. Acad. Sci. U.S.A.: 2010, 107(41);17639-44 PubMed 20876089 | PNAS


  • 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. (2016) Embryology Zygote. Retrieved May 31, 2016, from https://embryology.med.unsw.edu.au/embryology/index.php/Zygote

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© Dr Mark Hill 2016, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G