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Related Concept Videos

Meiosis II02:02

Meiosis II

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Meiosis II entails cell division and segregation of the sister chromatids, resulting in the production of four unique haploid gametes. The steps for meiosis II are similar to mitosis, except that meiosis II occurs in haploid cells, whereas mitosis occurs in diploid cells.
The timing and cell division patterns of meiosis differ between males and females. In male meiosis, the centrosomes are part of the formation of the meiotic spindle. However, in oocytes, including that of humans, Drosophila,...
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Oogenesis02:07

Oogenesis

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In human women, oogenesis produces one mature egg cell or ovum for every precursor cell that enters meiosis. This process differs in two unique ways from the equivalent procedure of spermatogenesis in males. First, meiotic divisions during oogenesis are asymmetric, meaning that a large oocyte (containing most of the cytoplasm) and minor polar body are produced as a result of meiosis I, and again following meiosis II. Since only oocytes will go on to form embryos if fertilized, this unequal...
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The Spindle Assembly Checkpoint02:19

The Spindle Assembly Checkpoint

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The spindle assembly checkpoint is a molecular surveillance mechanism ensuring the fidelity of chromosome segregation during anaphase. The checkpoint monitors the completion of all the prerequisite steps before chromosome segregation to determine whether the segregation process should proceed or be delayed.
Many proteins function together to control the spindle assembly checkpoint. Mutations affecting these proteins may allow cells to proceed into anaphase prematurely, resulting in the...
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Meiosis I01:49

Meiosis I

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Meiosis is a carefully orchestrated set of cell divisions, the goal of which—in humans—is to produce haploid sperm or eggs, each containing half the number of chromosomes present in somatic cells elsewhere in the body. Meiosis I is the first such division, and involves several key steps, among them: condensation of replicated chromosomes in diploid cells; the pairing of homologous chromosomes and their exchange of information; and finally, the separation of homologous chromosomes by...
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Heterochromatin02:38

Heterochromatin

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The extent of chromatin compaction can be studied by staining chromatin using specific DNA binding dyes. Under the microscope, the dense-compacted regions that take up more dye are called heterochromatin. Heterochromatin is further classified into two forms – constitutive heterochromatin and facultative heterochromatin.
Constitutive heterochromatin: It is a highly compact region of chromatin that is mostly concentrated in the centromere and telomere. Unlike euchromatin, the amino acid at...
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Anaphase Promoting Complex00:50

Anaphase Promoting Complex

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The stepwise destruction of specific proteins is necessary for the progression and completion of the cell cycle. Such proteins are ubiquitinated by ubiquitin ligases and then subsequently destroyed by the proteasome. The SCF (Skp1/Cullin/F-box) and the anaphase-promoting complex (APC) are two important ubiquitin ligases involved in cell cycle progression. While SCF is active throughout the cell cycle, APC gets activated during metaphase to anaphase transition. Cdc20 or Cdh1 binds to APC and...
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Related Experiment Video

Updated: Oct 4, 2025

Chromatin Spread Preparations for the Analysis of Mouse Oocyte Progression from Prophase to Metaphase II
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Chromatin Spread Preparations for the Analysis of Mouse Oocyte Progression from Prophase to Metaphase II

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The H3.3 chaperone Hira complex orchestrates oocyte developmental competence.

Rowena Smith1, Andrej Susor2, Hao Ming3

  • 1MRC Centre for Reproductive Health, University of Edinburgh, Queen's Medical Research Institute, 47 Little France Crescent, Edinburgh EH16 4TJ, UK.

Development (Cambridge, England)
|February 3, 2022
PubMed
Summary

The Hira complex, crucial for histone H3.3, is essential for oocyte competence and early embryo development. Its loss causes aberrant transcriptional silencing and developmental failure in mice.

Keywords:
Competent oocyteHira complexHistone H3.3Oocyte-to-embryo transitionZygotic genome activation

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Preparation of Meiotic Chromosome Spreads from Mouse Oocytes for Assessment of Synapsis and Recombination
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Analysis of Chromosome Segregation, Histone Acetylation, and Spindle Morphology in Horse Oocytes
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Analysis of Chromosome Segregation, Histone Acetylation, and Spindle Morphology in Horse Oocytes

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Analysis of Chromosome Segregation, Histone Acetylation, and Spindle Morphology in Horse Oocytes
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Area of Science:

  • Reproductive biology
  • Epigenetics
  • Developmental biology

Background:

  • Oocyte competence is vital for successful reproduction and early embryonic development.
  • The mechanisms and significance of transcriptional silencing in mature oocytes are poorly understood.
  • Histone H3.3, a variant histone, plays unique roles in chromatin structure and gene expression.

Purpose of the Study:

  • To characterize the function of the H3.3 chaperone Hira/Cabin1/Ubn1 complex in mouse oogenesis and early embryogenesis.
  • To investigate the impact of Hira complex loss of function on oocyte transcription and chromatin.
  • To elucidate the role of Zscan4d in oocyte developmental competence and its regulation by the Hira complex.

Main Methods:

  • Generation and analysis of mouse mutants lacking functional subunits of the Hira/Cabin1/Ubn1 complex.
  • Transcriptome and nascent RNA sequencing to assess transcriptional activity in mutant oocytes.
  • Histone mark analysis (H3K4me3, H3K9me3) and chromatin accessibility assays.
  • Zygote genome activation assays and manipulation of Zscan4 expression.

Main Results:

  • Loss of any Hira/Cabin1/Ubn1 subunit leads to early embryogenesis failure in mice.
  • Mutant oocytes exhibit aberrant transcriptional silencing, reduced H3K4me3 and H3K9me3 marks, and impaired chromatin accessibility.
  • Misregulation of Zscan4d, a key gene for zygote genome activation, was observed in mutant oocytes.
  • Oocyte-specific Zscan4 overexpression mimicked Hira mutant phenotypes, while Zscan4 knockdown partially rescued mutant oocyte development.

Conclusions:

  • The H3.3 chaperone Hira complex is essential for maternal effects in oocyte developmental competence.
  • This complex regulates chromatin condensation and transcriptional quiescence, ensuring proper oocyte maturation.
  • Fine-tuning of Zscan4 expression at the oocyte-to-embryo transition is critical for embryogenesis, mediated by the Hira complex.