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Related Concept Videos

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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Cell division is necessary for growth and reproduction in organisms. Mitosis aids cell growth and development by dividing somatic cells. In contrast, meiosis causes the division of germ cells and plays an essential role in sexual reproduction. Due to their unique functional requirements, mitosis and meiosis differ from each other in multiple aspects.
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Meiosis is the division of a diploid cell into haploid cells forming sperm and eggs in animals through differentiation. Meiosis I is the first stage of meiosis, where the genetic recombination of homologous chromosomes and the reduction of the ploidy level by half occurs.
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Among all the organelles in an animal cell, only mitochondria have their own independent genomes. Animal mitochondrial DNA is a double-stranded, closed-circular molecule with around 20,000 base pairs. Mitochondrial DNA is unique in that one of its two strands, the heavy, or H, -strand is guanine rich, whereas the complementary strand is cytosine rich and called the light, or L, -strand. Compared to nuclear DNA, mitochondrial DNA has a very low percentage of non-coding regions and is marked by...
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Nondisjunction is the failure of homologous chromosomes or sister chromatids to separate correctly and move to the opposite poles of the cells. This produces daughter cells with abnormal chromosome numbers.  Nondisjunction is common during anaphase I or anaphase II of meiosis.  Mutations in synaptonemal complex proteins that attach homologous chromosomes increase the chances of nondisjunction in anaphase I of meiosis I. In contrast, mutations in topoisomerases and condensins that hold...
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Meiosis II02:02

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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.
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Analysis of Chromosome Segregation, Histone Acetylation, and Spindle Morphology in Horse Oocytes
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Reproductive competency and mitochondrial variation in aged Syrian hamster oocytes.

Fang Li1, Frank J Castora2, Wentia Ford1

  • 1Department of Biological Sciences, Old Dominion University, 5115 Hampton Blvd, Norfolk, VA 23529, USA.

Reproduction, Fertility, and Development
|June 22, 2016
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Summary

Aging reduces fertility in female hamsters due to oocyte depletion and mitochondrial dysfunction. Older hamsters show lower fertilization rates and litter sizes, with significant changes in ovarian follicles and ova morphology.

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Area of Science:

  • Reproductive Biology
  • Mammalian Aging
  • Oocyte Biology

Background:

  • The Syrian hamster (Mesocricetus auratus) serves as a valuable model for human reproductive biology due to similarities in oocyte size and structural stability.
  • Understanding age-related changes in reproductive capacity is crucial for both human and animal fertility research.

Purpose of the Study:

  • To evaluate the impact of aging on fecundity, ovarian follicular dynamics, ova production, and oocyte quality in Syrian hamsters.
  • To investigate age-associated alterations in mitochondrial number, structure, function, and cytoplasmic lamellae (CL) within oocytes.

Main Methods:

  • Comparative analysis of young (2-4 months) and old (12-18 months) Syrian hamsters.
  • Assessment of fertilization rates, litter sizes, ovarian follicular counts (preantral), and MII oocyte numbers.
  • Microscopic examination of oocyte morphology, including cytoplasmic lamellae (CL) integrity, zona pellucida expansion, and perivitelline space.
  • Measurement of reactive oxygen species (ROS) levels and mitochondrial membrane potential.
  • Quantification of mitochondrial number and clarity in MII oocytes.

Main Results:

  • Young hamsters exhibited significantly higher fertilization rates (100% vs. 50%) and larger litter sizes (9.3±0.6 vs. 5.5±0.6) compared to old hamsters.
  • Old hamsters showed a marked decrease in preantral follicles (46%) and MII oocytes (39%), along with collapsed cytoplasmic lamellae (CL) and increased perivitelline space in ova.
  • Ova from old hamsters displayed elevated reactive oxygen species (ROS) levels, reduced mitochondrial membrane potential, fewer mitochondria (36% decrease), and lower mitochondrial clarity (31% decrease).

Conclusions:

  • The study supports the theory of oocyte depletion contributing to mammalian aging.
  • Morphological changes in mitochondria and cytoplasmic lamellae (CL) are implicated as key factors in the age-related decline of fertility.
  • Aging significantly impairs oocyte quality and reproductive potential in Syrian hamsters.