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Meiosis II

Meiosis II

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,...

Meiosis II

Meiosis II

Meiosis II is the second and final stage of meiosis. It relies on the haploid cells produced during meiosis I, each of which contain only 23 chromosomes—one from each homologous initial pair. Importantly, each chromosome in these cells is composed of two joined copies, and when these cells enter meiosis II, the goal is to separate such sister chromatids using the same microtubule-based network employed in other division processes. The result of meiosis II is two haploid cells, each...

Oogenesis

Oogenesis

Oogenesis, the process of developing egg cells (female gametes), occurs within the ovaries and is fundamental to female fertility. This sequence begins during fetal development when diploid oogonia in the developing ovaries undergo mitotic divisions to produce primary oocytes. By birth, these primary oocytes enter prophase I of meiosis but become arrested in this stage, remaining suspended until puberty.
Each primary oocyte is surrounded by a layer of pre-granulosa cells, forming what is...

Oogenesis

Oogenesis

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...

Positive Regulator Molecules

Positive Regulator Molecules

Mitotic cell division results in daughter cells that exactly resemble the parent cell. However, errors in the DNA replication or distribution of genetic material may lead to genetic mutations that may be passed down to every new cell formed from the resulting abnormal cell. Propagation of such mutant cells is restricted through checkpoint mechanisms present at different stages of the cell cycle. These checkpoints involve regulator molecules that either promote or demote cell cycle events.

Positive Regulator Molecules

Positive Regulator Molecules

To consistently produce healthy cells, the cell cycle—the process that generates daughter cells—must be precisely regulated.

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Related Experiment Video

Updated: Dec 21, 2025

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

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

Published on: February 26, 2018

Cyclin A2 is essential for mouse gonocyte maturation.

Fanhua Ma^1,2, Xiangyuan Wang², Sanny S W Chung²

¹Key Laboratory of Agriculture Animal Genetics, Breeding and Reproduction, College of Animal Science, Huazhong Agricultural University , Wuhan, Hubei, China.

Cell Cycle (Georgetown, Tex.)

|May 19, 2020

Summary

Cyclin A2 is essential for male germ cell development in mice. Its absence disrupts spermatogonial stem cell formation and leads to abnormal spermatogenesis, impacting male fertility.

Keywords:

Cyclin A2 gonocyte differentiation spermatogonial stem cells

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Last Updated: Dec 21, 2025

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

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Published on: February 26, 2018

Evaluation of the Spindle Assembly Checkpoint Integrity in Mouse Oocytes

Evaluation of the Spindle Assembly Checkpoint Integrity in Mouse Oocytes

Published on: September 13, 2022

Mouse Oocyte Microinjection, Maturation and Ploidy Assessment

Mouse Oocyte Microinjection, Maturation and Ploidy Assessment

Published on: July 23, 2011

Area of Science:

Reproductive Biology
Developmental Biology
Cell Cycle Regulation

Background:

Male gonocytes, originating from primordial germ cells, proliferate and differentiate into spermatogonial stem cells (SSCs) post-birth.
The molecular mechanisms governing gonocyte proliferation, migration, and differentiation remain largely unelucidated.
Cyclin A2 is a critical cell cycle regulator known to be involved in cell proliferation.

Purpose of the Study:

To investigate the role of Cyclin A2 in mouse male gonocyte development and the establishment of spermatogenesis.
To determine the impact of Cyclin A2 loss on SSC pool formation and function.

Main Methods:

Targeted gene disruption of Cyclin A2 in embryonic mouse gonocytes.
Analysis of gonocyte proliferation, migration, and differentiation in neonatal and adult testes.
Assessment of SSC pool size, self-renewal, and differentiation capacity.

Main Results:

Loss of Cyclin A2 function in male gonocytes disrupted the transition to SSCs.
A significant imbalance between SSC self-renewal and differentiation was observed.
Severely abnormal spermatogenesis was evident in adult testes lacking Cyclin A2 function.

Conclusions:

Cyclin A2 is indispensable for normal male gonocyte development and SSC niche establishment in mice.
Disruption of Cyclin A2 impacts SSC pool formation, leading to impaired spermatogenesis.
These findings highlight Cyclin A2 as a crucial factor in maintaining male reproductive potential.