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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...

Separation of Sister Chromatids

Separation of Sister Chromatids

At the transition from prophase to metaphase, there is a reduction in cohesion along the chromosomal arms, resulting in the resolution of sister chromatids. However, residual cohesin connections remain to hold the sister chromatids together until the transition from metaphase to anaphase. The residual connection prevents any premature separation of sister chromatids, blocking the risks of aneuploidy within the daughter cells.
At the onset of anaphase, separase, a proteolytic enzyme, is...

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.

The Spindle Assembly Checkpoint

The Spindle Assembly Checkpoint

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...

Inhibition of Cdk Activity

Inhibition of Cdk Activity

The orderly progression of the cell cycle depends on the activation of Cdk protein by binding to its cyclin partner. However, the cell cycle must be restricted when undergoing abnormal changes. Most cancers correlate to the deregulated cell cycle, and since Cdks are a central component of the cell cycle, Cdk inhibitors are extensively studied to develop anticancer agents. For instance, cyclin D associates with several Cdks, such as Cdk 4/6, to form an active complex. The cyclin D-Cdk4/6 complex...

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Related Experiment Video

Updated: Mar 22, 2026

Xenopus laevis as a Model to Identify Translation Impairment

Xenopus laevis as a Model to Identify Translation Impairment

Published on: September 27, 2015

Release from Xenopus oocyte prophase I meiotic arrest is independent of a decrease in cAMP levels or PKA activity.

Nancy Nader¹, Raphael Courjaret¹, Maya Dib¹

¹Department of Physiology and Biophysics, Weill Cornell Medicine Qatar, Education City - Qatar Foundation, Doha, Qatar 24144.

Development (Cambridge, England)

|April 29, 2016

Summary

Oocyte meiotic arrest in Xenopus is not released by decreased cyclic adenosine monophosphate (cAMP) or protein kinase A (PKA) activity. Progesterone does not appear to lower cAMP or PKA, suggesting an independent maturation pathway.

Keywords:

Oocyte maturation PKA Progesterone Xenopus cAMP

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Area of Science:

Cell Biology
Developmental Biology
Reproductive Biology

Background:

Vertebrate oocytes arrest at prophase I of meiosis due to high cyclic adenosine monophosphate (cAMP) and protein kinase A (PKA) activity.
Progesterone is traditionally thought to induce meiotic maturation by inhibiting adenylate cyclase, thus lowering cAMP and PKA levels.

Purpose of the Study:

To investigate the role of cAMP and PKA in progesterone-induced meiotic arrest release in Xenopus oocytes.
To clarify the precise timing and extent of cAMP level changes during meiotic maturation.

Main Methods:

Utilized real-time, single-cell in vivo reporters to monitor cAMP and PKA activity.
Devised experimental conditions to manipulate cAMP levels and assess their impact on meiotic arrest.

Main Results:

No significant changes in cAMP or PKA levels were detected in response to progesterone.
No correlation was observed between PKA inhibition levels and meiotic arrest release.
Meiotic arrest could be released even with sustained high cAMP levels.
Lowering endogenous cAMP did not induce spontaneous maturation.

Conclusions:

Oocyte meiotic arrest release in Xenopus is independent of reduced cAMP levels or PKA activity.
Progesterone-induced maturation likely proceeds through a cAMP/PKA-independent pathway.