Telophase in Mitosis & Meiosis: Key Processes & Significance

Introduction

Telophase is the final stage of mitosis and also the final stage of each division in meiosis, known as telophase I and telophase II. It is the stage when separated chromosomes arrive at opposite poles and the cell prepares to re-establish interphase conditions.

In this article you will learn what happens during telophase, how it occurs in mitosis with spindle disassembly, nuclear envelope reassembly and chromosome decondensation regulated by CDK dephosphorylation, and how telophase I and telophase II differ in meiosis leading to four genetically distinct cells.

What Happens During Telophase?

Telophase starts after anaphase when paired or sister chromosomes have been pulled to opposite poles. It is essentially the reverse of prophase and prometaphase.

During telophase, nuclear envelope reforms around each set of chromosomes. This separates nuclear DNA from cytoplasm. Chromosomes then start to decondense, becoming diffuse and less compact, returning to chromatin form. Nucleoli reappear. This phase is followed by cytokinesis, which divides cytoplasm of parent cell into daughter cells.

Telophase in mitosis results in two nuclei with identical chromosome sets, while in meiosis it contributes to reduction and diversity.

Telophase in Mitosis

Telophase in mitosis is significantly an extension of anaphase and metaphase events, controlled by dephosphorylation of mitotic cyclin-dependent kinase (CDK) substrates. Various coordinated mechanisms lead to formation of two daughter nuclei.

Dephosphorylation of the Mitotic Cyclin-Dependent Kinase Substrates

Phosphorylation vs Dephosphorylation

Phosphorylation of mitotic CDK substrates in early mitosis drives spindle assembly, chromosome condensation, and nuclear envelope breakdown in prophase and prometaphase.

Dephosphorylation occurs as mitotic cycle comes to an end in telophase. This allows disassembly of spindles, reassembly of nuclear envelope, and chromosome decondensation in new daughter cells.

Role of Cdc14 and Mitotic Exit Network (MEN)

One of most significant regulators is Cdc14 phosphatase, which is initially sequestered in nucleolus and released into nucleus and then cytoplasm.

Its initial function in early anaphase is stabilizing mitotic spindles and releasing more Cdc14 into nucleus where it becomes concentrated. In late anaphase and telophase it plays major role in Mitotic Exit Network (MEN) triggering spindle disassembly and nuclear envelope reassembly.

It also mediates dephosphorylation by activating downstream regulatory proteins specific for telophase such as Cdh1-activated APC/C and CHD1-associated proteins that target proteolysis of mitotic cyclins, leading to cellular switching from M phase to G1 phase of interphase.

Dephosphorylation also leads to:

• Distancing of chromosomes from metaphase plate triggering early telophase
• Activation of Cdc48/p97-dependent mechanisms for spindle disassembly, nuclear envelope assembly, and chromatin remodeling via ubiquitination and proteasomal degradation

Mitotic Spindle Disassembly

This involves shortening and disassembly of kinetochore microtubules after pulling chromosomes to poles, and dissolution of interpolar microtubules. Motor proteins and microtubule-severing proteins help dismantle spindle. Polar microtubules may transiently elongate before complete disassembly to push poles apart.

Nuclear Envelope Reassembly

This is reconstruction of double nuclear membrane, formation of nuclear pore complexes, and formation of internal nuclear lamina attached to inner nuclear membrane.

These structures are dismantled during prophase. Nuclear membrane components are absorbed by endoplasmic reticulum during metaphase. During telophase, targeting of nuclear membrane protein-containing vesicles from endoplasmic reticulum to chromatins takes place, influencing formation of nuclear envelope. Ran-GTPase and importins help recruit nucleoporins.

Chromosome Decondensation

Correction: Original text called this condensation, but telophase involves decondensation or decompaction, forming expanded chromatin. Compact chromosomes are needed for segregation, but decondensed chromatin is needed to restart transcription in interphase.

Decondensation occurs parallel to nuclear envelope assembly mediated by MEN-dependent CDK dephosphorylation which restarts interphase program. Histone modifications change, condensin complexes are released.

Telophase in Mitosis: Summary

• Telophase is final phase of mitosis, reverse of prophase events.
• New nuclear membrane forms, chromosomes unfold into chromatin, nucleoli reappear, cell starts to enlarge again.
• During this phase, sister chromatids have reached opposite poles.
• Small nuclear vesicles reform around chromosomes at each pole.
• Nuclear envelope reforms by associating with chromosomes, forming two nuclei in one cell before cytokinesis completes division into two cells.
• Kinetochore microtubules dissolve while polar microtubules continue to elongate transiently.
• As reformation of nuclear envelope takes place, chromosomes decondense, becoming more diffuse and transcriptionally active.

Cytokinesis usually begins in late anaphase and completes in telophase via contractile ring in animal cells or cell plate via phragmoplast in plant cells.

Telophase in Meiosis

Telophase I

Events of Telophase I

During telophase I, homologous chromosomes have separated and reached opposite poles, each pole now haploid with duplicated chromatids. The cell reforms nuclear envelope, disassembles spindle microtubules, and proceeds to cytokinesis.

Chromosome decondensation is partial and brief.

Interkinesis

After telophase I, cell goes through resting phase known as interkinesis or interphase II, which is short with no DNA replication. Some species skip nuclear envelope reformation and directly enter meiosis II.

Telophase II

Events of Telophase II

At this stage, sister chromatids are already separate after anaphase II. During telophase II they get surrounded by new nuclear membrane.

Cells originate from same parent but differentiation is created during recombination where parts of homologous chromosomes were exchanged in prophase I crossing over.

Four haploid cells are formed by end of meiosis with one allele for each gene separated in different combinations while combining with other alleles, generating genetic variation.

Comparison of Telophase in Mitosis and Meiosis

Key Takeaways

• Telophase is final stage of mitosis and of each meiotic division, starting after chromosomes reach opposite poles.
• Main events are nuclear envelope reassembly from ER vesicles, reassembly of nuclear pore complexes and lamina, spindle disassembly via dephosphorylation, and chromosome decondensation.
• Transition is controlled by dephosphorylation of mitotic CDK substrates, especially by Cdc14 phosphatase and Mitotic Exit Network, reversing early mitotic phosphorylation.
• In mitosis, telophase produces two diploid nuclei with identical chromatids, nucleoli reappear, and cytokinesis completes division.
• Telophase I separates homologous chromosomes into two haploid nuclei and is followed by interkinesis without DNA replication; telophase II separates sister chromatids into four haploid nuclei with genetic variation due to crossing over in prophase I.
• Chromosome condensation in early mitosis must not be confused with decondensation in telophase which allows transcription restart in G1.

Scientific References

1. Alberts B, Johnson A, Lewis J, Morgan D, Raff M, Roberts K, Walter P → Molecular Biology of the Cell → 6th Edition → Garland Science → Chapter 17 The Cell Cycle – M Phase, Mitotic Exit and Telophase.
2. Lodish H, Berk A, Kaiser CA, Krieger M, Bretscher A, Ploegh H, Amon A, Scott MP → Molecular Cell Biology → 8th Edition → W.H. Freeman → Chapter 19 Cell Cycle Regulation – CDK Regulation and Mitotic Exit.
3. Cooper GM, Hausman RE → The Cell: A Molecular Approach → 8th Edition → Oxford University Press → Chapter 14 Mitosis and Cytokinesis – Telophase and Nuclear Envelope Reassembly.
4. Karp G, Iwasa J, Marshall W → Karp's Cell Biology → 8th Edition → Wiley → Chapter 14 Cell Division – Stages of Mitosis and Meiosis – Telophase I and II.
5. Morgan DO → The Cell Cycle: Principles of Control → 2nd Edition → New Science Press → Chapter 5 Mitotic Exit – Cdc14 and MEN.
6. NCERT → Biology Textbook for Class XI → Reprint 2023-24 → National Council of Educational Research and Training, India → Chapter 10 Cell Cycle and Cell Division – Mitosis and Meiosis.
7. Steigemann P, Gerlich DW → Cytokinetic abscission – cellular dynamics at the midbody → Trends in Cell Biology → 2009 → Volume 19, Issue 11, Pages 606-616.
8. Wurzenberger C, Gerlich DW → Mitotic exit – Dephosphorylation and the reversal of mitotic phosphorylation → Journal of Cell Science → 2011 → Volume 124, Pages 1-5.
9. Afonso O, Matos I, Maiato H → Mitotic exit and temporal control of chromosomal segregation → Journal of Cell Biology → 2014 → Volume 205, Pages 283-287.
10. Hetzer MW → The nuclear envelope → Cold Spring Harbor Perspectives in Biology → 2010 → Volume 2, Article a000539.
11. Champion L, Linder MI, Kutay U → Cellular Reorganization During Mitotic Entry and Exit – Nuclear Pore Complex Assembly → Annual Review of Cell and Developmental Biology → 2017 → Volume 33, Pages 1-25.
12. Wandke C, Kutay U → Enclosing chromatin – Reassembly of the nucleus after open mitosis → Cell → 2013 → Volume 152, Issue 6, Pages 1222-1225.
13. Petronczki M, Siomos MF, Nasmyth K → Un Ménage à Quatre – The molecular biology of chromosome segregation in meiosis → Cell → 2003 → Volume 112, Issue 4, Pages 423-440.
14. Duro E, Marston AL → From equator to pole – Splitting chromosomes in mitosis and meiosis → Genes and Development → 2015 → Volume 29, Pages 637-653.
15. Nasmyth K → Segregating sister genomes – The molecular biology of chromosome segregation → Science → 2002 → Volume 297, Pages 559-565.