What is Karyokinesis?

Karyokinesis is the process of nuclear division that occurs during cell division, mitosis or meiosis, specifically in eukaryotic cells. It is the first step in the M phase of the cell cycle. It is followed by cytokinesis, which is the splitting of the cytoplasm and cell membrane. Karyokinesis is divided into five phases: Prophase, Metaphase, Anaphase, Telophase, and Cytokinesis.

The process of karyokinesis allows the growth and expansion of multicellular organisms. It also enables the regeneration of damaged tissues. In this article, we will study Karyokinesis, the stages of karyokinesis, its significance, and the difference between karyokinesis and cytokinesis.

Definition of Karyokinesis

Kayokinesis is a process where the nucleus divides to create two daughter nuclei during cell divison. It is followed by cytokinesis. 

What is Karyokinesis?

Karyokinesis is a process where the nucleus splits into two daughter nuclei during cell division. W. Schleicher coined the term "karyokinesis" in 1878. The term "karyokinesis" is derived from the Greek words "karyon," meaning "nucleus" and "kinesis," meaning "movement". It is the first step of the cell cycle. Karyokinesis occurs only in cells that are in the G0 phase of interphase. During karyokinesis, DNA condenses and chromosomal material splits into two equal halves and line up in the middle of the cell.

The chromosome divide equally between the two new nuclei. The phases of karyokinesis include prophase, metaphase, anaphase, and telophase. Karyokinesis is followed by cytokinesis, which is the splitting of the cytoplasm and cell membrane. The purpose of mitosis is cell growth and to replace or regenerate damaged cells or tissues.

Karyokinesis Diagram

The diagram of karyokinesis showing different stages are as follows:

Karyokinesis Phases

Karyokinesis involves the division of a cell nucleus during mitosis or meiosis. The two main types of karyokinesis are mitosis and meiosis. The stages of Karyokinesis include:

1. Prophase

Prophase is the initial stage of both mitosis and meiosis. It is the longest phase and is divided into two phases:

• Early prophase
• Late prophase

Early Phase

• It is the first stage of mitosis that follows the S and G2 phases of interphase.
• The nuclear envelope starts to break down.
• Chromatin fibers begin to condense into visible chromosomes.
• The mitotic spindle starts forming.
• Centrioles duplicate and move to the opposite poles of the cell.

Prometaphase

• Prometaphase is a stage of mitosis and meiosis I.
• The nuclear envelope breaks down.
• Spindle fibers attach to kinetochores of chromosomes.
• Centrosomes move to opposite poles.
• Kinetochores are connected to microtubules of the spindle.

2. Metaphase

• It is the second stage of mitosis that follows prophase.
• Chromosomes align at the cell's equator, forming the metaphase plate.
• The chromosomes are at their most condensed and coiled stage during metaphase.
• Spindle fibers from opposite poles attach to the kinetochore of each chromosome.
• Chromosomes are positioned for equal distribution to daughter cells in the upcoming anaphase.

3. Anaphase

• Anaphase is the fourth mitosis phase, where chromosomes move to opposite poles.
• Kinetochore microtubules shorten.
• Non-kinetochore microtubules lengthen.
• Centrosomes are pushed far apart and the cell elongates as spindle fibers continue to separate chromatids.
• This phase ensure that each daughter cell receives a complete set of chromosomes for genetic stability.

4. Telophase

• Telophase is the final stage of karyokinesis, followed by cytokinesis, dividing the cytoplasm.
• It starts when the replicated, paired chromosomes have been separated and pulled to opposite sides, or poles, of the cell.
• The decondensation of chromosomes starts.
• The spindle starts disappearing.
• The nuclear envelope assembly around each set of chromosomes.
• Telophase is usually followed by cytokinesis.

Karyokinesis Meiosis

Meiosis consists of two successive cell divisions, known as meiosis I and meiosis II:

Meiosis I

• Prophase I: Chromosomes condense, and homologous chromosomes undergo genetic recombination (crossing over).
• Metaphase I: Homologous chromosomes align at the cell's equator.
• Anaphase I: Homologous chromosomes separate and move to opposite poles.
• Telophase I: Two haploid cells are formed, each with half the chromosome number of the original cell.

Meiosis II: Similar to mitosis, resulting in the formation of four non-identical haploid daughter cells.

Significance of Karyokinesis

Karyokinesis plays an important role in the cell division, in growth, development and reproduction of eukaryotic organisms. Significance of karyokinesis are:

• It ensures the accurate distribution of genetic material including chromosomes to daughter cells during cell division.
• It help in maintaining genetic stability and preserving the species-specific information encoded in the DNA.
• The process is fundamental for growth, tissue repair, and the maintenance of the organism's overall structure.
• It is important for living organisms because it ensures that cells can regenerate. 
• It ensures that cells and tissues can mature, create, and redevelop within a finite time.

Disturbances of Karyokinesis

Karyokinesis is nuclear division. Disturbances of karyokinesis can include:

• Collapse of prophase
• Failure of cytokinesis
• Alterations of multicentric spindles
• Destruction of the tubulin cytoskeleton
• Alterations of spindle formation
• Inadequate development of the mitotic apparatus.

Difference Between Karyokinesis and Cytokinesis

The difference between Karyokinesis and Cytokinesis are as follows:

Related Reads,

• Difference Between Karyokinesis And Cytokinesis 
• Difference between Mitosis and Meiosis
• Cell Organelles