What is the Difference Between Open and Closed Mitosis

The key difference between open and closed mitosis is that in open mitosis, the segregation of chromosomes takes place after the nuclear envelope breaks down, while in closed mitosis, the segregation of chromosomes takes place without the nuclear envelope breaking down.

Mitosis is the division of one cell into two daughter cells such that each daughter cell inherits a single and complete copy of the genome of the mother cell. This takes place through the equal segregation of sister chromatids between the daughter cells. The division of other cellular components between these two daughter cells appears to follow a variety of patterns, such as open and closed mitosis. Depending on the cell type and organism, the nuclear envelope remains intact or disassembles before the segregation of chromosomes.

CONTENTS

1. Overview and Key Difference
2. What is Open Mitosis
3. What is Closed Mitosis
4. Similarities – Open and Closed Mitosis
5. Open vs Closed Mitosis in Tabular Form
6. Summary – Open vs Closed Mitosis

What is Open Mitosis?

Open mitosis is the segregation of chromosomes subsequent to nuclear envelope breakdown (NEBD). During open mitosis, the nuclear membrane and nuclear pore complexes dissemble at the start of mitosis. The nuclear proteins and cytoplasmic proteins are then mixed together. In organisms undergoing open mitosis, the nuclear pore complexes disassemble along with the nuclear envelope. This prevents nuclear transport during mitosis. The mitotic spindle becomes elongated from both poles of the microtubule organizing centre and captures the kinetochores.

Open mitosis is considered to have altered several times during evolution. Animals and plants both undergo open mitosis. Open mitosis is observed within five supergroups of eukaryotes, including Opisthokonts (fungi, animals, and some protists), Amoebozoa, Chromoalveolates, Archaeplastids, and Rhizaria. However, Excavates do not undergo open mitosis.

What is Closed Mitosis?

Closed mitosis is the segregation of chromosomes and the occurrence of spindle formation without nuclear envelope breakdown. When cells undergo closed mitosis in the absence of nuclear spindle microtubules, the contact between the nuclear envelope and chromatin promotes chromosomal segregation. This process is common in fungi.

Closed mitosis is known as the most ancient mechanism of eukaryotic cell division. It is observed within the six supergroups of eukaryotes, including Opisthokonts (fungi, animals, and some protists), Amoebozoa, Excavates, Chromoalveolates, Archaeplastids, and Rhizaria. Excavates significantly undergo only closed mitosis. Cell identity factors diffuse freely in two-dimensional membranes or three-dimensional liquid phases. These are segregated asymmetrically only if there is a restriction on their exchange between the sister cells. An example of this scenario is budding yeast cells that take advantage of closed mitosis to compartmentalize their nuclear division. This asymmetrically segregates cellular components such as non-chromosomal DNA and transcription factor Ace2.

Closed mitosis is a critical point for nuclear envelope integrity. Here, a unique rearrangement of nuclear shape is observed when the spherical metaphase nucleus transforms into an elongated dumbbell shape.

What are the Similarities Between Open and Closed Mitosis?

• Open and closed mitosis are two mechanisms of cell division in mitosis.
• It is present in eukaryotes.
• Both mechanisms are related to the nuclear envelope.
• Mitotic spindle generally segregates chromatids during mitosis in both types.

What is the Difference Between Open and Closed Mitosis?

Segregation of chromosomes takes place after the nuclear envelope breakdown in open mitosis, while the segregation of chromosomes takes place without the nuclear envelope breaking down in closed mitosis. Thus, this is the key difference between open and closed mitosis. Moreover, open mitosis mainly occurs in multicellular higher-level eukaryotes, while closed mitosis occurs mostly in lower eukaryotes like fungi.

The below infographic presents the differences between open and closed mitosis in tabular form for side-by-side comparison.

Summary – Open vs Closed Mitosis

Open and closed mitosis are two mechanisms of cell divisions where the mitotic spindle generally segregates chromatids during mitosis. Segregation of chromosomes takes place after the nuclear envelope breakdown in open mitosis. But in closed mitosis, chromosome segregation occurs without the nuclear envelope breakdown. Moreover, in open mitosis, the nuclear membrane and pore complexes dissemble at the start of mitosis, mixing up the nuclear and cytoplasmic proteins. Closed mitosis results in the occurrence of spindle formation without nuclear envelope breakdown. Here, cells undergo closed mitosis in the absence of nuclear spindle microtubules. Closed mitosis takes place mainly in fungi. So, this summarizes the difference between open and closed mitosis.

Reference:

1. Boettcher, Barbara, and Yves Barral. “The Cell Biology of Open and Closed Mitosis.” Nucleus, vol. 4, no. 3, 2013, pp. 160–165.
2. De Souza, Colin P., and Stephen A. Osmani. “Mitosis, Not Just Open or Closed.” Eukaryotic Cell, vol. 6, no. 9, 2007, pp. 1521–1527.

Image Courtesy:

1. “Mitosis classification open orthomitoses” By Baba66 – Own work (CC BY 4.0) via Commons Wikimedia
2. “Mitosis classification closed orthomitoses” By Baba66 – Own work (CC BY 4.0) via Commons Wikimedia