Distribution of Cytoplasmic Content

The nuclear envelope and endoplasmic reticulum are directly connected, so their distribution is coupled. During prophase, they merge together, and the sheet-like endoplasmic reticulum transforms into a tubular structure. It reorganizes near the cell cortex during metaphase, then encircles sister chromatids and reforms the nuclear envelope after chromosome segregation, ensuring both structures reach daughter cells.

During mitosis, mitochondria undergo fission to produce fragmented mitochondria that spread throughout the cell. These fragments are distributed to daughter cells through a stochastic or random process. After cell division, the fragmented mitochondria undergo fusion to regain their original shape and size, ensuring each daughter cell receives functional mitochondria.

The single Golgi body disassembles stepwise before segregating. The Golgi ribbon containing stacked cisternae breaks into mini stacks, then further disassembles into vesicles. In anaphase, vesicles fuse to form cisternae that restack. Small and large twin Golgis form near the midbody and centrosome in telophase, then merge during cytokinesis to form one Golgi body in each daughter cell.

Each organelle differs in structure, function, and copy number, requiring tailored distribution strategies. Small organelles like peroxisomes and lysosomes distribute through simple diffusion since cells have multiple copies. Large organelles like the endoplasmic reticulum require complex evolutionarily conserved mechanisms to ensure proper segregation and that each daughter cell receives at least one functional copy for survival.

Symmetrical division produces two identical daughter cells with the same fate, occurring in most cells. Asymmetrical division results in unequal inheritance of cell fate determinants, producing non-identical daughter cells. Stem cells exemplify asymmetric division, producing one daughter cell that behaves like the parent stem cell while the other follows a different cell lineage.

The conserved protein DRP1 constricts the outer mitochondrial membrane to bring about mitochondrial fission. Two mitotic kinases, Cyclin B-Cdk1 and Aurora-A, regulate the activation of DRP1. This regulated fission process ensures mitochondria fragment properly during mitosis so they can be distributed evenly between daughter cells.

The interphase endoplasmic reticulum is a continuous membrane that synthesizes membranes for various organelles. During mitosis, it may undergo fragmentation or remain as cisternae. In HeLa cells, the endoplasmic reticulum is maintained as cisternae and restricted to the cell cortex. The central cisternae associate with spindle microtubules, and the endoplasmic reticulum may be tethered to mitotic cell cortex walls before distribution.