In the gut, the stem cells are particularly active – in mice, they divide every day for 2.5 years, so they go through a thousand cell divisions.
The cells of all early animal embryos go through a phase of rapid division (cleavage) where particular cell cycle checkpoints are skipped until a specification event occurs directing these embryonic stem cells to their fated germ layer cell type.
The sperm or eggs of sexual organisms go through a series of cell divisions from the fertilized egg; mutations can occur at each division.
The unicellular microspores go through an asymmetric mitotic division (pollen mitosis I) to produce a pollen grain with two cells, a larger vegetative cell that hosts a smaller generative cell; the latter will divide once more to produce two sperm cells (Pollen mitosis II).
Neuroblasts undergo two rounds of mitotic activity: embryonic divisions produce lineages of primary neurons that build the larval nervous system; after a brief quiescence, the neuroblasts go through a second round of divisions in larval stage to produce secondary neurons which are integrated into the adult nervous system.
In contrast, inhibition of the telomerase gene also leads to cell growth inhibition, differentiation, and cell death, but only after cells go through a number of cell divisions (allowing telomere shortening).
The rate of shortening appears to be slow enough that the cells can go through a considerable number of cell divisions before essential genes are lost and the cells can ultimately no longer divide.
Neuroblasts in Drosophila are widely considered as neural stem cells as they are shown to go through a series of self-renewing divisions while siblings differentiating to form neurons. Remarkably, this is also seen in the culture, suggesting that this is an intrinsic property and not niche dependent.
After the initial phase of rapid cell divisions, vertebrate embryos must go through a variety of cell movements to form the primary axis of the body and arrange cells to give rise to different tissues.
Sixty-cell embryos were formed when blastomeres went through an equatorial division while the 4 micromeres experienced a meridional division.
