MadSci Network: Cell Biology |
There are a couple of concepts which are useful to review in light of this question. First of all, cells can differentiate into other cell types without undergoing "reproduction", or cell division (also termed "mitosis", or "entering cell cycle"). For example, undifferentiated stem cells can become blood or liver cells through remodeling their components and changing their gene expression, without having to divide. There are other cells which will never change their type (terminally differentiated), most of which can still divide and some of which can not, also called "replicative senescence" or "quiescence". Importantly, these limitations to division can be overcome in the case of cancers. You are right in that red blood cells (erythrocytes) lack a nucleus and do not divide. Gametes (sperm and ova) also cannot themselves undergo further division after they arise through meiosis. Muscle fibers also do not divide- these multinucleated "cells" arise through the fusion of hundreds to thousands of mononucleated muscle cells. As a final example it is generally thought that adult neurons cannot divide; although some have been recently found to express cell cycle proteins there is still argument over whether these neurons can produce new cells or simply expire through programmed cell death (apoptosis). Neuronal replacement can nonetheless occur slowly through differentiation of stem cells. These issues are medically relevant especially in the case of Alzheimer's disease, in which misfolded amyloid proteins can push neurons down this abortive division/death pathway.
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