Editing Programmed cell death (section)

===Role in neural development===
PCD in the developing nervous system has been observed in proliferating as well as post-mitotic cells.<ref name="Tau" /> One theory suggests that PCD is an adaptive mechanism to regulate the number of [[progenitor cells]]. In humans, PCD in progenitor cells starts at gestational week 7 and remains until the first trimester.<ref name="De la rosa">{{cite journal|last=De la Rosa|first=EJ|author2=De Pablo, F|title=Cell death in early neural development: beyond the neurotrophic theory|journal=Trends in Neurosciences|date=October 23, 2000|volume=23|issue=10|pages=454–458|doi=10.1016/s0166-2236(00)01628-3|pmid=11006461|s2cid=10493404}}</ref> This process of cell death has been identified in the germinal areas of the [[cerebral cortex]], [[cerebellum]], [[thalamus]], [[brainstem]], and [[spinal cord]] among other regions.<ref name="Buss" /> At gestational weeks 19–23, PCD is observed in post-mitotic cells.<ref name="Lossiand Merighi">{{cite journal|last=Lossi|first=L|author2=Merighi, A|title=In vivo cellular and molecular mechanisms of neuronal apoptosis in the mammalian CNS|journal=Progress in Neurobiology|date=April 2003|volume=69|issue=5|pages=287–312|doi=10.1016/s0301-0082(03)00051-0|pmid=12787572|s2cid=27052883}}</ref> The prevailing theory explaining this observation is the neurotrophic theory which states that PCD is required to optimize the connection between neurons and their afferent inputs and efferent targets.<ref name="Buss" /> Another theory proposes that developmental PCD in the nervous system occurs in order to correct for errors in neurons that have migrated ectopically, innervated incorrect targets, or have [[axons]] that have gone awry during path finding.<ref name="Finlay">{{cite journal|last=Finlay|first=BL|title=Control of cell number in the developing mammalian visual system|journal=Progress in Neurobiology|year=1989|volume=32|issue=3|pages=207–234|doi=10.1016/0301-0082(89)90017-8|pmid=2652194|s2cid=2788103}}</ref> It is possible that PCD during the development of the nervous system serves different functions determined by the developmental stage, cell type, and even species.<ref name="Buss" />