Editing Programmed cell death (section)

===Invertebrates and vertebrates===
[[File:A conserved apoptotic pathway in nematodes, mammals and fruitflies.jpg|thumb|right|A conserved apoptotic pathway in nematodes, mammals and fruitflies]]

Learning about PCD in various species is essential in understanding the evolutionary basis and reason for apoptosis in development of the nervous system. During the development of the [[invertebrate]] nervous system, PCD plays different roles in different species.<ref>{{Cite journal|last1=Buss|first1=Robert R.|last2=Sun|first2=Woong|last3=Oppenheim|first3=Ronald W.|title=Adaptive Roles of Programmed Cell Death During Nervous System Development|date=2006-07-21|journal=Annual Review of Neuroscience|volume=29|issue=1|pages=1–35|doi=10.1146/annurev.neuro.29.051605.112800|pmid=16776578|issn=0147-006X}}</ref> The similarity of the asymmetric cell death mechanism in the [[nematode]] and the [[leech]] indicates that PCD may have an evolutionary significance in the development of the nervous system.<ref name="Sulston">{{cite journal|last=Sulston|first=JE|title=The Caenorhabditis elegans male: postembryonic development of nongonadal structures|journal=Developmental Biology|year=1980|volume=78|issue=2|pages=542–576|doi=10.1016/0012-1606(80)90352-8|pmid=7409314}}</ref> In the nematode, PCD occurs in the first hour of development leading to the elimination of 12% of non-gonadal cells including neuronal lineages.<ref name="Sulston1">{{cite journal|last=Sulston2|first=JE|title=The embryonic cell lineage of the nematode Caenorhabditis elegans|journal=Developmental Biology|year=1983|volume=100|pages=64–119|doi=10.1016/0012-1606(83)90201-4|pmid=6684600|issue=1}}</ref> Cell death in [[arthropods]] occurs first in the nervous system when [[ectoderm]] cells differentiate and one daughter cell becomes a [[neuroblast]] and the other undergoes apoptosis.<ref name="Doe">{{cite journal|last=Doe|first=Cq|title=Development and segmental differences in the pattern of neuronal precursor cells|journal=Journal of Developmental Biology|year=1985|volume=111|issue=1|pages=193–205|doi=10.1016/0012-1606(85)90445-2|pmid=4029506}}</ref> Furthermore, sex targeted cell death leads to different neuronal innervation of specific organs in males and females.<ref name="Giebultowicz">{{cite journal|last=Giebultowicz|first=JM|title=Sexual differentiation in the terminal ganglion of the moth Manduca sexta: role of sex-specific neuronal death|journal=Journal of Comparative Neurology|year=1984|volume=226|issue=1|pages=87–95|doi=10.1002/cne.902260107|pmid=6736297|s2cid=41793799}}</ref> In ''[[Drosophila]]'', PCD is essential in segmentation and specification during development.{{cn|date=November 2024}}

In contrast to invertebrates, the mechanism of programmed cell death is found to be more conserved in [[vertebrates]]. Extensive studies performed on various vertebrates show that PCD of neurons and [[glia]] occurs in most parts of the nervous system during development. It has been observed before and during [[synaptogenesis]] in the central nervous system as well as the peripheral nervous system.<ref name="Buss" /> However, there are a few differences between vertebrate species. For example, [[mammals]] exhibit extensive arborization followed by PCD in the retina while birds do not.<ref name="Cook">{{cite journal|last=Cook|first=B|title=Developmental neuronal death is not a universal phenomenon among cell types in the chick embryo retina|journal=Journal of Comparative Neurology|year=1998|volume=396|issue=1|pages=12–19|doi=10.1002/(sici)1096-9861(19980622)396:1<12::aid-cne2>3.0.co;2-l|pmid=9623884|s2cid=25569721}}</ref> Although synaptic refinement in vertebrate systems is largely dependent on PCD, other evolutionary mechanisms also play a role.<ref name="Buss" />