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14-September-2008 12:50:26 - Programmed cell death Redirected from Cell death Programmed cell-death PCD is death of a cell in any form, mediated by an intracellular program.1 In contrast to necrosis, which is a form of cell-death that results from acute tissue injury and provokes an inflammatory response, PCD is carried out in a regulated process which generally confers advantage during an organism's life-cycle. PCD serves fundamental functions during both plant and metazoa multicellular animals tissue development. Contents 1 Types 2 History 3 Programmed cell-death in plant tissue 3.1 PCD in pollen prevents inbreeding 4 Programmed cell death in slime molds 5 Evolutionary origin of PCD 6 Programmed death of entire organisms 7 External links 8 References 9 See also Types Apoptosis or Type I cell-death Autophagic or Type II cell-death cytoplasmic: characterized by the formation of large vacuoles which eat away organelles in a specific sequence prior to the nucleus being destroyed.2 Besides these two types of PCD, other pathways have been discovered.3 Called non-apoptotic programmed cell-death or caspase-independent programmed cell-death or necrosis-like programmed cell-death these alternative routes to death are as efficient as apoptosis and can function as either backup mechanisms or the main type of PCD. Other forms of programmed cell death include anoikis, almost identical to apoptosis except in its induction; cornification, a form of cell death exlusive to the eyes; excitotoxicity and Wallerian degeneration. Plant cells undergo particular processes of PCD which are similar to autophagic cell death. However, some common features of PCD are highly conserved in both plants and metazoa. History The concept of programmed cell-death was used by Lockshin Williams4 in 1964 in relation to insect tissue development, around eight years before apoptosis was coined. Since then, PCD has become the more general of these two terms. PCD has been the subject of increasing attention and research efforts. This trend has been highlighted with the award of the 2002 Nobel Prize in Physiology or Medicine to Sydney Brenner United Kingdom, H. Robert Horvitz US and John E. Sulston UK.5 Programmed cell-death in plant tissue In APL regulates vascular tissue identity in Arabidopsis,6 Bonke and colleagues state that one of the two long-distance transport systems in vascular plants, xylem, consists of several cell-types the differentiation of which involves deposition of elaborate cell-wall thickenings and programmed cell-death. The authors emphasize that the products of plant PCD play an important structural role. Basic morphological and biochemical features of PCD have been conserved in both plant and animal kingdoms.7 It should be noted, however, that specific types of plant cells carry out unique cell-death programs. These have common features with animal apoptosis -- for instance, nuclear DNA degradation -- but they also have their own peculiarities, such as nuclear degradation being triggered by the collapse of the vacuole in tracheary elements of the xylem.8 Janneke Balk and Christopher J. Leaver, of the Department of Plant Sciences, University of Oxford, carried out research on mutations in the mitochondrial genome of sun-flower cells. Results of this research suggest that mitochondria play the same key role in vascular plant PCD as in other eukaryotic cells.9 PCD in pollen prevents inbreeding During pollination, plants enforce self-incompatibility SI as an important means to prevent self-fertilization. Research on the corn poppy Papaver rhoeas has revealed that proteins in the pistil on which the pollen lands, interact with pollen and trigger PCD in incompatible ie. self pollen. The researchers, Steven G. Thomas and Veronica E. Franklin-Tong, also found that the response involves rapid inhibition of pollen-tube growth, followed by PCD.10 Programmed cell death in slime molds The social slime mold Dictyostelium discoideum has the peculiarity of adopting either a predatory amoeba-like behavior in its unicellular form, or coalescing into a mobile slug-like form when dispersing the spores which will give birth to the next generation.11 The stalk is composed of dead cells which have undergone a type of PCD that shares many features of an autophagic cell-death: massive vacuoles forming inside cells, a degree of chromatin condensation, but no DNA-fragmentation.12 The structural role of the residues left by the dead cells is reminiscent of the products of PCD in plant tissue. D. discoideum is a slime mold, part of a branch which may have emerged from eukaryotic ancestors about a billion years before the present. They apparently emerged after the ancestors of green-plants and the ancestors of fungi and animals had differentiated. But in addition to their place in the evolutionary tree, the fact that PCD has been observed in the humble, simple, six-chromosome D. discoideum has additional significance: it permits the study of a developmental PCD path which does not depend on the caspases which are characteristic of apoptosis.13 Evolutionary origin of PCD Biologists had long suspected that mitochondria originated from bacteria which had been incorporated as endosymbionts living together inside of larger eukaryotic cells. It was Lynn Margulis who from 1967 on championed this theory, which has since become widely accepted.14 The most convincing evidence for this theory is the fact that mitochondria possess their own DNA and are equipped with genes and replication apparatus. This evolutionary step would have been more than risky for the primitive eukaryotic cells which began to engulf the energy-producing bacteria and conversely, a perilous step for the ancestors of mitochondria which began to invade their proto-eukaryotic hosts. This process is still evident today, between human white blood-cells and bacteria. Most of the time, invading bacteria are destroyed by the white blood-cells; however, it is not uncommon for the chemical warfare waged by prokaryotes to succeed, with the consequence known as infection by its resulting damage. One of these rare evolutionary events, about two billion years before the present, made it possible for certain eukaryotes and energy-producing prokaryotes not only to coexist, but to mutually benefit from their symbiosis.15 Mitochondriate eukaryotic cells live poised between life and death, because mitochondria still retain their repertoire of molecules which can trigger cell suicide.16 This process has now been evolved to happen only when programmed.citation needed Given certain signals to cells such as feedback from neighbors, stress or DNA-damage, mitochondria release caspase activators which trigger the cell-death inducing biochemical cascade. As such, the cell-suicide mechanism is now crucial to all of our lives. Programmed death of entire organisms Main article: Phenoptosis External links Apoptosis and Cell Death Labs International Cell Death Society References ^ Engelberg-Kulka H, Amitai S, Kolodkin-Gal I, Hazan R 2006. Bacterial Programmed Cell Death and Multicellular Behavior in Bacteria. PLoS Genetics 2 10: e135. doi:10.1371/journal.pgen.0020135. ^ Lawrence M. Schwartz et al. 1993. Do All Programmed Cell Deaths Occur Via Apoptosis?. PNAS 90 3: 980. doi:10.1073/pnas.90.3.980. PMID 8430112. ;and, for a more recent view, see W. Bursch et al. 2000. Programmed Cell Death PCD: Apoptosis, Autophagic PCD, or Others?. Annals of the New York Academy of Sciences 926: 1. ^ Kroemer G, Martin SJ 2005. Caspase-independent cell death. Nat Med. 11 7: 725-30. doi:10.1038/nm1263. ^ Richard A. Lockshin, Carroll M. Williams 1964. Programmed cell death-II. Endocrine potentiation of the breakdown of the intersegmental muscles of silkmoths. Journal of Insect Physiology 10 4: 643-649. doi:10.1016/0022-19106490034-4. ^ 2002 Nobel Prize in Medicine or Physiology1 ^ Martin Bonke et al., published in Nature Vol. 425, Nov. 13, 2003, p. 181. ^ Mazal Solomon, et al.: The Involvement of Cysteine Proteases and Protease Inhibitor Genes in the Regulation of Programmed Cell Death in Plants, The Plant Cell, Vol. 11, 431-444, March 1999. See also related articles in The Plant Cell Online, 2 ^ See Jun Ito and Hiroo Fukuda: ZEN1 Is a Key Enzyme in the Degradation of Nuclear DNA during Programmed Cell Death of Tracheary Elements, The Plant Cell, Vol. 14, 3201-3211, December 2002. ^ The PET1-CMS Mitochondrial Mutation in Sunflower Is Associated with Premature Programmed Cell Death and Cytochrome c Release, The Plant Cell, Vol. 13, 1803-1818, August 2001 ^ Thomas, and Franklin-Tong: Self-incompatibility triggers programmed cell death in Papaver pollen, Nature Vol. 429, 20 May 2004, p. 305. ^ Crespi B, Springer S: Ecology. Social slime molds meet their match Science 2003 Jan 3;2995603:105-6 3. ^ See the article by Levraud et al.: Dictyostelium cell death : early emergence and demise of highly polarized paddle cells, The Journal of Cell Biology Vol. 160, 7, p. 1105 4. ^ See also Roisin-Bouffay et al.: Developmental Cell Death in Dictyostelium Does Not Require Paracaspase, The Journal of Biological Chemistry Vol. 279, 12, p. 11489, 19 March 2004 5. ^ see The Birth of Complex Cells, by Christian de Duve, Scientific American Vol. 274, 4, April, 1996 ^ See Ancient Invasions: From Endosymbionts to Organelle, by Sabrina D. Dyall et al., Science Vol. 304 p. 253, 9 April. 20046. ^ see Chiarugi and Moskowitz, in Science 297, p. 2007 See also v d e Developmental biology Human embryogenesis development of embryo and development of fetus some dates are approximate - see Carnegie stages and a timeline Week 1 Fertilization - Egg activation - Zygote - Cleavage - Morula - Blastula Blastomere - Blastocyst - Inner cell mass Week 2 Bilaminar disc Hypoblast, Epiblast Week 3 Trilaminar embryo, germ layers Archenteron/Primitive streak Primitive pit, Primitive knot/Blastopore, Primitive groove - Gastrula/Gastrulation - Regional specification Ectoderm: Surface ectoderm - Neuroectoderm - Somatopleure - Neurulation - Neural crest Endoderm: Splanchnopleure Mesoderm: Chorda- - Paraxial Somite/Somitomere/Sclerotome/Myotome/Dermatome - Intermediate - Lateral plate Intraembryonic coelom, Splanchnopleure/Somatopleure Extraembryonic/uterus Trophoblast Cytotrophoblast, Syncytiotrophoblast Blastocoele - Yolk sack/exocoelomic cavity - Heuser's membrane - Extraembryonic coelom - Vitelline duct Umbilical cord Umbilical artery, Umbilical vein, Wharton's jelly - Allantois Placenta - Decidua Decidual cells - Chorionic villi/Intervillous space - Gestational sac Amnion/Amniotic sac/Amniotic cavity, Chorion Histogenesis Programmed cell death Apoptosis - Stem cells - Germ line development Organogenesis Limb development: Limb bud - Apical ectodermal ridge/AER other structures: Eye development - Cutaneous structure development - Heart development - Development of the urinary and reproductive organs Retrieved from http://en..org/wiki/Programmed_cell_death Categories: Mitochondria | Programmed cell deathHidden categories: All articles with statements | Articles with statements since April 2008 Views Article Discussion this page History Personal tools Log in / create account Navigation Main page Contents Featured content Current events Random article Search Go Search Interaction Community portal Recent changes Contact Donate to Help Toolbox What links here Related changes Upload file Special pages Printable version Permanent link Cite this page Languages العربية Deutsch Eesti עברית Magyar 日本語 SlovenÅ¡Ä?ina Türkçe اردو ä¸æ–‡ This page was last modified on 10 September 2008, at 12:16
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