Editing Spermatozoon (section)

==Mammalian spermatozoa==

===Humans===
The [[sperm cell]] of ''Homo sapiens'' is the small [[Gamete|reproductive cell]] produced by males, and can only survive in warm environments; upon leaving the body, it starts to degrade, thereby decreasing the total [[sperm quality]]. Sperm cells normally come in two types, "female" and "male", named for the resulting sex of the fertilized zygote each produces after fusing with the ovum. Sperm cells that produce female ([[karyotype]] '''XX''') offspring carry an X-chromosome, while sperm cells that produce male ('''XY''') offspring carry a Y-chromosome.<ref>{{cite book |last1=Scheinfeld |first1=Amram |title=You and Heredity |date=1939 |publisher=Frederick A. Stokes Company |location=New York |pages=39}}</ref> Errors of meiosis may lead to the formation of sperm containing different arrangements of sex chromosomes, either altogether missing (''[[monosomy]]'', designated "'''0'''"), or in multiples (''[[trisomy]]''), such as "'''XX'''", "'''XY'''", etc... some of the conditions known as [[Disorders of sex development|Disorders of Sex Development]] (DSD) are the result of fertilization by such defective sperm.{{cn|date=April 2025}}

A human sperm cell consists of a flat, disc shaped '''head''' approximately {{convert|5.1|by|3.1|pitch|mil|abbr=in}}, and a '''tail''', known as a [[Flagellum#Eukaryotic|flagellum]] {{convert|50|pitch|mil|abbr=in}} long.<ref>{{cite journal |last1=Smith |first1=D. J. |last2=Gaffney |first2=E. A. |last3=Blake |first3=J. R. |last4=Kirkman-Brown |first4=J. C. |title=Human sperm accumulation near surfaces: a simulation study |journal=Journal of Fluid Mechanics |date=25 February 2009 |volume=621 |pages=289–320 |doi=10.1017/S0022112008004953 |bibcode=2009JFM...621..289S |s2cid=3942426 |url=http://pure-oai.bham.ac.uk/ws/files/17448418/Smith2009_S0022112008004953a.pdf |access-date=10 September 2021 |archive-date=27 January 2022 |archive-url=https://web.archive.org/web/20220127073249/http://pure-oai.bham.ac.uk/ws/files/17448418/Smith2009_S0022112008004953a.pdf |url-status=live }}</ref> The flagellum propels the sperm cell at about {{convert|1|to|3|mm/min|mil/s|abbr=off}}.<ref>{{cite journal | last1 = Ishijima | first1 = Sumio | last2 = Oshio | first2 = Shigeru | last3 = Mohri | first3 = Hideo | year = 1986 | title = ''Flagellar movement of human spermatozoa'' | journal = Gamete Research | volume = 13 | issue = 3| pages = 185–197 | doi = 10.1002/mrd.1120130302 }}</ref>  Sperm have an olfactory  [[Chemotaxis|guidance mechanism]], and after reaching the [[fallopian tube]]s, must undergo a period of [[capacitation]] before penetration of the ovum.<ref>{{cite journal |last1=Eisenbach |first1=Michael |last2=Giojalas |first2=Laura C. |title=Sperm guidance in mammals — an unpaved road to the egg |journal=Nature Reviews Molecular Cell Biology |date=April 2006 |volume=7 |issue=4 |pages=276–285 |doi=10.1038/nrm1893 |pmid=16607290 |hdl=11336/57585 |s2cid=32567894 |hdl-access=free }}</ref>

'''Head:''' It has a compact nucleus with only chromatic substance and is surrounded by only a thin rim of cytoplasm. Above the nucleus lies a cap-like structure called the [[acrosome]], formed by modification of the [[Golgi apparatus|Golgi body]], which secretes the enzyme '''spermlysin''' (''hyaluronidase, corona-penetrating enzyme, zona lysin,'' or ''acrosin''), that is necessary for fertilization. As the spermatozoon approaches the ovum, it undergoes the [[acrosome reaction]] in which the membrane surrounding the acrosome fuses with the plasma membrane of the sperm's head, exposing the contents of the acrosome.<ref>{{cite journal |last1=del Río |first1=María José |last2=Godoy |first2=Ana |last3=Toro |first3=Alejandra |last4=Orellana |first4=Renán |last5=Cortés |first5=Manuel E. |last6=Moreno |first6=Ricardo D. |last7=Vigil |first7=Pilar |title=La reacción acrosómica del espermatozoide: avances recientes |journal=Revista Internacional de Andrología |date=October 2007 |volume=5 |issue=4 |pages=368–373 |doi=10.1016/S1698-031X(07)74086-4 }}</ref>

'''Neck:''' It is the smallest part, {{convert|0.03|pitch|mil}} long, with a [[Anatomical terms of location|proximal]] [[centriole]] parallel to the base of the nucleus, perpendicular to the distal [[centriole]]. The proximal centriole is retained in the mature spermatozoon; the distal centriole disappears after [[axoneme]] assembly. The proximal centriole enters into the ovum, which has no centriole, and starts the first cleavage division of the zygote thus formed. The distal centriole gives rise to the axial filament which forms the tail and has a (9+2) arrangement. A transitory membrane called the ''Manchette'' lies in the '''midpiece'''.

'''Midpiece:''' It has 10–14 spirals of mitochondria surrounding the axial filament in the cytoplasm. It provides motility, and hence is called the powerhouse of the sperm.  It also has a ring centriole (annulus) that form a diffusion barrier between the midpiece and the principal piece and serve as a stabilizing structure for tail rigidity.<ref>{{Cite web|url=https://www.yeastgenome.org/go/GO:0097227|title=sperm annulus {{!}} SGD|website=www.yeastgenome.org|access-date=2019-02-22|archive-date=2019-02-22|archive-url=https://web.archive.org/web/20190222152105/https://www.yeastgenome.org/go/GO:0097227|url-status=live}}</ref>

'''Tail:''' The flagellum is the longest part at approximately {{convert|50|pitch|mm }}, having an axial filament surrounded by cytoplasm and plasma membrane, but at the posterior end the axial filament is naked. The flagellum gives movement to the cell.{{cn|date=April 2025}}

[[Semen]] has an alkaline nature and the spermatozoa do not reach full motility (hypermotility) until they reach the [[vagina]], where the alkaline pH is neutralized by acidic vaginal fluids.  This gradual process takes 20–30 minutes. During this period, [[fibrinogen]] from the [[seminal vesicle]]s forms a clot, securing and protecting the sperm. Just as they become hypermotile, [[fibrinolysin]] from the [[prostate gland]] dissolves the clot, allowing the sperm to progress optimally.{{cn|date=April 2025}}

The spermatozoon is characterized by a minimum of [[cytoplasm]] and the most densely packed DNA known in [[eukaryote]]s. Compared to [[mitosis|mitotic]] chromosomes in [[somatic cell]]s, sperm DNA is at least sixfold more highly condensed.<ref name="Ward">{{cite journal |vauthors=Ward WS, Coffey DS |title=DNA packaging and organization in mammalian spermatozoa: comparison with somatic cells |journal=Biology of Reproduction |volume=44 |issue=4 |pages=569–74 |year=1991 |pmid=2043729| doi = 10.1095/biolreprod44.4.569|doi-access=free }}</ref>

The specimen contributes with [[DNA]]/[[chromatin]], a [[centriole]], and perhaps also an [[oocyte]]-activating factor (OAF).<ref name=barroso>{{cite journal |last1=Barroso |first1=Gerardo |last2=Valdespin |first2=Carlos |last3=Vega |first3=Eva |last4=Kershenovich |first4=Ruben |last5=Avila |first5=Rosaura |last6=Avendaño |first6=Conrado |last7=Oehninger |first7=Sergio |title=Developmental sperm contributions: fertilization and beyond |journal=Fertility and Sterility |date=September 2009 |volume=92 |issue=3 |pages=835–848 |doi=10.1016/j.fertnstert.2009.06.030 |pmid=19631936 |doi-access=free }}</ref> It may also contribute with paternal [[messenger RNA]] (mRNA), also contributing to embryonic development.<ref name=barroso/>
<gallery>
File:Spermatozoa-human-3140x.jpg|Electron [[micrograph]] of human spermatozoa magnified 3140 times.
File:Sperms (urine) - Spermler (idrar) - 01.png|Sperm cells in the urine sample of a 45-year-old male patient who is being followed with the diagnosis of [[benign prostate hyperplasia]].
File:Sperm Head Dimensions.png|Dimensions of the human sperm head measured from a 39-year-old healthy subject.

</gallery> The human spermatozoon contains at least 7500 different [[protein]]s.<ref>{{cite journal |last1=Amaral |first1=Alexandra |last2=Castillo |first2=Judit |last3=Ramalho-Santos |first3=João |last4=Oliva |first4=Rafael |title=The combined human sperm proteome: cellular pathways and implications for basic and clinical science |journal=Human Reproduction Update |date=1 January 2014 |volume=20 |issue=1 |pages=40–62 |doi=10.1093/humupd/dmt046 |pmid=24082039 |doi-access=free }}</ref>

Human sperm genetics has been associated with [[human evolution]], per a 2020 study.<ref>{{cite journal |last1=Xia |first1=Bo |last2=Yan |first2=Yun |last3=Baron |first3=Maayan |last4=Wagner |first4=Florian |last5=Barkley |first5=Dalia |last6=Chiodin |first6=Marta |last7=Kim |first7=Sang Y. |last8=Keefe |first8=David L. |last9=Alukal |first9=Joseph P. |last10=Boeke |first10=Jef D. |last11=Yanai |first11=Itai |title=Widespread Transcriptional Scanning in the Testis Modulates Gene Evolution Rates |journal=Cell |date=January 2020 |volume=180 |issue=2 |pages=248–262.e21 |doi=10.1016/j.cell.2019.12.015 |pmid=31978344 |pmc=7891839 }}</ref><ref>{{Cite web|url=https://phys.org/news/2020-01-scanning-sperm-human-evolution.html|title=Scanning system in sperm may control rate of human evolution|access-date=2020-01-24|archive-date=2020-01-28|archive-url=https://web.archive.org/web/20200128111658/https://phys.org/news/2020-01-scanning-sperm-human-evolution.html|url-status=live}}</ref><ref>{{Cite web|url=https://markets.businessinsider.com/news/stocks/genetic-scanning-system-in-sperm-may-control-rate-of-human-evolution-1028840950|title=Genetic Scanning System in Sperm May Control Rate of Human Evolution|access-date=2020-01-24|archive-date=2020-08-11|archive-url=https://web.archive.org/web/20200811163131/https://markets.businessinsider.com/news/stocks/genetic-scanning-system-in-sperm-may-control-rate-of-human-evolution-1028840950|url-status=live}}</ref>

In humans, recombination rates differ between maternal and paternal DNA:
* '''Maternal DNA:''' Recombines approximately '''42 times''' on average.
* '''Paternal DNA:''' Recombines approximately '''27 times''' on average.

===DNA damage and repair===
DNA damages present in spermatozoa in the period after [[meiosis]] but before [[Human fertilization|fertilization]] may be repaired in the fertilized egg, but if not repaired, can have serious deleterious effects on fertility and the developing embryo.  Human spermatozoa are particularly vulnerable to free radical attack and the generation of oxidative DNA damage.<ref name="pmid26178844">{{cite book |doi=10.1007/978-3-319-18881-2_2 |pmid=26178844 |chapter=Damage to Sperm DNA Mediated by Reactive Oxygen Species: Its Impact on Human Reproduction and the Health Trajectory of Offspring |title=The Male Role in Pregnancy Loss and Embryo Implantation Failure |volume=868 |pages=23–47 |series=Advances in Experimental Medicine and Biology |year=2015 |last1=Gavriliouk |first1=Dan |last2=Aitken |first2=Robert John |isbn=978-3-319-18880-5 }}</ref><ref>{{cite journal | last1 = Lozano | first1 = G.M. | last2 = Bejarano | first2 = I. | last3 = Espino | first3 = J. | last4 = González | first4 = D. | last5 = Ortiz | first5 = A. | last6 = García | first6 = J.F. | last7 = Rodríguez | first7 = A.B. | last8 = Pariente | first8 = J.A. | year = 2009 | title = Density gradient capacitation is the most suitable method to improve fertilization and to reduce DNA fragmentation positive spermatozoa of infertile men | url = https://www.researchgate.net/publication/259983025 | journal = Anatolian Journal of Obstetrics & Gynecology | volume = 3 | issue = 1 | pages = 1–7 | access-date = 2016-03-08 | archive-date = 2022-04-30 | archive-url = https://web.archive.org/web/20220430005522/https://www.researchgate.net/publication/259983025_Density_gradient_capacitation_is_the_most_suitable_method_to_improve_fertilization_and_to_reduce_DNA_fragmentation_positive_spermatozoa_of_infertile_men | url-status = live }}</ref> (see e.g. [[8-Oxo-2'-deoxyguanosine]])

Exposure of males to certain lifestyle, environmental or occupational hazards may increase the risk of [[Aneuploidy|aneuploid]] spermatozoa.<ref>{{cite journal |vauthors=Templado C, Uroz L, Estop A |title=New insights on the origin and relevance of aneuploidy in human spermatozoa |journal=Molecular Human Reproduction|volume=19 |issue=10 |pages=634–43 |year=2013 |pmid=23720770 |doi=10.1093/molehr/gat039 |doi-access= }}</ref>  In particular, risk of aneuploidy is increased by tobacco smoking,<ref name="pmid11468778">{{cite journal |vauthors=Shi Q, Ko E, Barclay L, Hoang T, Rademaker A, Martin R |title=Cigarette smoking and aneuploidy in human sperm |journal=Molecular Reproduction and Development |volume=59 |issue=4 |pages=417–21 |year=2001 |pmid=11468778 |doi=10.1002/mrd.1048 |s2cid=35230655 }}</ref><ref name="pmid9797104">{{cite journal |vauthors=Rubes J, Lowe X, Moore D, Perreault S, Slott V, Evenson D, Selevan SG, Wyrobek AJ |title=Smoking cigarettes is associated with increased sperm disomy in teenage men |journal=Fertility and Sterility |volume=70 |issue=4 |pages=715–23 |year=1998 |pmid=9797104 |doi= 10.1016/S0015-0282(98)00261-1|doi-access=free }}</ref> and occupational exposure to benzene,<ref name="pmid20418200">{{cite journal |vauthors=Xing C, Marchetti F, Li G, Weldon RH, Kurtovich E, Young S, Schmid TE, Zhang L, Rappaport S, Waidyanatha S, Wyrobek AJ, Eskenazi B |title=Benzene exposure near the U.S. permissible limit is associated with sperm aneuploidy |journal=Environmental Health Perspectives |volume=118 |issue=6 |pages=833–9 |year=2010 |pmid=20418200 |pmc=2898861 |doi=10.1289/ehp.0901531 }}</ref> insecticides,<ref name="pmid15363581">{{cite journal |vauthors=Xia Y, Bian Q, Xu L, Cheng S, Song L, Liu J, Wu W, Wang S, Wang X |title=Genotoxic effects on human spermatozoa among pesticide factory workers exposed to fenvalerate |journal=Toxicology |volume=203 |issue=1–3 |pages=49–60 |year=2004 |pmid=15363581 |doi=10.1016/j.tox.2004.05.018 |bibcode=2004Toxgy.203...49X |s2cid=36073841 }}</ref><ref name="pmid15615886">{{cite journal |vauthors=Xia Y, Cheng S, Bian Q, Xu L, Collins MD, Chang HC, Song L, Liu J, Wang S, Wang X |title=Genotoxic effects on spermatozoa of carbaryl-exposed workers |journal=Toxicological Sciences |volume=85 |issue=1 |pages=615–23 |year=2005 |pmid=15615886 |doi=10.1093/toxsci/kfi066 |doi-access=free }}</ref> and perfluorinated compounds.<ref name="pmid25382683">{{cite journal |vauthors=Governini L, Guerranti C, De Leo V, Boschi L, Luddi A, Gori M, Orvieto R, Piomboni P |title=Chromosomal aneuploidies and DNA fragmentation of human spermatozoa from patients exposed to perfluorinated compounds |journal=Andrologia |volume= 47|issue= 9|pages= 1012–9|year=2014 |pmid=25382683 |doi=10.1111/and.12371 |hdl=11365/982323 |s2cid=13484513 |doi-access=free }}</ref>  Increased aneuploidy of spermatozoa often occurs in association with increased DNA damage. [[DNA fragmentation]] and increased in situ DNA susceptibility to denaturation, the features similar to these seen during [[apoptosis]] of somatic cells, characterize abnormal spermatozoa in cases of [[male infertility]].<ref>{{cite journal | last1 = Gorczyca | first1 = W | last2 = Traganos | first2 = F | last3 = Jesionowska | first3 = H | last4 = Darzynkiewicz | first4 = Z | year = 1993 | title = Presence of DNA strand breaks and increased sensitivity of DNA in situ to denaturation in abnormal human sperm cells. Analogy to apoptosis of somatic cells | journal = Exp Cell Res | volume = 207 | issue = 1| pages = 202–205 | doi = 10.1006/excr.1993.1182 | pmid = 8391465 }}</ref><ref>{{cite journal | last1 = Evenson | first1 = DP | last2 = Darzynkiewicz | first2 = Z | last3 = Melamed | first3 = MR | year = 1980 | title = Relation of mammalian sperm chromatin heterogeneity to fertility | journal = Science | volume = 210 | issue = 4474| pages = 1131–1133 | pmid = 7444440 | doi=10.1126/science.7444440| bibcode = 1980Sci...210.1131E }}</ref>

Although [[DNA repair]] has long been considered impossible in human spermatozoa due to the high level of DNA compaction in these cells, human spermatozoa possess a truncated [[base excision repair]] pathway that is mediated by [[oxoguanine glycosylase|8-oxoguanine DNA glycosylase 1 (OGG1)]].<ref name = Smith2013>{{cite journal |vauthors=Smith TB, Dun MD, Smith ND, Curry BJ, Connaughton HS, Aitken RJ |title=The presence of a truncated base excision repair pathway in human spermatozoa that is mediated by OGG1 |journal=J Cell Sci |volume=126 |issue=Pt 6 |pages=1488–97 |date=March 2013 |pmid=23378024 |doi=10.1242/jcs.121657 |url=}}</ref> Thus mature spermatozoa appear to have a limited capacity to mount a DNA repair response to [[oxidative stress]].<ref name = Smith2013/>

===Avoidance of immune system response===

[[Glycoprotein]] molecules on the surface of ejaculated sperm cells are recognized by all human female immune systems, and interpreted as a signal that the cell should not be rejected. The female immune system might otherwise attack sperm in the [[reproductive tract]]. The specific glycoproteins coating sperm cells are also utilized by some cancerous and bacterial cells, some parasitic worms, and HIV-infected white blood cells, thereby avoiding an immune response from the [[Host (biology)|host organism]].<ref>{{cite news|work=BBC News|url=http://news.bbc.co.uk/2/hi/health/7143889.stm|title=Sperm clue to 'disease immunity'|date=2007-12-17|access-date=2013-11-03|archive-date=2013-11-04|archive-url=https://web.archive.org/web/20131104200212/http://news.bbc.co.uk/2/hi/health/7143889.stm|url-status=live}}</ref>

The [[blood-testis barrier]], maintained by the tight junctions between the [[Sertoli cell]]s of the seminiferous tubules, prevents communication between the forming spermatozoa in the testis and the blood vessels (and immune cells circulating within them) within the [[Interstitial fluid|interstitial space]]. This prevents them from eliciting an immune response. The blood-testis barrier is also important in preventing toxic substances from disrupting spermatogenesis.{{citation needed|date=August 2023}}