295:
187:
388:, are required for the fusion of nuclear membranes. The protamine Prm3 is located on the outer surface of each nuclear membrane, and is required for the fusion of the outer membrane. The exact mechanism is not known. Kar5, a kinesin-like protein, is necessary to expand the distance between the outer and inner membranes in a phenomenon known as bridge expansion. Kar8 and Kar2 are thought to be necessary to the fusing of the inner membranes. As described above, the reorganization of accessory and motor proteins during pronuclear migration also serves to orient the spindle pole bodies in the correct direction for efficient nuclear congression. Nuclear congression can still take place without this pre-orientation of spindle pole bodies, but it is slower. Ultimately the two pronuclei combine the contents of their
112:
266:, a process of chromosome duplication, recombination, and cell division, to create four new haploid gamete cells. One possible advantage of sexual reproduction is that it results in more genetic variability, providing the opportunity for adaptation through natural selection. Another advantage is efficient recombinational repair of DNA damages during meiosis. Thus, karyogamy is the key step in bringing together a variety of genetic material in order to ensure recombination in meiosis.
190:(a) In fission yeast, the mating process is triggered by nitrogen starvation when compatible partners are present. (b) Budding yeast cells of opposite mating type can instead mate spontaneously on rich medium to form stable diploids that undergo sporulation upon starvation. In both organisms after pheromone exchange, cells grow in a polarized manner in the direction of their partner and undergo fusion, karyogamy and sporulation.
344:
fusion in plasmogamy. After plasmogamy, the microtubule plus ends continue to grow towards the opposite pronucleus. It is thought that the growing plus end of the microtubule attaches directly to the motor protein of the opposite pronucleus, triggering a reorganization of the proteins at the half-bridge. The force necessary for migration occurs directly in response to this interaction.
20:
442:
source. Instead of fusing in the same way as lower eukaryotes do in karyogamy, the sperm nucleus vesiculates and its DNA decondenses. The sperm centriole acts as a microtubule organizing center and forms an aster which extends throughout the egg until contacting the egg's nucleus. The two pronuclei migrate toward each other and then fuse to form a diploid cell.
299:
shmoo tip. (D) Sliding cross-bridge model for nuclear congression. Oppositely oriented MTs overlap and are cross-linked along their lengths, whereas depolymerization is induced at the spindle poles. (E) Plus end model for nuclear congression. MT plus ends cross-link and induce depolymerization to draw opposing nuclei together.
441:
that interfere with microtubules prevent the fusion of the sperm and egg pronuclei. The gene KAR2 which plays a large role in karyogamy has a mammalian analog called Bib/GRP78. In both cases, genetic material is combined to create a diploid cell that has greater genetic diversity than either original
355:
to each other, and each attaching to the opposite nucleus at the plus end. This is the favored model. The alternative model proposes that the plus ends contact each other midway between the two pronuclei and only overlap slightly. In either model, it is believed that microtubule shortening occurs at
242:
signaling, which induces shmoo formation (a projection of the cell) and begins the process of microtubule organization and migration. Pheromones used in mating type recognition are often peptides, but sometimes trisporic acid or other molecules, recognized by cellular receptors on the opposite cell.
343:
and microtubule in a structure known as the half-bridge. Other proteins, such as Kar9 and Bim1 in yeast, attach to the plus end of the microtubules. They are activated by pheromone signals to attach to the shmoo tip. A shmoo is a projection of the cellular membrane which is the site of initial cell
298:
Nucleus is gray; Spindle pole body (SPB) is black circle; Microtubules (MTs) are black bars; actin filaments are gray cables; actin patches are small gray circles. (A) Nuclear orientation to the shmoo tip. (B) MT attachment to the shmoo tip. (C) Before cellâcell fusion, MTs are maintained at the
370:
has been shown to be essential for proper nuclear congression during karyogamy. Defective microtubule organization causes total failure of karyogamy, but does not totally interrupt meiosis and spore production in yeast. The failure occurs because the process of nuclear congression cannot occur
237:
meet, they are induced to leave the vegetative cycle and enter the mating cycle. In yeast, there are two mating types, a and α. In fungi, there can be two, four, or even up to 10,000 mating types, depending on the species. Mate recognition in the simplest eukaryotes is achieved through
420:
can turn pathogenic and is a particular problem in immunosuppressed patients. Unlike with most other fungi, diploid cells of different mating types fuse to create tetraploid cells which subsequently return to the diploid state by losing chromosomes.
400:
Although fungi are normally haploid, diploid cells can arise by two mechanisms. The first is a failure of the mitotic spindle during regular cell division, and does not involve karyogamy. The resulting cell can only be genetically
303:
The ultimate goal of karyogamy is fusion of the two haploid nuclei. The first step in this process is the movement of the two pronuclei toward each other, which occurs directly after plasmogamy. Each pronucleus has a
383:
of the pi occurs in three steps: fusion of the outer membrane, fusion of the inner membrane, and fusion of the spindle pole bodies. In yeast, several members of the Kar family of proteins, as well as a
409:
diploids if the two nuclei differ in genetic information. The formation of somatic diploids is generally rare, and is thought to occur because of a mutation in the karyogamy repressor gene (KR).
328:, but during nuclear congression, the plus ends are redirected. The microtubule plus ends attach to the opposite pronucleus, resulting in the pulling of the two pronuclei toward each other.
1084:"Microtubule configurations during fertilization, mitosis, and early development in the mouse and the requirement for egg microtubule-mediated motility during mammalian fertilization"
210:. Such organisms exist normally in a haploid state, containing only one set of chromosomes per cell. However, the mechanism remains largely the same among all haploid eukaryotes.
433:. This process is similar to karyogamy. As with karyogamy, microtubules play an important part in fertilization and are necessary for the joining of the sperm and egg (
147:
is fluid, and often influenced by the environment. Some organisms, in addition to their usual haploid state, can also exist as diploid for a short time, allowing
371:
without functional microtubules. Thus, the pronuclei do not approach close enough to each other to fuse together, and their genetic material remains separated.
347:
Two models of nuclear congression have been proposed: the sliding cross-bridge, and the plus end model. In the sliding cross-bridge model, the microtubules run
294:
23:
Karyogamy in the context of cell fusion. 1-haploid cells, 2-cell fusion, 3-single cell with two pronuclei, 4-fusing pronuclei (karyogamy), 5-diploid cell
868:"Spindle pole body-anchored Kar3 drives the nucleus along microtubules from another nucleus in preparation for nuclear fusion during yeast karyogamy"
174:
formation during the sexual reproduction cycle and instead creates variation within the somatic cells of an already developed organism, such as a
277:. Since the Amoeboza branched off early from the eukaryotic family tree, this finding suggests that karyogamy and meiosis were present early in
186:
320:, emerge at the spindle pole body. The attachment point to the spindle pole body marks the minus end, and the plus end extends into the
416:, a fungus that lives in the gastrointestinal tracts of many warm blooded animals, including humans. Although usually innocuous,
77:(a process of chromosome duplication, recombination, and division, to produce four new haploid cells), or continue to divide by
229:, resulting in many cellular changes that increase resistance to stress. Gamete formation in multicellular fungi occurs in the
273:
is a large group of mostly single-celled species that have recently been determined to have the machinery for karyogamy and
1039:
Noble, Suzanne M.; Johnson, Alexander D. (December 2007). "Genetics of
Candida albicans, a Diploid Human Fungal Pathogen".
254:. The pronuclei then fuse together in a well regulated process known as karyogamy. This creates a diploid cell known as a
676:
594:
512:
405:
since it is produced from one haploid cell. The second mechanism, involving karyogamy of somatic cells, can produce
1225:
Wassarman, Paul M.; Jovine, Luca; Litscher, Eveline S. (1 February 2001). "A profile of fertilization in mammals".
339:, such as Kar3 in yeast. Accessory proteins, such as Spc72 in yeast, act as a glue, connecting the motor protein,
720:
162:
during meiosis. In haploid organisms that lack sexual cycles, karyogamy can also be an important source of
348:
158:
Thus, karyogamy is the key step in bringing together two sets of different genetic material which can
429:
Mammals, including humans, also combine genetic material from two sources - father and mother - in
206:
800:"Nuclear Congression Is Driven by Cytoplasmic Microtubule Plus End Interactions in S. cerevisiae"
246:
The cell membranes and cytoplasm of these haploid cells then fuse together in a process known as
115:
Step labeled number 4 indicates karyogamy's place in the context of the life cycle of the fungus
866:
Gibeaux, Romain; Antonio Z. Politi; François Nédélec; Claude Antony; Michael Knop (2013-02-01).
151:
to occur. Karyogamy can occur within either mode of reproduction: during the sexual cycle or in
925:"Proper Microtubule Structure Is Vital for Timely Progression through Meiosis in Fission Yeast"
194:
The role of karyogamy in sexual reproduction can be demonstrated most simply by single-celled
1273:
159:
148:
1182:
Wassarman, PM; Jovine, L; Litscher, ES (Feb 2001). "A profile of fertilization in mammals".
81:. Mammalian fertilization uses a comparable process to combine haploid sperm and egg cells (
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There are, however, a few fungi that exist mostly in the diploid state. One example is
61:. Once the cell membranes, cytoplasm, and pronuclei fuse, the resulting single cell is
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Ni, Min; Marianna
Feretzaki; Sheng Sun; Xuying Wang; Joseph Heitman (December 2011).
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When subjected to environmental stress, such as nitrogen starvation in the case of
949:
1088:
Proceedings of the
National Academy of Sciences of the United States of America
627:
424:
1143:"KAR2, a karyogamy gene, is the yeast homolog of the mammalian BiP/GRP78 gene"
41:. Before karyogamy, each haploid cell has one complete copy of the organism's
1267:
1007:
891:
823:
635:
480:
430:
332:
233:, an organ specialized for such a process, usually by meiosis. When opposite
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Notably, pheromone signaling is absent in higher fungi such as mushrooms.
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389:
363:
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to each other for the entire distance between the two pronuclei, forming
234:
230:
584:
532:
984:"Distinct Roles for Key Karyogamy Proteins during Yeast Nuclear Fusion"
831:
585:
Raven, Peter H.; Ray
Franklin Evert; Susan E. Eichhorn (January 2005).
402:
352:
251:
247:
136:
58:
54:
34:
111:
57:. Once within the joined cell membrane, the nuclei are referred to as
1238:
1195:
456:
385:
321:
278:
270:
259:
239:
70:
50:
1140:
981:
923:
Yamashita, Akira; Yoshihiro Fujita; Masayuki
Yamamoto (2013-06-05).
748:"Comparative Genomics Supports Sex and Meiosis in Diverse Amoebozoa"
356:
the plus end and requires Kar3p (in yeast), a member of a family of
982:
Melloy, Patricia; Shu Shen; Erin White; Mark D. Rose (2009-09-01).
65:, containing two copies of the genome. This diploid cell, called a
1141:
Rose, Mark D.; Misra, Leanne M.; Vogel, Joseph P. (1 June 1989).
357:
336:
325:
274:
263:
167:
82:
78:
74:
62:
31:
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cells. Formation of somatic diploids circumvents the process of
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255:
218:
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175:
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66:
42:
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1081:
461:
226:
132:
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124:
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Similarities to and differences from mammalian fertilization
53:
of each cell must fuse with the other in a process known as
19:
797:
225:
in single-celled haploid organisms such as yeast is called
1038:
798:
Molk, Jeffrey N.; E. D. Salmon; Kerry Bloom (2006-01-02).
250:. This results in a single cell with two nuclei, known as
316:. Microtubules, an important fiber-like component of the
37:
cells, and refers specifically to the fusion of the two
30:
is the final step in the process of fusing together two
745:
669:
Guide to Yeast
Genetics and Molecular and Cell Biology
666:
16:
Fusion of the nuclei of two haploid eukaryotic cells
746:Hofstatter PG, Brown MW, Lahr DJG (November 2018).
616:
Cold Spring Harbor
Symposia on Quantitative Biology
694:"Tom Volk's Fungus of the Month for February 2000"
612:"Gamete Formation Resets the Aging Clock in Yeast"
106:
1082:Schatten, G; Simerly, C; Schatten, H (Jun 1985).
1265:
374:
331:Microtubule movement is mediated by a family of
392:and form a single envelope around the result.
181:
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667:Guthrie, Christine; Gerald R. Fink (2004).
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45:. In order for karyogamy to occur, the
1266:
1053:10.1146/annurev.genet.41.042007.170146
975:
660:
498:
496:
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312:and serves as an attachment point for
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166:during the process of forming somatic
85:) to create a diploid fertilized egg.
198:organisms such as the algae of genus
1134:
788:
712:
575:
528:
526:
524:
502:
721:"A fungus walks into a singles bar"
700:. University of Wisconsin-La Crosse
685:
603:
551:10.1146/annurev-genet-110410-132536
491:
324:. The plus end has normal roles in
13:
88:The term karyogamy comes from the
14:
1285:
718:
521:
691:
671:. Gulf Professional Publishing.
610:Ănal, E.; A. Amon (2011-01-01).
1218:
1175:
1075:
1032:
107:Importance in haploid organisms
473:
139:, in which the choice between
1:
988:Molecular Biology of the Cell
503:Cole, Garry T. (2012-12-02).
467:
375:Pronuclear fusion (karyogamy)
1160:10.1016/0092-8674(89)90058-5
950:10.1371/journal.pone.0065082
217:, cells are induced to form
7:
804:The Journal of Cell Biology
445:
182:Role in sexual reproduction
10:
1290:
628:10.1101/sqb.2011.76.011379
155:(non-reproductive) cells.
123:Haploid organisms such as
1041:Annual Review of Genetics
539:Annual Review of Genetics
505:Biology Of Conidial Fungi
396:Role in somatic diploids
308:that is embedded in the
207:Saccharomyces cerevisiae
1109:10.1073/pnas.82.12.4152
1000:10.1091/mbc.E09-02-0163
872:Genes & Development
262:, which can then enter
884:10.1101/gad.206318.112
437:) DNA. Drugs such as
300:
191:
120:
24:
816:10.1083/jcb.200510032
725:Cornell Mushroom Blog
297:
189:
149:genetic recombination
114:
22:
727:. Cornell University
366:organization in the
290:Pronuclear migration
145:asexual reproduction
1227:Nature Cell Biology
1184:Nature Cell Biology
1100:1985PNAS...82.4152S
941:2013PLoSO...865082Y
485:The Free Dictionary
452:Sexual reproduction
285:Cellular mechanisms
764:10.1093/gbe/evy241
301:
192:
121:
99:) 'nut' and ÎłÎŹÎŒÎżÏ
25:
994:(17): 3773â3782.
758:(11): 3118â3128.
587:Biology of Plants
381:nuclear envelopes
341:spindle pole body
306:spindle pole body
164:genetic variation
135:can have complex
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1239:10.1038/35055178
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1196:10.1038/35055178
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414:Candida albicans
360:-like proteins.
326:mitotic division
310:nuclear envelope
223:Gamete formation
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379:Merging of the
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73:can then enter
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5:
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1233:(2): E59âE64.
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1094:(12): 4152â6.
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878:(3): 335â349.
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535:"Sex in Fungi"
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1190:(2): E59â64.
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596:9780716710073
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589:. Macmillan.
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201:Chlamydomonas
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95:(from ÎșÎŹÏÏ
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68:
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47:cell membrane
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1274:Cell biology
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810:(1): 27â39.
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729:. Retrieved
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702:. Retrieved
697:
687:
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619:
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605:
586:
542:
538:
507:. Elsevier.
504:
484:
475:
439:griseofulvin
428:
417:
411:
407:heterozygous
399:
390:nucleoplasms
378:
368:cytoskeleton
362:
349:antiparallel
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318:cytoskeleton
314:microtubules
302:
268:
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235:mating types
214:
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103:'marriage'.
100:
96:
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87:
27:
26:
731:23 November
704:14 December
692:Volk, Tom.
545:: 405â430.
481:"karyogamy"
418:C. albicans
364:Microtubule
353:cross-links
281:evolution.
227:sporulation
137:cell cycles
468:References
403:homozygous
279:eukaryotic
248:plasmogamy
231:gametangia
55:plasmogamy
35:eukaryotic
1008:1059-1524
892:0890-9369
824:0021-9525
636:0091-7451
622:: 73â80.
457:Polyploid
386:protamine
335:known as
322:cytoplasm
271:Amoebozoa
260:zygospore
252:pronuclei
240:pheromone
160:recombine
71:zygospore
59:pronuclei
51:cytoplasm
28:Karyogamy
1268:Category
1247:11175768
1204:11175768
1069:31819376
1061:17614788
1026:19570912
969:23755176
929:PLOS ONE
910:23388829
850:16380440
782:30380054
654:21890640
569:21942368
446:See also
337:kinesins
117:Taphrina
1255:6172791
1212:6172791
1169:2661018
1128:3889922
1096:Bibcode
1017:2735476
960:3673945
937:Bibcode
901:3576518
841:2063526
832:4134115
773:6263441
645:3912942
560:3310392
358:kinesin
275:meiosis
264:meiosis
258:, or a
219:gametes
196:haploid
168:diploid
153:somatic
83:gametes
79:mitosis
75:meiosis
63:diploid
32:haploid
1253:
1245:
1210:
1202:
1167:
1126:
1119:397953
1116:
1067:
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848:
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830:
822:
780:
770:
675:
652:
642:
634:
593:
567:
557:
511:
435:oocyte
256:zygote
176:fungus
172:gamete
141:sexual
131:, and
97:karyon
93:karyo-
67:zygote
43:genome
39:nuclei
1251:S2CID
1208:S2CID
1065:S2CID
828:JSTOR
462:Fungi
133:algae
129:yeast
125:fungi
101:gamos
90:Greek
1243:PMID
1200:PMID
1165:PMID
1147:Cell
1124:PMID
1057:PMID
1022:PMID
1004:ISSN
965:PMID
906:PMID
888:ISSN
846:PMID
820:ISSN
778:PMID
733:2013
706:2013
673:ISBN
650:PMID
632:ISSN
591:ISBN
565:PMID
509:ISBN
269:The
49:and
1235:doi
1192:doi
1155:doi
1114:PMC
1104:doi
1049:doi
1012:PMC
996:doi
955:PMC
945:doi
896:PMC
880:doi
836:PMC
812:doi
808:172
768:PMC
760:doi
640:PMC
624:doi
555:PMC
547:doi
143:or
69:or
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