85:
154:
27:
67:. These three groups form segments by using a "growth zone" to direct and define the segments. While all three have a generally segmented body plan and use a growth zone, they use different mechanisms for generating this patterning. Even within these groups, different organisms have different mechanisms for segmenting the body. Segmentation of the body plan is important for allowing free movement and development of certain body parts. It also allows for regeneration in specific individuals.
1474:
279:
1486:
1462:
383:, with this gradient promotes the development of other structures, such as muscles, across the basic segments. Lower vertebrates such as zebrafish do not require retinoic acid repression of caudal Fgf8 for somitogenesis due to differences in gastrulation and neuromesodermal progenitor function compared to higher vertebrates.
258:
of the midline. The N and Q lineages contribute two blast cells for each segment, while the M, O, and P lineages only contribute one cell per segment. Finally, the number of segments within the embryo is defined by the number of divisions and blast cells. Segmentation appears to be regulated by the gene
404:
Segmentation can be seen as originating in two ways. To caricature, the 'amplification' pathway would involve a single-segment ancestral organism becoming segmented by repeating itself. This seems implausible, and the 'parcellization' framework is generally preferred – where existing organization of
257:
has been described as “budding” segmentation. Early divisions within the leech embryo result in teloblast cells, which are stem cells that divide asymmetrically to create bandlets of blast cells. Furthermore, there are five different teloblast lineages (N, M, O, P, and Q), with one set for each side
379:; retinoic acid repression of Fgf8 gene expression defines the wavefront as the point at which the concentrations of both retinoic acid and diffusible FGF8 protein are at their lowest. Cells at this point will mature and form a pair of somites. The interaction of other signaling molecules, such as
75:
Segmentation is a difficult process to satisfactorily define. Many taxa (for example the molluscs) have some form of serial repetition in their units but are not conventionally thought of as segmented. Segmented animals are those considered to have organs that were repeated, or to have a body
405:
organ systems is 'formalized' from loosely defined packets into more rigid segments. As such, organisms with a loosely defined metamerism, whether internal (as some molluscs) or external (as onychophora), can be seen as 'precursors' to eusegmented organisms such as annelids or arthropods.
355:, creating travelling waves of gene expression. The "wavefront" is where clock oscillations arrest, initiating gene expression that leads to the patterning of somite boundaries. The position of the wavefront is defined by a decreasing posterior-to-anterior gradient of
269:
Within the annelids, as with the arthropods, the body wall, nervous system, kidneys, muscles and body cavity are generally segmented. However, this is not true for all of the traits all of the time: many lack segmentation in the body wall, coelom and musculature.
391:
In other taxa, there is some evidence of segmentation in some organs, but this segmentation is not pervasive to the full list of organs mentioned above for arthropods and annelids. One might think of the serially repeated units in many
230:
Within the arthropods, the body wall, nervous system, kidneys, muscles and body cavity are segmented, as are the appendages (when they are present). Some of these elements (e.g. musculature) are not segmented in their sister taxon, the
191:
phylum in general, it is the most highly studied. Early screens to identify genes involved in cuticle development led to the discovery of a class of genes that was necessary for proper segmentation of the
686:
Dray, N.; Tessmar-Raible, K.; Le Gouar, M.; Vibert, L.; Christodoulou, F.; Schipany, K.; Guillou, A.; Zantke, J.; Snyman, H.; BĂ©hague, J.; Vervoort, M.; Arendt, D.; Balavoine, G. (2010).
215:, which set up the boundaries between the different segments. The gradients produced from gap gene expression then define the expression pattern for the
211:
axis is defined by maternally supplied transcripts giving rise to gradients of these proteins. This gradient then defines the expression pattern for
84:
51:
into a linear series of repetitive segments that may or may not be interconnected to each other. This article focuses on the segmentation of
571:
1441:
223:, expressed in regular stripes down the length of the embryo. These transcription factors then regulate the expression of
1406:
1251:
979:
166:
951:
76:
composed of self-similar units, but usually it is the parts of an organism that are referred to as being segmented.
1208:
994:
989:
886:"Mouse but not zebrafish requires retinoic acid for control of neuromesodermal progenitors and body axis extension"
343:. The "clock" refers to the periodic oscillation in abundance of specific gene products, such as members of the
1506:
1385:
1236:
227:, which define the polarity of each segment. Boundaries and identities of each segment are later defined.
1203:
380:
1452:
1395:
1261:
1093:
1088:
340:
20:
308:
the embryological process of segmentation has been studied in many vertebrate groups, such as fish (
356:
294:
396:, or the segmented body armature of the chitons (which is not accompanied by a segmented coelom).
1329:
1266:
1241:
1124:
1044:
1314:
1213:
1198:
1068:
600:
Peel AD; Chipman AD; Akam M (2005). "Arthropod
Segmentation: Beyond The Drosophila Paradigm".
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1319:
1246:
1145:
1083:
1078:
1009:
944:
224:
371:), the wavefront also depends upon an opposing anterior-to-posterior decreasing gradient of
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1177:
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220:
118:
8:
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703:
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153:
1119:
910:
885:
861:
834:
810:
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687:
625:
487:
313:
101:
Segmentation in animals typically falls into three types, characteristic of different
1380:
1160:
1155:
1064:
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866:
815:
766:
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617:
575:
537:
479:
475:
1364:
786:"Mechanisms of retinoic acid signalling and its roles in organ and limb development"
491:
1390:
1359:
1354:
1309:
937:
905:
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89:
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420:
259:
126:
901:
1490:
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1466:
929:
643:
Weisblat DA; Shankland M (1985). "Cell lineage and segmentation in the leech".
216:
761:
744:
26:
1500:
1368:
1282:
1150:
984:
961:
393:
372:
333:
290:
177:
probably had three body regions, each with a unique combination of Hox genes.
173:) by up to three segments. Segments with maxillipeds have Hox gene 7. Fossil
711:
558:
Pick, L (1998). "Segmentation: Painting
Stripes From Flies to Vertebrates".
459:
328:). Segmentation in chordates is characterized as the formation of a pair of
1473:
1193:
1014:
1004:
919:
870:
819:
770:
729:
688:"Hedgehog signaling regulates segment formation in the annelid Platynereis"
664:
621:
541:
483:
170:
169:. The Hox genes 7, 8, and 9 correspond in these groups but are shifted (by
672:
579:
278:
1129:
1109:
360:
325:
232:
106:
1373:
1073:
1026:
851:
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317:
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138:
114:
102:
56:
30:
1485:
16:
Division of some animal and plant body plans into a series of segments
1324:
1292:
1059:
965:
368:
344:
339:
In vertebrates, segmentation is most often explained in terms of the
309:
282:
250:
188:
174:
162:
142:
122:
94:
48:
801:
613:
572:
10.1002/(SICI)1520-6408(1998)23:1<1::AID-DVG1>3.0.CO;2-A
1461:
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352:
212:
204:
158:
110:
64:
60:
1019:
364:
329:
321:
286:
130:
685:
999:
835:"Location, Location, Location: Signals in Muscle Specification"
52:
41:
254:
134:
45:
332:
on either side of the midline. This is often referred to as
1297:
376:
417: – Segmented body with a serial repetition of organs
745:"Understanding the somitogenesis clock: what's missing?"
117:
form segments from a field of equivalent cells based on
55:
body plans, specifically using the examples of the taxa
599:
642:
1450:
777:
423: – Embryonic precursor structures in vertebrates
297:, as well as periodic oscillation of gene expression.
289:
through a process that is reliant upon gradients of
262:, suggesting its common evolutionary origin in the
783:
429: – Transient structure in animal development
1498:
959:
945:
832:
359:signalling. In higher vertebrates including
161:in the body segments of different groups of
301:Although perhaps not as well understood as
952:
938:
453:
451:
449:
447:
445:
443:
187:segmentation is not representative of the
909:
883:
877:
860:
850:
809:
760:
742:
719:
531:
513:
351:end of the embryo and moves towards the
277:
152:
83:
25:
679:
557:
509:
507:
505:
503:
501:
440:
375:which limits the anterior spreading of
1499:
1442:Index of evolutionary biology articles
784:Cunningham, T.J.; Duester, G. (2015).
595:
593:
591:
589:
553:
551:
347:gene family. Expression starts at the
933:
833:Chang, CN; Kioussi, C (18 May 2018).
498:
457:
884:Berenguer, M.; et al. (2018).
586:
548:
40:in biology is the division of some
13:
1252:Evolutionary developmental biology
645:Philos Trans R Soc Lond B Biol Sci
238:
167:evolutionary developmental biology
33:have a segmented vertebral column.
14:
1518:
345:Hairy and Enhancer of Split (Hes)
219:. The pair-rule genes are mostly
1484:
1472:
1460:
1209:Evolution of sexual reproduction
839:Journal of Developmental Biology
476:10.1046/j.1525-142X.2001.01041.x
243:While not as well studied as in
121:gradients. Vertebrates like the
460:"Why are arthropods segmented?"
980:Genotype–phenotype distinction
826:
736:
636:
97:with 170 segments and 662 legs
1:
1237:Regulation of gene expression
433:
386:
148:
79:
70:
1407:Endless Forms Most Beautiful
1187:Evolution of genetic systems
995:Gene–environment correlation
990:Gene–environment interaction
533:10.1016/j.devcel.2004.08.008
273:
266:of arthropods and annelids.
129:to define segments known as
7:
1386:Christiane NĂĽsslein-Volhard
902:10.1016/j.ydbio.2018.06.019
408:
381:myogenic regulatory factors
10:
1523:
1262:Hedgehog signaling pathway
1139:Developmental architecture
145:cells to define segments.
18:
1439:
1418:
1347:
1275:
1229:
1222:
1186:
1138:
1102:
1089:Transgressive segregation
1035:
972:
762:10.1016/j.mod.2007.06.004
464:Evolution and Development
399:
341:clock and wavefront model
113:. Arthropods such as the
21:Segmentation contractions
790:Nat. Rev. Mol. Cell Biol
199:To properly segment the
19:Not to be confused with
1267:Notch signaling pathway
1242:Gene regulatory network
1125:Dual inheritance theory
712:10.1126/science.1188913
285:form segments known as
133:. Annelids such as the
1315:cis-regulatory element
1223:Control of development
1103:Non-genetic influences
1069:evolutionary landscape
665:10.1098/rstb.1985.0176
298:
253:, segmentation in the
225:segment polarity genes
178:
141:budded off from large
98:
34:
1507:Developmental biology
1426:Nature versus nurture
1330:Cell surface receptor
1247:Evo-devo gene toolkit
1146:Developmental biology
1084:Polygenic inheritance
1010:Quantitative genetics
281:
221:transcription factors
156:
87:
29:
1335:Transcription factor
1050:Genetic assimilation
1037:Genetic architecture
458:Budd, G. E. (2001).
119:transcription factor
1431:Morphogenetic field
1348:Influential figures
704:2010Sci...329..339D
657:1985RSPTB.312...39W
1120:Genomic imprinting
852:10.3390/jdb6020011
743:Cinquin O (2007).
299:
179:
99:
35:
1448:
1447:
1381:Eric F. Wieschaus
1343:
1342:
1161:Pattern formation
1065:Fitness landscape
698:(5989): 339–342.
514:Tautz, D (2004).
1514:
1489:
1488:
1477:
1476:
1465:
1464:
1456:
1391:William McGinnis
1360:Richard Lewontin
1355:C. H. Waddington
1227:
1226:
1204:Neutral networks
954:
947:
940:
931:
930:
924:
923:
913:
881:
875:
874:
864:
854:
830:
824:
823:
813:
781:
775:
774:
764:
755:(7–8): 501–517.
740:
734:
733:
723:
683:
677:
676:
640:
634:
633:
597:
584:
583:
555:
546:
545:
535:
511:
496:
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324:), and mammals (
125:use oscillating
90:Illacme plenipes
1522:
1521:
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1515:
1513:
1512:
1511:
1497:
1496:
1495:
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1471:
1459:
1451:
1449:
1444:
1435:
1414:
1401:Sean B. Carroll
1339:
1271:
1218:
1182:
1134:
1115:Maternal effect
1098:
1031:
968:
958:
928:
927:
882:
878:
831:
827:
802:10.1038/nrm3932
782:
778:
741:
737:
684:
680:
651:(1153): 39–56.
641:
637:
614:10.1038/nrg1724
608:(12): 905–916.
598:
587:
556:
549:
512:
499:
456:
441:
436:
421:Pharyngeal arch
411:
402:
389:
276:
241:
239:Annelids: Leech
217:pair-rule genes
165:, as traced by
151:
127:gene expression
82:
73:
24:
17:
12:
11:
5:
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1413:
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1383:
1378:
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1365:François Jacob
1362:
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1099:
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1096:
1094:Sequence space
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1076:
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1062:
1057:
1052:
1047:
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1033:
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1012:
1007:
1002:
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992:
987:
982:
976:
974:
970:
969:
957:
956:
949:
942:
934:
926:
925:
896:(1): 127–131.
876:
825:
796:(2): 110–123.
776:
735:
678:
635:
585:
547:
526:(3): 301–312.
516:"Segmentation"
497:
438:
437:
435:
432:
431:
430:
424:
418:
410:
407:
401:
398:
388:
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275:
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240:
237:
157:Expression of
150:
147:
81:
78:
72:
69:
15:
9:
6:
4:
3:
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1371:
1370:
1369:Jacques Monod
1366:
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1313:
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1308:
1306:
1303:
1299:
1296:
1295:
1294:
1291:
1289:
1286:
1284:
1283:Homeotic gene
1281:
1280:
1278:
1274:
1268:
1265:
1263:
1260:
1258:
1255:
1253:
1250:
1248:
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1234:
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1228:
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1215:
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1210:
1207:
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1189:
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1176:
1174:
1171:
1169:
1166:
1162:
1159:
1157:
1154:
1153:
1152:
1151:Morphogenesis
1149:
1147:
1144:
1143:
1141:
1137:
1131:
1128:
1126:
1123:
1121:
1118:
1116:
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1042:
1040:
1038:
1034:
1028:
1025:
1021:
1018:
1017:
1016:
1013:
1011:
1008:
1006:
1003:
1001:
998:
996:
993:
991:
988:
986:
985:Reaction norm
983:
981:
978:
977:
975:
971:
967:
963:
955:
950:
948:
943:
941:
936:
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932:
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903:
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891:
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868:
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848:
844:
840:
836:
829:
821:
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803:
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772:
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750:
746:
739:
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689:
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674:
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658:
654:
650:
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631:
627:
623:
619:
615:
611:
607:
603:
602:Nat Rev Genet
596:
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581:
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569:
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525:
521:
517:
510:
508:
506:
504:
502:
493:
489:
485:
481:
477:
473:
470:(5): 332–42.
469:
465:
461:
454:
452:
450:
448:
446:
444:
439:
428:
425:
422:
419:
416:
413:
412:
406:
397:
395:
394:Cycloneuralia
384:
382:
378:
374:
373:retinoic acid
370:
366:
362:
358:
354:
350:
346:
342:
337:
335:
334:somitogenesis
331:
327:
323:
319:
316:), reptiles (
315:
311:
307:
305:
296:
292:
291:retinoic acid
288:
284:
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271:
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265:
261:
256:
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236:
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108:
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96:
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91:
86:
77:
68:
66:
62:
58:
54:
50:
47:
43:
39:
32:
28:
22:
1405:
1298:eyeless gene
1194:Evolvability
1168:Segmentation
1167:
1045:Canalisation
1015:Heterochrony
1005:Heritability
973:Key concepts
893:
889:
879:
842:
838:
828:
793:
789:
779:
752:
748:
738:
695:
691:
681:
648:
644:
638:
605:
601:
563:
559:
523:
519:
467:
463:
403:
390:
338:
302:
300:
268:
244:
242:
229:
203:embryo, the
200:
198:
193:
182:
180:
171:heterochrony
137:use smaller
100:
88:
74:
38:Segmentation
37:
36:
1396:Mike Levine
1305:Distal-less
1130:Polyphenism
1110:Epigenetics
962:development
566:(1): 1–10.
367:, (but not
233:onychophora
139:blast cells
107:vertebrates
31:Vertebrates
1374:Lac operon
1199:Robustness
1178:Modularity
1173:Metamerism
1079:Plasticity
1074:Pleiotropy
1027:Heterotopy
434:References
427:Rhombomere
415:Metamerism
387:Other taxa
320:), birds (
318:Corn Snake
304:Drosophila
246:Drosophila
201:Drosophila
194:Drosophila
184:Drosophila
175:trilobites
149:Arthropods
103:arthropods
80:Embryology
71:Definition
57:Arthropoda
49:body plans
1325:Morphogen
1310:Engrailed
1293:Pax genes
1214:Tinkering
1060:Epistasis
1055:Dominance
966:phenotype
890:Dev. Biol
845:(2): 11.
560:Dev Genet
369:Zebrafish
349:posterior
310:Zebrafish
283:Zebrafish
274:Chordates
251:zebrafish
213:gap genes
209:posterior
189:arthropod
181:Although
163:arthropod
159:Hox genes
143:teloblast
123:zebrafish
115:fruit fly
95:millipede
1501:Category
1288:Hox gene
1276:Elements
1257:Homeobox
920:29964026
871:29783715
820:25560970
771:17643270
749:Mech Dev
730:20647470
622:16341071
542:15363406
520:Dev Cell
492:37935884
484:11710765
409:See also
353:anterior
264:ancestor
260:Hedgehog
205:anterior
196:embryo.
111:annelids
65:Annelida
61:Chordata
1491:Science
1479:Animals
1467:Biology
1453:Portals
1419:Debates
1230:Systems
1156:Eyespot
1020:Neoteny
911:6064660
862:6027348
811:4636111
721:3182550
700:Bibcode
692:Science
673:2869529
653:Bibcode
630:7230856
580:9706689
330:somites
322:Chicken
287:somites
131:somites
1320:Ligand
1000:Operon
918:
908:
869:
859:
818:
808:
769:
728:
718:
671:
628:
620:
578:
540:
490:
482:
400:Origin
314:Medaka
109:, and
63:, and
53:animal
42:animal
626:S2CID
488:S2CID
365:Chick
361:Mouse
326:Mouse
255:leech
135:leech
46:plant
960:The
916:PMID
867:PMID
816:PMID
767:PMID
726:PMID
669:PMID
618:PMID
576:PMID
538:PMID
480:PMID
377:FGF8
363:and
293:and
249:and
93:, a
44:and
964:of
906:PMC
898:doi
894:441
857:PMC
847:doi
806:PMC
798:doi
757:doi
753:124
716:PMC
708:doi
696:329
661:doi
649:312
610:doi
568:doi
528:doi
472:doi
357:FGF
295:FGF
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