92:. The filopodia are 250 nm in diameter and 25 um long. At this point, the filopodia appear to move randomly along the surface of the inner blastocoel, making and breaking filopodial connections to the blastocoel wall. During the gastrula stage, once the blastopore has formed, the PMCs are localized within the prospective ventrolateral (from front to side) region of the blastocoel. It is here that they fuse into
80:
embryo, skeletal elements are exclusively produced by PMCs. Due to their nature in giving rise to the larval skeleton, they are sometimes called the skeletogenic mesenchyme. Certain SMCs have a skeletogenic potential, however, signals transmitted by the PMCs suppress this potential in the SMCs and
157:
The extent to which the molecular mechanisms underlying skeletogenesis in larval sea urchins has been characterized has led to comparative evolutionary developmental studies in distantly-related sea urchins, as well as other echinoderms, with the aim of understanding how this character has evolved.
145:
proteins has yet to be fully elucidated, but it is thought that they may function in the nucleation or orientation of crystal growth. It has also been found that the msp130 gene exhibits a complex pattern of spatial regulation within the PMC syncytium during skeletogenesis. It is suggested that the
131:
is also found associated with the syncytia and blastocoel wall. From gastrula to pluteus stages the skeleton grows in both size and complexity. Once the organism undergoes metamorphosis to form the juvenile sea urchin, the larval skeleton is “lost”, making its existence critical yet seemingly
174:
driving skeletogenic specification. However, there are also striking similarities in the signaling systems that position these cells in the embryo. Despite differences in timing of mesodermal ingression into the blastocoel and spatiotemporal differences in transcription factor gene expression,
144:
which has been implicated in calcium uptake and deposition, and SM50, SM30, and PM27 which are three proteins of the spicule matrix. SM50 and PM27 are thought to be structurally similar, nonglycosylated, basic proteins whereas SM30 is an acidic glycoprotein. The specific roles of these matrix
132:
transient in the overall life cycle of the sea urchin. The skeleton of the pluteus does, however, give rise to the spines of the juvenile sea urchin. These spines usually measure 1-3 centimeters in length and 1-2 millimeters thick, and in some species, may be poisonous.
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ancestral state reconstruction of genes critical to the specification of sea urchin skeletogenic cells supports the homology of this cell type, suggesting it arose some time before the divergence of cidaroids and euechinoids over 268 million years ago.
512:
Erkenbrack, E. M.; Ako-Asare, K.; Miller, E.; Tekelenburg, S.; Thompson, J. R.; Romano, L. (2016). "Ancestral state reconstruction by comparative analysis of a GRN kernel operating in echinoderms".
622:"A conserved role for VEGF signaling in specification of homologous mesenchymal cell types positioned at spatially distinct developmental addresses in early development of sea urchins"
349:"Skeletal morphogenesis in the sea urchin embryo: regulation of primary mesenchyme gene expression and skeletal rod growth by ectoderm-derived cues"
298:
Ettensohn CA, Ruffins SW. (1993). "Mesodermal cell interactions in the sea urchin embryo: properties of skeletogenic secondary mesenchyme cells".
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may play a role in controlling skeletal morphogenesis by regulating the expression of PMC-specific gene products involved in spicule biogenesis.
34:. The larval sea urchin does not resemble its adult form, because the sea urchin is an indirect developer, meaning its larva form must undergo
61:
812:
76:
cells in the sea urchin embryo, PMCs and secondary mesenchyme cells (SMCs), that regulates SMC fates and the process of skeletogenesis. In a
449:"Reorganization of sea urchin gene regulatory networks at least 268 million years ago as revealed by oldest fossil cidaroid echinoid"
279:
140:
The molecular mechanisms of skeletogenesis involve several PMC-specific gene products. These include Msp30, a sulfate cell-surface
447:
Thompson, Jeffrey R.; Petsios, Elizabeth; Davidson, Eric H.; Erkenbrack, Eric M.; Gao, Feng; Bottjer, David J. (2015-10-21).
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736:"Paleogenomics of echinoids reveals an ancient origin for the double-negative specification of micromeres in sea urchins"
565:"Conserved regulatory state expression controlled by divergent developmental gene regulatory networks in echinoids"
272:
171:
621:
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These studies, and others, have revealed that numerous differences have arisen during the evolution of the
679:"Cell type phylogenetics informs the evolutionary origin of echinoderm larval skeletogenic cell identity"
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Thompson, J. R.; Erkenbrack, E. M.; Hinman, V. F.; McCauley, B. R.; Petsios, E.; Bottjer, D. J. (2017).
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390:"Evolutionary rewiring of gene regulatory network linkages at divergence of the echinoid subclasses"
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and is of equal, although transient, importance in the development of the sea urchin, a marine
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Ettensohn CA. (1992). "Cell interactions and mesodermal cell fates in the sea urchin embryo".
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to form the juvenile adult. Here, the focus is on skeletogenesis in the sea urchin species
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cells (PMCs), the sole descendants of the large micromere daughter cells, undergo an
35:
23:
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127:. Upon reaching the pluteus stage (24 hours post fertilization), an abundance of
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of the larval skeletal rods, 13.5 hours post fertilization. Both optical
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Decker GL, Lennarz WJ. (1988). "Skeletogenesis in the sea urchin embryo".
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88:, the mesenchyme cells extend and contract long, thin processes called
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44:, as this species has been most thoroughly studied and characterized.
72:. It is a key interaction between the two principal populations of
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64:(EMT) and break away from the apical layer, thus entering the
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direct these cells into alternative developmental pathways.
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Erkenbrack, E. M.; Davidson, E. H.; Peter, I. S. (2018).
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Proceedings of the
National Academy of Sciences USA
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Proceedings of the
National Academy of Sciences USA
56:(9–10 hours post fertilization) when the primary
16:Embryonic developmental stage of the sea urchin
52:Skeletogenesis begins in the early sea urchin
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677:Erkenbrack, E. M.; Thompson, J. R. (2019).
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620:Erkenbrack, E. M.; Petsios, E. (2017).
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626:Journal of Experimental Zoology Part B
26:event in the embryonic development of
269:Developmental Biology: Eighth Edition
7:
388:Erkenbrack EM, Davidson EH. (2015).
14:
96:cables, forming the axis for the
62:epithelial–mesenchymal transition
123:indicated that the spicules are
68:, forming a cell cluster at the
514:Development Genes and Evolution
347:Guss KA, Ettensohn CA. (1997).
164:spatiotemporal gene expression
104:) (and a small amount, 5%, of
1:
271:. Sunderland, Massachusetts:
41:Strongylocentrotus purpuratus
813:Animal developmental biology
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695:10.1038/s42003-019-0417-3
526:10.1007/s00427-015-0527-y
273:Sinauer Associates, Inc.
761:10.1073/pnas.1610603114
415:10.1073/pnas.1509845112
366:10.1242/dev.124.10.1899
172:gene regulatory network
683:Communications Biology
312:10.1242/dev.117.4.1275
334:"SUE - P2M Animation"
215:10.1242/dev.103.2.231
168:transcription factors
48:Morphological changes
136:Molecular regulation
129:extracellular matrix
752:2017PNAS..114.5870T
647:10.1002/jez.b.22743
638:2017JEZB..328..423E
465:2015NatSR...515541T
406:2015PNAS..112E4075E
581:10.1242/dev.167288
453:Scientific Reports
746:(23): 5870–5877.
575:(24): dev167288.
473:10.1038/srep15541
359:(10): 1899–1908.
265:Gilbert, Scott F.
121:X-ray diffraction
98:calcium carbonate
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632:(5): 423–432.
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209:(2): 231–247.
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20:Skeletogenesis
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520:(1): 37–45.
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142:glycoprotein
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84:Once in the
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70:vegetal pole
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32:invertebrate
19:
18:
569:Development
353:Development
300:Development
238:Dev. Suppl.
203:Development
166:of several
125:crystalline
28:vertebrates
808:Echinoidea
802:Categories
179:References
160:sea urchin
86:blastocoel
74:mesodermal
66:blastocoel
58:mesenchyme
770:1091-6490
703:2399-3642
656:1552-5015
589:0950-1991
534:0949-944X
481:2045-2322
459:: 15541.
240:: 43–51.
162:clade in
153:Evolution
94:syncytial
90:filopodia
78:wild type
22:is a key
788:28584090
721:31069269
664:28544452
607:30470703
542:26781941
499:26486232
434:26170318
267:(2006).
147:ectoderm
113:spicules
54:blastula
779:5468677
748:Bibcode
712:6499829
689:: 160.
634:Bibcode
598:6307887
550:6067524
490:4614444
461:Bibcode
425:4522742
402:Bibcode
375:9169837
320:8404530
246:1299367
223:3066610
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538:PMID
530:ISSN
495:PMID
477:ISSN
430:PMID
371:PMID
316:PMID
276:ISBN
242:PMID
219:PMID
119:and
106:MgCO
774:PMC
756:doi
744:114
707:PMC
691:doi
642:doi
630:328
593:PMC
577:doi
573:145
522:doi
518:226
485:PMC
469:doi
420:PMC
410:doi
398:112
361:doi
357:124
308:doi
304:117
211:doi
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