primitive ectoderm



Overview

A single cell layer of extraembryonic, post-mitotic ectodermal cells bounding the embryo. The primitive ectoderm forms during Stage 2 and is thought to degenerate as the definitive epidermis forms during Stages 5-7.

 

primitive ectoderm

 

"PRIMITIVE ECTODERM" TERM REFERENCES

OCLC:20423827 , OCLC:464776945 , OCLC:82522822 , PLANA_REF:0000001

 

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Tissue Description

 

Sphere formation begins during S2 when some of the blastomeres exit the cell cycle and commit to primitive ectoderm fate (Hallez, 1887; Ijima, 1884; Le Moigne, 1963; Metschnikoff, 1883). These cells flatten, elaborate numerous processes, and ultimately generate a single cell layer bounding the sphere. The number of primitive ectoderm cells varied, with a mean of 21.5 +/- 2.9 per S3 embryo (Figure 1 – figure supplement 11 B). This observation is consistent with primitive ectoderm cell number estimations in Polycelis nigra embryos (Le Moigne, 1963). Moreover, the primitive ectoderm cell number remained constant during S4 as the embryo ingested yolk and increased in volume (Figure 1 – figure supplement 11 B-C). Consistent with this finding, cycling cells were not observed in the primitive ectoderm (Figure 3 A-E). Pan-embryonic cell markers, including EF1a-like-1 (SMED30004295), EF1a-like-2 (SMED30012165), and eIF4a-like (SMED30003202) were expressed in primitive ectoderm cells of S2-S3 embryos, (Figure 2A-B, Figure 5 E, Figure 5 – source data 3). gelsolin-like (SMED30014940) was expressed in blastomeres during S2, and primitive ectoderm cells and the temporary embryonic pharynx in S3-S4 embryos (Figure 1 – figure supplement 11 D). gelsolin-like mRNA was detected throughout the primitive ectoderm cell layer, with concentrated perinuclear staining. spondin-1-like (SMED30032088) was frequently detected in blastomeres during S2, and was expressed in primitive ectoderm cells with star-like morphology, as well as parenchymal cells, in S3-S4 embryos (Figure 1 – figure supplement 11 E).  Early embryo enriched (EEE) transcripts were not detected in the primitive ectoderm beyond S4 (Figure 5 – source data 3).

 

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Figures

Figure 1 – figure supplement 11: Molecular markers for the primitive ectoderm

A: Average RPKM values per embryo for primitive ectoderm markers gelsolin-like (SMED30014940, blue) and spondin1-like (SMED30032088, red) during embryogenesis, Y (yolk), S2-S8.  

B-C: The number of primitive ectoderm cells remained constant while embryo volume increased during S3-S4. Primitive ectoderm cell nuclei were scored in SPIM reconstructed S3 and S4 embryos. B) S3: Average number of primitive ectoderm nuclei per embryo: 21.5 +/- 2.9. S4: Average number of primitive ectoderm nuclei per embryo: 22 +/- 1.4. n=5 embryos. Unpaired t-test, two tailed p value = 0.72.  C) Average S3 embryo volume: 7.4 x 107 µm3. Average S4 embryo volume: 1.5 x 108 µm3. Unpaired t-test, two tailed p value = 0.01. Embryo volumes were calculated by generating a masked surface in Imaris. Embryos scored, S3: n= 22. S4: n=5. Error bars: Standard deviation of the mean.

 D-E: gelsolin-like (D) and spondin1-like (E) expression (blue) during embryogenesis, S2-S8. Black arrowheads: temporary embryonic pharynx. Red arrowheads: definitive pharynx. Yellow arrows: primitive ectoderm cells. O: oral hemisphere. A: aboral hemisphere. V: ventral. Scale bars: 100 µm.

 

 

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In Situ Hybridization Data

Smed IDAccessionNameAliasEnriched during stage(s)Tissue/PatternImages
SMED30003202SMED30003202eIF4a-likeStage 2, Stage 3, Stage 4blastomere, primitive ectoderm, temporary embryonic pharynx
SMED30014940SMED30014940gelsolin-likeStage 2, Stage 3, Stage 4primitive ectoderm, temporary embryonic pharynx
SMED30018602SMED30018602DDX5-likeStage 2, Stage 3, Stage 4blastomere, primitive ectoderm, temporary embryonic pharynx
SMED30025427SMED30025427tct-likeStage 2, Stage 3, Stage 4blastomere, primitive ectoderm, temporary embryonic pharynx
SMED30027646SMED30027646BTF3-likeStage 2, Stage 3, Stage 4blastomere, primitive ectoderm, temporary embryonic pharynx
SMED30032088SMED30032088spondin1-likeStage 2, Stage 3, Stage 4blastomere, primitive ectoderm
SMED30033466SMED30033466blastomere, neoblast, primitive ectoderm, temporary embryonic pharynx

 

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Sequences

smed_20140614 transcript sequences for genes validated by in situ hybridization (above).

>SMED30033466 ID=SMED30033466|Name=SMED30033466|organism=Schmidtea mediterranea sexual|type=transcript|length=421bp
GATCTCACTATATAAATAAGTATTTGTCCCTATTAATTCATAACAATTATTCAACATGTCTGGTCGAGGTAAAGGAGGAA
AAGGACTAGGAAAAGGTGGAGCAAAGCGTCACAGAAAAGTCCTTCGTGATAACATTCAAGGTATCACAAAGCCAGCAATC
AGAAGATTAGCTCGTCGAGGTGGTGTTAAGAGAATTTCTGGATTGATATATGAAGAAACCCGAGGTGTTCTTAAAGTATT
CTTGGAAAATGTTATTAGAGACGCTGTGACATACACTGAGCACGCTAAGCGCAAGACAGTAACTGCCATGGATGTCGTCT
ATGCTTTGAAACGACAAGGAAGAACTTTGTACGGTTTTGGAGGTTAAATAACACTTTCATATTTGTGAATGTTTTAGCGG
CCCTCTTTAGGGCCACAAATG
>SMED30003202 ID=SMED30003202|Name=SMED30003202|organism=Schmidtea mediterranea sexual|type=transcript|length=1324bp
ATTAATAACAATGGAAAATCCAGGAGAAATAGAAAGTAATTACGACAAAATAGTTGAATCATTTGAAGATTTAAACTTAA
AAGAAGATTTGTTAAGAGGAATCTTTGCTTATGGTTTTGAAAAACCTTCTGCTATTCAGAAGCGTGCTATTTTGCCAGCT
ATTGAAGGTCACGATGTCATTGCCCAAGCACAATCTGGAACCGGAAAAACTGCCACTTTCAGTATTGCTGTTTTGCAGAA
TATTGACACTTCTATCAATTCTACACAAGCTATTATTCTAGCACCTACCAGAGAACTTGCAGTTCAAATCCACAAAGTTA
TAATGACCCTTGGTGACTATATGGGAGCTAAATGTTGCTCATGCATTGGTGGAAGAAATGTCCGTGACGACATTAACAAT
TTGGAAAGTGGAATGCATGTTGTTGTCGGTACTCCAGGACGAGTTAAAGATATGATAAAGAAGGGCCATATTAAATCAGA
TTTCGTGAAAATGTTTGTCCTTGATGAAGCCGATGAAATGTTGAGTCGAGGTTTTCAAAATGACGTTTGTGAATGCGTTC
AATATTTATCTGCCGAAACCCAAAATTTCATTCTTTCTGCAACAATGCCAGATGAAGTTTTAAAAGTCAGTAACGAATTC
ATGAATAATCCAGTGAAAATTCTCGTTAAAAAAGAGGAATTGACTCTGGAAGGTATTCGTCAATTCTACGTTAACGTTAG
CCAAGAAGAATACAAATTTGATACCTTATGTGATTTATATGAATCTCTGACCATCACCCAAGCTGTCATTTTCTGTAACT
TCAAAAACAAAGTTATATTTTTAAATGATAACTTGAAAAGTAAAGGATTTGTTGTTTCATCAGTCCACGGTGACATGGAG
CAACAAGCTAGAGACCAGATTATGAAAGAGTTCCGAAGTGGATCAAGTAGAATTCTCATCACCACAGATTTGCTATGCCG
AGGTATTGACGTCCAACAAGTCTCAATGGTCATTAATTATGATTTGCCTAAAAACAAAGAAAATTATATTCATCGAATTG
GCAGAGGAGGCCGATTCGGAAGGAAAGGAGTTGCACTAAATTTTGTCACAGACAAAGATATTGCTGAAATGCAGGAGCTG
GAAAATTTTTATAACACCAAGATTGAAGAGATGCCCATTAATTTATCTGAATTCTTATAAATGATTTACCGCTATTTTTG
TAAATAAATTTTAATTTACAATTAAATTAGGTTATTCATAACTTCCTTTGTTACGTAATTTTTGCTATCTTATCTATTTT
TGTTAGTAATGTATTTATGCTGCGTCACATTTTTGTTGCAAATT
>SMED30032088 ID=SMED30032088|Name=SMED30032088|organism=Schmidtea mediterranea sexual|type=transcript|length=1776bp
TTACCTGAAAATAGATTAAATGTTAAGAGTCTCTTTACGTCAGGCTGGTTAAATGGGGAAGAACAGCTAAATGAAGAGCG
TTCTGGATTCGTTTCTGTTAATAGAACTCATAATTTATTTAGTATGATTTCAATGATGGGACCAAGTCCGGATTGGTGTA
CCGGAGTGTCAGGAATCGATCTTTGTATGGACGGATGCAAATGGAAATCAAATCTAACAATTCCTCTTTATCCTATCGAC
GCTGGAATACAAACTGGAGAGACCTACAAACCAAATAATGTCACAAGACTTGATGAACCCGACACTATTAGAGAAATTAA
TAAAATTTGGATGAAAAGTAATCCTTTTACTCCAGATACTCCAGTAGCAGAAATCACCCTCACCAGAGTAGAGCCACAGA
AAGACACACAATGTGTTAAAACTCCAGTTAAGGGTGTAAATGAATTTCAAAATGCACAAAAAGAGTCTAGATCTAACACG
CTCGGTAGAAATGGTGCCGTGGAAAAATATAATGTTCTAGATGATCCTCAGTTAGCTCAAATGGCAAAAGCCTTTTGTGG
ATTTTCCGAATGGACCAGCTGGTCACCATGTTCCGTAAAATGTGGAGAAGGTGAAACGTCTCGTACTAGAAATTTGATAA
AAAACTTGAAAAATGAATTGTGTATTCAATTGCCAAGAAAGGAGCAAAAAAATTGTGCCGGTGCTCGATTGGAATGTGAT
CTCTCAAAGAAATGTAGTCTATTACCTTGGAGCTCATGGAGTCCGTGTTCTGCATCTTGTACAACTGAAGGGAAAATGAT
CAGAATTAGAAAATTTGCGAGGTCAAAAGAAAAGGACGAATGCATGAAAAACGTCAAACCAGAAATTATTCTTCAACAAG
TGAAAACTTGTAAATTGGATAAAACGGACTTCCGATGTGATCCGATATCAATTTGCAGCGCCGGTAAATTGGCACCTTGC
ATCAATGGTAAACCCAAGACGAGATTTTTCTACCACATCAAAACTGGAAAATGCGAACCGTTTAAATACTATGATTGCAA
AAAAGGAAATCTGAACAATTTCCCAACTATAGATTCATGTGAAAATGTTTGCTCTAAAGTTATTCAGGAATTACCAAAAA
TAAGACGATCTAATTTAGCCTTGCTTCAAGCAAGAACATCTTATTCAGCTGAAGAGAGTCTTTCGCAAAAAGCCAAAAAC
ATTCCGGAATTCTGCTTTCATGAAGTGGATTCCAGTAAGACCTGCATGAAATCCAAACCAAAGACAATCTGGTATTATAG
TCATCGAAATCGAAAATGCCAATCACTGGTGGATTATGATTGTAAAGGAACTTTAAATAAGTTTTCGACTTTCGACGATT
GCATGAAAACCTGCCGACCTGATTCACAACTCGAATCATTGAAACTTGATAAAGTAGATTGTCAGGTCTCTGAATGGAGT
TTATGGAGGCCATGTTCAAAGTCATGCGGTTGGGGAACTCAATACAAGAAAAGAGTCATTCAAAAGGATTCATTGAATGG
GGGCTTACCATGTCCGGTGCTATATGAATCTCGAAAATGCTTTTCCAAACCTTGTTAATCTGTCAATATTTATTTAAAAA
TTGTTTTTTGTGAATTATAATTTCTATTTCTTAATCTATTTGAAAATGTAATAAATATTACTTTGCGTATTTGATTTAGT
TTAAAGTTTTCTCATTGGTCAATCCGCCGTTGCTAACCAATGAGATCGGCTACTACATCAATTGCGATAATTGACAGTGG
TGAGCAAACCTTTAAG
>SMED30027646 ID=SMED30027646|Name=SMED30027646|organism=Schmidtea mediterranea sexual|type=transcript|length=541bp
AAATTAATTTGTTTAAATAAATTTCTTTAGAATCACGCAATGGACGGTTTTAAAATTAACACTGAAAAATTAGAAAAACT
TAGTAAGTTGTCGGAAAATGTCCGAACAGGTGGTAAAGGTACAATGAGACGAAAGAAGAAGGTCATTGTCAAGAGTTCAG
CAGCAGATGATAAGAAATTAGAGGCAACCTTCAAATCATTGTCAATGAGCCCGGTTCCAGTTGAAGAAGTAAACATGTTC
AAGGATGATGGAACTGTTATTAATTTCGTTAATCCAAAAGTCAATGTGTCACTTCCATGCAACACTCTCTCAGTTACTGG
AAAATCCGAAATTAAGCAATTGACCGAAATACTTCCAAAAGTTTGGCAACAACTTGGCCCACTTAAAGGAGATCTTTTCA
AGAAAATTGCACAAAACATGGAAAATCAAGCAACTGTCGAAGATATTGATGATGAAGACGATGACGTTCCAACTCTCGTC
ACAGACTTCGATCAACAAAGCAAATTGGAATAACTTTTTAATATCAATAAATTTTTTGGAC
>SMED30014940 ID=SMED30014940|Name=SMED30014940|organism=Schmidtea mediterranea sexual|type=transcript|length=530bp
CAAATAAATTTTCGTTTCGTAATTATTTAAATTTCACATGTTTTTTATTTAACTATAAATTCTGGAAAATAAATTAATTT
TACATTCAATTAATTCAAACAATGAAATTAGATTTTAAAAGTAAATCATTTCTAGAATTTTTTGTTTTTTAAACTTTCTA
AAAAGGAAACAACTACGGAGCAGTCGAAGAAGTTCTTGTCACCGGACACAGAAAGTCTGACAAAACCGGAATGATAAAAC
AAAAAAACTACGATTGGAAAGATTCCAATTTGGCTTTGTTTGGATCAGACACGGAAAAATTAGTAAAAAAAACTTCCGCT
GAAACCGAACCAGCATGGAGAGTTGCTAAGGCAACTACGGTTCCAGGTTTATTTGTTTGGAGAATAGAAAAATTCAAAGT
CATCAGTTTACCAAAGGAAGAATTCGGAAAATTTTACAATGGAGATTCTTACATTATTTTGAAAATCAATAAAGAAGAAG
ACAGTCCGGAGTTGCTATACGATGTGCATTTTTGGATTGGAAAATATTCT
>SMED30018602 ID=SMED30018602|Name=SMED30018602|organism=Schmidtea mediterranea sexual|type=transcript|length=607bp
TATTCAAAAGATAAACGATTGTTAGAAGTTGTTAGCAAAACTCCACGGGACAAAATGATTGTGTTCGCAGAAACGAAAAG
GAAAGCTGATATGATTTGTTCTTTCCTACGTTCAAAACAATTCAGAGTTGGTGCAATGCATGGAGATAAGTCACAGAGCG
ACAGAGAATATATTCTTAATGGGTTTCGAGGTGAAAATTTAAATATTCTCGTGGCAACAGATGTAGCAAGCAGGGGTTTA
GATGTTGATGATATTAAAGTTGTAATCAATTACGACTTCCCTATTCAATTTGAAGATTACATTCATAGAATCGGTAGGAC
AGGCCGACGAGGAAAATCCGGTGTGTCTTATACATTTTTCAATAGAAAGAATTCGAAAAGTGCTCGTCAATTGGTGAAAG
TGATGGAAGAAGCTAATCAATCAGTTTCAGATAGTTTGTATGATCTTGCATATATACCAAGAAGTGAGCGTAGACAAAAT
TTCAATCGTCCGCCAATGCCAGTGCCGCAAGTAAATAATTATCAAGTACCTCCGCCTCAATATAATGGTGGAAATAACAT
GTATCCGCAACCAGATTTATATATGCAAAACGGAGCAGCACATCACA
>SMED30025427 ID=SMED30025427|Name=SMED30025427|organism=Schmidtea mediterranea sexual|type=transcript|length=570bp
AAGTAATACTTTTATCATTTAATTGAAAAAATGCTCATTTACAAGGATATTGTTGCCGGCGATGAGTTGTGCTCTGATAC
ATTCCCAATGACGATTGTCGACGATGTCGTTTACGAATTCAACGGAAGAAATATTACTATTAAAAACGGTATTTCTGACG
CCCTCTTTGGTGGAAATGCTTCAGAGGAAGCTGCTGGCGATGATGACGTTGCTGATTCGGACGAGACAGCAATTGACATT
GTATACAGCAACCGATTAGTCGAAATGAGCTTTGACAAGAAAGGTTACACGAGTTACATCAAAGGTTACATGAAAAGTAT
TTTGGAAAGATTGAATGCCACTAATAAAGAACGAGCTGAAATCTTCAAATCCAAAGTCGGTGCCTATGTTACAAAAATCA
TCAAAAATTTTGATGAATATCGTTTCTACTGTGGAGAGTCAATGAACCCTGACGGAATGATCATTCCATGCAATTACAGA
GAAGACCAAATTACCCCATACTTTGTTCTCTTCAAAGATGGCCTCGAAGAAGAAAAATGCTAGATTTCTGTTAAATAAAT
TTAGTGGAAC

 

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References

Hallez, P. (1887). Embryogénie des Dendrocoeles d’eau douce, Vol 16.

Ijima, I. (1884). Untersuchungeniiber den Bau und die Entwicklungsgeschichte der stisswasser-Dendrocoelen(Tricladen). Vol Bd. 40.

Le Moigne, A. (1963). Etude du developpement embryonnaire de Polycelis nigra (Turbellarie - Triclade). Bulletin de la Societe Zoologique de France 88, 403-422.

Metschnikoff, E. (1883). Die embryologie von Planaria polychroa. Zeitschrift fur wissenschaftliche Zoologie 38, 331-354.

 

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