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Embryonic expression of endogenous retroviral RNAs in somatic tissues adjacent to the Oikopleura germline.

Henriet S, Sumic S, Doufoundou-Guilengui C, Jensen MF, Grandmougin C, Fal K, Thompson E, Volff JN, Chourrout D - Nucleic Acids Res. (2015)

Bottom Line: Tor Env proteins are membrane-associated glycoproteins which exhibit some features of viral membrane fusion proteins.Such embryonic expression depends on determinants present in the Tor elements and not on their surrounding genomic environment.Our study shows that unusual modes of transcription and expression close to the germline may contribute to the proliferation of Tor elements.

View Article: PubMed Central - PubMed

Affiliation: Sars International Centre for Marine Molecular Biology, University of Bergen, Bergen, N-5008, Norway simon.henriet@sars.uib.no.

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Expression of Tor during development. (A) Schematic representation of the Oikopleura life cycle. (B) Tor expression in Oikopleura cDNA collected at different stages. (BA) The heat map represents variation of Tor expression as shown by cDNA hybridization on genomic tiling arrays. Hierarchical clustering reveals five groups of elements with similar expression, highlighted with squares on the heat map. (BB) RT-PCR profiling of piwi, brachyury and Tor env within 3 h pf. (BC) Northern blots performed with antisense env probes show Tor expression in poly-A+ RNA extracted either from embryos or from day 5 animals. The housekeeping gene rpl23 was used as a loading control. (C) WISH samples stained with NBT/BCIP show gene expression patterns obtained with antisense pol and env probes. Animals were collected at the tailbud stage or after hatching (CA). Yellow and blue arrows mark uncharacterized cells present in the epiderm and mesenchyme, respectively. Lines highlight positive cells in the notochord (green), tail muscle (red) and tail nerve chord (blue). The proportion of samples showing the same pattern is indicated. (CB) shows a magnified view of env signal in the tail. Dotted circles, muscle cell nuclei; white dots and arrows, notochord cell nuclei. (D) Double fluorescent WISH showing expression of Tor, vas4 and piwi. Samples were collected at 160 min pf for Tor4b-1 and at 180 min pf for the other probes. Probes were labelled with FITC (green) or Cy5 (red) and nuclei were stained with DAPI (blue). Arrows mark positive cells. Magnifications show signals in neighbouring cells or in the same cell for Tor3b-3 (yellow dotted circle). Scale bar, 5 μm. (E) WISH samples showing expression of piwi and env in day 5 and 6 animals: males (top), females (bottom). Magnification of the testis (top row) reveals follicular cells (arrows) present in day 5 animals at the interface between the gonad cavity (c) and the syncytium (s). Scale bar, 200 μm.
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Figure 4: Expression of Tor during development. (A) Schematic representation of the Oikopleura life cycle. (B) Tor expression in Oikopleura cDNA collected at different stages. (BA) The heat map represents variation of Tor expression as shown by cDNA hybridization on genomic tiling arrays. Hierarchical clustering reveals five groups of elements with similar expression, highlighted with squares on the heat map. (BB) RT-PCR profiling of piwi, brachyury and Tor env within 3 h pf. (BC) Northern blots performed with antisense env probes show Tor expression in poly-A+ RNA extracted either from embryos or from day 5 animals. The housekeeping gene rpl23 was used as a loading control. (C) WISH samples stained with NBT/BCIP show gene expression patterns obtained with antisense pol and env probes. Animals were collected at the tailbud stage or after hatching (CA). Yellow and blue arrows mark uncharacterized cells present in the epiderm and mesenchyme, respectively. Lines highlight positive cells in the notochord (green), tail muscle (red) and tail nerve chord (blue). The proportion of samples showing the same pattern is indicated. (CB) shows a magnified view of env signal in the tail. Dotted circles, muscle cell nuclei; white dots and arrows, notochord cell nuclei. (D) Double fluorescent WISH showing expression of Tor, vas4 and piwi. Samples were collected at 160 min pf for Tor4b-1 and at 180 min pf for the other probes. Probes were labelled with FITC (green) or Cy5 (red) and nuclei were stained with DAPI (blue). Arrows mark positive cells. Magnifications show signals in neighbouring cells or in the same cell for Tor3b-3 (yellow dotted circle). Scale bar, 5 μm. (E) WISH samples showing expression of piwi and env in day 5 and 6 animals: males (top), females (bottom). Magnification of the testis (top row) reveals follicular cells (arrows) present in day 5 animals at the interface between the gonad cavity (c) and the syncytium (s). Scale bar, 200 μm.

Mentions: To better understand the mechanisms by which Tor elements proliferate, we studied the expression of pol and env during development. We first tested for the presence of transcripts in cDNA samples prepared at successive developmental stages using RT-PCR and hybridizations on genome tiling arrays (23) (Figure 4B and Supplementary Figure S5C). Both techniques showed that for most elements, Tor RNA seemed to be absent or present in very low amounts during the first hours of development. Embryonic expression of Tor was first detected between 80 and 100 min pf, during early gastrulation (29) (Figure 4BB). On tiling arrays, we found that 29 out of 100 elements showed significant expression during tailbud and hatching stages (Figure 4BA). Among these, 13 elements were expressed only during embryogenesis, with the highest levels at tailbud or hatching stages. Other elements were expressed mainly after the larval tailshift. RT-PCR assays were in agreement with the tiling array data and for three Tor3b/4b elements we also confirmed the presence of gRNA and env mRNA in embryos (Figure 4BC). Expression profiling showed that for most Tor elements, increases in gene expression occurred during specific developmental stages. We next checked if Tor RNA is present in somatic tissues or in the germ line.


Embryonic expression of endogenous retroviral RNAs in somatic tissues adjacent to the Oikopleura germline.

Henriet S, Sumic S, Doufoundou-Guilengui C, Jensen MF, Grandmougin C, Fal K, Thompson E, Volff JN, Chourrout D - Nucleic Acids Res. (2015)

Expression of Tor during development. (A) Schematic representation of the Oikopleura life cycle. (B) Tor expression in Oikopleura cDNA collected at different stages. (BA) The heat map represents variation of Tor expression as shown by cDNA hybridization on genomic tiling arrays. Hierarchical clustering reveals five groups of elements with similar expression, highlighted with squares on the heat map. (BB) RT-PCR profiling of piwi, brachyury and Tor env within 3 h pf. (BC) Northern blots performed with antisense env probes show Tor expression in poly-A+ RNA extracted either from embryos or from day 5 animals. The housekeeping gene rpl23 was used as a loading control. (C) WISH samples stained with NBT/BCIP show gene expression patterns obtained with antisense pol and env probes. Animals were collected at the tailbud stage or after hatching (CA). Yellow and blue arrows mark uncharacterized cells present in the epiderm and mesenchyme, respectively. Lines highlight positive cells in the notochord (green), tail muscle (red) and tail nerve chord (blue). The proportion of samples showing the same pattern is indicated. (CB) shows a magnified view of env signal in the tail. Dotted circles, muscle cell nuclei; white dots and arrows, notochord cell nuclei. (D) Double fluorescent WISH showing expression of Tor, vas4 and piwi. Samples were collected at 160 min pf for Tor4b-1 and at 180 min pf for the other probes. Probes were labelled with FITC (green) or Cy5 (red) and nuclei were stained with DAPI (blue). Arrows mark positive cells. Magnifications show signals in neighbouring cells or in the same cell for Tor3b-3 (yellow dotted circle). Scale bar, 5 μm. (E) WISH samples showing expression of piwi and env in day 5 and 6 animals: males (top), females (bottom). Magnification of the testis (top row) reveals follicular cells (arrows) present in day 5 animals at the interface between the gonad cavity (c) and the syncytium (s). Scale bar, 200 μm.
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Related In: Results  -  Collection

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Figure 4: Expression of Tor during development. (A) Schematic representation of the Oikopleura life cycle. (B) Tor expression in Oikopleura cDNA collected at different stages. (BA) The heat map represents variation of Tor expression as shown by cDNA hybridization on genomic tiling arrays. Hierarchical clustering reveals five groups of elements with similar expression, highlighted with squares on the heat map. (BB) RT-PCR profiling of piwi, brachyury and Tor env within 3 h pf. (BC) Northern blots performed with antisense env probes show Tor expression in poly-A+ RNA extracted either from embryos or from day 5 animals. The housekeeping gene rpl23 was used as a loading control. (C) WISH samples stained with NBT/BCIP show gene expression patterns obtained with antisense pol and env probes. Animals were collected at the tailbud stage or after hatching (CA). Yellow and blue arrows mark uncharacterized cells present in the epiderm and mesenchyme, respectively. Lines highlight positive cells in the notochord (green), tail muscle (red) and tail nerve chord (blue). The proportion of samples showing the same pattern is indicated. (CB) shows a magnified view of env signal in the tail. Dotted circles, muscle cell nuclei; white dots and arrows, notochord cell nuclei. (D) Double fluorescent WISH showing expression of Tor, vas4 and piwi. Samples were collected at 160 min pf for Tor4b-1 and at 180 min pf for the other probes. Probes were labelled with FITC (green) or Cy5 (red) and nuclei were stained with DAPI (blue). Arrows mark positive cells. Magnifications show signals in neighbouring cells or in the same cell for Tor3b-3 (yellow dotted circle). Scale bar, 5 μm. (E) WISH samples showing expression of piwi and env in day 5 and 6 animals: males (top), females (bottom). Magnification of the testis (top row) reveals follicular cells (arrows) present in day 5 animals at the interface between the gonad cavity (c) and the syncytium (s). Scale bar, 200 μm.
Mentions: To better understand the mechanisms by which Tor elements proliferate, we studied the expression of pol and env during development. We first tested for the presence of transcripts in cDNA samples prepared at successive developmental stages using RT-PCR and hybridizations on genome tiling arrays (23) (Figure 4B and Supplementary Figure S5C). Both techniques showed that for most elements, Tor RNA seemed to be absent or present in very low amounts during the first hours of development. Embryonic expression of Tor was first detected between 80 and 100 min pf, during early gastrulation (29) (Figure 4BB). On tiling arrays, we found that 29 out of 100 elements showed significant expression during tailbud and hatching stages (Figure 4BA). Among these, 13 elements were expressed only during embryogenesis, with the highest levels at tailbud or hatching stages. Other elements were expressed mainly after the larval tailshift. RT-PCR assays were in agreement with the tiling array data and for three Tor3b/4b elements we also confirmed the presence of gRNA and env mRNA in embryos (Figure 4BC). Expression profiling showed that for most Tor elements, increases in gene expression occurred during specific developmental stages. We next checked if Tor RNA is present in somatic tissues or in the germ line.

Bottom Line: Tor Env proteins are membrane-associated glycoproteins which exhibit some features of viral membrane fusion proteins.Such embryonic expression depends on determinants present in the Tor elements and not on their surrounding genomic environment.Our study shows that unusual modes of transcription and expression close to the germline may contribute to the proliferation of Tor elements.

View Article: PubMed Central - PubMed

Affiliation: Sars International Centre for Marine Molecular Biology, University of Bergen, Bergen, N-5008, Norway simon.henriet@sars.uib.no.

Show MeSH
Related in: MedlinePlus