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Stem cells in Nanomia bijuga (Siphonophora), a colonial animal with localized growth zones.

Siebert S, Goetz FE, Church SH, Bhattacharyya P, Zapata F, Haddock SH, Dunn CW - Evodevo (2015)

Bottom Line: No evidence for i-cells is found in the stem between maturing zooids.We provide the first evidence for i-cells in a siphonophore.This restriction of stem cells to particular regions in the colony, in combination with localized budding and spatial patterning during pro-bud subdivision, may play a major role in facilitating the precision of siphonophore growth.

View Article: PubMed Central - PubMed

Affiliation: Department of Ecology and Evolutionary Biology, Brown University, 80 Waterman St. Box GW, Providence, RI 02912 USA.

ABSTRACT

Background: Siphonophores (Hydrozoa) have unparalleled colony-level complexity, precision of colony organization, and functional specialization between zooids (i.e., the units that make up colonies). Previous work has shown that, unlike other colonial animals, most growth in siphonophores is restricted to one or two well-defined growth zones that are the sites of both elongation and zooid budding. It remained unknown, however, how this unique colony growth and development is realized at the cellular level.

Results: To understand the colony-level growth and development of siphonophores at the cellular level, we characterize the distribution of proliferating cells and interstitial stem cells (i-cells) in the siphonophore Nanomia bijuga. Within the colony, we find evidence that i-cells are present at the tip of the horn, the structure within the growth zone that gives rise to new zooids. Co-localized gene expression of vasa-1, pl10, piwi, nanos-1, and nanos-2 suggests that i-cells persist in the youngest zooid buds and that i-cells become progressively restricted to specific regions within the zooids until they are mostly absent from the oldest zooids. The examined genes remain expressed in gametogenic regions. No evidence for i-cells is found in the stem between maturing zooids. Domains of high cell proliferation include regions where the examined genes are expressed, but also include some areas in which the examined genes were not expressed such as the stem within the growth zones. Cell proliferation in regions devoid of vasa-1, pl10, piwi, nanos-1, and nanos-2 expression indicates the presence of mitotically active epithelial cell lineages and, potentially, progenitor cell populations.

Conclusions: We provide the first evidence for i-cells in a siphonophore. Our findings suggest maintenance of i-cell populations at the sites of growth zones and that these sites are the main source of i-cells. This restriction of stem cells to particular regions in the colony, in combination with localized budding and spatial patterning during pro-bud subdivision, may play a major role in facilitating the precision of siphonophore growth. Spatially restricted maintenance of i-cells in mature zooids and absence of i-cells along the stem may explain the reduced developmental plasticity in older parts of the colony.

No MeSH data available.


Related in: MedlinePlus

Co-localized vasa-1, pl10, piwi, nanos-1, and nanos-2 expression in palpons suggests absence of stem cells in mature bodies and spatial restricted pools of i-cells. a–f Gene expression in mature palpons is restricted to the palpacle base and structures at the base of the zooid. Palpons were stained for pl10 (a), piwi (b), nanos-1 (c), vasa-1 (d–e), and nanos-2 (f). e Close-up of the boxed region in d. vasa-1 expression is restricted to the proximal end of the palpacle base, developing bracts, and young female gonophores. fnanos-2 transcript in the basigaster region and the palpacle base. Anterior is to the left. g Semi-thin longitudinal section of the palpon base, stained with toluidine blue, reveals interstitial cells in the palpacle base and nematoblasts (nb) in the basigaster region. Anterior is to the left. h Palpon buds at the anterior end of a cormidium (black arrows) with vasa-1 expression. The sphincter region marks the posterior end of the preceding cormidium. At the site of a sphincter the hollow stem can be constricted. Anterior is to the right. i Close-up of an early palpon cluster bud (arrowhead). j Close-up of a later developmental stage of a palpon cluster with the palpon bud visible in the center and further buds laterally. ba basigaster, bb bract bud, ect ectoderm, end endoderm, fg female gonodendron, ic interstitial cell, m mesoglea, nb nematoblast, p palpon, pb palpon bud, pba palpacle base, sp sphincter, sst siphosomal stem
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Fig4: Co-localized vasa-1, pl10, piwi, nanos-1, and nanos-2 expression in palpons suggests absence of stem cells in mature bodies and spatial restricted pools of i-cells. a–f Gene expression in mature palpons is restricted to the palpacle base and structures at the base of the zooid. Palpons were stained for pl10 (a), piwi (b), nanos-1 (c), vasa-1 (d–e), and nanos-2 (f). e Close-up of the boxed region in d. vasa-1 expression is restricted to the proximal end of the palpacle base, developing bracts, and young female gonophores. fnanos-2 transcript in the basigaster region and the palpacle base. Anterior is to the left. g Semi-thin longitudinal section of the palpon base, stained with toluidine blue, reveals interstitial cells in the palpacle base and nematoblasts (nb) in the basigaster region. Anterior is to the left. h Palpon buds at the anterior end of a cormidium (black arrows) with vasa-1 expression. The sphincter region marks the posterior end of the preceding cormidium. At the site of a sphincter the hollow stem can be constricted. Anterior is to the right. i Close-up of an early palpon cluster bud (arrowhead). j Close-up of a later developmental stage of a palpon cluster with the palpon bud visible in the center and further buds laterally. ba basigaster, bb bract bud, ect ectoderm, end endoderm, fg female gonodendron, ic interstitial cell, m mesoglea, nb nematoblast, p palpon, pb palpon bud, pba palpacle base, sp sphincter, sst siphosomal stem

Mentions: In situ hybridization was performed on Friday Harbor specimens, Monterey Bay blue-water specimens, and ROV-collected specimens and yielded consistent expression patterns. Four ROV-collected colonies per gene in four independent rounds of in situ hybridization were analyzed in detail (Figs. 2, 3, 4, 5, and 6, Additional files 2, 3, 4, 5, and 6). ROV specimens are presented in the figures since their gonodendra were more mature. Specimens were transferred into a Petri dish coated with Sylgard 184 (Dow Corning Corporation) and relaxed by adding isotonic 7.5 % MgCl2·6H2O in Milli-Q water at a ratio of approximately 1/3 MgCl2 and 2/3 FSW. After pinning them out in a stretched position using insect pins (Austerlitz Insect Pins, 0.2mm, Fine science tools), they were fixed in 0.5 % glutaraldehyde/4 % paraformaldehyde (PFA) in FSW for 2 min and incubated in 4 % PFA in FSW overnight at 4 °C. Mature nectophores and bracts tend to get detached when handling specimens in the dish and were therefore not accessible for analysis in all cases. Specimens were then washed three times in PTw (phosphate buffer saline and 0.1 % Tween). Dehydration was performed using EtOH with 15-min washes in 25 % EtOH/PTw, 50 % EtOH/PTw, 75 % EtOH/Milli-Q water, 2 × 100 % EtOH and then transferred to MetOH and stored at −20 °C. Use of EtOH for dehydration was empirically found to minimize tissue sloughing, detachment of endoderm from ectoderm.Fig. 2


Stem cells in Nanomia bijuga (Siphonophora), a colonial animal with localized growth zones.

Siebert S, Goetz FE, Church SH, Bhattacharyya P, Zapata F, Haddock SH, Dunn CW - Evodevo (2015)

Co-localized vasa-1, pl10, piwi, nanos-1, and nanos-2 expression in palpons suggests absence of stem cells in mature bodies and spatial restricted pools of i-cells. a–f Gene expression in mature palpons is restricted to the palpacle base and structures at the base of the zooid. Palpons were stained for pl10 (a), piwi (b), nanos-1 (c), vasa-1 (d–e), and nanos-2 (f). e Close-up of the boxed region in d. vasa-1 expression is restricted to the proximal end of the palpacle base, developing bracts, and young female gonophores. fnanos-2 transcript in the basigaster region and the palpacle base. Anterior is to the left. g Semi-thin longitudinal section of the palpon base, stained with toluidine blue, reveals interstitial cells in the palpacle base and nematoblasts (nb) in the basigaster region. Anterior is to the left. h Palpon buds at the anterior end of a cormidium (black arrows) with vasa-1 expression. The sphincter region marks the posterior end of the preceding cormidium. At the site of a sphincter the hollow stem can be constricted. Anterior is to the right. i Close-up of an early palpon cluster bud (arrowhead). j Close-up of a later developmental stage of a palpon cluster with the palpon bud visible in the center and further buds laterally. ba basigaster, bb bract bud, ect ectoderm, end endoderm, fg female gonodendron, ic interstitial cell, m mesoglea, nb nematoblast, p palpon, pb palpon bud, pba palpacle base, sp sphincter, sst siphosomal stem
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4471933&req=5

Fig4: Co-localized vasa-1, pl10, piwi, nanos-1, and nanos-2 expression in palpons suggests absence of stem cells in mature bodies and spatial restricted pools of i-cells. a–f Gene expression in mature palpons is restricted to the palpacle base and structures at the base of the zooid. Palpons were stained for pl10 (a), piwi (b), nanos-1 (c), vasa-1 (d–e), and nanos-2 (f). e Close-up of the boxed region in d. vasa-1 expression is restricted to the proximal end of the palpacle base, developing bracts, and young female gonophores. fnanos-2 transcript in the basigaster region and the palpacle base. Anterior is to the left. g Semi-thin longitudinal section of the palpon base, stained with toluidine blue, reveals interstitial cells in the palpacle base and nematoblasts (nb) in the basigaster region. Anterior is to the left. h Palpon buds at the anterior end of a cormidium (black arrows) with vasa-1 expression. The sphincter region marks the posterior end of the preceding cormidium. At the site of a sphincter the hollow stem can be constricted. Anterior is to the right. i Close-up of an early palpon cluster bud (arrowhead). j Close-up of a later developmental stage of a palpon cluster with the palpon bud visible in the center and further buds laterally. ba basigaster, bb bract bud, ect ectoderm, end endoderm, fg female gonodendron, ic interstitial cell, m mesoglea, nb nematoblast, p palpon, pb palpon bud, pba palpacle base, sp sphincter, sst siphosomal stem
Mentions: In situ hybridization was performed on Friday Harbor specimens, Monterey Bay blue-water specimens, and ROV-collected specimens and yielded consistent expression patterns. Four ROV-collected colonies per gene in four independent rounds of in situ hybridization were analyzed in detail (Figs. 2, 3, 4, 5, and 6, Additional files 2, 3, 4, 5, and 6). ROV specimens are presented in the figures since their gonodendra were more mature. Specimens were transferred into a Petri dish coated with Sylgard 184 (Dow Corning Corporation) and relaxed by adding isotonic 7.5 % MgCl2·6H2O in Milli-Q water at a ratio of approximately 1/3 MgCl2 and 2/3 FSW. After pinning them out in a stretched position using insect pins (Austerlitz Insect Pins, 0.2mm, Fine science tools), they were fixed in 0.5 % glutaraldehyde/4 % paraformaldehyde (PFA) in FSW for 2 min and incubated in 4 % PFA in FSW overnight at 4 °C. Mature nectophores and bracts tend to get detached when handling specimens in the dish and were therefore not accessible for analysis in all cases. Specimens were then washed three times in PTw (phosphate buffer saline and 0.1 % Tween). Dehydration was performed using EtOH with 15-min washes in 25 % EtOH/PTw, 50 % EtOH/PTw, 75 % EtOH/Milli-Q water, 2 × 100 % EtOH and then transferred to MetOH and stored at −20 °C. Use of EtOH for dehydration was empirically found to minimize tissue sloughing, detachment of endoderm from ectoderm.Fig. 2

Bottom Line: No evidence for i-cells is found in the stem between maturing zooids.We provide the first evidence for i-cells in a siphonophore.This restriction of stem cells to particular regions in the colony, in combination with localized budding and spatial patterning during pro-bud subdivision, may play a major role in facilitating the precision of siphonophore growth.

View Article: PubMed Central - PubMed

Affiliation: Department of Ecology and Evolutionary Biology, Brown University, 80 Waterman St. Box GW, Providence, RI 02912 USA.

ABSTRACT

Background: Siphonophores (Hydrozoa) have unparalleled colony-level complexity, precision of colony organization, and functional specialization between zooids (i.e., the units that make up colonies). Previous work has shown that, unlike other colonial animals, most growth in siphonophores is restricted to one or two well-defined growth zones that are the sites of both elongation and zooid budding. It remained unknown, however, how this unique colony growth and development is realized at the cellular level.

Results: To understand the colony-level growth and development of siphonophores at the cellular level, we characterize the distribution of proliferating cells and interstitial stem cells (i-cells) in the siphonophore Nanomia bijuga. Within the colony, we find evidence that i-cells are present at the tip of the horn, the structure within the growth zone that gives rise to new zooids. Co-localized gene expression of vasa-1, pl10, piwi, nanos-1, and nanos-2 suggests that i-cells persist in the youngest zooid buds and that i-cells become progressively restricted to specific regions within the zooids until they are mostly absent from the oldest zooids. The examined genes remain expressed in gametogenic regions. No evidence for i-cells is found in the stem between maturing zooids. Domains of high cell proliferation include regions where the examined genes are expressed, but also include some areas in which the examined genes were not expressed such as the stem within the growth zones. Cell proliferation in regions devoid of vasa-1, pl10, piwi, nanos-1, and nanos-2 expression indicates the presence of mitotically active epithelial cell lineages and, potentially, progenitor cell populations.

Conclusions: We provide the first evidence for i-cells in a siphonophore. Our findings suggest maintenance of i-cell populations at the sites of growth zones and that these sites are the main source of i-cells. This restriction of stem cells to particular regions in the colony, in combination with localized budding and spatial patterning during pro-bud subdivision, may play a major role in facilitating the precision of siphonophore growth. Spatially restricted maintenance of i-cells in mature zooids and absence of i-cells along the stem may explain the reduced developmental plasticity in older parts of the colony.

No MeSH data available.


Related in: MedlinePlus