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Cell-autonomous defects in thymic epithelial cells disrupt endothelial-perivascular cell interactions in the mouse thymus.

Bryson JL, Griffith AV, Hughes B, Saito F, Takahama Y, Richie ER, Manley NR - PLoS ONE (2013)

Bottom Line: We show that endothelial cells initially enter the thymus at E13.5, with PDGFR-β(+) mesenchymal cells following at E14.5.At subsequent stages there were fewer capillaries, leaky blood vessels, disrupted endothelium - perivascular cell interactions, endothelial cell vacuolization, and an overall failure of vascular organization.These data further demonstrate a novel TEC-mesenchyme-endothelial interaction required for proper fetal thymus organogenesis.

View Article: PubMed Central - PubMed

Affiliation: Department of Cellular Biology, University of Georgia, Athens, Georgia, USA.

ABSTRACT
The thymus is composed of multiple stromal elements comprising specialized stromal microenvironments responsible for the development of self-tolerant and self-restricted T cells. Here, we investigated the ontogeny and maturation of the thymic vasculature. We show that endothelial cells initially enter the thymus at E13.5, with PDGFR-β(+) mesenchymal cells following at E14.5. Using an allelic series of the thymic epithelial cell (TEC) specific transcription factor Foxn1, we showed that these events are delayed by 1-2 days in Foxn1 (Δ/Δ) mice, and this phenotype was exacerbated with reduced Foxn1 dosage. At subsequent stages there were fewer capillaries, leaky blood vessels, disrupted endothelium - perivascular cell interactions, endothelial cell vacuolization, and an overall failure of vascular organization. The expression of both VEGF-A and PDGF-B, which are both primarily expressed in vasculature-associated mesenchyme or endothelium in the thymus, were reduced at E13.5 and E15.5 in Foxn1 (Δ/Δ) mice compared with controls. These data suggest that Foxn1 is required in TECs both to recruit endothelial cells and for endothelial cells to communicate with thymic mesenchyme, and for the differentiation of vascular-associated mesenchymal cells. These data show that Foxn1 function in TECs is required for normal thymus size and to generate the cellular and molecular environment needed for normal thymic vascularization. These data further demonstrate a novel TEC-mesenchyme-endothelial interaction required for proper fetal thymus organogenesis.

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Related in: MedlinePlus

Electron Microscopic Analysis of E18.5 thymus vascular defects.Electron microscopy analysis of (A–B) Foxn1+/Δ thymus show compact arrangement of cells including endothelial cells and pericytes, while the (C–D) Foxn1Δ/Δ thymus display loose arrangement of cells, vacuolated endothelium, and indistinct vessel walls. Endothelial Cell (EC), Pericyte (P), Lumen of Blood Vessel (L), and Red Blood Cell (RBC) n = 3.
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pone-0065196-g007: Electron Microscopic Analysis of E18.5 thymus vascular defects.Electron microscopy analysis of (A–B) Foxn1+/Δ thymus show compact arrangement of cells including endothelial cells and pericytes, while the (C–D) Foxn1Δ/Δ thymus display loose arrangement of cells, vacuolated endothelium, and indistinct vessel walls. Endothelial Cell (EC), Pericyte (P), Lumen of Blood Vessel (L), and Red Blood Cell (RBC) n = 3.

Mentions: To investigate the origin of the ‘leaky’ vasculature phenotype identified by FITC-dextran injection (Figure 5B, D, F, H), we also assessed whether mature vessels with perivascular cell coverage developed in the Foxn1Δ/Δ thymus, based on a morphological analysis of endothelial cell-pericyte interactions. We observed pericytes associated with most vascular structures in the thymus (Figure 7A–D). Foxn1+/Δ thymi showed normal endothelial morphology and a compact arrangement of endothelium and pericytes (Figure 7A–B). In contrast, Foxn1Δ/Δ thymi showed vacuolated endothelium, edema, indistinct vessel walls, and an overall loose arrangement of cells due to separation and cellular swelling (Figure 7C–D). These results indicate that while endothelial cells in the Foxn1Δ/Δ thymus are competent to recruit perivascular cells, endothelium-pericyte interactions were altered and vascular patterning was defective in Foxn1Δ/Δ thymi.


Cell-autonomous defects in thymic epithelial cells disrupt endothelial-perivascular cell interactions in the mouse thymus.

Bryson JL, Griffith AV, Hughes B, Saito F, Takahama Y, Richie ER, Manley NR - PLoS ONE (2013)

Electron Microscopic Analysis of E18.5 thymus vascular defects.Electron microscopy analysis of (A–B) Foxn1+/Δ thymus show compact arrangement of cells including endothelial cells and pericytes, while the (C–D) Foxn1Δ/Δ thymus display loose arrangement of cells, vacuolated endothelium, and indistinct vessel walls. Endothelial Cell (EC), Pericyte (P), Lumen of Blood Vessel (L), and Red Blood Cell (RBC) n = 3.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3672159&req=5

pone-0065196-g007: Electron Microscopic Analysis of E18.5 thymus vascular defects.Electron microscopy analysis of (A–B) Foxn1+/Δ thymus show compact arrangement of cells including endothelial cells and pericytes, while the (C–D) Foxn1Δ/Δ thymus display loose arrangement of cells, vacuolated endothelium, and indistinct vessel walls. Endothelial Cell (EC), Pericyte (P), Lumen of Blood Vessel (L), and Red Blood Cell (RBC) n = 3.
Mentions: To investigate the origin of the ‘leaky’ vasculature phenotype identified by FITC-dextran injection (Figure 5B, D, F, H), we also assessed whether mature vessels with perivascular cell coverage developed in the Foxn1Δ/Δ thymus, based on a morphological analysis of endothelial cell-pericyte interactions. We observed pericytes associated with most vascular structures in the thymus (Figure 7A–D). Foxn1+/Δ thymi showed normal endothelial morphology and a compact arrangement of endothelium and pericytes (Figure 7A–B). In contrast, Foxn1Δ/Δ thymi showed vacuolated endothelium, edema, indistinct vessel walls, and an overall loose arrangement of cells due to separation and cellular swelling (Figure 7C–D). These results indicate that while endothelial cells in the Foxn1Δ/Δ thymus are competent to recruit perivascular cells, endothelium-pericyte interactions were altered and vascular patterning was defective in Foxn1Δ/Δ thymi.

Bottom Line: We show that endothelial cells initially enter the thymus at E13.5, with PDGFR-β(+) mesenchymal cells following at E14.5.At subsequent stages there were fewer capillaries, leaky blood vessels, disrupted endothelium - perivascular cell interactions, endothelial cell vacuolization, and an overall failure of vascular organization.These data further demonstrate a novel TEC-mesenchyme-endothelial interaction required for proper fetal thymus organogenesis.

View Article: PubMed Central - PubMed

Affiliation: Department of Cellular Biology, University of Georgia, Athens, Georgia, USA.

ABSTRACT
The thymus is composed of multiple stromal elements comprising specialized stromal microenvironments responsible for the development of self-tolerant and self-restricted T cells. Here, we investigated the ontogeny and maturation of the thymic vasculature. We show that endothelial cells initially enter the thymus at E13.5, with PDGFR-β(+) mesenchymal cells following at E14.5. Using an allelic series of the thymic epithelial cell (TEC) specific transcription factor Foxn1, we showed that these events are delayed by 1-2 days in Foxn1 (Δ/Δ) mice, and this phenotype was exacerbated with reduced Foxn1 dosage. At subsequent stages there were fewer capillaries, leaky blood vessels, disrupted endothelium - perivascular cell interactions, endothelial cell vacuolization, and an overall failure of vascular organization. The expression of both VEGF-A and PDGF-B, which are both primarily expressed in vasculature-associated mesenchyme or endothelium in the thymus, were reduced at E13.5 and E15.5 in Foxn1 (Δ/Δ) mice compared with controls. These data suggest that Foxn1 is required in TECs both to recruit endothelial cells and for endothelial cells to communicate with thymic mesenchyme, and for the differentiation of vascular-associated mesenchymal cells. These data show that Foxn1 function in TECs is required for normal thymus size and to generate the cellular and molecular environment needed for normal thymic vascularization. These data further demonstrate a novel TEC-mesenchyme-endothelial interaction required for proper fetal thymus organogenesis.

Show MeSH
Related in: MedlinePlus