Lymphatic vessels arise from specialized angioblasts within a venous niche

Abstract

How cells acquire their fate is a fundamental question in developmental and regenerative biology. Multipotent progenitors undergo cell-fate restriction in response to cues from the microenvironment, the nature of which is poorly understood. In the case of the lymphatic system, venous cells from the cardinal vein are thought to generate lymphatic vessels through trans-differentiation. Here we show that in zebrafish, lymphatic progenitors arise from a previously uncharacterized niche of specialized angioblasts within the cardinal vein, which also generates arterial and venous fates. We further identify Wnt5b as a novel lymphatic inductive signal and show that it also promotes the ‘angioblast-to-lymphatic’ transition in human embryonic stem cells, suggesting that this process is evolutionarily conserved. Our results uncover a novel mechanism of lymphatic specification, and provide the first characterization of the lymphatic inductive niche. More broadly, our findings highlight the cardinal vein as a heterogeneous structure, analogous to the haematopoietic niche in the aortic floor.

Vegfc acts through ERK to induce sprouting and differentiation of trunk lymphatic progenitors

“…TD formation entails a complex migratory process in which Prox1-positive endothelial cells sprout from the posterior cardinal vein (PCV) beginning at 30 hpf (Koltowska et al, 2015;Nicenboim et al, 2015;Yaniv et al, 2006). After sprouting dorsally, Prox1-positive lymphatic endothelial cells branch laterally and sprout along the horizontal myoseptum as parachordal cells (PACs).…”

“…GFP immunostaining was performed as previously described (Covassin et al, 2006). Immunostaining for Prox1, ERK and Flt4 was performed using a protocol described elsewhere (Nicenboim et al, 2015) with some modifications. Briefly, embryos were permeabilized sequentially with water and PBSTw (PBS containing 0.1% Tween 20)/1% Triton X-100.…”

Development of the lymphatic system: new questions and paradigms

“…developmental stages that go beyond the established time window for LEC specification (∼22-36 hpf ) (Koltowska et al, 2015a;Nicenboim et al, 2015), these results might suggest a negative role for Bmp2b during LEC fate maintenance, rather than a role in the specification of LEC fate. The molecular mechanisms by which the two proposed functions of Bmp2b (inducer of venous cell fate and repressor of LEC specification) act in a coordinated manner remain unclear.…”

“…Although the exact developmental stage at which LEC progenitors become specified towards a lymphatic fate was suggested to differ between mice and zebrafish , recent reports suggest that the process is in fact similar in both species. At E9.5 in mice and at ∼24-36 hpf in zebrafish, the first Prox1-positive cells are detected in the CV, marking the onset of LEC specification (Koltowska et al, 2015a;Nicenboim et al, 2015;Wigle and Oliver, 1999). In mice, intersomitic veins represent an additional source of LECs (Yang et al, 2012).…”

“…The discovery that, like in mammals, Prox1a is detected in a subpopulation of pre-specified LECs within the PCV of zebrafish embryos, and is required for proper lymphatic development (Koltowska et al, 2015a;Nicenboim et al, 2015), clearly highlights the conservation of this process across vertebrate species. It seems likely that the generation of additional zebrafish maternal-zygotic Box 1.…”