Distinct Origins of Adult and Embryonic Blood in Xenopus

Abstract

Whether embryonic and adult blood derive from a single (yolk sac) or dual (yolk sac plus intraembryonic) origin is controversial. Here, we show, in Xenopus, that the yolk sac (VBI) and intraembryonic (DLP) blood compartments derive from distinct blastomeres in the 32-cell embryo. The first adult hematopoietic stem cells (HSCs) are thought to form in association with the floor of the dorsal aorta, and we have detected such aortic clusters in Xenopus using hematopoietic markers. Lineage tracing shows that the aortic clusters derive from the blastomere that gives rise to the DLP. These observations indicate that the first adult HSCs arise independently of the embryonic lineage.

Wnt/β-catenin signaling is involved in the induction and maintenance of primitive hematopoiesis in the vertebrate embryo

“…In Xenopus this compartment has a dual origin. The anterior part (aVBI) is derived from the dorsal mesoderm and can be traced back to blastomeres C1 and D1 of 32-cell stage embryos (14). In 16-cell stage embryos, this region can be targeted by injecting the CD1 blastomere (also called the D2.1).…”

Hematopoietic cytokines, transcription factors and lineage commitment

“…Developmentally, there are two waves of hematopoiesis, so probably with two corresponding origins for HSCs (Ciau-Uitz et al, 2000). Primitive hematopoiesis, distinguished from de®nitive hematopoiesis by large and nucleated erythrocytes and speci®cally expressed fetal hemoglobin isoforms, occurs as a transient wave preceding the advent of de®nitive hematopoiesis.…”

Migratory path of definitive hematopoietic stem/progenitor cells during zebrafish development

“…5 However, the singular hematopoietic origin from yolk sac/VBI is challenged by substantial evidence from experiments with various species that reveals another evolutionary conserved intraembryonic hematopoietic site: the para-aortic splanchnopleurae (pSP) and later referred as aorta-gonad-mesonephros (AGM). [6][7][8][9][10][11] Hence, it is currently believed that yolk sac/VBI mainly supports primitive hematopoiesis, whereas definitive hematopoiesis is autonomously initiated, at least in part, in the pSP/AGM region.…”

“…5 However, the singular hematopoietic origin from yolk sac/VBI is challenged by substantial evidence from experiments with various species that reveals another evolutionary conserved intraembryonic hematopoietic site: the para-aortic splanchnopleurae (pSP) and later referred as aorta-gonad-mesonephros (AGM). [6][7][8][9][10][11] Hence, it is currently believed that yolk sac/VBI mainly supports primitive hematopoiesis, whereas definitive hematopoiesis is autonomously initiated, at least in part, in the pSP/AGM region.The journey of definitive HSPCs is best characterized both temporally and spatially in mice. 4 Although multipotential hematopoietic progenitor cells revealed by in vitro colony assays, injection into yolk sac cavity, transplantation into fetal liver of newborn mice or reconstitution of immunodeficient mice, can be detected in the pSP/AGM region and yolk sac at earlier developmental stages, 12-15 the first definitive HSPCs, defined as cells fully competent to provide long-term reconstitution of irradiated adult recipients, emerge in the pSP/AGM region at embryonic day (E) 10.5.…”