Stem Cell Microenvironments and Beyond

37

FGF provides a precise temporal mechanism to both activate and inhibit its own
signaling activity to modulate HSC formation.
Work from the Currie laboratory found that not only does the somite provide
signals as the PLM migrates, but cells derived from the somite can migrate and form
a supportive niche within the dorsal aorta (Nguyen et  al. 2014 ). Zebrafish choker

Blood flow

Estrogen

Vegfa

Runx1

Gata2b

TgfβR2

Tnfα

Notch

Adenosine

NC

DA

CV

Somite

Granulocyte

IFN

A.

B.

Tgfβ1a/b

Notch

ligands

C.

Macrophage

Endothelial Cell

Hemogenic

Endothelial Cell

HSC

Runx1

Gata2b

c-Myb

Neural Crest

Progenitor

Wnt1 6

Fgf

Endotomal-derived

Cell

Cxcl8

G-csf

Fig. 4.2 The HSC specification niche. (a) Diagram showing the position within the zebrafish
shown in the panel (b) cross-section. (b) Diagram of a cross-section within the dorsal aorta HSC
specification niche in a zebrafish embryo. The legend is shown to the right. (c) The bottom panel
highlights the most recent findings on the signaling pathways involved in the HSC specification
niche. HSC hematopoietic stem cell, NC notochord, DA dorsal aorta, CV caudal vein, vegfa vascu-
lar endothelial growth factor a, FGF fibroblast growth factor, TGFβ 1 a/b-transforming growth
factor β 1 a/b, Tnfα tumor necrosis factor α, IFN interferon, Cxcl8-CXC chemokine ligand 8, Gcsf
granulocyte-colony stimulating factor

4 Developmental HSC Microenvironments: Lessons from Zebrafish