Combinatorial control of vein and tip cell identity by Islet2 and
CoupTF transcription factors
Chang-Yi Wu1,2 and Sarah Childs2
1
Department of Biological Sciences, National Sun Yat-Sen University, Kaohsiung, Taiwan
2
Department of Biochemistry and Molecular Biology, University of Calgary, CANADA
Genetic programs and signaling pathways are required for proper growth and
patterning of blood vessels, however, little known about vein identity and intersegmental
vessels (ISV) patterning in zebrafish. Here, we identify that Islet2 (Isl2), a
LIM-homeodomain transcription factor is required for specification of the vein and ISV
growth. Isl2 mRNA and protein are expressed in vein as early as the 15-16 somite stage
of zebrafish, and knockdown of isl2 expression by morpholino results in decreased
numbers of vein cells and reduced expression of the vein specific markers, the VEGF-C
receptor (flt4), consistent with an effect on vein cell specification. In addition, loss of isl2
causes defect of ISV growth suggesting that isl2 can promote tip-stalk cells specification
through the regulation of flt4 expression. We confirmed the effect of isl2 knockdown is
autonomous to endothelial cells using cell transplantation. We also show that Isl2
expression is negatively regulated by Notch signaling. When Notch signaling is repressed
using an Rbpsuh morpholino or DAPT treatment, Isl2 expression is upregulated. These
data suggests that isl2 acts as an intermediate between notching signaling and flt4
expression, and promote vein specification and ISV growth. To date, only one
transcription factor CoupTFII, an orphan nuclear receptor, has been shown to be involved
in vein identity in mice. Here we show that transcription factor CoupTFIb (a family of
orphan nuclear receptors) is also involved in vein specification and ISV growth in
addition to isl2. To identify the molecular mechanism of vein and tip cell specification
controlled by coupTFIb and islet2, I performed microarray experiments. The results
showed highly overlapping downstream targets of coupTFIb and islet2, suggesting that
coupTFIb and islet2 cooperatively regulate endothelial cell identity.
Keywords: Angiogenesis, vein and tip cell identity, Notch signaling,
ISV (intersegmental vessel), zebrafish