Zygotic hypoxia-inducible factor alpha regulates spicule elongation in the sea urchin embryo

Distinct regulatory states control the elongation of individual skeletal rods in the sea urchin embryo

“…The expression of Alx1 in skeletogenic cells at the tips of the body rods was also observed in Sun and Ettenshon 21 and Chang and Su . 23 A faint expression of VEGFR2 is detected in these cells at both time points and is reduced under VEGFR inhibition (Figures 2 and 3, panels K,M,N). The cells along the mid-ventral rods express the genes encoding the transcription factors Alx1 and Erg at the prism and pluteus stages, independently of late VEGF signaling (Figures 2 and 3, panels D,E,M,N).…”

“…Ets1/2 expression at the tips of the anterolateral rods was also observed in Chang and Su. 23 The expression of VEGFR in this domain is reduced in late VEGFR inhibition while the expression of the other regulatory genes is unchanged (Figures 2 and 3 panels C,J-K,N). The expression of erg and FGFR2 is observed in cells along the anterolateral rods at the prism stage, in both control and late VEGFR inhibition, and the expression of alx1 is detected in this domain only in late VEGFR inhibition, suggesting an inhibitory role of VEGF signaling on alx1 (Figure 1D,E,J-K,M,N).…”

“…21 Relatedly, as the spicules elongate, the expression of some skeletogenic genes becomes restricted to the cells proximal to the growing tips, possibly to enhance spicule growth at these sites (Figure 1C). [21][22][23] . As all the skeletogenic cells are connected through their cytoplasm, the regulation of localized gene expression within the skeletogenic-syncytium is quite intriguing.…”

“…A prominent regulator of skeletal growth and gene expression is the vascular endothelial growth factor (VEGF) signaling pathway. 7,11,15,16,21,23 At the gastrula stage, the VEGF ligand is secreted from two lateral ectodermal domains while the VEGF receptor (VEGFR) is F I G U R E 1 Sea urchin larval skeletogenesis and gene expression. (A) Sea urchin embryo at the gastrula stage.…”

“…A weak expression of VEGFR is also observed at the tips of the body rods, but VEGF is not expressed near these cells. 15 Accordingly, late inhibition of VEGF signaling inhibits the elongation of the postoral and distal anterolateral rods and downregulates the expression of skeletogenic genes at the tips of these rods, but not at the body rods (Figure 1C-H [21][22][23] ). Thus, VEGF signaling is one of the factors regulating localized gene expression and directing spicule growth, yet, little is known about the regulatory states at the tips of the rods and the mechanisms that mediate the transcriptional response to VEGF signaling.…”