Fig. 3.

Inhibition of mouth formation and ventral concentration of the nervous system in the sea urchin larvae. (A) Control S. purpuratus embryos cultured with 250 ng/mL BSA or DMSO. (B) Embryos treated with 250 ng/mL mBMP for 4 h during early gastrulation (from 24 to 28 h postfertilization). (C) Embryos treated with 250 ng/mL mBMP for 24 h (from 24 to 48 h postfertilization). (D) Embryos treated with 10 μM SB431542 (SB), a Nodal signaling inhibitor, for 4 h alone. (E) Cotreatment with SB and mBMP for 4 h blocked mouth formation and further centralized the nervous system to the ventral ectoderm. The first and fifth columns display the pluteus larval stage (4 d postfertilization), and the second, third, and fourth columns are embryos at the gastrula stage (2 d postfertilization). All images are side views unless indicated otherwise. VV, ventral view (viewed from the mouth opening side). The black asterisk denotes a mouth opening, indicating the ventral side; the white asterisk, lack of a mouth opening. The arrowhead denotes an opening of the hydropore, indicating the dorsal side, and the empty arrowhead denotes the ectodermal, stomodeal expression of bra and foxa. The data represent the phenotypes of most samples (>95%).