Fig. 3. Patterning defects caused by overexpression of fgfA in sea urchin. Embryos overexpressing fgfA or treated with bFGF were observed at the early gastrula stage (A,B) or at 48 hours (C-H) or fixed at the mesenchyme blastula stage for in situ hybridization with a pax2/5/8 probe (I-L). fgfA overexpression induces radial (K) or broadened (L) expression of pax2/5/8. See text for details. vv, vegetal view. Arrows indicate the positions of the spicule rudiments; red square indicates the presence of an ectopic spicule.