Fig. 1. Temporal and spatial expression of nlk during sea urchin development. (A) Northern blot (e) Egg, (16) 16-cell stage, (60) 60-cell stage, (B1) very early blastula, (B3) early blastula, (B5) hatching blastula, (sB) swimming blastula, (mB) mesenchyme blastula, (eG) early gastrula, (G) gastrula, (Pr) prism, (Pl) pluteus. (B-Q) Spatial distribution of nlk and (R-Y) Delta transcripts. Embryos at the indicated stage were hybridized with sense (not shown) and antisense probes for nlk or Delta. (B) Egg, (C) 60 cell stage, (D) early blastula, (E) hatching blastula, (F,G,R,S) swimming blastula, (H,I,T,U) mesenchyme blastula, (J,K,V,W) early gastrula, (L,M,X) late gastrula, (N,O) prism, (P,Y) early pluteus, (Q) pluteus. All pictures are lateral views with the animal pole at the top and the oral side on the left, except G,I,K,M,O,S,U,W, which are (vv) vegetal pole views. Note the similarities in the salt and pepper expression pattern of nlk and Delta gastrula and early pluteus stages (arrows in panels N,P and X,Y).