Fig. 2. Whole-mount in situ hybridizations showing alx1 mRNA expression in S. purpuratus (A-H) and L. variegatus (I-L) embryos. (A) 56-cell stage embryo, the earliest stage at which alx1 mRNA is detectable in the four large micromeres (arrow). Initially, staining is limited to one to two small, intracellular spots in each cell. (B,C) Two focal planes of a 56-cell stage embryo, viewed along the animal-vegetal axis. Alx1 mRNA is present in the large micromeres (B, arrow) but not the small micromeres (C, arrow). (D,E) Lateral and vegetal views, respectively, of 128-cell stage embryos, showing alx1 mRNA in the eight progeny of the large micromeres (arrows). (F) Mid-blastula stage. (G) Mesenchyme blastula. (H) Late gastrula. Alx1 transcript continues to be restricted to large micromere progeny throughout blastula and gastrula stages (arrows). In L. variegatus, alx1 is expressed in a similar pattern, although expression is first detectable, by in situ hybridization, one cell cycle later than in S. purpuratus, after the large micromeres have divided once. (I) Blastula, showing expression in 16 large micromere progeny (arrow). (J) Early gastrula. (K) Mid-gastrula. (L) Late gastrula. Alx1-expressing PMCs are indicated by arrows. By the end of gastrulation, levels of Lvalx1 expression have declined in most embryos.

Return to article