Fig. 2. Whole-mount in situ hybridization showing LvEndo16 transcription. At the hatched blastula (A) and mesenchyme blastula (B) stages (lateral views), LvEndo16 is expressed throughout the vegetal plate. Vegetal views (a,b) reveal that the PMCs (black arrow), which are derived from the center of the vegetal plate, do not express LvEndo16. As gastrulation proceeds, LvEndo16 is expressed throughout the invaginating archenteron, as seen in lateral (C) and vegetal (c) views. Near the end of gastrulation, LvEndo16 expression still extends throughout the archenteron (D). Expression is downregulated in SMCs (white arrow) as they ingress and migrate away from the tip of the archenteron. A lateral view (E) reveals that LvEndo16 expression also is downregulated in the anterior third of the archenteron (prospective foregut, asterisk) as it bends to make contact with the oral ectoderm. LvEndo16 continues to be expressed in the middle third (prospective midgut) and posterior third (prospective hindgut) of the archenteron. Lateral (F) and aboral (G) views show that LvEndo16 expression is completely extinguished in the prospective foregut, but is maintained in the prospective midgut (black arrowhead) and hindgut (white arrowhead) at the prism stage. LvEndo16 expression persists in both the midgut and hindgut of the pluteus larva until at least the four-arm stage (H-J). Scale bars: 50 µm for A-G; 100 µm for H-J.