Figure 5

Anteroposterior patterning of the digestive system in Priapulus caudatus . Whole-mount in situ hybridization in priapulid embryos at the gastrula and introvertula stage. (A-D) The foregut marker NK2.1 is expressed in the oral ectoderm at the gastrula stage, and in the mouth of the introvertula. (E-H) The apical ectoderm marker foxQ2 is expressed in the animal and oral ectoderm of the gastrula, as well as around the blastopore (black arrow in E). In the introvertula, foxQ2 is expressed in the mouth and developing nervous system (black arrows in G, H). (I-L) FGF8/17/18 is expressed in the animal ectoderm during gastrulation, and in mouth, anus, and six ectodermal clusters (black arrows in L) of the introvert during organogenesis. (M-P) The midgut markers GATA456 and (Q-T) HNF4 are expressed in anterior midgut cells (black arrows in O and S) at the introvertula stage. (U-X) The posterior markers wnt1 and (Y-AB) evx are expressed at the blastopore and vegetal pole during gastrulation, and in the posterior end of the trunk and anus at the introvertula stage. In all panels, the asterisk indicates the vegetal/posterior region. The pairs of arrowheads in C, G, K, O, S, W, and AA indicate the position of the introvert-trunk boundary. The schematic drawings of the gastrula and introvertula stage depict the reported expression domains. Drawings are not to scale. The slight elongation in the animal-vegetal axis of embryos at the gastrula stage is an artifact of fixation.