Figure 6. Expression domains within the coelomic pouch.

Double fluorescent in situ hybridization of six3 with vasa shows a tight apposition of their expression domains but a lack of co-localization (A–A′′′′). Z projection of six3 and vasa is seen in (A), and individual Z sections are seen from aboral to oral most locations in the embryo in (A′–A′′′′). Insets on panels A–A′′′′ show a zoomed perspective of just the left coelomic pouch apposed expression of six3 and vasa. six3 and eya were seen to overlap in the aboral coelomic pouch in both the Z projection (B) and Z sections (B′′ and B′′′) but not in Z sections (B′ or B′′′′). myosin expression was seen to be in the most oral expression domain of the coelomic pouch, distinct of six3 (C–C′′′′). An illustration demonstrating the expression domains observed in the coelomic pouch from our data and the data of Luo and Su, 2012 is displayed in (D) from both the lateral and oral views.

DOI: http://dx.doi.org/10.7554/eLife.08827.014

Figure 6—figure supplement 1. Spatial and temporal expression of homing genes by whole mount in situ hybridization.

Dach1, dachshund, is first detected early in development. It becomes spatially restricted around mesenchyme blastula to the coelomic pouch mesoderm (A3). During gastrulation, it is found throughout and at the tip of the archenteron in the presumptive coelomic pouch cells (A5-8) and is maintained in that tissue and gut throughout coelomic pouch coalescence with the small micromeres at the pluteus stage (A7-8). six3's earliest detectable expression is at early blastula (B1). It is found in the animal pole region, and expression in the coelomic pouch mesoderm begins around mesenchyme blastula (B3). Throughout gastrulation, six3 is found in the apical plate domain and the future coelomic pouch cells (B3-4). As was seen in Wei 2009, the six3 apical domain of expression is responsible for giving rise to neural fates. Post-gastrulation, six3 is expressed in both coelomic pouches (B8). Six1/2 is seen to be expressed in the NSM beginning at mesenchyme blastula (C3). It maintains expression in the NSM throughout early development and is in the coelomic pouches by early pluteus (C7). Genes activated at mid-gastrula stage at the tip of the archenteron and endure throughout gastrulation include foxc and eya. mRNA expression is detected in the coelomic pouch mesoderm at the tip of the archenteron and end up in the coelomic pouches. eya begins expression at mid-gastrula in the aboral coelomic pouch at the tip of the archenteron (D4). eya expression by 32 hpf is found in the left coelomic pouch (D8). pax6 expression begins at mid to late gastrula stage in the aboral coelomic pouch at the tip of the archenteron, roughly at the time of ectopic small micromere homing (E5), and by 32 hpf is found in the left coelomic pouch and two lateral patches of ectoderm presumed to be neural in fate (E8).

DOI: http://dx.doi.org/10.7554/eLife.08827.015