Fig. 4

Trh activates the hatching gland of medaka (O. latipes). (A) Schematic illustrations of the differences in hatching glands (arrowheads) between zebrafish and medaka. The zebrafish hatching gland is located on the yolk sac, whereas medaka HGCs line the palate and the gill area. (B) Immunolabeling of the Trh circuit in prehatching 7-dpf medaka embryos (left) and posthatching 8-dpf medaka embryos (right). Red arrowheads mark the location of hindbrain Trh projections in prehatching embryos. (C) Intracerebroventricular injection of medaka embryos. Brightfield images of a saline-injected embryo (top) and an embryo injected with Trh (bottom). Images on the right are magnified views of the boxed area in the corresponding left images that show HGCs (circled). The time elapsed from injection is shown at the top. (D) Quantification of hatching gland integrity in saline-injected (n = 5) and Trh-injected (n = 5) embryos. (E) Histochemistry [hematoxylin and eosin (H&E) staining] of the gill area of a noninjected, unhatched embryo (top left), unhatched embryos injected with saline (bottom left) or Trh (bottom right), and a naturally hatched embryo (top right). Pink-stained HGCs are marked with black arrowheads.