Dab2 immunoreactivity in the developing choroid plexus, subcommissural organ and pineal gland. Sections through the hindbrain (Hb) at stages from E9.5 to E11.5 (A to C; B' and C' represent the high magnification of the boxes in B and C, respectively) show Dab2 expression in the roof plate of the hindbrain (arrows) and on scattered round cells (mononuclear phagocytes). Note that the adjacent hindbrain neuroepithelium is negative for Dab2 staining (arrowheads in B, C). Sections through the hindbrain (Hb) at stages from E12.5 to adulthood (D to G, D' is the higher magnification of the choroid plexus shown in D) show Dab2 staining in the choroid plexus (e.g. arrow in D) of the fourth ventricle (4V). Note the stronger Dab2 staining in the luminal (apical) surface of the epithelial cells as compared to the corresponding basal surface in embryos (arrowheads in D), but however, in the adult choroid plexus, the basal surface shows stronger Dab2 staining than the luminal (apical) surface of the epithelial cells (arrowheads in G). Also note the scattered and strongly Dab2 positive macrophages (arrows in D'). Sagittal sections show Dab2 staining in the subcommissural organ along the dorsal midline at different stages (H to K; H' and I' represent the higher magnification of the boxes in H and I, respectively). Note that Dab2 protein is expressed in the neuroepithelium of the subcommissural organ (sco) located in the roof plate of the diencephalon (Di). It lies underneath the posterior commissure (pc), anterior to the midbrain (Mb) (I', J, K). Also note the thin processes (arrows in I', J, K), which are also Dab2 positive, extending from the subcommissural organ into the posterior commissure. Coronal section (L) shows absence of Dab2 staining in the adult subcommissural organ. Double labeling of Dab2 (green, M) with PGP9.5 (red, M') shows that they are not co-localized (M"). Arrowheads in M indicate autofluorescence in blood cells. The sagittal section (N) shows Dab2 staining in the developing pineal gland (pg) along the dorsal midline at E16.5. Fb: forebrain; Mb: midbrain; Hb: hindbrain. Di: diencephalon. 4V: 4th ventricle; pc: posterior commissure; sco: subcommissural organ; pg: pineal gland. Scale bar: 50 μm.