Figure 5.

Notch1 is expressed by embryonic mouse OECs, while Jag1 and Jag2 are expressed by olfactory receptor neurons. Sections of the embryonic olfactory system in mouse (E14.5 parasagittal; E16.5 coronal). (A) In E14.5 mouse embryos, Notch1 is expressed by the basal layer of the olfactory epithelium and in the subventricular zone of the forebrain. (B) Higher‐power view of boxed region in (A), showing expression of Notch1 in the olfactory nerve layer around the olfactory bulb. (B¹) Same section as (B) immunostained for Tubb3‐positive axons, with a false‐colour overlay of Notch1. (C–D¹) At E16.5, Notch1 is expressed by OECs on the olfactory nerve and in the olfactory nerve layer of the olfactory bulb. (E–F¹) At E14.5, Jag1 is expressed by Tubb3‐positive olfactory receptor neurons and their axons (black/white arrowheads), in non‐neuronal apical support cells in the olfactory epithelium (yellow arrowheads), and in non‐neuronal cells close to the olfactory epithelium, likely mesenchymal cells of the lamina propria (black/white arrows). (G–H¹) By E16.5, Jag1 expression is restricted to apical (sustentacular) cells in the olfactory epithelium and to non‐neuronal cells apposed to the olfactory epithelium and near, but not directly associated with, Tubb3‐positive olfactory axons (most likely mesenchymal cells of the lamina propria, arrows). [NB Expression around the olfactory bulbs, seen at low‐power in (G), is not within the olfactory nerve layer but deep to it.] (I–J¹) At E14.5, Jag2 is expressed by all cells in the olfactory epithelium, though more weakly in the most apical cells (arrowheads, J,J¹). Jag2 expression can also be detected in olfactory axons (arrows). In contrast to Jag1, Jag2 is not expressed by mesenchymal cells in the lamina propria (compare with F,F¹). (K–L¹) By E16.5, expression of Jag2 is essentially reciprocal to Jag1: it remains strong in olfactory receptor neurons in the intermediate layer, and in basal progenitors, but is more weakly expressed by the most apical layer. No expression is seen in mesenchymal cells in the lamina propria (compare with H,H¹). [NB Expression around the olfactory bulbs, seen at low‐power in (K), is not within the olfactory nerve layer but deep to it.] FB, forebrain; OB, olfactory bulb; OE, olfactory epithelium; ON, olfactory nerve. Scale bar: 100 μm.