Expression of Skn-1a in the developing main olfactory epithelia. (A) In situ hybridization with RNA probes for Skn-1a in coronal sections of mouse MOE at embryonic days 13.5 and 16.5 and postnatal days 0, 7, 14, and 30. The expression of Skn-1a was first detected at embryonic day 13.5 and was observed during subsequent development. The Skn-1a-expressing cells were located in apical, intermediate, and basal positions in the MOE during embryonic stages and were gradually restricted to apical and basal positions in postnatal development. (B) The expression of Skn-1a in the rostral-caudal axis of the MOE at postnatal day 7. Skn-1a expression was observed throughout the MOE, in terms of the rostral-caudal and the dorsal-ventral axis. (C) In the adult MOE, Skn-1a-expressing cells were distributed in graded fashion: low density in the dorsomedial region to high density in the lateral region. Left and right images are higher-magnification images of the dorsomedial and lateral regions (the areas enclosed by the dashed boxes in the center image), respectively. (D) In situ hybridization of signaling molecules in SCCs on coronal sections of adult MOE. Expression of Tas1r3, Tas2r105, Tas2r108, Gnat3, and Plcb2 was not observed. Only the signal of Trpm5 mRNA was detected in the superficial layer of the MOE. Scale bars: 50 μm in A and D, 500 μm in B and C.