BF are indispensable for BB alignment. (A) Live imaging of Odf2^{ΔEx6,7/ΔEx6,7} GFP-centrin2 MTECs in which the BBs lack BF. In the absence of BF, BBs transitioned from the floret to scatter pattern, but failed to develop into the alignment pattern. Stills are from Video 8, with time stamps shown in hours:minutes. (B) The Ia of eight cells from Odf2^{ΔEx6,7/ΔEx6,7}GFP-centrin2 MTECs remained low. A, alignment; F, floret P, partial alignment; S, scatter. (C) Disorganized BB array observed in the Odf2^{ΔEx6,7/ΔEx6,7}GFP-centrin2 tracheal cells lacking BF. The trachea was isolated from mice at postnatal 24 d. Bars, 10 µm.