Fig. 4. Distribution of the mouse Ush1 proteins in wild-type hair bundles during development. Hair bundles from E16.5, E18.5, P1 and P5 wild-type mouse cochlear sensory cells stained with phalloidin (red) and antibodies to myosin VIIa (Myo7a-F1, A-F), harmonin-b (harmonin-H1b, G-L), cadherin 23a (Cdh23-N1, M-P), or protocadherin 15a/b (Pcdh15-cter, Q-T) (green). Unless otherwise stated, views are from the basal cochlear turn. At E16.5, the four Ush1 proteins are detected in the actin-rich protrusions that grow on top of the newly differentiated hair cells, with a particular concentration at their actin-free distal end (A,G,M,Q). Similar distribution patterns are also observed later, at E18.5, in the stereocilia and surrounding hair cell microvilli, which have become distinguishable by their different lengths (B,H,N,R). Note in M and N the strong Cdh23-N1 signals at the tip of the tallest protrusions adjacent to the kinocilia (arrowheads), which are stained for acetylated tubulin (blue) in M and Q. During postnatal stages, both Cdh23-N1 and Pcdh15-cter signals become restricted to stereocilia tips (O,P,S,T), whereas the harmonin-H1b signal is relocalized from the tip to the tip link upper insertion region in tall and medium stereocilia (arrowheads in J-L). A new Myo7a-F1 signal is detected near stereocilia bases during this period of hair bundle development (C-F), and the shafts of the growing stereocilia also stain positive for myosin VIIa (not shown). Scale bars: 2 µm.