Type II hair cell processes in adult mouse utricles have a range of morphologies. All
images are from mice between 6 and 9 weeks of age. A–C are horizontal confocal
slices showing the basal portion (i.e., the cytoplasm below the waist) of type II hair
cells from the lateral extrastriolar region of an adult C57/Bl6 mouse utricle labeled with
antibodies to myosin VIIa (myo, green). A. The arrow points to a type II hair cell in
which the basal cytoplasm has a simple bulbous shape. B. The arrow points to the bulbous
portion of a type II hair cell from which two long processes (arrowheads) emerge. C. The
arrow points to the bulbous portion of a type II hair cell, and arrowheads point to its
processes. The circle indicates the approximate location and size of the cell body
(located in a more apical plane) relative to the basal portion. D,E. 3-D reconstructions
of the basal portions of calretinin-labeled type II hair cells from different slices of
the lateral extrastriolar region of a Swiss Webster mouse utricle. D = view from
the side of the cell. E = ¾ view from the top of the cell. 1 (cyan)
= hair cell with a simple bulbous basal portion. 2 (green) = hair cell
with 1–2 basolateral processes. 3 (red) = hair cell with 3 or more
basolateral processes. Some processes are obscured from view. F,G are ultrathin TEM
sections through the extrastriolar region of an adult CBA/CaJ mouse utricle. F. Transverse
section showing two type II hair cells (HCII) with basal processes (green tint,
arrows). The type II hair cell on the right has a lateral extension (upper arrowhead)
emanating from its basal process and passing under a type I hair cell (HCI).
The type II hair cell on the left has a foot process (lower arrowhead) that descends close
to a supporting cell nucleus (SC). G. Horizontal section at the level near the type I hair
cell and supporting cell nuclear layers showing a type II hair cell process (P, green
tint) extending laterally near supporting cell nuclei (SC). G, inset. The red circle
encompasses polyribosomes in the type II hair cell process at the position indicated in
the boxed region in G. Scale bars: A = 5 μm (applies to A–C); F
= 4 μm; and G = 4 μm.