The present study has identified a population of
cone photoreceptors in the murine retina that are uniquely
immunoreactive for protein kinase C (PKC). Wavelength-sensitive
cone subtypes are segregated along the dorso-ventral axis
in the mouse retina with ventral retina occupied exclusively
by ultraviolet wavelength-sensitive (UVWS) cones, and dorsal
retina dominated by middle wavelength-sensitive cones.
PKC-positive cones are found primarily in the ventral retina,
and double-label immunocytochemistry using a short wavelength-sensitive
opsin antibody confirms that they specifically correspond
to the UVWS cone subtype. The PKC antibody, as documented
in other mammals, also identifies rod bipolar cells in
the mouse retina. UVWS cones and bipolar cells have previously
been shown to share transcriptional regulatory elements,
as observed in transgenic mice encoding a portion of the
human SWS-opsin promoter controlling the lacZ
reporter gene. In such mice, the transgene product, β-galactosidase,
is expressed in populations of both cones and bipolar cells.
The present study confirms that lacZ-expressing
photoreceptors are indeed PKC-positive photoreceptors,
but that the lacZ-expressing bipolar cells are
not the PKC-positive rod bipolar cells. These cells must
correspond to a type of cone bipolar cell.