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Fig. 4. UV opsin immunoreactivity (-ir) in the retina, visualized with a secondary
antibody attached to Alexa Fluor 488 (green) or Cy3 (red). Cell nuclei were
stained with DAPI (blue). (A) Frontal section showing the distally twisted
rhabdomeres with UV opsin-ir (arrow). Note the strong autofluorescence of the
crystalline cones (cc). (B) Tangential section of the central part of the eye
showing three types of ommatidia, those with zero (double arrowhead), one
(single arrowhead) and two (arrows) UV opsin-ir rhabdomeres. An electron
microscopy study of the bumblebee fused rhabdom indicates that the rhabdomeres
of R1, 2 and 5,6 are physically separated by the rhabdomeres of the other
photoreceptor cells (Meyer-Rochow,
1981). (C) Semi-tangential section showing the heterogeneous UV
opsin-ir in the rhabdomeres of different ommatidia. Ommatidium with one
(arrowhead), two (arrows) and no (double arrowhead) UV opsin-ir retinula
cells. Note the UV opsin-ir vesicles (flecks) in the cell bodies adjacent to
the UV opsin-ir rhabdoms. (D) Tangential section showing UV opsin mRNA
expression in the cell bodies of R1 and R5 photoreceptor cells, visualized
with antisense digoxigenin-labeled riboprobes and an alkaline
phosphatase-conjugated anti-digoxigenin antibody. Dotted lines indicate the
boundaries of individual ommatidia. Three ommatidial types are shown, those
with zero, one or two UV opsin mRNA-expressing photoreceptor cells. (E)
Diagram of a longitudinal view of a single bee ommatidium showing the cornea
(c), crystalline cone (cc), primary pigment cells (darkly speckled), secondary
pigment cells (lightly speckled) and retinular cells (white) surrounding the
fused rhabdom (hatched). Tangential views of the three ommatidial types
observed in the Bombus retina with respect to UV opsin-ir (purple)
are shown. Numbers indicate retinula cells R18. The R1 and R5 cells are
UV opsin-ir, following the convention of Menzel and Blakers
(1976). Note that in ommatidia
in which only one rhabdomere is UV opsin-ir, that cell can be either the R1 or
R5 cell (only one shown). (F) Longitudinal section of the retina showing the
more densely packed UV opsin-ir dorsal rim area (Dra) (arrow). La, lamina; Re,
retina. Scale bars, 20 µm (A,C); 10 µm (B); 25 µm (D); 50 µm
(F).