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Fig. 5. Diagram of an ommatidium and opsin mRNA expression in the swallowtail
butterfly Papilio glaucus, newly presented here. Methods used for the
in situ hybridizations are as detailed previously
(Briscoe et al., 2003). (A)
Longitudinal view of an ommatidium. In Papilio spp., the
photoreceptor cell bodies that contribute to the fused rhabdom are organized
into three tiers: I, II and III. c, cornea; cc, crystalline cone; n,
photoreceptor nucleus; L, lamina; M, medulla. (B) Tangential views of an
ommatidium. The most distal tier (I) contains the cell bodies of the R1 and 2
and R3 and 4 cells. The proximal tier (II) contains the cell bodies of the
R5–8 cells, and the basal tier (III) contains the R9 cell body. Gray
indicates the identity of the photoreceptor cells in which specific opsin mRNA
expression is shown in the panels to the right. (C) Digoxigenin-labeled
antisense riboprobe of UV (PglRh5) indicating the expression
of this opsin mRNA in the distal tier of photoreceptor cells. This opsin is
homologous to the UV opsin gene of P. xuthus, PxUV, shown in
Fig. 2. (D) A semi-tangential
section showing double labeling of R1 and R2 cells with antisense
biotin-labeled UV (PglRh5) (brown) and digoxigenin-labeled
B opsin mRNA (PglRh6) (blue). The latter is homologous to
the blue (B) opsin gene of P. xuthus, PxB, shown in
Fig. 2. Three subtypes of
ommatidia are evident: UV–UV, UV–B and B–B. (E) UV opsin
expression (red) in R1 and R2 cells using a rabbit anti-PglRh5 peptide
antibody generated by the author (see
Lampel et al., 2005) and
visualized with a Cy3-conjugated goat anti-rabbit secondary antibody.
Tangential section showing opsin staining in both the rhabdom (white arrow)
and cytoplasm. Two subtypes of ommatidia are shown here, UV–UV and
UV–?, although all three subtypes implied by D are present elsewhere in
the section. (F) Tangential section of the ventral retina showing staining of
all R3 and R4 cells with a digoxigenin-labeled antisense PglRh1
riboprobe. PglRh1 is homologous to P. xuthus PxRh1 shown in
Fig. 2. (G) Tangential view of
an adjacent section to F of the ventral retina showing staining of all R3 and
R4 cells with digoxigenin-labeled antisense PglRh2 riboprobe, and
indicating co-expression of PglRh1 and PglRh2 in these cells
in the ventral retina. In the dorsal eye, only PglRh2 is present in
the R3 and R4 cells (data not shown). (H) Longitudinal section of the eye
indicating staining of the proximal (R5–8) tier of photoreceptor cells
with a digoxigenin-labeled antisense riboprobe to PglRh3. (I)
Tangential section showing strong staining of the R5–8 cells (arrow) of
some ommatidia with a digoxigenin-labeled anti-sense riboprobe to
PglRh3. (J) Tangential section showing strong staining of the
R5–8 cells (arrow) of some ommatidia with a digoxigenin-labeled
antisense riboprobe to PglRh2. (K) Dissociated ommatidium in which
the R9 cell (arrow), but not the adjoining R5–8 cells, is clearly
stained with a digoxigenin-labeled antisense riboprobe to PglRh2.
This represents one (Type I) of three ommatidial subtypes defined by Arikawa
(Arikawa, 2003). (L)
Dissociated ommatidium in which both the R9 cell (arrow) and the R5–8
cells are clearly stained with a digoxigenin-labeled antisense riboprobe to
PglRh2. This ommatidial subtype corresponds to either the Type II or
Type III subtype (Arikawa,
2003).
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