Unique regionalization and distribution of duplicated opsins in the eye of the Common Blue Bottle, Graphium sarpedon
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1
The Graduate University for Advanced Studies (Sokendai), School of Advanced Sciences, Japan
The compound eyes of butterflies are complex, typically with more than eight types of spectral receptors embedded in the ommatidia. Accumulated evidence indicates that the spectral organization of butterfly eyes is diverse among species. Some of the diversity is attributed to duplicated genes encoding visual pigment opsins. In the lineage of Papilionidae, duplication of long wavelength-absorbing (L) opsin occurred repeatedly. Three L opsins exist in Papilio (tribe Papilionini), while only two exist in Parnassius (tribe Parnassini). We here studied the eyes of the Common Blue Bottle, Graphium sarpedon, belonging to the tribe Leptocircini, and found a unique pattern of opsin expression.
First we identified five mRNAs encoding opsins of an ultraviolet- (GsUV), a blue- (GsB) and three long wavelength (L)-absorbing visual pigments. All three L opsins are orthologs of Papilio L opsins (L1-L3), but a phylogenetic analysis reveals that two of them cluster in the L3 clade, with the remaining one in the L2 clade. This is also the case in Graphium macleayanum, so we termed the L opsins of G. sarpedon as GsL2, GsL3a and GsL3b.
Localization of these mRNAs in serial vertical sections reveals three distinct eye regions; very-dorsal, dorsal and ventral. The very-dorsal region consists of about 20 rows of ommatidia expressing UV, B and L2 mRNAs; this region is not the dorsal rim area (DRA), which usually consists of just a few rows. In the dorsal region, a sparse labeling of L3a was detected in addition to the three opsins found more dorsally. The ventral region expresses all five opsins including L3b. According to the hypothesis (based on recent studies in a few other species) that newly-acquired opsins are restricted to the ventral region, it appears that GsL2 is the most ancestral and GsL3b was acquired most recently.
We further studied the mRNA expression in the dorsal and ventral regions at the cellular level. Among nine photoreceptors (R1-9) in a single ommatidium, R1-2 express either UV or B in three distinct combinations, making three ommatidial types: UV/B (type I), UV/UV (II) and B/B (III). The R3-8 cells express L opsins in a complicated manner. In the dorsal region, all R3-4 express L2. R5-8 of type I and II express L3a, while those of type III express L2. In the ventral region, R3-4 of type III express L2, but other R3-8 co-express at least two of three L opsins (L3a+L3b in R3-8 of I and R5-8 of II; L2+L3b in R3-4 of II and R5-8 of III). This expression pattern suggests that Graphium have various unique L receptors that have never been found in any other species. In fact, we have detected twelve different spectral sensitivities in the eye in our preliminary electrophysiology.
Keywords:
Eye regionalization,
Gene Duplication,
Opsin
Conference:
Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012.
Presentation Type:
Poster Presentation (see alternatives below as well)
Topic:
Evolution
Citation:
Awata
H,
Matsushita
A and
Arikawa
K
(2012). Unique regionalization and distribution of duplicated opsins in the eye of the Common Blue Bottle, Graphium sarpedon
.
Conference Abstract:
Tenth International Congress of Neuroethology.
doi: 10.3389/conf.fnbeh.2012.27.00145
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Received:
27 Apr 2012;
Published Online:
07 Jul 2012.
*
Correspondence:
Dr. Hiroko Awata, The Graduate University for Advanced Studies (Sokendai), School of Advanced Sciences, Hayama, Kanagawa, 240-0193, Japan, awakumaya@gmail.com