Conservation of Silk Genes in Trichoptera and Lepidoptera |
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Authors: | Naoyuki Yonemura Kazuei Mita Toshiki Tamura Franti?ek Sehnal |
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Institution: | (1) National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-8634, Japan;(2) Biology Centre, Academy of Sciences, Institute of Entomology, Branišovská 31, 370 05 České Budějovice, Czech Republic |
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Abstract: | Larvae of the sister orders Trichoptera and Lepidoptera are characterized by silk secretion from a pair of labial glands.
In both orders the silk filament consists of heavy (H)- and light (L)-chain fibroins and in Lepidoptera it also includes a
P25 glycoprotein. The L-fibroin and H-fibroin genes of Rhyacophila obliterata and Hydropsyche angustipennis caddisflies have exon/intron structuring (seven exons in L-fibroin and two in H-fibroin) similar to that in their counterparts in Lepidoptera. Fibroin cDNAs are also known in Limnephilus decipiens, representing the third caddisfly suborder. Amino acid sequences of deduced L-fibroin proteins and of the terminal H-fibroin
regions are about 50% identical among the three caddisfly species but their similarity to lepidopteran fibroins is <25%. Positions
of some residues are conserved, including cysteines that were shown to link the L-fibroin and H-fibroin by a disulfide bridge
in Lepidoptera. The long internal part of H-fibroins is composed of short motifs arranged in species-specific repeats. They
are extremely uniform in R. obliterata. Motifs (SX)n, GGX, and GPGXX occur in both Trichoptera and Lepidoptera. The trichopteran H-fibroins further contain charged amphiphilic
motifs but lack the strings of alanines or alanine-glycine dipeptides that are typical lepidopteran motifs. On the other hand,
sequences composed of a motif similar to ERIVAPTVITR surrounded by the (SX)4-6 strings and modifications of the GRRGWGRRG motif occur in Trichoptera and not in Lepidoptera.
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Keywords: | Silk evolution Trichoptera Lepidoptera Fibroin DNA repeats Protein polymers Insect genes |
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