Daimon T, Katsuma S, Iwanaga M, Kang WK, Shimad T. The BmChi-h gene, a bacterial-type chitinase gene of Bombyx mori, encodes a functional exochitinase that plays a role in the chitin degradation during the molting process. Insect Biochemistry and Molecular Biology
The silkworm, Bombyx mori, has been recently demonstrated to contain a bacterial-type chitinase gene (BmChi-h) in addition to a well-characterized endochitinase gene (BmChitinase). The deduced amino acid sequence of BmChi-h showed extensive structural similarities with chitinases from bacteria such as Serratia marcescens chiA and baculoviruses (v-CHIA). Bacterial-type chitinase genes have not been found from any eukaryotes and viruses except for lepidopteran insects and lepidopteran baculoviruses. Thus, it was suggested that BmChi-h may be derived from a bacterial or baculovirus chitinase gene via horizontal gene transfer. In this report, we investigated the biological function of BmChi-h. Our enzymological study indicated that a chitinase encoded by BmChi-h has exo-type substrate preference, which is the same as S. marcescens chiA and v-CHIA, and different from BmChitinase, which has endo-type substrate preference. An immunohistochemical study revealed that BmChi-h localizes in the chitin-containing tissues during the molting stages, indicating that it plays a role in chitin degradation during molting. These results suggest that BmChi-h (exochitinase) and BmChitinase (endochitinase) may catalyze a native chitin by a concerted mechanism. Cloning and comparison of BmChi-h orthologues revealed that bacterial-type chitinase genes are highly conserved among lepidopteran insects, suggesting that the utilization of a bacterial-type chitinase during the molting process may be a general feature of lepidopteran insects.
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- "When Bmptp-h was inserted into the genome of BmPTPD, wandering was partially recovered , suggesting that Bmptp-h is a functional homolog of BmNPV ptp (see Section 4 for more detail ). In contrast, we revealed that B. mori chitinase BmChi-h (Daimon et al. 2005), which shows a marked homology to and a specific cross-immune reactivity with baculoviral chitinase V-CHIAs (Fig. 7), was not able to functionally compensate for a defect of V-CHIA (Daimon et al. 2006) (Fig. 5) (see Section 3 for more detail). These results suggest that baculoviruses selectively maintain or modify functions of the captured host genes to obtain evolutionary advantages. "
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- "The phrase "type of gene" refers to a transferred event, because a transferred gene may or may not duplicate in the recipients genome after its transfer. All previously revealed silkworm HTGs including 9 bacterial-origin HT genes in Zhu et al.'s result are included in our results [18-20,27,28]. Twenty one candidates were mapped in the silkworm chromosomes by SilkMap (a tool in SilkDB) , except for BGIBMGA005696. "
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ABSTRACT: Horizontal gene transfer (HGT), a source of genetic variation, is generally considered to facilitate hosts' adaptability to environments. However, convincing evidence supporting the significant contribution of the transferred genes to the evolution of metazoan recipients is rare.
In this study, based on sequence data accumulated to date, we used a unified method consisting of similarity search and phylogenetic analysis to detect horizontally transferred genes (HTGs) between prokaryotes and five insect species including Drosophila melanogaster, Anopheles gambiae, Bombyx mori, Tribolium castaneum and Apis mellifera. Unexpectedly, the candidate HTGs were not detected in D. melanogaster, An. gambiae and T. castaneum, and 79 genes in Ap. mellifera sieved by the same method were considered as contamination based on other information. Consequently, 14 types of 22 HTGs were detected only in the silkworm. Additionally, 13 types of the detected silkworm HTGs share homologous sequences in species of other Lepidopteran superfamilies, suggesting that the majority of these HTGs were derived from ancient transfer events before the radiation of Ditrysia clade. On the basis of phylogenetic topologies and BLAST search results, donor bacteria of these genes were inferred, respectively. At least half of the predicted donor organisms may be entomopathogenic bacteria. The predicted biochemical functions of these genes include four categories: glycosyl hydrolase family, oxidoreductase family, amino acid metabolism, and others.
The products of HTGs detected in this study may take part in comprehensive physiological metabolism. These genes potentially contributed to functional innovation and adaptability of Lepidopteran hosts in their ancient lineages associated with the diversification of angiosperms. Importantly, our results imply that pathogens may be advantageous to the subsistence and prosperity of hosts through effective HGT events at a large evolutionary scale.
Available from: Qin Wang
- "The bacterial-type GH18 member, BmChi-h, is found in B. mori and other lepidopteran species. It has exo-type substrate preference and plays a role in chitin degradation during molting (Daimon et al. 2005). When blasting the protein sequence of BmChi-h against known genomes of insect, eight homologous genes were identified that all belong to lepidopteras. "
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ABSTRACT: The glycoside hydrolase 18 (GH18) family of chitinases is a multigene family that plays various roles, such as ecdysis, embryonic
development, allergic inflammation and so on. Efforts are still needed to reveal their functional diversification in an evolutionary
and systematic manner. We collected 85 GH18 genes from eukaryotic representatives. The domain architectures of GH18 proteins
were analyzed and several conserved patterns were identified. It was observed that some (11 proteins) GH18 members in Ecdysozoa
or fungi possess repeats of catalytic domains and/or chitin-binding domains (ChtBs). The domain repeats are likely to meet
requirements for higher efficiency of chitin degradation in chitin-containing species. On the contrary, all vertebrate GH18
proteins contain no more than one catalytic domain or ChtB. The results from homologous analysis, domain architectures, exon
arrangements and synteny loci supported two evolutionary paths for the GH18 family. One path experienced gene expansion and
contraction several times during evolution, covering most of GH18 members except CHID1 (stabilin-1 interacting partner) and its homologs. Proteins in this path underwent frequent domain gain and loss, as well
as domain recombination, that could achieve versatility in function. The other path is comparatively conserved. The CHID1 gene evolved without gene duplication except in Danio rerio. Domain architectures of CHID1 orthologs are all identical. The diverse phylogeny of the GH18 family in arthropod is also
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