ANNOTATION AND EVOLUTION OF THE ANTIOXIDANT GENES IN THE SILKWORM, Bombyx mori

Abstract

Antioxidant system, which is composed of multiple gene families, plays a major role in reducing oxidative damage and xenobiotic detoxification in all living organisms. We identified 50 silkworm antioxidant genes from nine gene families based on the assembled genome sequence. A comparative analysis of the antioxidant genes of the silkworm with other order insects Anopheles gambiae, Apis mellifera, Drosophila melanogaster, and Tribolium castaneum, was performed. We found that most of the antioxidant gene families are highly conserved but Catalase (CAT) and heme-containing peroxidase (HPX) families were lineage-specifically expanded in the silkworm. The expression patterns of the silkworm antioxidant genes were investigated with the known ESTs, microarray data, and reverse transcription-polymerase chain reaction (RT-PCR). Forty two of the 50 silkworm antioxidant genes were transcribed and most of the transcribed genes showed tissue-specific expression patterns. More than a half of lineage-specifically expanded BmCATs lacked 15 or more than 15 of the 36 heme-binding residues and might lose catalase activities. However, the genes encoding these BmCATs showed almost a ubiquitous tissue expression pattern, indicating that they might have evolved new functions. In addition, the lineage-specifically expanded BmHPXs could function in maintaining cell homeostasis in the process of the synthesis of large amounts of silk proteins because they were predominantly expressed in silk gland of the silkworm. The lineage-specific expansion of antioxidant gene families in the silkworm provides useful information for understanding evolution and functional versatility of antioxidant genes in the silkworm even Lepidopteran insects.

Identification of an Anopheles Lineage-Specific Unique Heme Peroxidase HPX15: A Plausible Candidate for Arresting Malaria Parasite Development

“…However, we observed its ortholog in Drosophila (Figure 3). In addition, the anophelines heme peroxidases also experienced a lineage-specific expansion as reported in other insects [33]. The phylogenetic relationship among 16 A. gambiae heme peroxidases and 8 non heme peroxidases revealed that both types of peroxidases appear in two different clades and have diverged from each other a long before ( Figure S3).…”

“…This indicates that in A. gambiae there is a large expansion of heme peroxidases and that may be associated with their geographical distribution or biological behaviors as reported in other organisms [33]. It is also noticeable that some lineage-specific heme peroxidses are present only in anophelines and do not have any ortholog in other animals including Aedes and Culex mosquitoes.…”

“…However, the heme peroxidase AgHPX12 has no paralog even in A. gambiae (Figure 3). These unique peroxidases might have some crucial role in biology, physiology, geographical distribution or environmental adaptations of Anopheles mosquito as reported in case of other genes [33]. We emphasize that these peroxidases may be considered unique targets to synthesize blockers for regulating the biological activities of the malaria vector.…”

“…This crosslinking is a fundamental feature of basal membranes and essential as an elemental mechanism of tissue biogenesis [37,38]. Heme peroxidases are also extensively involved in the evolution and adaptations to the environment [33]. Thus, HPXs superfamily is considered to be a group of highly diversified members.…”

“…Interestingly, AgHPX3 orthologs are present only in arthropod as well as C. elegans. AgHPX1, AgHPX5, AgHPX6, AgHPX7 and AgDBLOX are arthropod-specific heme peroxidases ( Figure 3) and might have conserved function across insect species irrespective of their blood feeding or non blood feeding behaviors as observed in case of other genes [33]. These peroxidases might have been selected by gene duplications that occurred prior to the most recent common ancestor (MRCA) of Hemimetabolous (e.g., Pediculus humanus, Ph) and Holometabolous (e.g.…”