The Japanese oak silkmoth, Antheraea yamamai Guérin-Méneville 1861 (Lepidoptera: Saturniidae), is one of the important natural resources possessing industrial value for silk fiber production. In this study, ten microsatellite markers and two mitochondrial DNA (mtDNA) gene sequences (COI and ND4) were used to investigate the genetic variation and geographic structure of A. yamamai populations in South Korea. Two mtDNA gene sequences revealed very low total genetic variation and resultant low geographic variation, validating to use further variable molecular markers. Population-based FIS, FST, RST, and global Mantel test consistently support that A. yamamai populations are overall well interconnected with a relatively high gene flow. Nevertheless, STRUCTURE analysis using microsatellite data and mtDNA sequences coincidently indicate the presence of two genetic pools in many populations.

Screening for antimicrobial peptide genes in the immune-induced Antheraea yamamai larvae led to the identification of a novel antifungal moricin-like peptide (MLP10) gene. The complete MLP10 cDNA is comprised of 403 bp with 174 bp open reading frame encoding a 58 amino acid precursor that contains a putative 23-residue signal peptide, a 2-residue propeptide and a 33-residue mature peptide. The deduced amino acid sequence of MLP10 has 26∼52% identity to those of moricin-related peptides from lepidopteran insects. The MLP10 was highly expressed in E. coli BL21(DE3) by fusing with ketosteroid isomerase (KSI) to avoid the cell death during induction. The resulting expressed KSI-MLP10 fusion protein was in a insoluble form. Recombinant MLP10 was released by cleavage of the fusion protein with cyanogen bromide (CNBr). Subsequently, we purified pure active MLP10 by FPLC chromatography, and 5.2mg of MLP10 was obtained from 1L culture medium. The purified MLP10 was prevented the growth of candida albicans at 6.25 uM, and was also active against gram negative and gram positive bacteria. This potent antimicrobial activity suggests that MLP10 may play a role in the immune response of A. yamamai.

The antimicrobial peptide cecropin was isolated from the larval hemolymph of immune-challenged japanese oak silkworm, Antheraea yamamai. The full-length cDNA of A. yamamai cecropin (Ay-cecA) was cloned by a combination of RT-PCR and 3' RACE based on N-terminal sequence obtained by Edman degradation. The cloned cDNA consists of 419 nucleotides encoding a 64 amino acid precursor containing a 37-residue mature peptide. Like many insect cecropins, Ay-cecA also harbored a glycine residue for C-terminal amidation at the C-end. To understand this peptide better, we successfully expressed bioactive recombinant Ay-cecA in E. coli BL21(DE3) by fusing with ketosteroid isomerase (KSI) to avoid the cell death during induction. The fusion CecA-KSI protein was expressed as inclusion body at high level. Recombinant Ay-cecA was easily released by cleavage of the fusion protein with cyanogen bromide (CNBr), and purified by FPLC chromatography. The purified recombinant Ay-cecA showed considerably antibacterial activity against Gram-negative bacteria, E. coli ML 35, Klebsiella pneumonia and Pseudomonas aeruginosa. The time-kill assay showed that Ay-CecA displayed a time-dependent bactericidal activity, as was also seen after treatment with melittin. our results proved that Ay-cecA can be developed into novel antibacterial agent.

We determined the complete mitochondrial genome (mitogenome) of the Japanese Oak Silkmoth, Antheraea yamamai (Lepidoptera: Saturniidae) from two overlapping fragments and subsequent shotgun sequencing. The 15,601-bp long A. yamamai mitogenome contains gene arrangement and content identical to the most common arrangement found in lepidopteran insects. Most individual A. yamamai mitochondrial (mt) genes were well within the range found in the respective genes of other insects, except for small ribosomal RNA (1,037 bp). The 336-bp A+T-rich region is relatively smaller than that of other lepidopteran insects. The region is interesting in that it contains tRNA-like structures as found in the A+T-rich regions of other insect mitogenomes. The start codon of A. yamamai COI gene is unusual in that no typical one (ATN) is available. Three of the 13 protein-coding genes have incomplete termination codon T or TA. All tRNA formed stable stem-and-loop structure, except for tRNASer(AGN), the DHU arm of which formed a simple loop as seen in many other metazoan mt tRNASer(AGN).

We investigated starvation of hatching larvae, occasional artificial hatching and incubation method to establish year-round rearing of the wild silkmoth, Antheraea yamamai. In the test of starvation of hatching larvae for brushing at a time, the survival rate of the fourth instar of larvae starved for 1 day after hatching in 25℃ and 5℃ was 83.3% and 96.0%, respectively. The result represents that the survival rate is high at low temperature during starvation. In the occasional artificial hatching test for multi-times rearing of A. yamamai, the useful hatchability is high at 5℃ in case of preserving eggs for 2 months from incubation time, and at both 2.5℃ and 0℃ in case of over 6 months. A new incubation method with pre-incubation at 15℃ and 24 D photoperiod showed high hatchability about 80% for only 2 days compared with hatching for 5-6 days in traditional incubation method with the preservation at 25℃.