Molecular characterization and phylogenetic analysis of the eukaryotic translation initiation factor 4A gene in Antheraea pernyi (Lepdoptera: Saturniidae)

Characterization of an Ecdysteroid-Regulated 16 kDa Protein Gene in Chinese Oak Silkworm, Antheraea pernyi (Lepidoptera: Saturniidae)

A large number of ecdysteroid-regulated 16 kDa proteins (ESR16s) of insects have been isolated and annotated in GenBank; however, knowledge on insect ESR16s remain limited. In the present study, we characterized an ecdysteroid-regulated 16 kDa protein gene isolated in Chinese oak silkworm, Antheraea pernyi Guérin-Méneville ('ApESR16' in the following), an important silk-producing and edible insect. The obtained cDNA sequence of ApESR16 is 1,049 bp, harboring an open reading frame of 441 bp that encodes a polypeptide of 146 amino acids. CD-search revealed that ApESR16 contains the putative cholesterol/lipid binding sites on conserved domain Npc2_like (Niemann-Pick type C-2) belonging to the MD-2-related lipid-recognition superfamily. Sequence comparison revealed that ApESR16 exhibits 51-57% identity to ESR16s of lepidopteran insects, 36-41% identity to ESR16 or NPC2a of nonlepidopteran insects, and 28-32% identity to NPC2a of vertebrates, indicating a high sequence divergence during the evolution of animals. Phylogenetic analysis found that the used sequences were divided into two groups corresponding to vertebrates and invertebrates, and the used insect sequences were also well clustered according to their families. The A. pernyi ESR16 mRNA is expressed during all four developmental stages and in all tested tissues. Injection of 20-hydroxyecdysone (20-E) into A. pernyi diapausing pupae triggering diapause termination induced upregulation of ESR16 mRNA compared to the diapausing pupae, with the highest expression level at day 2 in the ovaries but day 12 in the fat body. Our results suggested that ApESR16 might be a diapause-related gene and plays a vital role in the pupal diapause of A. pernyi.

Identification and Characterization of a Novel Microvitellogenin from the Chinese Oak Silkworm Antheraea pernyi

Microvitellogenin (mVg) is a relatively small vitellogenic protein only characterized in the eggs of the lepidopteran insects Manduca sexta and Bombyx mori. In the present study, we report a novel mVg (ApmVg) isolated from the Chinese oak silkworm Antheraea pernyi. The obtained ApmVg cDNA sequence contains an open reading frame of 783 bp encoding a protein of 260 amino acids with a predicted molecular weight of 29.96 kDa. This gene does not contain introns. Structural analysis revealed that this protein shares putative conserved domains with the lepidopteran low-molecular weight lipoprotein, which belongs to the lipoprotein_11 superfamily. The protein sequence of ApmVg exhibits 48% sequence identity with mVg from M. sexta and 40-47% sequence identity with the 30K lipoproteins from B. mori. Phylogenetic analysis suggests that ApmVg is a novel member of the lepidopteran low-molecular weight lipoproteins. Transcriptional analysis indicated that ApmVg mRNA is mainly expressed in the fat body (both female and male) during post-diapause development of the pupal stage, and it was also detected in ovaries and spermaries in smaller amounts. RT-PCR and Western blot analyses revealed that ApmVg is synthesized by the fat body and secreted into hemolymph and ultimately accumulates in eggs. The ApmVg transcript can be detected in the fat bodies of female pupae four days after treatment with 20-hydroxyecdysone and shows an expression pattern distinct from that of vitellogenin (Vg), which is detectable throughout diapausing and in post-diapause development. ApmVg decreased dramatically during embryonic development. These results represent the first study of mVg outside M. sexta and B. mori and provide insight into the physiological role and evolution of mVgs.