Identification of Highly Active Genes from the Posterior Silk Gland of the Oak Silkworm, Antheraea yamamai, Through Expressed Sequence Tag (EST) Strategy

Abstract

Gene discovery from highly specialized tissues is important for understanding of development and tissue-dependent gene regulation in organism. To identify highly active genes from the posterior silk gland of the oak silkworm, Antheraea yamamai, which is specialized for the production of silk proteins, we constructed an oligo (dT) primed directional cDNA library from the posterior silk gland of the final star larvae. One hundred and three expressed sequence tags (ESTs) were generated by single-run partial sequencing from the primary cDNA library. Their sequence analysis indicated that 59 clones exhibited a significant homology to known genes, and 6 clones to ESTs of unknown functions, and 33 clones were novel transcripts. In the expression profile, the most abundant gene was found to be fibroin (25.2%), followed by TAXREB107 (5.8%) and ribosomal protein S9 (2.9%). Northern blot analyses confirmed that fibroin and TAXREB107 genes are actively expressed in the posterior silk gland of the final instar larvae of the oak silk worm. This study demonstrated that the expression profile of the silk gland ESTs could be a useful tool for isolating the highly active genes in insect tissues.