Silkworms which have (i) a DNA encoding a transcriptional regulator operably linked downstream of a promoter of a DNA encoding a protein specifically expressed in the silk gland and (ii) a DNA encoding TRACP5 operably linked downstream of a target promoter of the transcriptional regulator were produced. The result showed that active TRACP5b was produced from the silkworms. This means that TRACP5 produced from the silk gland of the silkworms undergoes processing in the silk gland that is similar to the processing taking place at bone resorption sites.
