Hidetoshi Teramoto1, Tetsuya Iizuka2, Tsunenori Kameda1, Eiji Okada2, Hideki Sezutsu2

1Silk Materials Research Unit, 2Transgenic Silkworm Research Unit

［Abstract］

We developed a successful novel screening strategy using transgenic tobacco for isolation of DNA elements that could prevent transcriptional gene silencing (TGS) to protect a flanking transgene from TGS. We isolated three different DNA sequences with anti-silencing function from Lotus japonicus.

［Keywords］

sericin, high molecular weight, characteristic silkworm races, cosmetic materials, application research

［Background］

Silk sericin, an adhesive protein family of Bombyx mori cocoons, has been attracting much attention as a cosmetic material because it consists of many hydrophilic amino acids including serine. The technique to recover sericin from the waste of silk processing had been put into practical use, and the recovered sericin has been commercially utilized as a cosmetic material. However, the sericin recovered during silk processing loses its natural film-forming ability due to hydrolysis that induces a reduction in molecular weight. This study aims to explore the potential of ‘Virgin Sericin’, a high molecular weight intact sericin for commercial applications as a cosmetic material in collaboration with companies by utilizing ‘Sericin Hope’, a silkworm race we previously developed which produced cocoons made exclusively of sericin.

［Results and Discussion］

1. The aqueous solution of ‘Virgin Sericin’ can be prepared by dissolving the cocoon shells of ‘Sericin Hope’ in LiBr solution followed by dialysis to remove the LiBr. However, the solution easily turns into gel because the ‘Virgin Sericin’ molecules have strong tendency to aggregate with each other. We have overcome this problem by: (1) maintaining good air circulation during cocooning of silkworms to avoid irreversible aggregation of the ‘Virgin Sericin’ molecules arising from absorption and desorption of moisture; and (2) controlling the pH of the ‘Virgin Sericin’ solution during dialysis between neutral to weak alkaline (Fig. 1).
   
2. An improved race of ‘Sericin Hope’ with better cocoon productivity and adaptivity toward artificial diet than the original race was developed. Technical assistance is provided to a silkworm egg producing company for large-scale production of high quality raw cocoons that will facilitate stable supply of raw cocoons for commercial applications (Fig. 2).
   
3. The technology for preparation of the aqueous solution of ‘Virgin Sericin’ has been transferred to a cosmetics company. Cosmetic products containing ‘Virgin Sericin’ were exhibited at the Cosme Innovation in Tokyo on June 2012 and test-launched on the market in 2013 (Fig. 3).

1. Our technical assistance to commercial companies involved in raw cocoon production and processing of aqueous solution of Virgin Sericin facilitated the commercialization of cosmetics containing Virgin Sericin.
   
2. Based on this research, novel applications of Virgin Sericin could be achieved in the near future if the production system of Virgin Sericin solution, which had not been suitable for practical applications due to its strong aggregating property, would be constructed on a commercial basis.
   
3. The ‘Virgin Sericin’ solution could be used in the preparation of hydrogels or film materials with strong mechanical strength. Such properties could be further explored in developing a technical platform for application of ‘Virgin Sericin’ in health care or medical fields.
   
4. This research would encourage sericulture-related industries to develop high-value-added products utilizing characteristic silkworm races developed in Japan.

Fig.1. Preparation of aqueous solution of ‘Virgin Sericin’ from the cocoons of ‘Sericin Hope’. It is important to maintain good air circulation during cocooning and control the pH during dialysis to obtain high-quality solution.

Fig.2. (A) Comparison of cocoon production from the improved race and the original ‘Sericin Hope’. (B) Cocooning process of the improved race as conducted in a company and the harvested cocoon shells.

Fig.3. (A) Prototypes of cosmetics containing ‘Virgin Sericin’ displayed at the Cosme Innovation (Tokyo, June 2012). (B) Cosmetics products containing ‘Virgin Sericin’ such as facial wash and cream were test-launched in the market in 2013.

 

[Reference]

1. Teramoto H, Murakami M, Kameda T (2014) Desalting of high-molecular-weight sericin solution by using circulating dialysis The Journal of Silk Science and Technology of Japan 22:51-56 (in Japanese with English summary)
   
2. International Publication # WO2014/065217
   
3. Patent # 4714890 (Japan)