All About Silk: Biodesigning of a silk production unit

Themulberry silkworm Bombyx mori hasbeen exploited for thousands of years for the commercial production of silk.India being the second largest producer of silk in the world, provides a meansof livelihood to nearly 6million farmers through this agro-based cottageindustry. Although mulberry silk accounts for more than 90% of the silkmarketed , three other variants of silk, viz.Eri, Muga and Tasar derived from semi-domesticated or wild silk moths are alsoimportant commercial products. The molecular aspects of silk synthesis havebeen extensively studied in B.mori.This organism possesses a pair of silk glands, which are long tubularstructures originating from the labial segment of the larval head and extendingup to the posterior most caudal segment. The silk glands are anatomically andphysiologically divided into three distinct compartments. The posterior partsof the silk glands (PSG) produce large quantities of the silk fibre proteinswhich are secreted into the lumen and gets transported and stored in the middlesilk glands (MSG). MSGs are further sub compartmented into three parts, andeach of them produce different splice variants of the glue proteins, sericins,which coat the fibroins in different layers. The sericins being highlyhygroscopic, abstracts the water molecules from the fibroins to bring them tothe surface so that when the highly polymerized silk proteins are extruded, thewater molecules evaporate to make the filaments dry. The molecular designingand patterning of the silk glands , which are the factories for silk productionwithin the silkworm larvae, have been elucidated by our group. The operation ofthe canonical Wnt signaling pathwayand concerted action of a set of homeotic genes in this process will be thefocus of the discussion.

Glimpsesof the exploitation of Silkworms as Natural Bioreactor to produce largequantities of recombinant DNA products will also be presented.