SYNTHESIS AND SECRETION OF LOW-MOLECULAR-WEIGHT CUTICULAR PROTEINS DURING HEAT-SHOCK IN THE TOBACCO HORNWORM, MANDUCA-SEXTA

In the tobacco hornworm, Manduca sexta, heat shock normally elicits synthesis of the classic heat-shock proteins. A 1-hr heat shock of 42-degrees-C and above can also increase the relative synthesis of certain 12-18 kD proteins in the epidermis. These 12-18 kD proteins were identified as cuticular proteins for several reasons. Like cuticular proteins, they appear only in the epidermis. They can be precipitated from epidermal homogenates with an antiserum to larval cuticle. The same conditions that increased labeled 12-18 kD proteins in the epidermis also increased labeled 12-18 kD proteins in the cuticle. Some of the epidermal increase may result from a partial inhibition of secretion to the cuticle during 46-degrees-C heat shock, causing abnormal accumulation in the epidermis. However, slight increases also occur at lower temperatures, which do not inhibit secretion detectably. Preliminary results also indicate that total quantities of at least one cuticular protein mRNA may increase during heat shock, either because of increased transcription or increased mRNA stability.