Ordered flow of secretion from accessory glands to specific layers of the spermatophore of mealworm beetles: demonstration with a monoclonal antibody.

Monoclonal antibodies were produced against the secretory product of the bean-shaped accessory gland (BAG) of male mealworm beetles (Tenebrio molitor). Antibodies from one clone (PL 6.3) recognized a 9,600 dalton protein with a pI of 6.6 which was found in homogenates of the BAG. The PL 6.3 antigen was first detected on Western blots of BAG proteins from 2-day adults, and amounts increased for the next 6 days until reproductive maturation was achieved. The antibody also recognized a polypeptide with a molecular weight (mw) of about 5,000 daltons which we believe to be derived from the larger 9,600 dalton antigen. There are eight types of secretory cells in the BAG. By using light microscopic immunohistochemistry, we localized the antigens recognized by PL 6.3 in cell type 7 (intense staining) and cell type 5 (weak staining). Results from electron microscopic immunocytochemistry showed that antigen PL 6.3 was concentrated in the secretory granules characteristic of each of these two cell types and was absent in all other cell types. PL 6.3 antigens were traced from the BAG into its secretory product and then into the prespermatophoric mass in the ejaculatory duct. The antigen was not randomly mixed with other secretory products of the accessory glands. As it flowed from the BAG and into the ejaculatory duct, it remained in a coherent, precisely localized mass. Within the definitive spermatophore, the PL 6.3 antigen was concentrated in discrete layers of material that line the lumen.