Fine structure of the glandular epithelium during secretory silk production in the black widow spider latrodectus mactans

Abstract

Among the silk glands in the black widow spider Latrodectus mactans, the ampullate one is the most predominant gland in both sexes, and is composed of three functional parts ‐ excretory duct, storage ampulla and convoluted tail regions. This experiment was performed using mechanical pulling stimulation with electric motor equipment to reveal a correlation between silk usage and silk producing system in this poisonous spider. The mature secretory products in glandular epithelium are closely packed and appear as electron‐opaque spherical vesicles. A part of the vesicles with fine fibrillar paracrystalline texture seems to store some proteins which will function at the time of final assembly into fibrils. Most of the secretory silk products which originated from the rough endoplasmic reticula of the glandular epithelial cells are grown by fusion with surrounding small vesicles. However, the Golgi complex does not seem to play an important role in this process of secretion. According to progressive maturation of secretory silk product, these granules are progressively filled with a fine fibrillar material, and thus appear much more electron‐dense than those of earlier states. When the secretory product is extruded from the glandular cavity, the epithelium is rapidly changed to a thinner layer of tall columnar cells with less definitive cell membranes. After extruding there are a few secretory droplets within these cells, thus causing this region to stain much lighter.