Morphology and Composition of the Spider Major Ampullate Gland and Dragline Silk

Abstract

Spider silk is made of unique proteins-spidroins-secreted and stored as a protein solution (dope) in specialized glands. The major ampullate gland, source of the dragline silk, is composed of a tail, a sac and an elongated duct. For this gland, several different types of epithelial cells and granules have been described, but it is largely unknown how they correlate with spidroin production. It is also not settled what parts of the large spidroins end up in the final silk, and it has been suggested that the N-terminal domain (NT) is lacking. Here we show that NT is present in the dope and throughout dragline silk fibers, including the skin layer, and that the major ampullate tail and sac consist of three different and sharply demarcated zones (A-C), each with a distinct epithelial cell type. Finally, we show that spidroins are produced in the A and B zone epithelia, while the C zone granules lack spidroins.

Carbonic Anhydrase Generates CO2 and H+ That Drive Spider Silk Formation Via Opposite Effects on the Terminal Domains

“…By use of a histochemical method [14] we could indeed identify abundant CA activity in intracellular vesicles and at the apical cell membrane of the epithelium in the distal part of the major and minor ampullate sacs and ducts, as well as in aggregate gland ducts and tubuliform glands (Figure 2A–E). The site in the major ampullate epithelium where CA was found to emerge (Figure 2A) exactly coincides with the location where the glandular epithelium ceases to produce spidroins [15]. To investigate whether CA is responsible for generating and maintaining the pH gradient, we immersed freshly dissected N. clavipes major ampullate glands in buffers containing methazolamide, a membrane-permeable CA inhibitor [16].…”

Silk Spinning in Silkworms and Spiders

“…Herein, we focus on the major ampullate gland, which produces the dragline silk. The major ampullate gland is present in pairs and is, similarly to the silkworm silk gland, divided into three parts; the tail, the sac and the duct (Figure 1b) [9,13]. …”

“…The cells in the most proximal parts of the glands are responsible for secreting the major constituent of the silk, fibroins/spidroins (purple in Figure 1c,d) [8,9,17]. The cells in the MSG of B. mori glands secrete different types of sericin (purple, Figure 1c) [7,8,14], which will form a coat surrounding the fibroin.…”

Nanostructural and mechanical property changes to spider silk as a consequence of insecticide exposure

“…MAS is secreted from the major ampullate gland, which consists of a tail, sac and duct region (Andersson et al, 2013;Rising and Johansson, 2015;Blamires et al, 2017). The spidroins are secreted into the tail of the major ampullate gland and stored in the sac as a solution called dope (Heim et al, 2009;Vollrath et al, 2013).…”