A comparison of dragline silk genes between different guilds of spiders.
Spider silks have various function, composition and structure and are produced by different spinning glands. Dragline silk produced by ampullate glands has greatest strength than other types of silks thus have been the focus of most studies. Previous studies had demonstrated that the amino acid sequences translated from dragline genes of orb-weaving spiders exhibited many consensus repeats and formed specific structures. However, there are few studies on dragline silks produced by other guilds of spiders such as space web builders and wandering spiders. In this study, the relationship between web-related predation behaviors and silk gene structures is studied by examining DNA and amino acid sequences of major ampullate silk genes amplified from different spider guilds. Dragline gene partial sequences were amplified from the genomic DNA of the orb-weavers Nephila pipipes and Octonoba varians, the space web builders Cyrtophora moluccensis and Psechrus sinensis, and the primitive funnel-web builder Macrothele holsti. In the repetitive region of these partial sequences, GGX, poly-GA and poly-A motifs were present in all the species examined. Besides, among these partial sequences, the non-repetitive C-terminal regions are highly similar to each other and are in accordance with the non-repetitive regions of published sequences. Non-repetitive sequences are also obtained from N. pipipes and C. moluccensis by RT-PCR method. The space web builder P. sinensis is phylogenetically related to the wandering spider Dolomedes, however, its dragline gene non-repetitive portion is more similar to that of orb-weavers. The extreme similarity in dragline gene non-repetitive portions of web builders from different clades suggests that this sequence exhibits important function. In addition, previous studies have proposed that spider dragline silk may be expressed by a multiple gene system. Currently, there is no supporting evidence for this hypothesis. In this study, we also amplified partial dragline gene sequences from the same individual of N. pilipes using same the primers. The sequences obtained were very similar in non-repetitive regions but were different in repetitive regions. All these sequences exhibited GGX, GA and poly-A motifs but the numbers and arrangement patterns differed greatly. These results suggest that dragline silk genes of N. pilipes may have multiple alleles and operate like a multiple gene system, or, it is a single locus but with multiple exons each exhibit different sequence.
Updated: Mar-10-2014 01:22:51 (Taiwan, GMT+08:00).