Evolution of repetitive proteins: spider silks from Nephila clavipes (Tetragnathidae) and Araneus bicentenarius (Araneidae)1GenBank assigned accession number(s):Araneus: U20328; Nephila: cDNA = U20329, PCR = U375201 (original) (raw)
Related papers
Inter-specific sequence conservation and intra-individual sequence variation in a spider silk gene
International Journal of Biological Macromolecules, 2004
Currently, studies on major ampullate spidroin 1 (MaSp1) genes of non-orb weaving spiders are few, and it is not clear whether genes of these organisms exhibit the same characteristics as those of orb-weavers. In addition, many studies have proposed that MaSp1 might be a single gene with allelic variants, but supporting evidence is still lacking. In this study, we compared partial DNA and amino acid sequences of MaSp1 cloned from different spider guilds. We also cloned partial MaSp1 sequences from genomic DNA and cDNA of the same individuals of spiders using the same primer combination to see if different molecular forms existed. In the repetitive region of partial MaSp1 sequences obtained, GGX, GA and poly-A motifs were present in all Araneomorphae and Mygalomorpae species examined. An extreme similarity in MaSp1 non-repetitive portions was found in sequences of ecribellate, cribellate and Mygalomorphae web-builders and such a result suggested that this sequence might exhibit an important function. A comparison of sequences amplified from the same individual showed that substitutions in amino acids occurred in both repetitive and non-repetitive regions, with a much higher variation in the former. These results suggest that the MaSp1 of Araneomorphae spiders exhibits several forms in an individual spider and it might be either a multiple gene or a single gene with a multiple exon/intron organization.
Intragenic homogenization and multiple copies of prey-wrapping silk genes in Argiope garden spiders
BMC Evolutionary Biology, 2014
Background: Spider silks are spectacular examples of phenotypic diversity arising from adaptive molecular evolution. An individual spider can produce an array of specialized silks, with the majority of constituent silk proteins encoded by members of the spidroin gene family. Spidroins are dominated by tandem repeats flanked by short, non-repetitive N-and C-terminal coding regions. The remarkable mechanical properties of spider silks have been largely attributed to the repeat sequences. However, the molecular evolutionary processes acting on spidroin terminal and repetitive regions remain unclear due to a paucity of complete gene sequences and sampling of genetic variation among individuals. To better understand spider silk evolution, we characterize a complete aciniform spidroin gene from an Argiope orb-weaving spider and survey aciniform gene fragments from congeneric individuals.
Piriform Spider Silk Sequences Reveal Unique Repetitive Elements
2010
Orb-weaving spider silk fibers are assembled from very large, highly repetitive proteins. The repeated segments contain, in turn, short, simple, and repetitive amino acid motifs that account for the physical and mechanical properties of the assembled fiber. Of the six orb-weaver silk fibroins, the piriform silk that makes the attachment discs, which lashes the joints of the web and attaches dragline silk to surfaces, has not been previously characterized. Piriform silk protein cDNAs were isolated from phage libraries of three species: A. trifasciata, N. claVipes, and N. cruentata. The deduced amino acid sequences from these genes revealed two new repetitive motifs: an alternating proline motif, where every other amino acid is proline, and a glutamine-rich motif of 6-8 amino acids. Similar to other spider silk proteins, the repeated segments are large (>200 amino acids) and highly homogenized within a species. There is also substantial sequence similarity across the genes from the three species, with particular conservation of the repetitive motifs. Northern blot analysis revealed that the mRNA is larger than 11 kb and is expressed exclusively in the piriform glands of the spider. Phylogenetic analysis of the C-terminal regions of the new proteins with published spidroins robustly shows that the piriform sequences form an ortholog group.
Molecular Biology and Evolution, 2013
Spider silk fibers have impressive mechanical properties and are primarily composed of highly repetitive structural proteins (termed spidroins) encoded by a single gene family. Most characterized spidroin genes are incompletely known because of their extreme size (typically >9 kb) and repetitiveness, limiting understanding of the evolutionary processes that gave rise to their unusual gene architectures. The only complete spidroin genes characterized thus far form the dragline in the Western black widow, Latrodectus hesperus. Here, we describe the first complete gene sequence encoding the aciniform spidroin AcSp1, the primary component of spider prey-wrapping fibers. L. hesperus AcSp1 contains a single enormous ($19 kb) exon. The AcSp1 repeat sequence is exceptionally conserved between two widow species ($94% identity) and between widows and distantly related orb-weavers ($30% identity), consistent with a history of strong purifying selection on its amino acid sequence. Furthermore, the 16 repeats (each 371-375 amino acids long) found in black widow AcSp1 are, on average, >99% identical at the nucleotide level. A combination of stabilizing selection on amino acid sequence, selection on silent sites, and intragenic recombination likely explains the extreme homogenization of AcSp1 repeats. In addition, phylogenetic analyses of spidroin paralogs support a gene duplication event occurring concomitantly with specialization of the aciniform glands and the tubuliform glands, which synthesize egg-case silk. With repeats that are dramatically different in length and amino acid composition from dragline spidroins, our L. hesperus AcSp1 expands the knowledge base for developing silk-based biomimetic technologies.
Chromosome Mapping of Dragline Silk Genes in the Genomes of Widow Spiders (Araneae, Theridiidae)
PLoS ONE, 2010
With its incredible strength and toughness, spider dragline silk is widely lauded for its impressive material properties. Dragline silk is composed of two structural proteins, MaSp1 and MaSp2, which are encoded by members of the spidroin gene family. While previous studies have characterized the genes that encode the constituent proteins of spider silks, nothing is known about the physical location of these genes. We determined karyotypes and sex chromosome organization for the widow spiders, Latrodectus hesperus and L. geometricus (Araneae, Theridiidae). We then used fluorescence in situ hybridization to map the genomic locations of the genes for the silk proteins that compose the remarkable spider dragline. These genes included three loci for the MaSp1 protein and the single locus for the MaSp2 protein. In addition, we mapped a MaSp1 pseudogene. All the MaSp1 gene copies and pseudogene localized to a single chromosomal region while MaSp2 was located on a different chromosome of L. hesperus. Using probes derived from L. hesperus, we comparatively mapped all three MaSp1 loci to a single region of a L. geometricus chromosome. As with L. hesperus, MaSp2 was found on a separate L. geometricus chromosome, thus again unlinked to the MaSp1 loci. These results indicate orthology of the corresponding chromosomal regions in the two widow genomes. Moreover, the occurrence of multiple MaSp1 loci in a conserved gene cluster across species suggests that MaSp1 proliferated by tandem duplication in a common ancestor of L. geometricus and L. hesperus. Unequal crossover events during recombination could have given rise to the gene copies and could also maintain sequence similarity among gene copies over time. Further comparative mapping with taxa of increasing divergence from Latrodectus will pinpoint when the MaSp1 duplication events occurred and the phylogenetic distribution of silk gene linkage patterns.
Scientific Reports
Spider silk synthesis is an emerging model for the evolution of tissue-specific gene expression and the role of gene duplication in functional novelty, but its potential has not been fully realized. Accordingly, we quantified transcript (mRNA) abundance in seven silk gland types and three non-silk gland tissues for three cobweb-weaving spider species. Evolutionary analyses based on expression levels of thousands of homologous transcripts and phylogenetic reconstruction of 605 gene families demonstrated conservation of expression for each gland type among species. Despite serial homology of all silk glands, the expression profiles of the glue-forming aggregate glands were divergent from fiber-forming glands. Also surprising was our finding that shifts in gene expression among silk gland types were not necessarily coupled with gene duplication, even though silk-specific genes belong to multi-paralog gene families. Our results challenge widely accepted models of tissue specialization and significantly advance efforts to replicate silk-based high-performance biomaterials.
Untangling spider silk evolution with spidroin terminal domains
BMC Evolutionary Biology, 2010
Background: Spidroins are a unique family of large, structural proteins that make up the bulk of spider silk fibers. Due to the highly variable nature of their repetitive sequences, spidroin evolutionary relationships have principally been determined from their non-repetitive carboxy (C)-terminal domains, though they offer limited character data. The few known spidroin amino (N)-terminal domains have been difficult to obtain, but potentially contain critical phylogenetic information for reconstructing the diversification of spider silks. Here we used silk gland expression data (ESTs) from highly divergent species to evaluate the functional significance and phylogenetic utility of spidroin N-terminal domains. Results: We report 11 additional spidroin N-termini found by sequencing~1,900 silk gland cDNAs from nine spider species that shared a common ancestor > 240 million years ago. In contrast to their hyper-variable repetitive regions, spidroin N-terminal domains have retained striking similarities in sequence identity, predicted secondary structure, and hydrophobicity. Through separate and combined phylogenetic analyses of N-terminal domains and their corresponding C-termini, we find that combined analysis produces the most resolved trees and that N-termini contribute more support and less conflict than the C-termini. These analyses show that paralogs largely group by silk gland type, except for the major ampullate spidroins. Moreover, spidroin structural motifs associated with superior tensile strength arose early in the history of this gene family, whereas a motif conferring greater extensibility convergently evolved in two distantly related paralogs.
Insect molecular biology (Print), 2008
Spider dragline silk is primarily composed of proteins called major ampullate spidroins (MaSp) that consist of a large repeat array flanked by non-repetitive N-and C-terminal domains. Until recently, there has been little evidence for more than one gene encoding each of the two major spidroin silk proteins, MaSp1 and MaSp2. Here, we report the deduced N-terminal domain sequences for two distinct MaSp1 genes from Nephila clavipes (MaSp1A and MaSp1B) and for MaSp2. All three MaSp genes are co-expressed in the major ampullate gland. A search of the GenBank database also revealed two distinct MaSp1 C-terminal domain sequences. Sequencing confirmed that both MaSp1 genes are present in all seven Nephila clavipes spiders examined. The presence of nucleotide polymorphisms in these genes confirmed that MaSp1A and MaSp1B are distinct genetic loci and not merely alleles of the same gene. We have experimentally determined the transcription start sites for all three MaSp genes and established preliminary pairing between the two MaSp1 N-and C-terminal domains. Phylogenetic analysis of these new sequences and other published MaSp N-and C-terminal domain sequences illustrated that duplications of MaSp genes may be widespread among spider species.
Nature genetics, 2017
Spider silks are the toughest known biological materials, yet are lightweight and virtually invisible to the human immune system, and they thus have revolutionary potential for medicine and industry. Spider silks are largely composed of spidroins, a unique family of structural proteins. To investigate spidroin genes systematically, we constructed the first genome of an orb-weaving spider: the golden orb-weaver (Nephila clavipes), which builds large webs using an extensive repertoire of silks with diverse physical properties. We cataloged 28 Nephila spidroins, representing all known orb-weaver spidroin types, and identified 394 repeated coding motif variants and higher-order repetitive cassette structures unique to specific spidroins. Characterization of spidroin expression in distinct silk gland types indicates that glands can express multiple spidroin types. We find evidence of an alternatively spliced spidroin, a spidroin expressed only in venom glands, evolutionary mechanisms for...