New insights into the evolution of spider silk proteins illuminated by long-read transcriptomes
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Abstract
Spider silk has long fascinated scientists because of its exceptional mechanical properties, yet the evolutionary origins and diversification of spider silk proteins (spidroins) remain incompletely understood. By analyzing long-read spidroin transcripts from spiders representing key evolutionary lineages, we identify two ancestral proteins present in basal spiders: an alanine–serine-rich (AS-type) protein and a glycine–serine-rich (GS-type) protein. These ancestral proteins likely served as primary evolutionary templates for the diversification of modern spider silks. We show that the AS-type ancestral spidroin remained relatively conserved and ultimately gave rise to the specialized tubuliform spidroin (TuSp) used in eggcase silk. In contrast, the GS-type protein underwent extensive functional radiation, evolving into differentiated minor ampullate spidroins (MiSp) through the acquisition of distinct terminal domains and β-sheet–associated structural innovations. Our results further suggest that major ampullate spidroins (MaSp) may have originated from MiSp, with the GS motif representing an evolutionarily favorable genetic substrate for the emergence of high-performance silk proteins. Finally, we propose a revised evolutionary trajectory for flagelliform spidroins (Flag), suggesting that they were co-opted as components of ampullate silk during functional degeneration in modern non-web-weaving RTA clade spiders. Together, these findings provide a high-resolution framework for understanding the genetic innovations that drove the diversification of spider silk.
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the most ancient
Similar to my comment about not referring to extant proteins as ancestral, I would not refer to species that are currently alive as "ancient". Early-diverging is more accurate.
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two34ancestral proteins present in basal spiders: an alanine–serine-rich (AS-type) protein and35a glycine–serine-rich (GS-type) protein. These ancestral proteins likely served as36primary evolutionary templates for the diversification of modern spider silks.
I noticed multiple references to these newly discovered extant proteins in an early diverging spider lineage as "ancestral proteins". I would steer clear from that language. Ancestral proteins implies that these proteins are no longer extant, and that they precede the existence of modern proteins. These are usually lost to time, but the term is reserved for proteins created with ancestral sequence reconstruction or archeologically recovered DNA. I would instead refer to these proteins as early-diverging, or belonging to spiders from an early-diverging lineage of Araneae.
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cient spidroin.
I'm noticing in multiple figures the annotations of domains and the labelling of silk protein types are pixelated and unreadable inside the figure. This is something to note when exporting the figures in the final paper. I would consider using simpler symbols to signify the different classes of spider silk proteins containing only the name of the protein family.
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red arrows indicate the location of two624ancient spider silk proteins
I noticed that red arrows are mentioned in the figure, but I am not seeing those arrows in the figure itself. It might work to simply highlight the name of the taxon in red instead.
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