Division of Invertebrate Zoology and Sackler Institute for Comparative Genomics, American Museum of Natural History, New York, NY 10024, USA.
Department of Systems Pharmacology and Translational Therapeutics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
G3 (Bethesda). 2021 Jan 18;11(1). doi: 10.1093/g3journal/jkaa039.
Spider silks are renowned for their high-performance mechanical properties. Contributing to these properties are proteins encoded by the spidroin (spider fibroin) gene family. Spidroins have been discovered mostly through cDNA studies of females based on the presence of conserved terminal regions and a repetitive central region. Recently, genome sequencing of the golden orb-web weaver, Trichonephila clavipes, provided a complete picture of spidroin diversity. Here, we refine the annotation of T. clavipes spidroin genes including the reclassification of some as non-spidroins. We rename these non-spidroins as spidroin-like (SpL) genes because they have repetitive sequences and amino acid compositions like spidroins, but entirely lack the archetypal terminal domains of spidroins. Insight into the function of these spidroin and SpL genes was then examined through tissue- and sex-specific gene expression studies. Using qPCR, we show that some silk genes are upregulated in male silk glands compared to females, despite males producing less silk in general. We also find that an enigmatic spidroin that lacks a spidroin C-terminal domain is highly expressed in silk glands, suggesting that spidroins could assemble into fibers without a canonical terminal region. Further, we show that two SpL genes are expressed in silk glands, with one gene highly evolutionarily conserved across species, providing evidence that particular SpL genes are important to silk production. Together, these findings challenge long-standing paradigms regarding the evolutionary and functional significance of the proteins and conserved motifs essential for producing spider silks.
蜘蛛丝以其出色的机械性能而闻名。促成这些特性的是由丝氨酸（蜘蛛丝蛋白）基因家族编码的蛋白质。丝氨酸主要是通过对雌性蜘蛛的 cDNA 研究发现的，这是基于保守的末端区域和重复的中心区域存在的情况下发现的。最近，对金蛛， Trichonephila clavipes 的基因组测序提供了丝氨酸多样性的完整图景。在这里，我们对 T. clavipes 丝氨酸基因的注释进行了细化，包括对一些基因的重新分类为非丝氨酸。我们将这些非丝氨酸命名为丝氨酸样（SpL）基因，因为它们具有重复序列和与丝氨酸相似的氨基酸组成，但完全缺乏丝氨酸的典型末端结构域。然后通过组织和性别特异性基因表达研究来研究这些丝氨酸和 SpL 基因的功能。通过 qPCR，我们发现尽管雄性一般产生的丝较少，但一些丝基因在雄性丝腺中比在雌性中上调。我们还发现一种缺乏丝氨酸 C 末端结构域的神秘丝氨酸高度表达在丝腺中，这表明丝氨酸可以在没有典型末端区域的情况下组装成纤维。此外，我们发现两个 SpL 基因在丝腺中表达，其中一个基因在物种间高度保守，这表明特定的 SpL 基因对丝的产生很重要。总之，这些发现挑战了关于产生蜘蛛丝的蛋白质和保守基序的进化和功能意义的长期模式。
