Recruitment and diversification of an ecdysozoan family of neuropeptide hormones for black widow spider venom expression |
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Authors: | Caryn McCowan Jessica E. Garb |
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Affiliation: | Department of Biological Sciences, University of Massachusetts Lowell, Lowell, MA 01854, USA |
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Abstract: | Venoms have attracted enormous attention because of their potent physiological effects and dynamic evolution, including the convergent recruitment of homologous genes for venom expression. Here we provide novel evidence for the recruitment of genes from the Crustacean Hyperglycemic Hormone (CHH) and arthropod Ion Transport Peptide (ITP) superfamily for venom expression in black widow spiders. We characterized latrodectin peptides from venom gland cDNAs from the Western black widow spider (Latrodectus hesperus), the brown widow (Latrodectus geometricus) and cupboard spider (Steatoda grossa). Phylogenetic analyses of these sequences with homologs from other spider, scorpion and wasp venom cDNAs, as well as CHH/ITP neuropeptides, show latrodectins as derived members of the CHH/ITP superfamily. These analyses suggest that CHH/ITP homologs are more widespread in spider venoms, and were recruited for venom expression in two additional arthropod lineages. We also found that the latrodectin 2 gene and nearly all CHH/ITP genes include a phase 2 intron in the same position, supporting latrodectin's placement within the CHH/ITP superfamily. Evolutionary analyses of latrodectins suggest episodes of positive selection along some sequence lineages, and positive and purifying selection on specific codons, supporting its functional importance in widow venom. We consider how this improved understanding of latrodectin evolution informs functional hypotheses regarding its role in black widow venom as well as its potential convergent recruitment for venom expression across arthropods. |
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Keywords: | aa, amino acid(s) AIC, Akaike Information Criterion α-Latrotoxin LMWPs, α-latrotoxin associated low molecular weight proteins BEB, Bayes Empirical Bayes bp, base pair(s) cDNA, DNA complementary to RNA CHH, Crustacean Hyperglycemic Hormone CPP, Clade Posterior Probability dN, nonsynonymous substitutions per nonsynonymous site ds, double strand(ed) dS, synonymous substitutions per synonymous site EST, Expressed Sequence Tag(s) FEL, fixed effects likelihood FUBAR, Fast Unbiased Bayesian AppRoximation GTR+I+G, Generalized Time Reversible plus Gamma plus Invariant model ICK, Inhibitor Cystine Knot ITP, Ion Transport Peptide LRT, likelihood ratio test MEME, Mixed Effects Model of Episodic Diversifying Selection ML, maximum likelihood NCBI, National Center for Biotechnology Information RTA, Random Taxon Additions RTA clade, Retrolateral Tibial Apophysis clade SLAC, single-likelihood ancestor counting TPM3uf+I+G, three parameter with unequal base frequencies plus gamma plus Invariant model |
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