Project description:The repressive capacity of cytosine DNA methylation is mediated by recruitment of silencing complexes by methyl-CpG binding domain (MBD) proteins. Unexpectedly, we discovered that a family of arthropod Copia retrotransposons have incorporated a host-derived MBD domain. We functionally demonstrate how retrotransposon encoded MBDs preferentially bind to CpG-dense methylated regions, which correspond to transposable element regions of the host genome, in the myriapod Strigamia maritima. Consistently, young MBD-encoding Copia retrotransposons (CopiaMBD) accumulate in regions with higher CpG-densities than other LTR-retrotransposons also present in the genome. This would suggest that retrotransposons use MBDs to integrate into heterochromatic regions in Strigamia, avoiding potentially harmful insertions into host genes. In contrast, CopiaMBD insertions in the spider Stegodyphus dumicola genome disproportionately accumulate in methylated gene bodies when compared to other spider LTR-retrotransposons. Given that transposons are not actively targeted by DNA methylation in the spider genome, this distribution bias would also support a role for MBDs in the integration process. Together, these data demonstrate that retrotransposons can co-opt host-derived epigenome readers, potentially harnessing the host epigenome landscape to advantageously tune the retrotransposition process.
Project description:Spiders are a highly diverse group of arthropods that occur in most habitats on land. Notably, spiders have significant ecological impact as predators because of their extraordinary prey capture adaptations, venom and silk. Spider venom is among the most heterogeneous animal venoms and has pharmacological applications, while spider silk is characterized by great toughness with potential for biomaterial application. We describe the genome sequences of two spiders representing two major taxonomic groups, the social velvet spider Stegodyphus mimosarum (Araneomorphae), and the Brazilian white-knee tarantula Acanthoscurria geniculata (Mygalomorphae). We annotate genes using a combination of transcriptomic and in-depth proteomic analyses. The genomes are large (2.6 Gb and 6 Gb, respectively) with short exons and long introns and approximately 50% repeats, reminiscent of typical mammalian genomes. Phylogenetic analyses show that spiders and ticks are sister groups outgrouped by mites, and phylogenetic dating using a molecular clock dates separation of velvet spider and tarantula at 270 my. Based on the genomes and proteomes, we characterize the genetic basis of venom and silk production of both species in detail. Venom protein composition differs markedly between the two spiders, with lipases as the most abundant protein in the velvet spider and present only at low concentration in tarantula. Venom in both spiders contains proteolytic enzymes, and our analyses suggest that these enzymes target and process precursor peptides that subsequently mediate the toxic effects of venom. Complete analysis of silk genes reveal a diverse suite of silk proteins in the velvet spider including novel types of spidroins, and dynamic evolution of major ampullate spidroin genes, whereas silk protein diversity in tarantula is far less complex. The difference in silk proteins between species is consistent with a more complex silk gland morpholgy and use of three-dimentional capture webs consisting of multiple silk types in aranomorph spiders.