# The Early Evolution of Tudor Genes in Holozoa and How Their Distribution Was Influenced by Life History Traits in Metazoa

## TL;DR

This paper explores how Tudor genes evolved in early animals and how their distribution relates to life history traits like reproduction and genome complexity.

## Contribution

The study provides a holozoan-wide analysis of Tudor gene evolution and links their expansion to life history traits and genomic events in metazoans.

## Key findings

- Tudor genes expanded in metazoans, especially those involved in Piwi-interacting RNA pathways.
- Variability in Tudor gene numbers correlates with life history traits and genomic events like whole-genome duplications.
- Elements of the Piwi-interacting RNA pathway were likely present in the holozoan common ancestor.

## Abstract

Early metazoan evolution was characterized by the expansion of multiple gene families, such as the Tudor family, involved in novel multicellularity-related functions. In eukaryotes, Tudor genes (i.e. genes including at least one Tudor domain) are numerous, heterogeneous, and mostly associated with gene expression regulation. However, they underwent an animal-specific expansion, with novel elements almost exclusively involved in retrotransposon regulation through Piwi-interacting RNAs, as spatiotemporal regulators of the key-element Piwi, another previously considered animal-specific gene. Here, we used online-available proteomes covering 25 major taxonomic groups to characterize the Tudor gene family at a holozoan-wide level, confirming the apomorphic metazoan expansion of Piwi-interacting RNA-related Tudor genes. However, we also annotated elements of the Piwi-interacting RNA pathway (Tudor and Piwi genes) in Ichthyosporea species, suggesting that elements of the Piwi-interacting RNA pathway were already present in the holozoan common ancestors. We observed an outstanding variability (34-fold) of Tudor gene number between and within metazoan phyla that could be associated with convergent genomic and phenotypic evolutions: expansions were usually sided by whole-genome duplications and/or life history traits such as parthenogenesis; reductions were mostly associated to overall phenotypic and genomic simplifications, like in almost all considered endoparasites. Lastly, we phylogenetically tested, and mostly (but not completely) confirmed, a previously proposed model for the evolution of the Tudor domain secondary structures.