The arms race of ray-finned fish against the derepression of LTR retroelements.

Transposable elements (TEs) are dynamic components of eukaryotic genomes that are important in speciation. Evolutionary pressure has led to the evolution of silencing mechanisms, such as the involvement of Krüppel box-associated zinc finger proteins (KRAB-ZFPs) that regulate TE transcription via TRIM28-mediated NuRD complex recruitment in sarcopterygians. The transcriptional activity of genes that encode proteins of the NuRD complex was also detected in actinopterygians, even though genes encoding crucial proteins such as TRIM28 and KRAB-ZNF are missing in this evolutionary lineage. This study hypothesized that TRIM33 could serve as a replacement for TRIM28 in this lineage and suggested an evolutionary relationship between the sarcopterygian KRAB-ZFPs, the actinopterygian KRAB-like ZNFs and the fish N-terminal zinc-associated domain (FiNZ) ZNFs that are specific to cyprinids. Through coimmunoprecipitation analyses conducted in the basal teleost Anguilla marmorata and the cyprinid Danio rerio, we evaluated the interaction of TRIM33 with the KRAB-like and FiNZ ZFPs. Moreover, we explored the expression profiles of TEs and genes that encode proteins that are potentially involved in their silencing during zebrafish development. Our results may provide new evidence for more thoroughly understanding the evolutionary mechanisms underlying the adaptation of ray-finned fish.