From Defenders to Hosts: The Arm-in-Arm Expansion of KRAB-Zinc Finger Gene Repertoires and Retroviral Integrations in Mammals.
- 1Independent Researcher, 80053 Castellammare di Stabia, Italy.
Abstract
KRAB-zinc finger proteins (KZFPs) constitute one of the largest and most rapidly evolving families of transcription factors in vertebrates, with particularly extensive expansion and diversification in mammals. While several KZFPs are conserved across species, numerous lineage- and species-specific genes have emerged during mammalian evolution, with a large fraction recognizing and repressing transposable elements (TEs), and particularly endogenous retroviruses (ERVs). The evolutionary relationship between KZFPs and ERVs has traditionally been interpreted through an "arms-race" model, in which recurrent retroviral invasions drive the emergence of new KZFP specificities, while retroelements evolve to escape host repression. This review examines the evidence linking the evolutionary dynamics of KZFPs and ERVs and discusses how their relationship may extend beyond reciprocal adaptation at the level of sequence recognition. In particular, recent comparative genomic analyses reveal that young KZFP genes are frequently organized in highly repetitive genomic clusters that are themselves enriched in young ERVs. Structural variation and segmental duplication within these regions can simultaneously expand KZFP and ERV copy numbers, providing a potential genomic mechanism for their concerted diversification. These observations motivate an "arm-in-arm" model, in which KZFPs and ERVs are not only antagonistic evolutionary partners but can also become physically and evolutionarily intertwined within the same genomic environments. The possibility that KZFP clusters may have a dual role in the evolutionary fate of retroviral sequences is also considered: while KZFP-mediated repression can limit the deleterious effects of newly integrated retroelements and facilitate their persistence, the repetitive and structurally dynamic nature of these loci may create opportunities for subsequent duplication and diversification. Together, these observations broaden the classical arms-race framework and highlight how the interplay between retroviral invasion, host defense, genomic architecture, and sequence cooption can contribute to the generation of genomic and regulatory diversity.
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BibTeX
@article{bruno2026from,
title = {{From Defenders to Hosts: The Arm-in-Arm Expansion of KRAB-Zinc Finger Gene Repertoires and Retroviral Integrations in Mammals.}},
author = {Melania Bruno},
journal = {Viruses},
year = {2026},
month = oct,
doi = {10.3390/v18101153},
url = {https://europepmc.org/article/MED/42944072},
note = {CC BY},
}
RIS
TY - JOUR
TI - From Defenders to Hosts: The Arm-in-Arm Expansion of KRAB-Zinc Finger Gene Repertoires and Retroviral Integrations in Mammals.
AU - Melania Bruno
PY - 2026
DA - 2026/10/17
JO - Viruses
DO - 10.3390/v18101153
UR - https://europepmc.org/article/MED/42944072
AB - KRAB-zinc finger proteins (KZFPs) constitute one of the largest and most rapidly evolving families of transcription factors in vertebrates, with particularly extensive expansion and diversification in mammals. While several KZFPs are conserved across species, numerous lineage- and species-specific genes have emerged during mammalian evolution, with a large fraction recognizing and repressing transposable elements (TEs), and particularly endogenous retroviruses (ERVs). The evolutionary relationship between KZFPs and ERVs has traditionally been interpreted through an "arms-race" model, in which recurrent retroviral invasions drive the emergence of new KZFP specificities, while retroelements evolve to escape host repression. This review examines the evidence linking the evolutionary dynamics of KZFPs and ERVs and discusses how their relationship may extend beyond reciprocal adaptation at the level of sequence recognition. In particular, recent comparative genomic analyses reveal that young KZFP genes are frequently organized in highly repetitive genomic clusters that are themselves enriched in young ERVs. Structural variation and segmental duplication within these regions can simultaneously expand KZFP and ERV copy numbers, providing a potential genomic mechanism for their concerted diversification. These observations motivate an "arm-in-arm" model, in which KZFPs and ERVs are not only antagonistic evolutionary partners but can also become physically and evolutionarily intertwined within the same genomic environments. The possibility that KZFP clusters may have a dual role in the evolutionary fate of retroviral sequences is also considered: while KZFP-mediated repression can limit the deleterious effects of newly integrated retroelements and facilitate their persistence, the repetitive and structurally dynamic nature of these loci may create opportunities for subsequent duplication and diversification. Together, these observations broaden the classical arms-race framework and highlight how the interplay between retroviral invasion, host defense, genomic architecture, and sequence cooption can contribute to the generation of genomic and regulatory diversity.
SN - 1999-4915
ER -