Fish Shellfish Immunol 2025 Feb 16;160:110204. doi: 10.1016/j.fsi.2025.110204.

Evolutionary and functional insights into Fibrinogen-related protein (FREP) dynamics in sea cucumbers.

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The Fibrinogen-related protein (FREP) gene family is a cornerstone of immune defense in metazoans, yet its evolution and functional specialization in invertebrates, particularly sea cucumbers, remain underexplored. By analyzing genomic data from 1004 species, this study reveals a significant and lineage-specific expansion of FREP genes in sea cucumbers. These genes are categorized into single-domain FREPs (sFREPs) and multi-domain FREPs (mFREPs), with the latter containing unique TIL domains associated with immune defense. Comparative analyses show that chromosomal rearrangements and gene duplications have driven FREP diversification, while transcriptomic profiling highlights tissue-specific expression and immune activation of TIL-containing mFREPs. These findings illuminate the adaptive evolution of FREPs and their pivotal role in pathogen recognition, emphasizing chromosomal dynamics and domain architecture in shaping invertebrate immunity. This study provides a foundation for deeper insights into the molecular basis of immune adaptation in sea cucumbers and other invertebrates.

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