COMPARATIVE GENOMIC IDENTIFICATION AND ANALYSES OF EPIDERMAL DIFFERENTIATION COMPLEX GENES IN TURTLES

The epidermal differentiation complex (EDC) is a cluster of genes highly associated with keratinocytes differentiation and epidermal keratinization. This gene cluster plays an important role in the differentiation of epidermal tissues in amniotes, the formation of various skin appendages, and the keratinization process. Therefore, exploring the sequence characteristics and evolution of EDC genes in turtles can help elucidate the genetic basis and evolutionary history of their shell epidermis traits. Currently, there is a lack of systematic comparative analysis of the sequence characteristics and evolutionary levels of EDC genes across different turtle groups. This study performed comparative genomics identification of EDC in 28 turtles, including chromosomal localization, amino acid composition, domain analysis, protein spatial structure analysis, and the reconstruction of evolutionary history. The EDC genes in turtles exhibit the same four gene families found in other reptiles, with members of the SEDC gene family expanding through multiple tandem repeat events. The amino acid composition of turtle SEDC proteins is highly diverse, with SEDC and SFTP protein amino acid content showing group-specific characteristics (hard-shelled, soft-shelled, leatherback), which supports the diversity of shell epidermal structures in turtles. The functional domains and protein spatial structures of S100A and SFTP are highly conserved across turtle species, with motif 3 of PGLYRP3 showing a loss specific to the family Trionychidae. The turtle-specific EDPCV originates from EDP1, and mutations have enriched cysteine and valine, facilitating gene expansion through tandem duplication. This study provides a data foundation and theoretical basis for further research on the role of EDPCV in turtles.