CHICKEN GENE NOMENCLATURE IN PROTOCADHERINS

Abstract

Protocadherins (PCDHs), a major subgroup of the cadherin superfamily, play essential roles in neural development by mediating calcium-dependent, homophilic cell-cell adhesion. These molecules are highly expressed in the nervous system, where they contribute to neuronal identity and circuit formation through their diverse extracellular domains and gene cluster arrangements. Unlike classical cadherins, protocadherin diversity arises from large gene clusters that permit numerous expression combinations, especially in neurons, serving as molecular identity codes that prevent self-synapsing and enable proper neural wiring. Protocadherins are broadly conserved across vertebrates, yet their gene organization and evolutionary trajectories vary significantly. This study highlights the genomic organization of the chicken PCDH gene clusters, revealing a unique expansion in the beta subcluster and divergence from mammalian synteny, particularly in the arrangement and number of clustered genes. The lack of direct orthology between species due to differences in cluster organization necessitates a standardized nomenclature system based on functional equivalence and phylogenetic relationships rather than strict gene order conservation. Through detailed manual review, this research assigns standardized names to chicken PCDH genes following international nomenclature guidelines, facilitating cross-species comparisons. Notably, all human non-clustered PCDHs are conserved in chickens, underscoring strong evolutionary conservation, although significant annotation differences required manual curation for proper classification. The observed expansion of the chicken beta-cluster by 13 additional genes suggests species-specific adaptations. This work addresses the challenges of gene name discrepancies in comparative genomics by applying a unified nomenclature system across vertebrates. The standardized classification of chicken PCDHs enhances the utility of the chicken genome as a reference model for avian species and supports its role in biomedical and developmental studies. More broadly, this study contributes to a coherent framework for vertebrate gene nomenclature, which is vital for efficient data sharing, evolutionary studies, and integrative genomic research.