Tissue-specific expression of young small-scale duplications in human central nervous system regions

Gene duplication, a mechanism that has been occurring in the genome throughout evolution and has led to refined patterns of spatial expression and biological functions, is a major contributor to tissue complexity in humans. The accumulating evidence, from inter-species and inter-organ comparisons, points to the relevance of exploring tissue expression through the lens of duplication type and date. In this study, we use the transcriptional profiles of human central nervous system (CNS) tissues to identify evolutionary features associated with the spatial expression of paralogs and gene families. We show that paralogs, especially those originating from small-scale duplications younger (ySSD) than whole-genome duplication (WGD), are significantly implicated in tissue-specific expression in CNS territories. Interestingly, we observe that both the young age of the ySSD and the duplication type are associated with their tissue-specificity. The exploration of these paralog properties at the family level of organization shows that the families composed of a majority of genes co-expressed across CNS tissues are enriched in tandem duplications, ySSDs and tissue-specific paralogs. Moreover, these families are strongly enriched in tissue-specific families, suggesting that co-expression analysis is able to capture shared tissue-specificity, especially of ySSDs, within paralog families. Overall, our study provides new evidence for the major involvement of ySSDs in the differentiation of CNS territories, that extend ySSDs properties already established from comparative expression analyses across organs and species.