Fig. 5: Multi-layered dosage compensation of the avian Z-chromosome.

a Transcriptional upregulation of the single female Z chromosome is driven by increased transcriptional burst frequency resulting in a transcriptionally hyperactive female Z chromosome (Z”). In addition, dosage compensation is further achieved through increased translational efficiency of Z-linked transcripts in females, mediated by increased ribosomal occupancy compared to Z-linked transcripts in males. b Schematic representation of a multi-layered model of avian Z-chromosome dosage compensation. At the genomic level, the single female Z chromosome does not display enhanced accessibility. At the gene expression level, compensatory transcriptional upregulation of the female Z is apparent, and driven by increased transcription burst frequency. Z-linked transcripts display higher translational efficiency, partially contributing to an overall rebalancing and near-complete dosage compensation between ZZ males and ZW females at the proteomic level. Plotted as median ± 95% confidence interval (C.I) of Male:Female gene expression ratios for each modality based on ATAC-seq (chrZ genes = 548), bulk RNA-seq (chrZ genes = 501), Ribo-seq (chrZ genes = 443) and proteomics (chrZ genes = 90) data. Male:Female ratios based on chicken embryonic fibroblasts derived from n = 2 male and n = 2 female F1 chicken embryos.