Sorigue, P. | Search bioRxiv

bioRxiv2026

Genome-wide DNA methylation profiling of the zebrafish forebrain

The zebrafish forebrain is a central hub for cognitive and social behaviors, yet a comprehensive, region-specific DNA methylation reference for this tissue is not available. To address this gap, we generated a genome-wide methylation map of the adult zebrafish forebrain using Oxford Nanopore Technologies (ONT) long-read sequencing. Forebrains from six individuals were profiled, enabling direct detection of multiple DNA base modifications at single-base resolution. The resulting dataset includes CpG-associated 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC), as well as non-CpG 5mC and N6-methyladenine (6mA), with 96.8% genome coverage. CpG methylation was widespread, with 64.2% of CpG sites classified as highly 5mC-modified. In contrast, 5hmC and non-CpG methylation were markedly less abundant, and 6mA was detected at very low levels. CpG islands showed a bimodal distribution of methylation, promoter regions displayed elevated variability compared to gene bodies, and CC-context non-CpG methylation exhibited significant strand asymmetry. This resource provides a high-resolution epigenomic baseline for the adult zebrafish forebrain.

genomics↗

bioRxiv2025

Nonapeptide molecular evolution during the adaptive radiation of Tanganyika cichlids

Oxytocin (OT) and vasotocin (VT) are evolutionarily conserved nonapeptides that regulate a wide range of physiological and behavioural processes in vertebrates. Their receptor families have undergone gene duplications that facilitated functional diversification throughout vertebrate evolution. Using the diverse cichlid species in Lake Tanganyika, which have undergone repeated evolutionary transitions between social phenotypes, we investigated the molecular evolution of the nonapeptide system and its potential involvement in social behaviour. We performed a positive selection analysis based on the dN/dS ratio and examined the correlation between amino acid variants and two social phenotypes. We also analysed gene expression data to explore associations between brain receptor expression and social phenotype variation. Our findings reveal that, while most sites in nonapeptide receptors are under strong purifying selection, a few sites - primarily in the extended intracellular loop 3 (IL3) of VTR2A receptors - show signatures of positive selection. Additionally, a specific amino acid in VTR2Aa correlates with pair-bonding, suggesting its potential role in social attachment. Together, our results provide new insights into the evolution of the nonapeptide system and its contribution to social diversity in cichlids.

evolutionary biology↗