From silence to song: Testosterone triggers extensive transcriptional changes in the female canary HVC.

Seasonal song production in canaries is influenced by gonadal hormones, but the molecular mechanisms underlying testosterone-induced song development in adult female canaries, which rarely sing naturally, remain poorly understood. We explored testosterone-induced song development in adult female canaries by comparing gene regulatory networks in the song-controlling brain area HVC at multiple time points (1 h to 14 days) post-treatment with those of placebo-treated controls. Females began vocalizing within 4 days of testosterone treatment, with song complexity and HVC volume increasing progressively over 2 weeks. Rapid transcriptional changes involving 2739 genes preceded song initiation. Over 2 weeks, 9913 genes-approximately 64% of the canary's protein-coding genome-were differentially expressed, with 98% being transiently regulated. These genes are linked to various biological functions, with early changes at the cellular level and later changes affecting the nervous system level after prolonged hormone exposure. Our findings suggest that testosterone-induced song development is accompanied by extensive and dynamic transcriptional changes in the HVC, implicating widespread neuronal involvement. These changes underpin the gradual emergence of singing behavior, providing insights into the neural basis of seasonal behavioral patterns.