Sensory- and motor-regulated transcripts
Auditory experience, a fundamental consequence of social interactions within and across songbird species, had been previously shown to strongly affect gene regulatory events in the auditory forebrain . It was found that in the auditory forebrain of animals in silent conditions, approximately 40% of the detected transcripts are non-coding, indicating that regulatory microRNAs may have a central role in brain homeostasis. When birds were stimulated with playbacks of recorded song, thousands of transcripts were upregulated or downregulated , and analyses of their genomic sequences revealed that roughly two-thirds of the downregulated transcripts were non-coding RNAs. Furthermore, known and novel microRNAs were found to be expressed in the auditory forebrain, and their binding sites were detected in the untranslated regions of regulated genes.
Singing behavior also drives robust gene expression programs in structures of the song control system, a specialized brain network required for sensorimotor integration and vocal output . By using a microarray platform with oligonucleotides generated as part of this project, the songbird genome consortium was able to uncover a series of transcriptional regulators whose expression was modulated by the act of singing. Changes in transcription factor expression that occurred early after singing were strongly correlated with later modifications in the expression patterns of groups of their predicted target genes . In fact, many of these targets have been identified for the first time and will now enable researchers to develop testable hypotheses about the gene regulatory interactions that are induced during a learned behavior.
Overall, these findings highlight the role of microRNAs and non-coding RNAs in the control of gene expression in the songbird brain, in addition to the active regulation of transcription factors and their respective target genes. When comparing hearing-driven transcripts with genes thought to have been positively selected in songbirds, a significant over-representation of genes encoding ion channels was uncovered, consistent with robust and complex expression patterns of ion channel-associated transcripts in stations of the song-control circuit .