An improved isochronous pulse after lentiviral knock-down of STEP in Area X of juvenile zebra finches

The zebra finch is one of the most commonly used animal models for studying the genetic mechanisms underlying vocal learning. To investigate the genetic basis of vocal learning, various genes have been knocked down in Area X—a brain region involved in birdsong acquisition—during the critical learning period. All genes that affect speech when mutated in humans similarly impair song learning in zebra finches. To date, no study has demonstrated that not all genes downregulated in Area X result in decreased song learning. Therefore, we sought a candidate gene to knock down in Area X that could either have no effect or potentially improve song learning. STEP is a protein that dephosphorylates many targets in the brain, and its knockout in mice has resulted in enhanced learning. In this study, a lentiviral knockdown of STEP in Area X during song learning resulted in birds producing normal song in almost all parameters and levels of song analysis. This stands in contrast to the knockdown of other genes like all FoxP subfamily members, which resulted in diminished song learning in previous studies. The only parameter positively affected by STEP knockdown was song rhythmicity, as evidenced by a lower deviation of song element onsets from an isochronous pulse than even their tutors. These results demonstrate for the first time that not all knockdowns in Area X lead to deterioration of song learning and validate the specificity of the method and previous findings. Significance Statement This is the first coding gene knockdown in Area X without negatively affecting song learning.