Molecular characterization of the song control nucleus HVC in Bengalese finch brain.

Songbirds have a specialized neural substrate for learned vocalization, called the song circuit, which consists of several song nuclei in the brain. The song control nucleus HVC (a letter-based name) is the intersection point of the song learning and vocal motor pathways. Knowledge of the types of genes expressed in the HVC is essential in understanding the molecular aspects of the HVC. Gene expression in the HVC under silent conditions shows the competence necessary for singing. To investigate this, we compared the HVC with its adjacent tissues in searching for the molecular specificities of the song nucleus HVC using an in-house cDNA microarray of the Bengalese finch (Lonchura striata var. domestica). Our microarray analysis revealed that 70 genes were differentially expressed in the HVC compared with the adjacent tissue. We investigated 27 of the microarray-selected genes that were enriched or repressed in the HVC by in situ hybridization. We found that multiple calcium-binding proteins (e.g., CAPS2, parvalbumin and ATH) were enriched in the HVC. Meanwhile, the adult HVC showed low expression levels of plasticity-related genes (e.g., CAMK2A and MAP2K1) compared with the juvenile HVC. The HVC plays an important role during song learning, but our results suggest that the plasticity of this nucleus may be suppressed during adulthood. Our findings provide new information about the molecular features that characterize the HVC.