Singing with Genes (Simmons)

Back in 2010, the fully sequenced genome of Taeniopygia guttata, the Zebra finch, was completed. It was the second bird, after the chicken, and the first of the passerines to have its genome completely sequenced. The Zebra finch, unlike the chicken, is a songbird, and, as a result, several studies focused on this characteristic’s relationship to its genomic sequence. In addition, the Zebra finch and other song birds communicate with “learned vocalizations,” which, so far, have only been observed in humans (Warren et al. 2010*). A research article published in Nature science journal by Warren et al. in 2010 provided an overview of the studies conducted by a research group from Washington University School of Medicine. The group highlights findings regarding the genome’s “active involvement” in neural processes involved in song behavior and communication (Warren et al. 2010). This includes their findings on how vocal communication has an effect on the expression of various genetic material, including microRNAs and transcription factors through having an effect on “gene regulatory networks” in the Zebra finch brain.

In Zebra finch culture, only the males sing, and, as a result, more fully develop the “song control nuclei” located in their forebrains. In addition, these increase in size and change in organization during the males’ juvenile stage, when they learn to sing, providing strong evidence for neural plasticity in songbirds (Warren et al. 2010*). The article also highlights how song behavior has been found to influence gene expression in songbirds. When learning songs, gene response changes in as quickly as the course of a day.

A Zebra Finch

In their studies, the research group used males, the homogametic sex with ZZ rather than ZW, in order to more thoroughly cover the Z chromosome. In addition, because the research group wanted to study the genes relevant to song behavior and brain development, they chose juvenile males and adult males in the study. The group used both “sequence alignment and fluorescent in situ hybridization” processes on the chromosomes of both the Zebra finches and chickens, the only other fully sequenced bird genome available at the time in order to explore questions regarding the species’ evolution. With regard to this, they found that both genomes lacked genes that encode for proteins involved in the creation of “vomeronasal receptors,” teeth, and breast milk. They also found that the Zebra finch genes for the development of major histocompatibility complex, involved in white blood cell function, are unusually dispersed across multiple chromosomes, in comparison to chicken and human MHC genes being more locally distributed. The article also addresses the controversy behind how birds balance Z chromosome expression in the homogametic sex, especially with regard to species that have a large difference between male and female appearance and behavior. The article suggests, that in most bird species, this could be linked to male hypermethylated RNA dosages, which, oddly, Zebra finches lack.

*_{Warren, et al. (2010) The Genome of a Song Bird. Nature 464: 757-762. dol:10.1038/nature08819}