Exploring the zebra finch Taeniopygia guttata as a novel animal model for the speech-language deficit of fragile X syndrome

FoxP2 isoforms delineate spatiotemporal transcriptional networks for vocal learning in the zebra finch

Human speech is one of the few examples of vocal learning among mammals yet ~half of avian species exhibit this ability. Its neurogenetic basis is largely unknown beyond a shared requirement for FoxP2 in both humans and zebra finches. We manipulated FoxP2 isoforms in Area X, a song-specific region of the avian striatopallidum analogous to human anterior striatum, during a critical period for song development. We delineate, for the first time, unique contributions of each isoform to vocal learning. Weighted gene coexpression network analysis of RNA-seq data revealed gene modules correlated to singing, learning, or vocal variability. Coexpression related to singing was found in juvenile and adult Area X whereas coexpression correlated to learning was unique to juveniles. The confluence of learning and singing coexpression in juvenile Area X may underscore molecular processes that drive vocal learning in young zebra finches and, by analogy, humans.

Songbirds, much like in humans, have a critical period in youth when they are best at learning vocal communication skills. In birds, this is when they learn a song they will use later in life as a courtship song. In humans, this is when language skills are most easily learned. After this critical period ends, it is much harder for people to learn languages, and for certain bird species to learn their song.

When birds sing every morning, the activity of a gene called FoxP2 drops, which causes a coordinated change in the activity of thousands of other genes. It is suspected that FoxP2 – and the changes it causes – could be a part of the molecular basis for vocal learning. FoxP2 is also known to play a role in speech in humans, and both birds and humans have a long and a short version of this gene. Previous research has shown that when the long version of the gene was altered so its activity would no longer decrease when birds were singing, the birds failed to learn their song. Moreover, humans with a mutation in the long version have problems with their speech. However, until now, it was not known if modifications to the short version had the same effect.

Burkett et al. investigated whether there was a noticeable pattern in the effects of FoxP2 before and after the critical period in a songbird. The analysis found that during the critical period, a set of genes changed together as young birds learned to sing. This particular pattern disappeared as the birds aged and the critical period ended. Burkett et al. confirmed that when birds had the long version of FoxP2 altered, they were less able to learn. However, changing the short version of FoxP2 had little effect on learning but led to changes in the birds’ song.

The genetic pathways identified in the experiments are known to be present in many different species, including humans. Related pathways have also been found to play a role in non-vocal learning in organisms as distantly related as rats and snails. This suggests that they could be acting as a blueprint for learning new skills. Few treatments for language impairments have been developed so far due to poor understanding of the molecular basis for vocal communication. The findings of this study could help to create new treatments for speech problems in people, such as children with autism or people with mutated versions of FoxP2.

Embryological staging of the Zebra Finch, Taeniopygia guttata

Zebra Finches (Taeniopygia guttata) are the most commonly used laboratory songbird species, yet their embryological development has been poorly characterized. Most studies to date apply Hamburger and Hamilton stages derived from chicken development; however, significant differences in development between precocial and altricial species suggest that they may not be directly comparable. We provide the first detailed description of embryological development in the Zebra Finch under standard artificial incubation. These descriptions confirm that some of the features used to classify chicken embryos into stages are not applicable in an altricial bird such as the Zebra Finch. This staging protocol will help to standardize future studies of embryological development in the Zebra Finch.

Neurogenetics of birdsong

Songbirds are a productive model organism to study the neural basis of auditory-guided vocal motor learning. Like human babies, juvenile songbirds learn many of their vocalizations by imitating an adult conspecific. This process is a product of genetic predispositions and the individual's life experience and has been investigated mainly by neuroanatomical, physiological and behavioral methods. Results have revealed general principles governing vertebrate motor behavior, sensitive periods, sexual dimorphism, social behavior regulation and adult neurogenesis. More recently, the emerging field of birdsong neurogenetics has advanced the way we think about genetic contributions to communication, mechanistically and conceptually.