The unveiling of the zebra finch genome also provides exciting insights into the evolution of avian and mammalian species. As detailed by the consortium authors [3
], the genome lacks genes that encode milk, salivary and vomeronasal receptor proteins, similarly to what has been documented for the chicken, a non-vocal-learning avian species whose genome was uncovered 6 years ago [13
]. Curiously, similarly to chickens, zebra finches lack the synapsin I gene, which encodes a phosphoprotein involved in the regulation of neurotransmitter vesicle availability in pre-synaptic membranes. This finding suggests that the synaptic transmission machinery differs between mammalian and avian species, although it is not clear if such molecular changes translate into functional modifications at the systems level.
Duplications of a variety of genes relative to chickens or humans, including growth hormone and caspase-3, the latter of which is associated with the induction of apoptosis, and gene family expansions, including of the PAK3
genes, which are involved in dendritic plasticity and transcriptional regulation, respectively, were also found in the zebra finch genome [3
]. Interestingly, multiple duplications of the PHF7
gene seem to have occurred independently in zebra finches and chickens, suggesting that some aspects of transcriptional regulation may have been under evolutionary pressure in avian species. Whereas these avian lineages have groups of 17 and 18 PHF7
genes, respectively, the human genome has been shown to contain only one PHF7
Finally, the zebra finch genome was found to have a significant fraction of transcribed mobile elements and a higher degree of intrachromosomal rearrangement relative to chicken. An example detailed by the consortium authors [3
] refers to genes of the major histocompatibility complex, which are scattered across several chromosomes in the zebra finch genome; in the chicken and human genomes, such genes have a well established syntenic organization. Despite these informative species-specific differences, the population of coding genes and the syntenic organization of the zebra finch genome were found to be highly similar to that of the chicken and, in many respects, to that of humans.