HOUSTON – Whether you're a songbird or a human, there's a
lot we can learn from our elders when learning vocalization. A
University of Houston researcher was part of a team that uncovered
the genome of the zebra finch, which may one day help people who
suffer from speech impairments, learning disabilities and problems
with forming social connections.
Preethi Gunaratne, an assistant professor of biology and
biochemistry at UH, played a lead role in microRNA discovery and
analysis in relation to changes in the auditory forebrain of zebra
finches in response to song. This research eventually will be used
to study vocal learning in humans. Wesley Warren from the Genome
Sequencing Center at Washington University in St. Louis and David
Clayton from the University of Illinois at Urbana-Champaign led the
team of scientists.
Their findings are described in a paper titled "The Genome of
the Zebra Finch: Special Insights into Vocal Learning and
Communication," appearing April 1 in Nature, the weekly
scientific journal for biological and physical sciences
research.
Songbirds – and, in this case, the zebra finch
(Taeniopygia guttata) – are the only animal model for
studying the evolution of speech and language in humans. They have
been studied as a paradigm to understand how vocal communication
can be used to tell apart individuals when selecting partners
during courtship and forming social boundaries.
"Interestingly, although both males and females are able to
differentiate between different song types, the ability to learn
and copy a particular song type that is specific to the family
lineage is passed down only through the males," Gunaratne said.
"Young males learn and copy the song that is vocalized by their
father, and this song learning must be accomplished during early
infancy. After learning the song of their father, the sons are able
to vocalize the specific song of their father very accurately.
Therefore, the songbird has much to offer in relation to our
efforts to understand the role of learning and memory in acquired
human speech."
Among the key findings of this paper is that although the
overall structure of the zebra finch genome is similar to that of
chickens, which do not learn or vocalize songs and are the only
birds to have been sequenced until now, the genes expressed in the
brain that have to do with neurological functions have evolved more
rapidly in songbirds. In addition, Gunaratne was surprised to find
that this ability to learn and vocalize engages a large number of
RNAs (molecules involved in the transmission of genetic
information) that do not code for proteins and were previously
considered to be junk. In the last decade, she says, there has been
a paradigm shift where small non-coding RNAs, called microRNAs,
have emerged as important regulatory molecules that can diminish
the levels of hundreds of genes that cooperate to form a network
that supports a specific biological process. Each individual small
RNA acts as a magnet to capture a specific set of gene
transcripts.
Gunaratne, who is also an assistant professor in the pathology
department at the Human Genome Sequencing Center at the Baylor
College of Medicine, is a pioneer in the field of microRNAs in
Houston. In collaboration with Clayton, who is a pioneer in the
application of molecular genetics and genomics to songbird
research, the team determined the complete set of microRNAs
expressed in the auditory forebrain – the part of the brain
that is involved in vocal learning – of male and female zebra
finches exposed to song versus silent conditions. The auditory
forebrain is of central importance in controlling the neural
circuits needed for learning and vocalization of song in these
birds.
The researchers found the set of microRNAs that are expressed in
the auditory forebrain when a songbird is listening to a song is
very different from the set of microRNAs that are expressed when
the song is discontinued. A number of microRNAs that can
potentially manipulate hundreds of genes that originally cooperated
to support a specific function like song learning are induced in
the absence of song. This allows the brain to clear out gene
transcripts that are needed for song learning when they are no
longer needed under the silent conditions.
"Similarly, when the young bird hears the father's song a second
time, a new set of microRNAs that can potentially support song
learning are expressed and now act to potentially clear gene
transcripts that cooperate to support the brain function under
silent conditions," Gunaratne said. "Basically, because a single
microRNA can concurrently diminish the levels of hundreds of genes,
they allow major shifts in gene networks to happen when we go from
one situation to another."
Two of Gunaratne's graduate students, Ashley Benham and Jayantha
Tennakoon, along with Jong Kim, an undergraduate student from her
lab, and Ya-chi Lin, a graduate student from the Clayton lab,
played important roles in this project. Their contributions on the
details of the role of microRNAs in song learning in zebra finches
is in preparation for yet another publication, demonstrating the
type of student success essential to Tier-One status.
Gunaratne says this work would not have been possible without
the Illumina Next Generation Sequencing instrument housed in the
Institute for Molecular Design at UH. In 2008, UH became one of the
first academic institutions to acquire state-of-the art sequencing
technology that allows rapid sequencing of entire genomes within
weeks. This investment has transformed the research of not only UH
faculty, but also of a large number of faculty in the Texas Medical
Center, as well as other national and international universities
and institutions through collaborations with researchers at UH.
SOURCE