Sarah E. London

The genome of a songbird.

The zebra finch is an important model organism in several fields with unique relevance to human neuroscience. Like other songbirds, the zebra finch communicates through learned vocalizations, an ability otherwise documented only in humans and a few other animals and lacking in the chicken—the only bird with a sequenced genome until now. Here we present a structural, functional and comparative analysis of the genome sequence of the zebra finch (Taeniopygia guttata), which is a songbird belonging to the large avian order Passeriformes. We find that the overall structures of the genomes are similar in zebra finch and chicken, but they differ in many intrachromosomal rearrangements, lineage-specific gene family expansions, the number of long-terminal-repeat-based retrotransposons, and mechanisms of sex chromosome dosage compensation. We show that song behaviour engages gene regulatory networks in the zebra finch brain, altering the expression of long non-coding RNAs, microRNAs, transcription factors and their targets. We also show evidence for rapid molecular evolution in the songbird lineage of genes that are regulated during song experience. These results indicate an active involvement of the genome in neural processes underlying vocal communication and identify potential genetic substrates for the evolution and regulation of this behaviour.

Parallel FoxP1 and FoxP2 Expression in Songbird and Human Brain Predicts Functional Interaction

Humans and songbirds are two of the rare animal groups that modify their innate vocalizations. The identification of FOXP2 as the monogenetic locus of a human speech disorder exhibited by members of the family referred to as KE enables the first examination of whether molecular mechanisms for vocal learning are shared between humans and songbirds. Here, in situ hybridization analyses for FoxP1 and FoxP2 in a songbird reveal a corticostriatal expression pattern congruent with the abnormalities in brain structures of affected KE family members. The overlap in FoxP1 and FoxP2 expression observed in the songbird suggests that combinatorial regulation by these molecules during neural development and within vocal control structures may occur. In support of this idea, we find that FOXP1 and FOXP2 expression patterns in human fetal brain are strikingly similar to those in the songbird, including localization to subcortical structures that function in sensorimotor integration and the control of skilled, coordinated movement. The specific colocalization of FoxP1 and FoxP2 found in several structures in the bird and human brain predicts that mutations in FOXP1 could also be related to speech disorders.

Functional identification of sensory mechanisms required for developmental song learning

A young male zebra finch (Taeniopygia guttata) learns to sing by copying the vocalizations of an older tutor in a process that parallels human speech acquisition. Brain pathways that control song production are well defined, but little is known about the sites and mechanisms of tutor song memorization. Here we test the hypothesis that molecular signaling in a sensory brain area outside of the song system is required for developmental song learning. Using controlled tutoring and a pharmacological inhibitor, we transiently suppressed the extracellular signal–regulated kinase signaling pathway in a portion of the auditory forebrain specifically during tutor song exposure. On maturation, treated birds produced poor copies of tutor song, whereas controls copied the tutor song effectively. Thus the foundation of normal song learning, the formation of a sensory memory of tutor song, requires a conserved molecular pathway in a brain area that is distinct from the circuit for song motor control.

Loneliness: Clinical Import and Interventions

In 1978, when the Task Panel report to the US Presidents Commission on Mental Health emphasized the importance of improving health care and easing the pain of those suffering from emotional distress syndromes including loneliness, few anticipated that this issue would still need to be addressed 40 years later. A meta-analysis (Masi et al., 2011) on the efficacy of treatments to reduce loneliness identified a need for well-controlled randomized clinical trials focusing on the rehabilitation of maladaptive social cognition. We review assessments of loneliness and build on this meta-analysis to discuss the efficacy of various treatments for loneliness. With the advances made over the past 5 years in the identification of the psychobiological and pharmaceutical mechanisms associated with loneliness and maladaptive social cognition, there is increasing evidence for the potential efficacy of integrated interventions that combine (social) cognitive behavioral therapy with short-term adjunctive pharmacological treatments.In 1978, when the Task Panel report to the U.S. President’s Commission on Mental Health emphasized the importance of improving health care and easing the pain of those suffering from emotional distress syndromes including loneliness, few anticipated that this issue would still need to be addressed 40 years later. In 2011, a meta-analysis on the efficacy of treatments to reduce loneliness identified a need for well-controlled randomized clinical trials focusing on the rehabilitation of maladaptive social cognition. We review assessments of loneliness and build on this meta-analysis to discuss the efficacy of various treatments for loneliness. With the advances made over the past 5 years in the identification of the psychobiological and pharmaceutical mechanisms associated with loneliness and maladaptive social cognition, there is increasing evidence for the potential efficacy of integrated interventions that combine (social) cognitive behavioral therapy with short-term adjunctive pharmacological treatments.

Cloning of the zebra finch androgen synthetic enzyme CYP17: A study of its neural expression throughout posthatch development

Male zebra finches develop a robust neural song system that supports singing, but females have a minimal song circuit and do not sing. Estrogens masculinize the song circuit and are especially potent during the first 3 weeks of posthatch development. The gonads do not seem to supply the masculinizing steroids, implying that another tissue synthesizes steroids. Evidence suggests that the brain is capable of synthesizing neurosteroids, which in developing zebra finches may be required for song system differentiation. Aromatase, the enzyme that synthesizes estrogen from androgen, is equally abundant in male and female brains. To investigate further the potential for neurosteroidogenesis in the zebra finch brain, we cloned and examined the expression of 17α‐hydroxylase/17,20 lyase (CYP17), the enzyme that synthesizes the androgenic substrate for aromatase. We used Northern blots, reverse transcription‐polymerase chain reaction, and in situ hybridization to show that CYP17 is transcribed in developing and adult brains. CYP17 is transcribed at developmental stages and in brain areas potentially important to aspects of the developing song system, although no sex difference was detected in mRNA levels. Our results support the hypothesis that neurosteroids may act to influence brain organization and function in the zebra finch. J. Comp. Neurol. 467:496–508, 2003.

Neurosteroids and brain sexual differentiation

There is new evidence that the brain of developing songbirds can synthesize estradiol de novo. In males, this neurally derived estrogen might masculinize a connection within the neural song system. These results challenge traditional concepts about mechanisms of brain sexual differentiation and reveal a significant function for neurosteroids.

Integrating Genomes, Brain and Behavior in the Study of Songbirds

Songbirds share some essential traits but are extraordinarily diverse, allowing comparative analyses aimed at identifying specific genotype-phenotype associations. This diversity encompasses traits like vocal communication and complex social behaviors that are of great interest to humans, but that are not well represented in other accessible research organisms. Many songbirds are readily observable in nature and thus afford unique insight into the links between environment and organism. The distinctive organization of the songbird brain will facilitate analysis of genomic links to brain and behavior. Access to the zebra finch genome sequence will, therefore, prompt new questions and provide the ability to answer those questions.

Steroidogenic enzymes along the ventricular proliferative zone in the developing songbird brain

Neural development requires regulation and coordination of the differentiation, migration, and survival of newly divided cells, most of which derive from the region surrounding the lateral ventricles. While many factors are involved in these maturational processes, studies of cell proliferation and neurogenesis in songbirds indicate that sex steroids may provide crucial cues to newly divided cells and may be fundamental to the organization of a specific neural circuit, the song system. In the case of the zebra finch, steroids that impact song system masculinization are most likely not synthesized from the gonads but from the brain, and evidence is mounting that both developing and adult zebra finches have the capacity for neurosteroidogenesis. Therefore, we hypothesized that during early development, all of the genes required for de novo sex steroid synthesis would be expressed in regions that would indicate a role for neurosteroids in neural organization. We found that the genes necessary for de novo neurosteroid synthesis at posthatch day 1 (P1) and P5 show a broad expression distribution. Most strikingly, the spatial distribution of expression for all of the genes necessary for androgen synthesis is similar to the previously described pattern of proliferating neuronal precursors along the lateral border of the lateral ventricle. Due to the increasing evidence for neurosteroid action on multiple cell traits, it may be that locally synthesized neurosteroids impact cells along the proliferative zone to influence early events in neural development generally and song system masculinization specifically. J. Comp. Neurol. 502:507–521, 2007.

Developmental shifts in gene expression in the auditory forebrain during the sensitive period for song learning

A male zebra finch begins to learn to sing by memorizing a tutors song during a sensitive period in juvenile development. Tutor song memorization requires molecular signaling within the auditory forebrain. Using microarray and in situ hybridizations, we tested whether the auditory forebrain at an age just before tutoring expresses a different set of genes compared with later life after song learning has ceased. Microarray analysis revealed differences in expression of thousands of genes in the male auditory forebrain at posthatch day 20 (P20) compared with adulthood. Furthermore, song playbacks had essentially no impact on gene expression in P20 auditory forebrain, but altered expression of hundreds of genes in adults. Most genes that were song‐responsive in adults were expressed at constitutively high levels at P20. Using in situ hybridization with a representative sample of 44 probes, we confirmed these effects and found that birds at P20 and P45 were similar in their gene expression patterns. Additionally, eight of the probes showed male–female differences in expression. We conclude that the developing auditory forebrain is in a very different molecular state from the adult, despite its relatively mature gross morphology and electrophysiological responsiveness to song stimuli. Developmental gene expression changes may contribute to fine‐tuning of cellular and molecular properties necessary for song learning.

Impact of experience-dependent and -independent factors on gene expression in songbird brain

Songbirds provide rich natural models for studying the relationships between brain anatomy, behavior, environmental signals, and gene expression. Under the Songbird Neurogenomics Initiative, investigators from 11 laboratories collected brain samples from six species of songbird under a range of experimental conditions, and 488 of these samples were analyzed systematically for gene expression by microarray. ANOVA was used to test 32 planned contrasts in the data, revealing the relative impact of different factors. The brain region from which tissue was taken had the greatest influence on gene expression profile, affecting the majority of signals measured by 18,848 cDNA spots on the microarray. Social and environmental manipulations had a highly variable impact, interpreted here as a manifestation of paradoxical “constitutive plasticity” (fewer inducible genes) during periods of enhanced behavioral responsiveness. Several specific genes were identified that may be important in the evolution of linkages between environmental signals and behavior. The data were also analyzed using weighted gene coexpression network analysis, followed by gene ontology analysis. This revealed modules of coexpressed genes that are also enriched for specific functional annotations, such as “ribosome” (expressed more highly in juvenile brain) and “dopamine metabolic process” (expressed more highly in striatal song control nucleus area X). These results underscore the complexity of influences on neural gene expression and provide a resource for studying how these influences are integrated during natural experience.