Striatal FoxP2 is actively regulated during songbird sensorimotor learning - PubMed (original) (raw)
Striatal FoxP2 is actively regulated during songbird sensorimotor learning
Ikuko Teramitsu et al. PLoS One. 2010.
Abstract
Background: Mutations in the FOXP2 transcription factor lead to language disorders with developmental onset. Accompanying structural abnormalities in cortico-striatal circuitry indicate that at least a portion of the behavioral phenotype is due to organizational deficits. We previously found parallel FoxP2 expression patterns in human and songbird cortico/pallio-striatal circuits important for learned vocalizations, suggesting that FoxP2's function in birdsong may generalize to speech.
Methodology/principal findings: We used zebra finches to address the question of whether FoxP2 is additionally important in the post-organizational function of these circuits. In both humans and songbirds, vocal learning depends on auditory guidance to achieve and maintain optimal vocal output. We tested whether deafening prior to or during the sensorimotor phase of song learning disrupted FoxP2 expression in song circuitry. As expected, the songs of deafened juveniles were abnormal, however basal FoxP2 levels were unaffected. In contrast, when hearing or deaf juveniles sang for two hours in the morning, FoxP2 was acutely down-regulated in the striatal song nucleus, area X. The extent of down-regulation was similar between hearing and deaf birds. Interestingly, levels of FoxP2 and singing were correlated only in hearing birds.
Conclusions/significance: Hearing appears to link FoxP2 levels to the amount of vocal practice. As juvenile birds spent more time practicing than did adults, their FoxP2 levels are likely to be low more often. Behaviorally-driven reductions in the mRNA encoding this transcription factor could ultimately affect downstream molecules that function in vocal exploration, especially during sensorimotor learning.
Conflict of interest statement
Competing Interests: The authors have declared that no competing interests exist.
Figures
Figure 1. Deafening at 35d causes abnormal song development.
A) Time line for experiments conducted during song learning which ends at ∼90d. One group of birds was either untreated, sham-operated or deafened at 25d, during sensory acquisition (dashed and dotted line) and prior to the onset of sensorimotor learning (dotted line). Their _FoxP_2 levels were measured at 50d. Another group of birds was either untreated or deafened at 35d, the onset of sensorimotor learning, and their FoxP2 levels measured at either 65 or 75d. B) Exemplar spectrograms of a 75d hearing (top) and a deaf (bottom) bird. Although yet immature, the 75d hearing bird's song shows structures typical of zebra finch songs including introductory notes (i) and repeated motifs, which are composed of 4–7 easily identified syllables (a or a' – d). In contrast, songs of 75d deafened males were disrupted, and motifs were not identifiable. Signal at ∼6.5 kHz represents background noise. C) Left - schematic of major nuclei of the song circuit indicates the plane of section used to examine FoxP2 levels in area X (arrowhead in the Nissl stain; right). Abbreviations: d – dorsal, DLM – medial portion of the dorsolateral nucleus of the anterior thalamus, HVC – acronym used as a proper name, l – lateral, LMAN – lateral magnocellular nucleus of the anterior nidopallium, r – rostral, RA – robust nucleus of the arcopallium, X – area X of the medial striatum. Axis lines underneath the Nissl section (right) indicate 1mm.
Figure 2. Basal FoxP2 levels are similar between hearing and deafened juveniles.
A) Exemplar hemi-coronal sections show FoxP2 signals detected with either the mid or 3′-probe at 50, 65 and 75d in hearing (H; left hemi-sections) or deaf (D; right hemi-sections) birds. B) Quantification of pixel density within area X, normalized to values of the outlying striatum, reveals stable expression regardless of age or hearing condition. With each probe, at each age, and in each condition (white boxes = hearing, shaded boxes = deaf), values exceed unity (1.0), indicating slightly higher expression within area X. No differences were detected with either probe (Mean±SEM: H-NS vs. D-NS – 3′-probe: 50d, 1.07±0.02 vs. 1.09±0.02; 65d, 1.12±0.03 vs. 1.11±0.02; 75d, 1.18±0.02 vs. 1.15±0.07. Kruskal-Wallis H = 10.7, df = 5, p = 0.06; mid-probe: 50d, 1.08±0.02 vs 1.09±0.01; 65d, 1.06±0.01 vs. 1.03±0.01; 75d, 1.14±0.03 vs. 1.10±0.04. Kruskal-Wallis H = 8.7 p = 0.12). ‘Box and whiskers’ plots show the median (line), average (filled small rectangle), 25th and 75th percentiles (box) and 5th and 95th percent confidence intervals (whiskers) for each group. The number of birds per group is indicated beneath. For each bird, multiple sections were analyzed, then averaged, to produce a single metric per bird.
Figure 3. Singing down-regulates FoxP2 in both hearing and deaf juveniles.
A) Representative sections show Fo_xP2_ signals detected with the 3′-probe in hearing and deaf 75d birds. Signals within area X appear slightly stronger than in the surrounding striatum in the non-singer (NS), whereas they appear lower in area X of the singer (S). B) Quantification of the pixel intensity within area X is normalized to that of the outlying striatum. In both hearing (n = 7) and deaf (n = 10) birds, area X FoxP2 levels are higher in the non-singing group (gray boxes) relative to the singing group (white boxes). Mean±SEM for hearing birds: 75NS-H vs. 75S-H: 1.18±0.02 vs. 0.99±0.04, Mann-Whitney U = 5.7, p<0.02. Mean±SEM for deaf birds: 75NS-D vs. 75S-D: 1.15±0.03 vs. 0.94±0.02, Mann-Whitney U = 8, p<0.005. ‘Box and whiskers’ plots show the median (line), average (triangle), 25th and 75th percentiles (box) and 5th and 95th percent confidence intervals (whiskers) for each group. Individual values are plotted to the left.
Figure 4. Hearing links amount of singing with FoxP2 levels.
The amount of time that 75d birds spent singing (x axis) and area X FoxP2 levels measured using the mid-probe (y axis) are correlated in hearing (left; Spearman Rho = −0.86, R2 = 0.69; p<0.02), but not in deaf (right; Spearman Rho = −0.19, R2 = 0.04; p = 0.60), juveniles.
Figure 5. 75d birds practice more than adults.
Data from 75d males (n = 5) is shown in shades of purple, adult aviary males (n = 4) in gold and adult pair-bonded males (n = 5) in maroon. Left) The amount of song sung while in sound attenuation chambers is shown. Individual data are plotted where squares represent days 2–5 (day one was not counted to allow for acclimation) and color intensity shows percent of total motifs sung each day. Compared with older birds, 75d males tended to sing on the first recording day and sang more overall (Mean±SEM in secs: 75d = 12,958±1,731, adult aviary males = 4,494±1,042, adult pair-bonded males = 2,034±894; Kruskal-Wallis H = 10.7, DF = 2, p<0.005). Right) The daily pattern of singing is shown. For each group, the average number of motifs (z axis) is plotted in 2.5 hour time-blocks (x axis) across the 4 days. Each day is represented by one ribbon on the y axis and the 4 days are clustered by group.
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