Motor-induced transcription but sensory-regulated translation of ZENK in socially interactive songbirds

Abstract

The ZENK gene, depending upon singing activity, is transcribed within all the telencephalic nuclei controlling vocal behavior in songbirds. We show here that singing by deafened or completely isolated adult zebra finches induced high levels of ZENK transcription. This mRNA however, was not translated into high levels of ZENK protein. Instead, high levels of singing-driven ZENK protein translation were found in socially interactive birds. This dissociation between ZENK mRNA and ZENK protein was regionally specific to the robust nucleus of the arcopallium (RA), a region that is well known for its control of vocal-motor behavior in birds. Our results suggest cooperation between motor and sensory processes for regulating mRNA induction and subsequent protein synthesis in socially active songbirds.

Figure 1

Schematic view of zebra finch CNS showing the relative locations of songbird vocal nuclei and their axonal connections. Two nuclei in the caudal telencephalon (HVC and RA) are important during song learning and adult vocal behavior, whereas song regions in the anterior fore-brain (lMAN, DLM, Area X, the pallial-basal ganglia-thalamic loop) play an important role in vocal plasticity but are not necessary for maintenance of stereotyped adult vocal behavior. Here we propose that HVC input to RA drives ZENK mRNA and lMAN input modulates translation of ZENK protein (see text for additional details). Avian brain regions are referred to by their modern nomenclature (Reiner et al., 2004). Abbreviations: Area X, Area X of subpallium; DLM, medial portion of the dorsolateral nucleus of the thalamus; DM/ICo, dorsomedial nucleus of the intercollicular complex; HVC, high vocal center; lMAN, lateral magnocellular nucleus of the anterior nidopallium; RA, robust nucleus of the arcopallium; nXIIts, hypoglossal nucleus, tracheosyringeal portion.

Figure 2

In HVC singing drives ZENK protein translation, regardless of hearing status or sensory context. Whether deafened (A), sham operated (B), in social isolation (C), or in a male duo context (D), all birds showed similar levels of ZENK expression within the borders of HVC after singing; mRNA data are not shown. Tissue sections are 20 μM and coronal, medial is right. Scale bar in (B) = 100 μm.

Figure 3

In RA singing drives ZENK mRNA, while ZENK protein varies as a function of sensory context. ZENK protein-labeled cells are shown at low and high magnification in RA for birds that sang after being deafened (A,B) or sham-operated (D,E). Similar photomicrographs are shown for birds that sang in social isolation (G,H) or in the acoustic presence of a singing conspecific (J,K). For these birds a mean of 89 bouts were sung in a 45 min period. Immunoreactivity for ZENK protein in RA is low after singing in deafened and isolated birds compared to sham-operated and male duo birds [compare (A,G) to (D,J)]. The latter two groups of birds sang and heard a singing conspecific before measurement of ZENK. For comparison, ZENK mRNA-labeled cells in RA are shown in high power brightfield autoradiograph images of captured silver grains over thioninstained cells [(C,F,I,L); an example ZENK mRNA-labeled cell is denoted by the arrow in (C)]. The brightfield images show that singing induced ZENK mRNA-labeled cells regardless of hearing status or auditory context. Sections are 20 μM, and coronal, right is medial. Scale bar in (A) = 100 μm and in (C) = 10 μm.

Figure 4

Translation of motor-driven ZENK mRNA in RA, but not HVC, depends upon sensory context. HVC showed no significant differences in the ZENK translation ratio (protein to mRNA) after deafening or manipulation of the auditory context. However, in RA the translation ratios for ZENK differed significantly among the hearing-manipulated and auditory context groups. Translation ratios were low for deafened and solo context birds compared to birds that sang and heard a singing conspecific, the sham-operated group and the male duo context group. Histogram bars are means ± SEM.