Seasonal Changes in Patterns of Gene Expression in Avian Song Control Brain Regions

Abstract

Photoperiod and hormonal cues drive dramatic seasonal changes in structure and function of the avian song control system. Little is known, however, about the patterns of gene expression associated with seasonal changes. Here we address this issue by altering the hormonal and photoperiodic conditions in seasonally-breeding Gambel's white-crowned sparrows and extracting RNA from the telencephalic song control nuclei HVC and RA across multiple time points that capture different stages of growth and regression. We chose HVC and RA because while both nuclei change in volume across seasons, the cellular mechanisms underlying these changes differ. We thus hypothesized that different genes would be expressed between HVC and RA. We tested this by using the extracted RNA to perform a cDNA microarray hybridization developed by the SoNG initiative. We then validated these results using qRT-PCR. We found that 363 genes varied by more than 1.5 fold (>log2 0.585) in expression in HVC and/or RA. Supporting our hypothesis, only 59 of these 363 genes were found to vary in both nuclei, while 132 gene expression changes were HVC specific and 172 were RA specific. We then assigned many of these genes to functional categories relevant to the different mechanisms underlying seasonal change in HVC and RA, including neurogenesis, apoptosis, cell growth, dendrite arborization and axonal growth, angiogenesis, endocrinology, growth factors, and electrophysiology. This revealed categorical differences in the kinds of genes regulated in HVC and RA. These results show that different molecular programs underlie seasonal changes in HVC and RA, and that gene expression is time specific across different reproductive conditions. Our results provide insights into the complex molecular pathways that underlie adult neural plasticity.

Postsynaptic neural activity regulates neuronal addition in the adult avian song control system

“…A possible mechanism through which postsynaptic activity can influence neuronal addition is by activity-induced regulation of genes encoding molecules that promote survival of adult-born HVC neurons, axon path finding, and/or synapse formation (33,34). Interestingly, activity-induced guidance molecules are seasonally regulated in RA neurons of WCS; microarray analysis of cDNA extracted from RA revealed that the expression of guidance cue genes, including netrin 4 and galectin, is increased in breeding-condition birds (35). Activity in RA may modulate recruitment via activity-induced trophic factors produced by target neurons that are transported retrogradely to influence the survival of new neurons.…”

“…In canaries, expression levels of brainderived neurotrophic factor (BDNF) mRNA in HVC are higher in singing birds compared with nonsinging birds, and infusion of BDNF protein near HVC in nonsinging birds increases neuronal addition in HVC (16,36). Microarray analysis also revealed that the expression of the proneurogenic genes, including insulin-like growth factor 1 and neuromodulin, is increased in breeding-condition WCS (35). In HVC, the mRNA expression of sex steroid receptors, which facilitate the retrograde transport of trophic factors bound to their receptor toward the neuronal soma, also increases during breeding conditions (37,38).…”

Neurogenesis in the Adult Avian Song-Control System

“…The retrograde transport of activity-induced trophic factors produced by target neurons that influence the survival of new HVC RA neurons may be modulated by activity in RA. Microarray analysis also showed that the expression of proneurogenic genes, including IGF-1 and neuromodulin, is increased in RA of breeding-condition birds (Thompson et al 2012). In HVC, the expression of mRNA for sex steroid receptors, which facilitate the retrograde transport toward the neuronal soma of trophic factors bound to their receptor, also increases during breeding conditions (Fusani et al 2000;Jezierski and Sohrabji 2003;Fraley et al 2010).…”

“…3) (Warren et al 2010;Thompson et al 2012). Thompson et al (2012) identified 132 genes in HVC cells in adult male white-crowned sparrows (Zonotrichia leucophrys), which changed in expression between breeding and nonbreeding physiological conditions when compared with gene expression in RA, a nonneurogenic nucleus . In general, genes that promote proliferation, angiogenesis, and neurite extension were up-regulated, whereas genes that support programmed cell death were down-regulated in HVC under breeding conditions.…”

“…Activity-induced regulation of genes encoding molecules that promote survival of adult-born HVC neurons, axonal path finding, and/or synapse formation is likely to be important (Zhang et al 2001;Kay et al 2011). Interestingly, activity-induced guidance molecules are seasonally regulated in RA neurons of white-crowned sparrows; microarray analysis of cDNA extracted from RA showed that the expression of axonal guidance cue genes, including netrin 4 and galectin, is increased in breeding-condition birds (Thompson et al 2012). The retrograde transport of activity-induced trophic factors produced by target neurons that influence the survival of new HVC RA neurons may be modulated by activity in RA.…”