Steroid receptor expression in the fish inner earvaries with sex, social status, and reproductive state

Abstract

BackgroundGonadal and stress-related steroid hormones are known to influence auditory function across vertebrates but the cellular and molecular mechanisms responsible for steroid-mediated auditory plasticity at the level of the inner ear remain unknown. The presence of steroid receptors in the ear suggests a direct pathway for hormones to act on the peripheral auditory system, but little is known about which receptors are expressed in the ear or whether their expression levels change with internal physiological state or external social cues. We used qRT-PCR to measure mRNA expression levels of multiple steroid receptor subtypes (estrogen receptors: ERα, ERβa, ERβb; androgen receptors: ARα, ARβ; corticosteroid receptors: GR2, GR1a/b, MR) and aromatase in the main hearing organ of the inner ear (saccule) in the highly social African cichlid fish Astatotilapia burtoni, and tested whether these receptor levels were correlated with circulating steroid concentrations.ResultsWe show that multiple steroid receptor subtypes are expressed within the main hearing organ of a single vertebrate species, and that expression levels differ between the sexes. We also show that steroid receptor subtype-specific changes in mRNA expression are associated with reproductive phase in females and social status in males. Sex-steroid receptor mRNA levels were negatively correlated with circulating estradiol and androgens in both males and females, suggesting possible ligand down-regulation of receptors in the inner ear. In contrast, saccular changes in corticosteroid receptor mRNA levels were not related to serum cortisol levels. Circulating steroid levels and receptor subtype mRNA levels were not as tightly correlated in males as compared to females, suggesting different regulatory mechanisms between sexes.ConclusionsThis is the most comprehensive study of sex-, social-, and reproductive-related steroid receptor mRNA expression in the peripheral auditory system of any single vertebrate. Our data suggest that changes in steroid receptor mRNA expression in the inner ear could be a regulatory mechanism for physiological state-dependent auditory plasticity across vertebrates.

Social descent with territory loss causes rapid behavioral, endocrine, and transcriptional changes in the brain

“…Tissue was collected directly into lysis buffer (RNeasy Micro Kit, Qiagen, Valencia, CA, USA), frozen on dry ice and stored at -80°C until RNA isolation. Total RNA was isolated from homogenized pituitaries and microdissected brain tissue following standard methods (RNeasy Plus Micro Kit, Qiagen) described previously (Maruska and Fernald, 2010c;Maruska et al, 2011), reverse transcribed to cDNA (iScript cDNA Synthesis Kit, Bio-Rad Laboratories, Hercules, CA, USA) and diluted 1:3 prior to use as a template for qRT-PCR reactions. qRT-PCR was used to measure mRNA levels of two IEGs, egr-1 and cfos, and two reference genes, g3pdh and 18s rRNA.…”

“…Primers were commercially synthesized (Invitrogen, Carlsbad, CA, USA) and were identical to those used in previous studies (Burmeister and Fernald, 2005;Zhao and Fernald, 2005;Burmeister et al, 2007;Maruska and Fernald, 2010b). qRT-PCR was performed using a previously described protocol (Maruska and Fernald, 2010c) with 20μl duplicate reactions (SSoFast EvaGreen Supermix, Bio-Rad) run on a Bio-Rad CFX96 qPCR machine.…”

“…Plasma levels of 11-ketotestosterone (11-KT), 17β-estradiol (E 2 ) and cortisol were measured using commercially available Enzyme ImmunoAssay (EIA) kits (Cayman Chemical, Ann Arbor, MI, USA) as previously described and validated for this species (Maruska and Fernald, 2010c). For 11-KT and E 2 assays, plasma samples were extracted with ethyl ether (extraction efficiency 87-91%) and reconstituted in assay buffer (1:60 dilution).…”

“…While coloration and behavioral changes that signal submission happen within minutes, physiological changes along the reproductive axis occur over days to weeks, likely as an adaptation to prolong reproductive capacity in anticipation of a future return to dominance (White et al, 2002;Maruska and Fernald, 2011b;Kustan et al, 2012). A previous study also showed that visual cues alone from a larger dominant male are sufficient to cause loss of bright coloration and submissive behaviors in a smaller dominant male (Chen and Fernald, 2011), but other sensory cues may be required for the full physiological suppression characteristic of the subordinate phenotype (Maruska and Fernald, 2010c;.…”

Seasonal plasticity of auditory hair cell frequency sensitivity correlates with plasma steroid levels in vocal fish

“…The occurrence of estrogen receptors in the auditory epithelium of vertebrates including fishes [midshipman (Forlano et al, 2005); cichlid (Maruska and Fernald, 2010)], songbird (Noirot et al, 2009), rodents (Stenberg et al, 1999) and humans (Stenberg et al, 2001) suggests a widespread occurrence of steroid-dependent auditory plasticity among vertebrates. Several mechanisms might account for this plasticity (see also Sisneros et al, 2004a).…”