title: Removal of reproductive suppression reveals latent sex differences in brain steroid hormone receptors in naked mole-rats, Heterocephalus glaber.
abstract: BACKGROUND
  Naked mole-rats are eusocial mammals, living in large colonies with a single breeding female and 1-3 breeding males. Breeders are socially dominant, and only the breeders exhibit traditional sex differences in circulating gonadal steroid hormones and reproductive behaviors. Non-reproductive subordinates also fail to show sex differences in overall body size, external genital morphology, and non-reproductive behaviors. However, subordinates can transition to breeding status if removed from their colony and housed with an opposite-sex conspecific, suggesting the presence of latent sex differences. Here, we assessed the expression of steroid hormone receptor and aromatase messenger RNA (mRNA) in the brains of males and females as they transitioned in social and reproductive status.
  
  
  METHODS
  We compared in-colony subordinates to opposite-sex subordinate pairs that were removed from their colony for either 1 day, 1 week, 1 month, or until they became breeders (i.e., produced a litter). Diencephalic tissue was collected and mRNA of androgen receptor (Ar), estrogen receptor alpha (Esr1), progesterone receptor (Pgr), and aromatase (Cyp19a1) was measured using qPCR. Testosterone, 17β-estradiol, and progesterone from serum were also measured.
  
  
  RESULTS
  As early as 1 week post-removal, males exhibited increased diencephalic Ar mRNA and circulating testosterone, whereas females had increased Cyp19a1 mRNA in the diencephalon. At 1 month post-removal, females exhibited increased 17β-estradiol and progesterone. The largest changes in steroid hormone receptors were observed in breeders. Breeding females had a threefold increase in Cyp19a1 and fivefold increases in Esr1 and Pgr, whereas breeding males had reduced Pgr and increased Ar.
  
  
  CONCLUSIONS
  These data demonstrate that sex differences in circulating gonadal steroids and hypothalamic gene expression emerge weeks to months after subordinate animals are removed from reproductive suppression in their home colony.
authors.affiliation: Department of Psychology, University of Toronto Mississauga, 3359 Mississauga Road, Mississauga, ON L5L 1C6 Canada.
authors.forename: Ashlyn
authors.initials: A
authors.lastname: Swift-Gallant
authors.affiliation: Department of Psychology, University of Toronto Mississauga, 3359 Mississauga Road, Mississauga, ON L5L 1C6 Canada.
authors.forename: Kaiguo
authors.initials: K
authors.lastname: Mo
authors.affiliation: Department of Psychology, University of Toronto Mississauga, 3359 Mississauga Road, Mississauga, ON L5L 1C6 Canada.
authors.forename: Deane E
authors.initials: DE
authors.lastname: Peragine
authors.affiliation: Department of Psychology, University of Toronto Mississauga, 3359 Mississauga Road, Mississauga, ON L5L 1C6 Canada ; Department of Cell and Systems Biology, University of Toronto, 100 St. George Street, Toronto, ON M5S 3G3 Canada.
authors.forename: D Ashley
authors.initials: DA
authors.lastname: Monks
authors.affiliation: Department of Psychology, University of Toronto Mississauga, 3359 Mississauga Road, Mississauga, ON L5L 1C6 Canada ; Department of Cell and Systems Biology, University of Toronto, 100 St. George Street, Toronto, ON M5S 3G3 Canada ; Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, ON M5S 3B2 Canada.
authors.forename: Melissa M
authors.initials: MM
authors.lastname: Holmes
keywords: Androgen receptor; Aromatase; Estradiol; Estrogen receptor; Eusocial; Naked mole-rat; Progesterone receptor; Reproductive suppression; Sex difference; Testosterone