Swift-Gallant Ashlyn, Mo Kaiguo, Peragine Deane E, Monks D Ashley, Holmes Melissa M
Department of Psychology, University of Toronto Mississauga, 3359 Mississauga Road, Mississauga, ON L5L 1C6 Canada.
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.
Biol Sex Differ. 2015 Dec 10;6:31. doi: 10.1186/s13293-015-0050-x. eCollection 2015.
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.
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.
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.
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.
裸鼹鼠是群居性哺乳动物，生活在大型群体中，有一只繁殖雌鼠和1至3只繁殖雄鼠。繁殖者在社会中占主导地位，只有繁殖者在循环性腺甾体激素和生殖行为方面表现出传统的性别差异。非繁殖从属个体在总体体型、外部生殖器形态和非生殖行为方面也未表现出性别差异。然而，如果从属个体从其群体中移出并与异性同种个体饲养在一起，它们可以转变为繁殖状态，这表明存在潜在的性别差异。在此，我们评估了雄性和雌性裸鼹鼠在社会和生殖状态转变过程中，其大脑中甾体激素受体和芳香化酶信使核糖核酸（mRNA）的表达情况。
我们将群体内的从属个体与从群体中移出1天、1周、1个月或直至成为繁殖者（即产仔）的异性从属个体对进行比较。收集间脑组织，使用定量聚合酶链反应（qPCR）测量雄激素受体（Ar）、雌激素受体α（Esr1）、孕激素受体（Pgr）和芳香化酶（Cyp19a1）的mRNA。同时也测量血清中的睾酮、17β-雌二醇和孕酮。
早在移出后1周，雄性间脑Ar mRNA和循环睾酮增加，而雌性间脑Cyp19a1 mRNA增加。移出后1个月，雌性17β-雌二醇和孕酮增加。在繁殖者中观察到甾体激素受体的最大变化。繁殖雌性Cyp19a1增加三倍，Esr1和Pgr增加五倍，而繁殖雄性Pgr减少，Ar增加。
这些数据表明，在从属动物从其原生群体的生殖抑制中移出数周至数月后，循环性腺甾体激素和下丘脑基因表达的性别差异才会出现。
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