Duncan Kelli A, Carruth Laura L
Department of Biology, Center for Behavioral Neuroscience, Georgia State University, Atlanta, GA 30303, USA.
Dev Neurobiol. 2007 Dec;67(14):1852-66. doi: 10.1002/dneu.20539.
Sex differences in the zebra finch (Taeniopygia guttata) brain are robust and include differences in morphology (song control nuclei in males are significantly larger) and behavior (only males sing courtship songs). In zebra finches, hormonal manipulations during development fail to reverse sex differences in song nuclei size and suggest that the classical model of sexual differentiation is incomplete for birds. Coactivators act to initiate transcriptional activity of steroid receptors, and may help explain why hormonal manipulations alone are not sufficient to demasculinize the male zebra finch brain. The present study investigated the expression and localization of L7/SPA (an estrogen receptor coactivator) mRNA and protein expression across the development of zebra finch song nuclei from males and females collected on P1 (song nuclei not yet formed), P10 (posthatch day 10, song nuclei formed), P30 (30 days posthatch, sexually immature but song nuclei formed and birds learning to sing), and adult birds (older than 65 days and sexually mature). Northern blot analysis showed a significant sex difference in P1 and adult L7/SPA mRNA expression while Western blot analysis also showed enhanced expression in the male brain at all age points. Both in situ hybridization and immunohistochemistry demonstrated that L7/SPA mRNA and protein were located in the song nuclei as well as expressed globally. Elevated coactivator expression may be a possible mechanism controlling the development of male song control nuclei, and coactivators such as L7/SPA may be important regulators of the masculinizing effects of estradiol on brain sexual differentiation.
斑胸草雀（Taeniopygia guttata）大脑中的性别差异十分显著，包括形态学上的差异（雄性的鸣唱控制核显著更大）以及行为上的差异（只有雄性会唱求偶歌曲）。在斑胸草雀中，发育过程中的激素处理无法逆转鸣唱核大小的性别差异，这表明经典的性分化模型对于鸟类来说并不完整。共激活因子可启动类固醇受体的转录活性，这或许有助于解释为何仅靠激素处理不足以使雄性斑胸草雀的大脑去雄性化。本研究调查了L7/SPA（一种雌激素受体共激活因子）mRNA和蛋白质在雄性和雌性斑胸草雀鸣唱核发育过程中的表达及定位，这些斑胸草雀分别采集于出壳后第1天（P1，鸣唱核尚未形成）、第10天（P10，出壳后第10天，鸣唱核已形成）、第30天（P30，出壳后30天，性未成熟但鸣唱核已形成且鸟类正在学习唱歌）以及成年鸟（65日龄以上且性成熟）。Northern印迹分析显示，P1和成年期的L7/SPA mRNA表达存在显著的性别差异，而Western印迹分析也表明在所有年龄段雄性大脑中的表达均增强。原位杂交和免疫组织化学均表明，L7/SPA mRNA和蛋白质位于鸣唱核中，并且在全身都有表达。共激活因子表达升高可能是控制雄性鸣唱控制核发育的一种潜在机制，而诸如L7/SPA这样的共激活因子可能是雌二醇对大脑性分化产生雄性化作用的重要调节因子。
