RSL, A NOVEL REGULATOR OF SEXUALLY DIMORPHIC LIVER GENES

男女之间的差异，从生理到分子水平，发生在比主要涉及生殖的系统多样化得多的系统中。一个已知的范例是肝脏中一系列代谢类固醇和药物或在妊娠期发挥作用的蛋白质的基因表达的性别特异性模式。这些表达上的差异是由性类固醇通过脑垂体诱导的，以指导生长激素分泌的特定特征。虽然研究对象主要是啮齿动物，但这条调节轴也存在于人类中，它可能影响药物敏感性的性别差异、某些肝脏疾病的发病率或妊娠并发症。因此，确定这种精确的组织特异性和激素控制机制是至关重要的。携带rsl等位基因（性别限制调节因子）的小鼠揭示了雄性特异性肝脏基因表达的雄激素独立控制。Rsl参与小鼠性别限制蛋白（Slp）基因的调控，该基因通常在成年男性的肝脏和肾脏中表达受限。在rsl纯合子小鼠中，Slp也在青春期的雌性中表达。Slp合成在rsl雄性中也增加，甚至在缺乏雄激素受体的rsl小鼠中也发生，表明这种调节不依赖于雄激素诱导。我们已经证明，rsl效应是肝脏特异性的，而不作用于肾脏中的Slp，并且它影响男性特异性肝脏基因的阵列，包括p450和小鼠尿蛋白（MUPs），导致它们在女性中表达。rsl变异表明，野生型rsl的正常功能通过抑制雌性雄性特异性基因的负调控来加强肝脏二态基因的表达。一种可能的机制是通过转录抑制作用于Rsl靶基因，在两性中，通过青春期激素诱导在男性中被克服。该项目的总体目标是表征这种新的组织和基因特异性负调控途径，并鉴定Rsl基因。我们将：1)根据Rsl基因的染色体位置克隆Rsl基因，该基因已经缩小到1.2 cM的遗传间隔；II)通过鉴定作为Rsl通路靶点的Slp顺式作用元件来确定作用的分子基础；III)明确Rsl控制与靶基因激素诱导之间的时空相互作用。建立Rsl通路的基础将增强我们对基因表达基本机制的认识。此外，小鼠的Rsl控制可能会对人类肝脏基因的调节产生独特的见解。

Differences between men and women, from physiological to molecular levels, occur in systems far more diverse than those primarily involved in reproduction. A known paradigm is the sex- specific pattern of gene expression in liver for a broad array of proteins that metabolize steroids and drugs, or function in pregnancy. These distinctions in expression are induced by the sex steroids acting via the pituitary to direct a specific profile of growth hormone secretion. Although studied mostly in rodents, this regulatory axis exists also in humans, where it may impact sex differences in drug sensitivity, incidence of certain liver diseases, or complications in pregnancy. Therefore, it is critical to ascertain mechanisms in such precise tissue-specific and hormonal control. An androgen-independent control in male-specific liver gene expression is revealed by mice carrying rsl alleles (regulator of sex-limitation). Rsl is involved in regulation of the mouse sex- limited protein (Slp) gene, which is normally restricted in expression to adult male liver and kidney. In mice homozygous for rsl, Slp also is expressed in females at puberty. Slp synthesis is also increased in the rsl males, and occurs even in rsl mice lacking androgen receptor, indicating that this regulation is independent of androgen induction. We have shown that the rsl effect is liver-specific and does not act on Slp in kidney, and that it affects the array of male-specific liver genes, including P450s and mouse urinary proteins (MUPs), to cause their expression in females. The rsl variant reveals that wild type Rsl's normal function enforces dimorphic liver gene expression by negative regulation that silences male-specific genes in females. A likely mechanism is via transcriptional repression that acts on Rsl target genes in both sexes, and is overcome in males by puberal hormonal induction. The overall goal of this project is to characterize this novel tissue- and gene-specific negative regulatory pathway and to identify the Rsl gene. We will: I) Clone the Rsl gene based on its chromosomal position, which is already narrowed to a genetic interval of 1.2 cM; II) Define the molecular basis of action by identifying Slp cis-acting elements that are targets of the Rsl pathway; III) Define temporal and spatial interaction between Rsl control and hormonal induction of the target genes. Establishing the basis of the Rsl pathway will enhance our understanding of basic mechanisms of gene expression. Further, Rsl control in mice may yield unique insights into regulation of liver genes in humans.