Shashikant C S, Ruddle F H
Department of Biology, Yale University, New Haven, CT 06520, USA.
Proc Natl Acad Sci U S A. 1996 Oct 29;93(22):12364-9. doi: 10.1073/pnas.93.22.12364.
We have used a transgene mutation approach to study how expression domains of Hoxc8 are established during mouse embryogenesis. A cis-regulatory region located 3 kb upstream from the Hoxc8 translational start site directs the early phase of expression. Four elements, termed A, B, C, and D, were previously shown to direct expression to the neural tube. Here we report that a fifth element, E, located immediately downstream of D directs expression to mesoderm in combination with the other four elements. These elements are interdependent and partially redundant. Different combinations of elements determine expression in different posterior regions of the embryo. Neural tube expression is determined minimally by ABC, ABD, or ACD; somite expression by ACDE; and lateral plate mesoderm expression by DE. Neural tube and lateral plate mesoderm enhancers can be separated, but independent somite expression has not been achieved. Furthermore, mutations within these elements result in posteriorization of the reporter gene expression. Thus, the anterior extent of expression is determined by the combined action of these elements. We propose that the early phase of Hoxc8 expression is directed by two separate mechanisms: one that determines tissue specificity and another that determines anterior extent of expression.
我们采用转基因突变方法来研究Hoxc8的表达结构域在小鼠胚胎发育过程中是如何建立的。位于Hoxc8翻译起始位点上游3 kb处的一个顺式调控区域指导表达的早期阶段。先前已表明四个元件，称为A、B、C和D，可将表达导向神经管。在此我们报告，位于D紧邻下游的第五个元件E与其他四个元件共同作用时可将表达导向中胚层。这些元件相互依赖且部分冗余。元件的不同组合决定了胚胎不同后部区域的表达。神经管表达最少由ABC、ABD或ACD决定；体节表达由ACDE决定；侧板中胚层表达由DE决定。神经管和侧板中胚层增强子可以分离，但尚未实现独立的体节表达。此外，这些元件内的突变导致报告基因表达后移。因此，表达的前部范围由这些元件的联合作用决定。我们提出Hoxc8表达的早期阶段由两种独立机制指导：一种决定组织特异性，另一种决定表达的前部范围。
