Yu Y, Pick L
Brookdale Center for Molecular Biology, Mount Sinai School of Medicine, New York, NY 10029, USA.
Mech Dev. 1995 Apr;50(2-3):163-75. doi: 10.1016/0925-4773(94)00333-i.
We have examined the expression pattern of the segmentation gene fushi tarazu (ftz) by in situ hybridization to whole mount embryos using digoxygenin labeled probes. This method has revealed previously undetected stages in the development of the ftz RNA pattern. The ftz stripes arise individually in a distinct, non-linear order along the anterior-posterior axis of the embryo. In addition, the stripes develop differentially along the dorsal-ventral axis; most stripes emerge on the ventral side and then gradually spread dorsally until they surround the entire circumference of the embryo. The order of appearance of ftz stripes is not inversely correlated with the order of appearance of hairy (h) stripes as would be expected if ftz stripes were generated by h repression. Furthermore, the seven ftz stripes are correctly established in embryos carrying mutations in h, eve or runt, with normal expression patterns decaying only after cellularization. Thus, the so called primary pair-rule genes are involved in the refinement rather than establishment of the ftz stripes. The contribution of cis-acting regulatory elements to the ftz pattern was examined. The zebra and upstream elements interact to generate seven correctly positioned stripes at the end of cellularization. However, stripe establishment is not correctly mimicked by any ftz/lac fusion gene: stripes arise in an order drastically different from the endogenous ftz gene suggesting the existence of ftz regulatory elements outside the 10-kb region examined to date. These observations suggest that the ftz pattern is directed by at least two independent regulatory systems: first, stripe establishment is directed by regionally distributed factors that act differentially in individual stripes along both anterior-posterior and dorsal-ventral axes of the egg and, second, stripe refinement and maintenance are mediated by pair-rule gene products that interact with previously identified ftz regulatory elements. This multi-level regulation provides a back-up system that ensures the development of seven stripes in the blastoderm.
我们使用地高辛标记的探针通过对完整胚胎进行原位杂交来检测体节基因ftz（腹节基因）的表达模式。这种方法揭示了ftz RNA模式发育过程中以前未被检测到的阶段。ftz条纹沿着胚胎的前后轴以独特的、非线性顺序逐个出现。此外，条纹沿着背腹轴差异发育；大多数条纹出现在腹侧，然后逐渐向背侧扩散，直到围绕胚胎的整个圆周。ftz条纹出现的顺序与毛状（h）条纹出现的顺序并不呈负相关，而如果ftz条纹是由h抑制产生的话，情况就会是这样。此外，在携带h、eve或runt突变的胚胎中，七条ftz条纹能够正确建立，正常的表达模式仅在细胞化后才会衰减。因此，所谓的初级成对规则基因参与了ftz条纹的细化而非建立过程。我们研究了顺式作用调节元件对ftz模式的贡献。斑马元件和上游元件相互作用，在细胞化结束时产生七条位置正确的条纹。然而，任何ftz/lac融合基因都不能正确模拟条纹的建立：条纹出现的顺序与内源性ftz基因有很大不同，这表明在迄今为止检测的10kb区域之外存在ftz调节元件。这些观察结果表明，ftz模式至少由两个独立的调节系统指导：第一，条纹的建立由区域分布的因子指导，这些因子在卵的前后轴和背腹轴上的各个条纹中起不同作用；第二，条纹的细化和维持由成对规则基因产物介导，这些产物与先前鉴定的ftz调节元件相互作用。这种多层次调节提供了一个备份系统，确保胚盘中有七条条纹的发育。
