Grossniklaus U, Cadigan K M, Gehring W J
Department of Cell Biology, University of Basel, Switzerland.
Development. 1994 Nov;120(11):3155-71. doi: 10.1242/dev.120.11.3155.
In contrast to the segmentation of the embryonic trunk region which has been extensively studied, relatively little is known about the development and segmentation of the Drosophila head. Proper development of the cephalic region requires the informational input of three of the four maternal coordinate systems. Head-specific gene expression is set up in response to a complex interaction between the maternally provided gene products and zygotically expressed genes. Several zygotic genes involved in head development have recently been characterized. A genetic analysis suggests that the segmentation of the head may use a mechanism different from the one acting in the trunk. The two genes of the sloppy paired locus (slp1 and slp2) are also expressed in the embryonic head. slp1 plays a predominant role in head formation while slp2 is largely dispensible. A detailed analysis of the slp head phenotype suggests that slp is important for the development of the mandibular segment as well as two adjacent pregnathal segments (antennal and ocular). Our analysis of regulatory interactions of slp with maternal and zygotic genes suggests that it behaves like a gap gene. Thus, phenotype and regulation of slp support the view that slp acts as a head-specific gap gene in addition to its function as a pair-rule and segment polarity gene in the trunk. We show that all three maternal systems active in the cephalic region are required for proper slp expression and that the different systems cooperate in the patterning of the head. The terminal and anterior patterning system appear to be closely linked. This cooperation is likely to involve a direct interaction between the bcd morphogen and the terminal system. Low levels of terminal system activity seem to potentiate bcd as an activator of slp, whereas high levels down-regulate bcd rendering it inactive. Our analysis suggests that dorsal, the morphogen of the dorsoventral system, and the head-specific gap gene empty spiracles act as repressor and corepressor in the regulation of slp. We discuss how positional information established independently along two axes can act in concert to control gene regulation in two dimensions.
与已被广泛研究的胚胎躯干区域的分割形成对比的是，人们对果蝇头部的发育和分割了解相对较少。头部区域的正常发育需要四个母体坐标系统中的三个提供信息输入。头部特异性基因表达是在母体提供的基因产物与合子表达基因之间复杂相互作用的响应下建立的。最近已经鉴定了几个参与头部发育的合子基因。遗传分析表明，头部的分割可能使用一种不同于作用于躯干的机制。草率配对位点的两个基因（slp1和slp2）也在胚胎头部表达。slp1在头部形成中起主要作用，而slp2在很大程度上是可有可无的。对slp头部表型的详细分析表明，slp对于下颌节段以及两个相邻的孕节段（触角和眼节）的发育很重要。我们对slp与母体和合子基因的调控相互作用的分析表明，它的行为类似于间隙基因。因此，slp的表型和调控支持了这样一种观点，即slp除了在躯干中作为成对规则基因和节段极性基因发挥作用外，还作为头部特异性间隙基因发挥作用。我们表明，在头部区域活跃的所有三个母体系统对于slp的正确表达都是必需的，并且不同的系统在头部的模式形成中协同作用。末端和前部模式形成系统似乎紧密相连。这种协同作用可能涉及bcd形态发生素与末端系统之间的直接相互作用。低水平的末端系统活性似乎增强了bcd作为slp激活剂的作用，而高水平则下调bcd使其失活。我们的分析表明，背腹系统的形态发生素背侧和头部特异性间隙基因空气门在slp的调控中分别作为阻遏物和共阻遏物起作用。我们讨论了沿两个轴独立建立的位置信息如何协同作用以在二维中控制基因调控。
