Crozatier M, Valle D, Dubois L, Ibnsouda S, Vincent A
Centre de Biologie du Développement, UMR 5547, CNRS/Université Paul Sabatier, 31062 TOULOUSE 04 cedex, France.
Development. 1999 Oct;126(19):4385-94. doi: 10.1242/dev.126.19.4385.
Whereas the segmental nature of the insect head is well established, relatively little is known about the genetic and molecular mechanisms governing this process. In this paper, we report the phenotypic analysis of mutations in collier (col), which encodes the Drosophila member of the COE family of HLH transcription factors and is activated at the blastoderm stage in a region overlapping a parasegment (PS0: posterior intercalary and anterior mandibular segments) and a mitotic domain, MD2. col mutant embryos specifically lack intercalary ectodermal structures. col activity is required for intercalary-segment expression both of the segment polarity genes hedgehog, engrailed, and wingless, and of the segment identity gene cap and collar. The parasegmental register of col activation is controlled by the combined activities of the head-gap genes buttonhead and empty spiracles and the pair-rule gene even skipped; it therefore integrates inputs from both the head and trunk segmentation systems, which were previously considered as being essentially independent. After gastrulation, positive autoregulation of col is limited to cells of anterior PS0. Conversely, heat-pulse induced ubiquitous expression of Col leads to disruption of the head skeleton. Together, these results indicate that col is required for establishment of the PS(-1)/PS0 parasegmental border and formation of the intercalary segment. Our data support neither a simple combinatorial model for segmental patterning of the head nor a direct activation of segment polarity gene expression by head-gap genes, but rather argue for the existence of parasegment-specific second order regulators acting in the head, at a level similar to that of pair-rule genes in the trunk.
尽管昆虫头部的节段性质已得到充分确立，但对于控制这一过程的遗传和分子机制却知之甚少。在本文中，我们报告了collier（col）基因突变的表型分析，col编码果蝇中HLH转录因子COE家族的成员，在囊胚期于一个与副节（PS0：后间插节和前颌节）和一个有丝分裂域MD2重叠的区域被激活。col突变体胚胎特异性地缺少间插外胚层结构。col的活性对于间插节段中节段极性基因刺猬蛋白、 engrailed和无翅基因，以及节段身份基因cap和collar的表达是必需的。col激活的副节登记由头部间隙基因buttonhead和空气门以及成对规则基因even skipped的联合活动控制；因此，它整合了来自头部和躯干节段化系统的输入，而这两个系统以前被认为基本是独立的。原肠胚形成后，col的正向自调控仅限于前PS0的细胞。相反，热脉冲诱导的Col普遍表达会导致头部骨骼的破坏。总之，这些结果表明col对于PS（-1）/PS0副节边界的建立和间插节段的形成是必需的。我们的数据既不支持头部节段模式形成的简单组合模型，也不支持头部间隙基因对节段极性基因表达的直接激活，而是支持存在作用于头部的副节特异性二级调节因子，其作用水平与躯干中的成对规则基因类似。
