Christiaen Lionel, Bourrat Franck, Joly Jean-Stéphane
INRA junior group, UPR2197 DEPSN, INAF, CNRS, 1 Avenue De La Terrasse, F-91198 Gif-sur-Yvette, France.
Dev Biol. 2005 Jan 15;277(2):557-66. doi: 10.1016/j.ydbio.2004.10.008.
Pituitary homeobox (pitx) genes have been identified in vertebrates as critical molecular determinants of various craniofacial ontogenetic processes including pituitary organogenesis. Accordingly, a prominent conserved feature of pitx genes in chordates is their early expression in the anterior neural boundary (ANB) and oral ectoderm, also known as the stomodaeum. Here we used the ascidian model species Ciona intestinalis to investigate pitx gene organization and cis-regulatory logic during early stages of oral development. Two distinct Ci-pitx mRNA variants were found to be expressed in mutually exclusive embryonic domains. Ci-pitx and vertebrate pitx2 genes display remarkably similar exon usage and organization, suggesting ancestry of the pitx transcriptional unit and regulation in chordates. We next combined phylogenetic footprinting, transient transgenesis, and confocal imaging methods to study the Ci-pitx cis-regulatory system, with special emphasis on the regulation of isoform-specific ANB/stomodaeal expression. Among 10 conserved noncoding sequences (CNSs) interspersed in C. intestinalis and Ciona savignyi pitx loci, we identified two separate cis-regulatory modules (CRMs) that drive ANB/stomodaeal expression in complementary spatiotemporal patterns. We discuss the developmental relevance of these data that provide an entry point to investigate the gene regulatory networks (GRNs) that position and shape oral structures in chordates.
垂体同源框（pitx）基因在脊椎动物中已被确定为各种颅面发育过程（包括垂体器官发生）的关键分子决定因素。因此，脊索动物中pitx基因的一个显著保守特征是它们在前神经边界（ANB）和口外胚层（也称为口凹）中的早期表达。在这里，我们使用海鞘模式物种肠鳃纲玻璃海鞘来研究口部发育早期阶段的pitx基因组织和顺式调控逻辑。发现两种不同的Ci-pitx mRNA变体在相互排斥的胚胎区域中表达。Ci-pitx和脊椎动物pitx2基因显示出非常相似的外显子使用和组织方式，这表明pitx转录单位和脊索动物中的调控具有共同祖先。接下来，我们结合系统发育足迹法、瞬时转基因法和共聚焦成像方法来研究Ci-pitx顺式调控系统，特别强调对异构体特异性ANB/口凹表达的调控。在散布于肠鳃纲玻璃海鞘和萨氏玻璃海鞘pitx基因座中的10个保守非编码序列（CNSs）中，我们鉴定出两个独立的顺式调控模块（CRMs），它们以互补的时空模式驱动ANB/口凹表达。我们讨论了这些数据的发育相关性，这些数据为研究在脊索动物中定位和塑造口部结构的基因调控网络（GRNs）提供了一个切入点。
