Quint E, Zerucha T, Ekker M
Loeb Health Research Institute at the Ottawa Hospital, Ontario, Canada.
J Exp Zool. 2000 Oct 15;288(3):235-41. doi: 10.1002/1097-010x(20001015)288:3<235::aid-jez4>3.0.co;2-j.
Dlx homeobox genes of vertebrates are often organised as physically linked pairs in which the two genes are transcribed convergently (tail-to-tail arrangement). Three such Dlx pairs have been found in mouse, human, and zebrafish and are thought to have originated from the duplication of an ancestral gene pair. These pairs include Dlx1/Dlx2, Dlx7/Dlx3, and Dlx6/Dlx5 (the zebrafish orthologue of Dlx5 is named dlx4). Expression patterns of physically linked Dlx genes overlap extensively. Furthermore, orthologous Dlx genes often show highly similar expression patterns. We analysed Dlx expression during the gastrula and early somitogenesis of the mouse and zebrafish. It was found that expression of the mouse Dlx6 gene takes place in the rostral ectoderm and presumptive olfactory and otic placodes with patterns similar to the previously reported expression of the physically linked Dlx5 gene. However, we observed only very weak expression of the mouse Dlx3 gene at the same stage. This contrasts with the expression of dlx genes in zebrafish where dlx3 and dlx7, but not dlx4 and dlx6 are expressed during gastrulation in the rostral ectoderm and presumptive placodes. Thus, Dlx expression patterns at early stages are better conserved between paralogous pairs of physically linked genes than between orthologous pairs. This suggests that early expression of Dlx genes existed prior to the duplications that led to the multiple pairs of physically linked genes but was differentially conserved in different paralogs in zebrafish and mice.
脊椎动物的Dlx同源框基因通常以物理连锁对的形式组织，其中两个基因以反向转录的方式转录（尾对尾排列）。在小鼠、人类和斑马鱼中发现了三个这样的Dlx对，它们被认为起源于一个祖先基因对的复制。这些对包括Dlx1/Dlx2、Dlx7/Dlx3和Dlx6/Dlx5（斑马鱼中Dlx5的直系同源基因名为dlx4）。物理连锁的Dlx基因的表达模式广泛重叠。此外，直系同源的Dlx基因通常表现出高度相似的表达模式。我们分析了小鼠和斑马鱼原肠胚期和早期体节形成过程中的Dlx表达。发现小鼠Dlx6基因在头侧外胚层以及假定的嗅觉和耳基板中表达，其模式与之前报道的物理连锁的Dlx5基因的表达相似。然而，我们在同一阶段仅观察到小鼠Dlx3基因非常微弱的表达。这与斑马鱼中dlx基因的表达形成对比，在斑马鱼中，dlx3和dlx7在原肠胚形成期间在头侧外胚层和假定的基板中表达，而dlx4和dlx6不表达。因此，在早期阶段，物理连锁基因的旁系同源对之间的Dlx表达模式比直系同源对之间的Dlx表达模式保守性更好。这表明Dlx基因的早期表达在导致多对物理连锁基因的复制之前就已存在，但在斑马鱼和小鼠的不同旁系同源基因中差异保守。
