Lutz B, Lu H C, Eichele G, Miller D, Kaufman T C
Department of Biochemistry, Baylor College of Medicine, Houston, Texas 77030, USA.
Genes Dev. 1996 Jan 15;10(2):176-84. doi: 10.1101/gad.10.2.176.
Hox complexes are important players in the establishment of the body plan of invertebrates and vertebrates. Sequence comparison demonstrates a remarkable phylogenetic conservation of key structural features of Hox genes. The correlation between the physical order of genes along the chromosomes and their domains of function along the body axis is conserved between arthropods and vertebrates. Ectopic expression experiments suggest that the functions of homeo proteins also are conserved between invertebrates and vertebrates. However, it remains an open question whether vertebrate Hox genes expressed under the control of Drosophila regulatory sequences can substitute the function of Drosophila Hox genes. We have studied this issue with the Drosophila labial (lab) gene and its chicken ortholog gHoxb-1. We fused the entire protein-coding region of gHoxb-1 with previously identified regulatory sequences of lab. This approach places gHoxb-1 into the normal embryonic spatiotemporal context in which lab acts. Ten transgenic lines carrying gHoxb-1 were established and tested for their ability to rescue lab null mutant animals. Eight lines rescued with high efficiency, embryonic lethality, and abnormal head morphogenesis, two defects observed in lab null mutant embryos. The rescue with the gHoxb-1 minigene was close to the efficiency of that obtained with the Drosophila lab minigene. This indicates that gHoxb-1 protein can regulate lab target genes and thereby restore embryonic viability. This is striking, as Lab and gHoxb-1 proteins are divergent except for their homeo domains and a short stretch of amino acids amino-terminal to the homeo domain. Our findings demonstrate a functional conservation of the lab class homeo proteins between insects and vertebrates and support the view that function of Hox genes resides in relatively few conserved motifs and largely in the homeo domain.
Hox复合体在无脊椎动物和脊椎动物身体结构的建立过程中发挥着重要作用。序列比较显示Hox基因的关键结构特征在系统发育上具有显著的保守性。沿染色体的基因物理顺序与其沿身体轴的功能域之间的相关性在节肢动物和脊椎动物之间是保守的。异位表达实验表明，同源蛋白的功能在无脊椎动物和脊椎动物之间也是保守的。然而，在果蝇调控序列控制下表达的脊椎动物Hox基因是否能够替代果蝇Hox基因的功能，这仍然是一个悬而未决的问题。我们用果蝇的唇（lab）基因及其鸡的直系同源基因gHoxb-1研究了这个问题。我们将gHoxb-1的整个蛋白质编码区域与先前鉴定的lab调控序列融合。这种方法将gHoxb-1置于lab发挥作用的正常胚胎时空环境中。建立了10个携带gHoxb-1的转基因品系，并测试它们拯救lab基因缺失突变动物的能力。8个品系高效拯救了胚胎致死率和异常头部形态发生，这是在lab基因缺失突变胚胎中观察到的两个缺陷。用gHoxb-1小基因进行的拯救效率接近用果蝇lab小基因获得的效率。这表明gHoxb-1蛋白可以调节lab靶基因，从而恢复胚胎活力。这很引人注目，因为Lab和gHoxb-1蛋白除了它们的同源结构域和同源结构域氨基末端的一小段氨基酸外是不同的。我们的研究结果证明了昆虫和脊椎动物之间lab类同源蛋白的功能保守性，并支持这样一种观点，即Hox基因的功能存在于相对较少的保守基序中，并主要存在于同源结构域中。
