Telford M J
Department of Zoology, The Natural History Museum, London, SW7 5BD, UK.
Curr Biol. 2000 Mar 23;10(6):349-52. doi: 10.1016/s0960-9822(00)00387-0.
The DNA-binding homeobox motif was first identified in several Drosophila homeotic genes but also in fushi tarazu, a gene found in the Hox cluster yet involved in segmentation, not anteroposterior patterning [1]. Homeotic transformations are not seen in insect ftz mutants, and insect ftz genes do not have Hox-like expression except within the nervous system [2] [3]. Insect ftz homeobox sequences link them to the Antp-class genes and Tribolium and Schistocerca orthologs have Antp-class YPWM motifs amino-terminal to the homeobox [2] [3]. Orthologs of ftz cloned from a centipede and an onychophoran [4] show that it predates the emergence of the arthropods, but the inability to pinpoint non-arthropodan orthologs suggested that ftz is the product of a Hox gene duplication in the arthropod ancestor [4] [5]. I have cloned ftz orthologs from a mite and a tardigrade, arthropod outgroups of the insects [6]. Mite ftz is expressed in a Hox-like pattern, confirming its ancestral role in anteroposterior patterning. Phylogenetic analyses indicate that arthropod ftz genes are orthologous to the Lox5 genes of lophotrochozoans (a group that includes molluscs) [7] and, possibly, with the Mab-5 genes of nematodes and Hox6 genes of deuterostomes and would therefore have been present in the triploblast ancestor.
DNA结合同源异型框基序最初是在几个果蝇同源异型基因中被鉴定出来的，但在腹节基因中也有发现，腹节基因位于Hox基因簇中，却参与体节形成，而非前后模式形成[1]。在昆虫腹节突变体中未观察到同源异型转化，并且昆虫腹节基因除了在神经系统内之外没有类似Hox的表达[2][3]。昆虫腹节同源异型框序列将它们与Antp类基因联系起来，而拟谷盗和美洲沙漠蝗的直系同源基因在同源异型框的氨基末端具有Antp类YPWM基序[2][3]。从蜈蚣和栉蚕中克隆的腹节直系同源基因[4]表明，它在节肢动物出现之前就已存在，但无法确定非节肢动物的直系同源基因，这表明腹节是节肢动物祖先中Hox基因复制的产物[4][5]。我从螨类和缓步动物（昆虫的节肢动物外类群）中克隆了腹节直系同源基因[6]。螨类腹节以类似Hox的模式表达，证实了其在前后模式形成中的祖先作用。系统发育分析表明，节肢动物的腹节基因与冠轮动物（包括软体动物的一组动物）的Lox5基因直系同源[7]，并且可能与线虫的Mab-5基因以及后口动物的Hox6基因直系同源，因此在三胚层祖先中就已存在。
