Minguillón Carolina, Garcia-Fernàndez Jordi
Departament de Genètica, Facultat de Biologia, Universitat de Barcelona, Spain.
Genome Biol. 2003;4(2):R12. doi: 10.1186/gb-2003-4-2-r12. Epub 2003 Jan 23.
Hox and ParaHox gene clusters are thought to have resulted from the duplication of a ProtoHox gene cluster early in metazoan evolution. However, the origin and evolution of the other genes belonging to the extended Hox group of homeobox-containing genes, that is, Mox and Evx, remains obscure. We constructed phylogenetic trees with mouse, amphioxus and Drosophila extended Hox and other related Antennapedia-type homeobox gene sequences and analyzed the linkage data available for such genes.
We claim that neither Mox nor Evx is a Hox or ParaHox gene. We propose a scenario that reconciles phylogeny with linkage data, in which an Evx/Mox ancestor gene linked to a ProtoHox cluster was involved in a segmental tandem duplication event that generated an array of all Hox-like genes, referred to as the 'coupled' cluster. A chromosomal breakage within this cluster explains the current composition of the extended Hox cluster (with Evx, Hox and Mox genes) and the ParaHox cluster.
Most studies dealing with the origin and evolution of Hox and ParaHox clusters have not included the Hox-related genes Mox and Evx. Our phylogenetic analyses and the available linkage data in mammalian genomes support an evolutionary scenario in which an ancestor of Evx and Mox was linked to the ProtoHox cluster, and that a tandem duplication of a large genomic region early in metazoan evolution generated the Hox and ParaHox clusters, plus the cluster-neighbors Evx and Mox. The large 'coupled' Hox-like cluster EvxHox/MoxParaHox was subsequently broken, thus grouping the Mox and Evx genes to the Hox clusters, and isolating the ParaHox cluster.
Hox和ParaHox基因簇被认为是后生动物进化早期一个原始Hox基因簇复制的结果。然而，属于含同源异型框基因的扩展Hox组的其他基因，即Mox和Evx的起源和进化仍然不清楚。我们构建了包含小鼠、文昌鱼和果蝇扩展Hox及其他相关触角足型同源异型框基因序列的系统发育树，并分析了这些基因可用的连锁数据。
我们认为Mox和Evx都不是Hox或ParaHox基因。我们提出了一种将系统发育与连锁数据相协调的设想，即一个与原始Hox簇相连的Evx/Mox祖先基因参与了一个片段串联重复事件，该事件产生了一系列所有类Hox基因，称为“耦合”簇。该簇内的染色体断裂解释了扩展Hox簇（包含Evx、Hox和Mox基因）和ParaHox簇的当前组成。
大多数关于Hox和ParaHox簇起源和进化的研究都没有包括与Hox相关的基因Mox和Evx。我们的系统发育分析和哺乳动物基因组中可用的连锁数据支持一种进化设想，即Evx和Mox的一个祖先与原始Hox簇相连，并且后生动物进化早期一个大基因组区域的串联重复产生了Hox和ParaHox簇，以及簇邻基因Evx和Mox。随后，大的“耦合”类Hox簇EvxHox/MoxParaHox断裂，从而将Mox和Evx基因归入Hox簇，并分离出ParaHox簇。
