Georg-August-Universität, Johann-Friedrich-Blumenbach-Institut für Zoologie und Anthropologie, Abteilung Entwicklungsbiologie, GZMB, Ernst-Caspari-Haus, Justus-von-Liebig-Weg 11, 37077 Göttingen, Germany.
BMC Evol Biol. 2010 Mar 30;10:88. doi: 10.1186/1471-2148-10-88.
The Sp-family of transcription factors are evolutionarily conserved zinc finger proteins present in many animal species. The orthology of the Sp genes in different animals is unclear and their evolutionary history is therefore controversially discussed. This is especially the case for the Sp gene buttonhead (btd) which plays a key role in head development in Drosophila melanogaster, and has been proposed to have originated by a recent gene duplication. The purpose of the presented study was to trace orthologs of btd in other insects and reconstruct the evolutionary history of the Sp genes within the metazoa.
We isolated Sp genes from representatives of a holometabolous insect (Tribolium castaneum), a hemimetabolous insect (Oncopeltus fasciatus), primitively wingless hexapods (Folsomia candida and Thermobia domestica), and an amphipod crustacean (Parhyale hawaienis). We supplemented this data set with data from fully sequenced animal genomes. We performed phylogenetic sequence analysis with the result that all Sp factors fall into three monophyletic clades. These clades are also supported by protein domain structure, gene expression, and chromosomal location. We show that clear orthologs of the D. melanogaster btd gene are present even in the basal insects, and that the Sp5-related genes in the genome sequence of several deuterostomes and the basal metazoans Trichoplax adhaerens and Nematostella vectensis are also orthologs of btd.
All available data provide strong evidence for an ancestral cluster of three Sp-family genes as well as synteny of this Sp cluster and the Hox cluster. The ancestral Sp gene cluster already contained a Sp5/btd ortholog, which strongly suggests that btd is not the result of a recent gene duplication, but directly traces back to an ancestral gene already present in the metazoan ancestor.
Sp 转录因子家族是进化上保守的锌指蛋白，存在于许多动物物种中。不同动物中 Sp 基因的同源性尚不清楚，因此其进化历史存在争议。这尤其适用于 Sp 基因 buttonhead（btd），它在果蝇的头部发育中起着关键作用，并被提出是由最近的基因复制产生的。本研究的目的是追踪 btd 在其他昆虫中的同源物，并重建 metazoa 内 Sp 基因的进化历史。
我们从完全变态昆虫（Tribolium castaneum）、半变态昆虫（Oncopeltus fasciatus）、原始无翅六足动物（Folsomia candida 和 Thermobia domestica）和甲壳纲动物（Parhyale hawaienis）的代表中分离出 Sp 基因。我们用来自完全测序的动物基因组的数据补充了这个数据集。我们进行了系统发育序列分析，结果表明所有 Sp 因子都分为三个单系群。这些分支也得到了蛋白质结构域、基因表达和染色体位置的支持。我们表明，即使在基础昆虫中，也存在与 D. melanogaster btd 基因明显同源的基因，并且在几个后口动物和基础后生动物 Trichoplax adhaerens 和 Nematostella vectensis 的基因组序列中，Sp5 相关基因也是 btd 的同源物。
所有可用的数据都提供了强有力的证据，证明存在一个祖先的三个 Sp 家族基因簇，以及这个 Sp 簇和 Hox 簇的同线性。祖先的 Sp 基因簇已经包含了一个 Sp5/btd 同源物，这强烈表明 btd 不是最近基因复制的结果，而是直接追溯到后生动物祖先中已经存在的一个祖先基因。
