Fahey Bryony, Larroux Claire, Woodcroft Ben J, Degnan Bernard M
School of Integrative Biology, University of Queensland, Brisbane QLD 4072, Australia.
Biol Bull. 2008 Jun;214(3):205-17. doi: 10.2307/25470664.
A huge discrepancy in morphological diversity exists between poriferans and eumetazoans. The disparate evolutionary outcomes of these two ancient metazoan lineages may be reflected in the composition, architecture, and regulation of genomes of modern representatives. As a case study, we compare the sizes of upstream intergenic regions of genes found within the NK homeobox cluster of the demosponge Amphimedon queenslandica with eumetazoan orthologs. This analysis includes NK genes as well as five structural genes interspersed in the cluster. The upstream intergenic regions of the homeobox genes are significantly smaller in Amphimedon than in eumetazoan orthologs, suggesting that the sponge genes house less cis-regulatory information. In contrast, the upstream intergenic regions of the structural genes are not significantly different. The simple developmental expression patterns of representative NK genes in Amphimedon lends support to the proposition that their regulatory apparatuses, unlike those of bilaterians, do not encode the information for dynamic, pleiotropic gene expression. On the basis of this example, we suggest that the size of the intergenic regions upstream of the transcription start site may act as a proxy for estimating regulatory complexity and reflect the limitations of the sponge genome to direct complex and varied morphogenetic processes.
多孔动物门和真后生动物之间在形态多样性上存在巨大差异。这两个古老后生动物谱系截然不同的进化结果可能反映在现代代表物种基因组的组成、结构和调控方面。作为一个案例研究，我们比较了海绵动物昆士兰双盘海绵（Amphimedon queenslandica）NK同源异型框基因簇中基因的上游基因间区域大小与真后生动物直系同源基因的大小。该分析包括NK基因以及散布在基因簇中的五个结构基因。双盘海绵中同源异型框基因的上游基因间区域明显小于真后生动物的直系同源基因，这表明海绵基因所包含的顺式调控信息较少。相比之下，结构基因的上游基因间区域没有显著差异。双盘海绵中代表性NK基因简单的发育表达模式支持了这样一种观点，即与两侧对称动物不同，它们的调控机制不编码动态、多效性基因表达的信息。基于这个例子，我们认为转录起始位点上游基因间区域的大小可能作为估计调控复杂性的一个指标，并反映海绵基因组在指导复杂多样的形态发生过程方面的局限性。
