Alx1 is a pivotal transcription factor in a gene regulatory network that controls skeletogenesis throughout the echinoderm phylum. We performed a structure-function analysis of sea urchin Alx1 using a rescue assay and identified a novel, conserved motif (Domain 2) essential for skeletogenic function. The paralogue of Alx1, Alx4, was not functionally interchangeable with Alx1, but insertion of Domain 2 conferred robust skeletogenic function on Alx4. We used cross-species expression experiments to show that Alx1 proteins from distantly related echinoderms are not interchangeable, although the sequence and function of Domain 2 are highly conserved. We also found that Domain 2 is subject to alternative splicing and provide evidence that this domain was originally gained through exonization. Our findings show that a gene duplication event permitted the functional specialization of a transcription factor through changes in exon-intron organization and thereby supported the evolution of a major morphological novelty.

中文翻译：

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旁系同源转录因子的功能差异支持棘皮动物生物矿化的进化


Alx1 是基因调控网络中的关键转录因子，控制整个棘皮动物门的骨骼发生。我们使用救援分析对海胆 Alx1 进行了结构功能分析，并鉴定了一个对于骨骼形成功能至关重要的新型保守基序（结构域 2）。 Alx1 的旁系同源物 Alx4 在功能上不能与 Alx1 互换，但结构域 2 的插入赋予了 Alx4 强大的成骨功能。我们使用跨物种表达实验表明，尽管结构域 2 的序列和功能高度保守，但来自远缘棘皮动物的 Alx1 蛋白不可互换。我们还发现域 2 受到选择性剪接的影响，并提供证据表明该域最初是通过外显化获得的。我们的研究结果表明，基因复制事件允许转录因子通过外显子-内含子组织的变化实现功能特化，从而支持主要形态新颖性的进化。