Genome studies have uncovered many examples of essential gene loss, raising the question of how ancient genes transition from essentiality to dispensability. We explored this process for the deeply conserved E3 ubiquitin ligase Murine double minute (Mdm), which is lacking in Drosophila despite the conservation of its main regulatory target, the cellular stress response gene p53. Conducting gene expression and knockdown experiments in the red flour beetle Tribolium castaneum, we found evidence that Mdm has remained essential in insects where it is present. Using bioinformatics approaches, we confirm the absence of the Mdm gene family in Drosophila, mapping its loss to the stem lineage of schizophoran Diptera and Pipunculidae (big-headed flies), about 95–85 million years ago. Intriguingly, this gene loss event was preceded by the de novo origin of the gene Companion of reaper (Corp), a novel p53 regulatory factor that is characterized by functional similarities to vertebrate Mdm2 despite lacking E3 ubiquitin ligase protein domains. Speaking against a 1:1 compensatory gene gain/loss scenario, however, we found that hoverflies (Syrphidae) and pointed-wing flies (Lonchopteridae) possess both Mdm and Corp. This implies that the two p53 regulators have been coexisting for ~ 150 million years in select dipteran clades and for at least 50 million years in the lineage to Schizophora and Pipunculidae. Given these extensive time spans of Mdm/Corp coexistence, we speculate that the loss of Mdm in the lineage to Drosophila involved further acquisitions of compensatory gene activities besides the emergence of Corp. Combined with the previously noted reduction of an ancestral P53 contact domain in the Mdm homologs of crustaceans and insects, we conclude that the loss of the ancient Mdm gene family in flies was the outcome of incremental functional regression over long macroevolutionary time scales.

中文翻译：

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致力于重建古代必需基因的二萜死亡：E3泛素连接酶鼠科动物双分钟。

基因组研究发现了许多必需基因缺失的例子，这引发了一个问题，即古代基因如何从必需性转变为可分配性。我们为深度保守的E3泛素连接酶鼠 双分钟（Mdm）探索了这一过程，尽管果蝇的主要调控靶标是细胞应激反应基因p53，但它在果蝇中却缺乏。在红色面粉甲虫Tribolium castaneum中进行基因表达和敲除实验，我们发现证据表明Mdm在存在昆虫的昆虫中仍然必不可少。使用生物信息学方法，我们证实了Mdm基因家族的缺失果蝇，将其损失映射到大约95-85百万年前的裂殖壶菌Diptera和Pipunculidae（大头蝇）的茎系。有趣的是，此基因丢失事件之前是“收割者伴侣”（Corp）的从头起源，后者是一种新型的p53调节因子，尽管缺乏E3泛素连接酶蛋白结构域，但其功能与脊椎动物Mdm2相似。谈到对一个1：1的补偿基因收益/损失的情况，但是，我们发现，食蚜蝇（食蚜蝇科）和尖翅蝇（Lonchopteridae）同时具有MDM和公司。这意味着两个p53监管者在精选的双足类进化枝中共存在了约1.5亿年，在裂殖藻和Pi科中共存了至少5,000万年。考虑到Mdm / Corp共存的时间跨度很长，我们推测果蝇Mdm在果蝇谱系中的丢失除了Corp.的出现外，还涉及获得补偿性基因活动。结合先前指出的甲壳类和昆虫的Mdm同源物中祖先P53接触域的减少，我们得出结论，古代Mdm的丧失 苍蝇中的基因家族是在较长的宏观进化时间尺度上增量功能回归的结果。