Identification of the evolutionarily conserved nuclear envelope proteins Lem2 and MicLem2 in Tetrahymena thermophila
Identification of the evolutionarily conserved nuclear envelope proteins Lem2 and MicLem2 in Tetrahymena thermophila
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DOI：
10.1016/j.gene.2019.100006
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发表时间：
2019-01
期刊：
影响因子：
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通讯作者：
M. Iwamoto;Y. Fukuda;Hiroko Osakada;Chie Mori;Y. Hiraoka;T. Haraguchi
中科院分区：
文献类型：
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作者：
M. Iwamoto;Y. Fukuda;Hiroko Osakada;Chie Mori;Y. Hiraoka;T. Haraguchi
Lem 2家族蛋白，即含有LAP 2-Emerin-MAN 1（LEM）结构域的核膜蛋白，从酵母到人类都是高度保守的，两者都属于后鞭毛纲超类群。然而，它们的同源物是否存在于其他真核生物中仍不清楚。在本研究中，我们在一个隶属于SAR超群的四膜虫中发现了两个Lem 2同源蛋白，分别命名为Lem 2和MicLem 2。Lem 2定位于大核（MAC）和微核（MIC）的核膜，而MicLem 2仅定位于MIC的核膜。免疫电镜显示Lem 2在嗜热毛癣菌中定位于MAC和MIC的内、外核膜，而MicLem 2主要定位于MIC的核孔。使用GFP融合蛋白的分子结构域分析表明，N-末端和管腔结构域，包括跨膜片段，负责核膜定位。在有性生殖过程中，Lem 2富集在待降解的MAC和MIC的核膜中，而MicLem 2富集在逃避降解的MIC的核膜中。这些发现表明了四膜虫Lem 2蛋白的独特特征。我们的研究结果提供了深入了解核膜蛋白的进化分歧。
Lem2 family proteins, i.e. theLAP2-Emerin-MAN1 (LEM) domain-containing nuclear envelope proteins, are well-conserved from yeasts to humans, both of which belong to the Opisthokonta supergroup. However, whether their homologs are present in other eukaryotic phylogenies remains unclear. In this study, we identified two Lem2 homolog proteins, which we named as Lem2 and MicLem2, in a ciliateTetrahymena thermophilabelonging to the SAR supergroup. Lem2 was localized to the nuclear envelope of the macronucleus (MAC) and micronucleus (MIC), while MicLem2 was exclusively localized to the nuclear envelope of the MIC. Immunoelectron microscopy revealed that Lem2 inT. thermophilawas localized to both the inner and outer nuclear envelopes of the MAC and MIC, while MicLem2 was mostly localized to the nuclear pores of the MIC. Molecular domain analysis using GFP-fused protein showed that the N-terminal and luminal domains, including the transmembrane segments, are responsible for nuclear envelope localization. During sexual reproduction, enrichment of Lem2 occurred in the nuclear envelopes of the MAC and MIC to be degraded, while MicLem2 was enriched in the nuclear envelope of the MIC that escaped degradation. These findings suggest the unique characteristics ofTetrahymenaLem2 proteins. Our findings provide insight into the evolutionary divergence of nuclear envelope proteins.