van Esbroeck Annelot C M, Verhagen Rob F M, Biagioni Martina, Fossati Matteo, Distel Ben, Elgersma Ype
Department of Clinical Genetics, Erasmus MC, Rotterdam, Dr. Molewaterplein 40, 3015GD Rotterdam, The Netherlands.
Erasmus MC Expertise Center for Neurodevelopmental Disorders (ENCORE), Dr. Molewaterplein 40, 3015GD Rotterdam, The Netherlands.
Hum Mol Genet. 2025 Jun 4;34(12):1009-1016. doi: 10.1093/hmg/ddaf044.
The human UBE3A gene encodes three isoforms of Ubiquitin E3 ligase A, which differ in their N-terminal sequence, abundance, and localization. The most abundant isoforms are the short human UBE3A isoform 1 (hUBE3A-Iso1) (80%) and the long hUBE3A-Iso3 (17%), which are highly conserved across mammals. In mouse and human neurons, UBE3A levels are most prominent in the nucleus, which is largely attributed to the abundant short hUBE3A-Iso1 which is enriched in the nucleus. In mice, the cytosolic UBE3A staining is predominantly the result of cytosolically enriched long m(ouse)UBE3A-Iso2. Despite the high sequence conservation between the long mUBE3A-Iso2 and its human ortholog hUBE3A-Iso3, we previously reported nuclear enrichment for hUBE3A-Iso3. This finding was not only surprising, but also seemed at odds with the substantial cytosolic UBE3A staining that is observed in human neurons. Here, we revisited the localization of hUBE3A-Iso3, as well as an Angelman syndrome-associated variant in the N-terminal sequence of hUBE3A-Iso3. We now conclude that hUBE3A-Iso3 isoform and its mouse ortholog mUBE3A-Iso2 show in fact a very similar mostly cytosolic localization. Our previous, erroneous, conclusions are explained by the finding that N-terminal amino acid substitutions affect the localization of these two orthologs in different ways. Specifically, amino acid substitutions at the p.Met21 position of hUBE3A-Iso3 result in a partial shift of the hUBE3A-Iso3 isoform from the cytosol to the nucleus.
人类UBE3A基因编码泛素E3连接酶A的三种亚型，它们在N端序列、丰度和定位上有所不同。最丰富的亚型是短的人类UBE3A亚型1（hUBE3A-Iso1）（80%）和长的hUBE3A-Iso3（17%），它们在哺乳动物中高度保守。在小鼠和人类神经元中，UBE3A水平在细胞核中最为显著，这主要归因于在细胞核中富集的丰富的短hUBE3A-Iso1。在小鼠中，胞质UBE3A染色主要是由于胞质中富集的长的小鼠UBE3A-Iso2。尽管长的mUBE3A-Iso2与其人类同源物hUBE3A-Iso3之间的序列保守性很高，但我们之前报道hUBE3A-Iso3在细胞核中富集。这一发现不仅令人惊讶，而且似乎与在人类神经元中观察到的大量胞质UBE3A染色不一致。在这里，我们重新研究了hUBE3A-Iso3的定位，以及hUBE3A-Iso3 N端序列中与天使综合征相关的变体。我们现在得出结论，hUBE3A-Iso3亚型及其小鼠同源物mUBE3A-Iso2实际上显示出非常相似的主要胞质定位。我们之前错误的结论可以通过以下发现来解释：N端氨基酸取代以不同方式影响这两个同源物的定位。具体而言，hUBE3A-Iso3的p.Met21位置的氨基酸取代导致hUBE3A-Iso3亚型从胞质部分转移到细胞核。
