The human UBE3A gene, which is essential for normal neurodevelopment, encodes three Ubiquitin E3 ligase A (UBE3A) protein isoforms. However, the subcellular localization and relative abundance of these human UBE3A isoforms are unknown. We found, as previously reported in mice, that UBE3A is predominantly nuclear in human neurons. However, this conserved subcellular distribution is achieved by strikingly distinct cis-acting mechanisms. A single amino-acid deletion in the N-terminus of human hUBE3A-Iso3, which is homologous to cytosolic mouse mUBE3A-Iso2, results in its translocation to the nucleus. This singe amino-acid deletion is shared with apes and Old World monkeys and was preceded by the appearance of the cytosolic hUBE3A-Iso2 isoform. This hUBE3A-Iso2 isoform arose after the lineage of New World monkeys and Old World monkeys separated from the Tarsiers (Tarsiidae). Due to the loss of a single nucleotide in a non-coding exon, this exon became in frame with the remainder of the UBE3A protein. RNA-seq analysis of human brain samples showed that the human UBE3A isoforms arise by alternative splicing. Consistent with the predominant nuclear enrichment of UBE3A in human neurons, the two nuclear-localized isoforms, hUBE3A-Iso1 and -Iso3, are the most abundantly expressed isoforms of UBE3A, while hUBE3A-Iso2 maintains a small pool of cytosolic UBE3A. Our findings provide new insight into UBE3A localization and evolution and may have important implications for gene therapy approaches in Angelman syndrome.

中文翻译：

---

非同源亚型促进了人类和小鼠之间保守的 UBE3A 亚细胞分布。

人类 UBE3A 基因对正常神经发育至关重要，编码三种泛素 E3 连接酶 A (UBE3A) 蛋白亚型。然而，这些人类 UBE3A 亚型的亚细胞定位和相对丰度尚不清楚。正如之前在小鼠中报道的那样，我们发现 UBE3A 在人类神经元中主要位于核内。然而，这种保守的亚细胞分布是通过显着不同的顺式作用机制实现的。人 hUBE3A-Iso3 的 N 末端的单个氨基酸缺失（与细胞质小鼠 mUBE3A-Iso2 同源）导致其易位至细胞核。这种单一氨基酸缺失为猿类和旧世界猴所共有，并且在胞质 hUBE3A-Iso2 亚型出现之前出现。这种 hUBE3A-Iso2 亚型是在新世界猴和旧世界猴的谱系从眼镜猴（眼镜猴科）中分离出来后出现的。由于非编码外显子中单个核苷酸的丢失，该外显子与 UBE3A 蛋白的其余部分符合读码框。人脑样本的 RNA-seq 分析表明，人 UBE3A 亚型是通过选择性剪接产生的。与人类神经元中 UBE3A 的主要核富集一致，两种核定位同种型 hUBE3A-Iso1 和 -Iso3 是 UBE3A 表达最丰富的同种型，而 hUBE3A-Iso2 则维持一小部分胞质 UBE3A。我们的研究结果为UBE3A定位和进化提供了新的见解，并且可能对天使综合征的基因治疗方法具有重要意义。