Department of Pediatrics and Neonatology, Nagoya City University Graduate School of Medical Sciences, Nagoya, Japan.
Department of Comparative and Experimental Medicine, Nagoya City University Graduate School of Medical Sciences, Nagoya, Japan.
PLoS One. 2020 Aug 17;15(8):e0237814. doi: 10.1371/journal.pone.0237814. eCollection 2020.
Schaaf-Yang syndrome (SYS) is a neurodevelopmental disorder caused by truncating variants in the paternal allele of MAGEL2, located in the Prader-Willi critical region, 15q11-q13. Although the phenotypes of SYS overlap those of Prader-Willi syndrome (PWS), including neonatal hypotonia, feeding problems, and developmental delay/intellectual disability, SYS patients show autism spectrum disorder and joint contractures, which are atypical phenotypes for PWS. Therefore, we hypothesized that the truncated Magel2 protein could potentially produce gain-of-function toxic effects. To test the hypothesis, we generated two engineered mouse models; one, an overexpression model that expressed the N-terminal region of Magel2 that was FLAG tagged with a strong ubiquitous promoter, and another, a genome-edited model that carried a truncating variant in Magel2 generated using the CRISPR/Cas9 system. In the overexpression model, all transgenic mice died in the fetal or neonatal period indicating embryonic or neonatal lethality of the transgene. Therefore, overexpression of the truncated Magel2 could show toxic effects. In the genome-edited model, we generated a mouse model carrying a frameshift variant (c.1690_1924del; p(Glu564Serfs*130)) in Magel2. Model mice carrying the frameshift variant in the paternal or maternal allele of Magel2 were termed Magel2P:fs and Magel2M:fs, respectively. The imprinted expression and spatial distribution of truncating Magel2 transcripts in the brain were maintained. Although neonatal Magel2P:fs mice were lighter than wildtype littermates, Magel2P:fs males and females weighed the same as their wildtype littermates by eight and four weeks of age, respectively. Collectively, the overexpression mouse model may recapitulate fetal or neonatal death, which are the severest phenotypes for SYS. In contrast, the genome-edited mouse model maintains genomic imprinting and distribution of truncated Magel2 transcripts in the brain, but only partially recapitulates SYS phenotypes. Therefore, our results imply that simple gain-of-function toxic effects may not explain the patho-mechanism of SYS, but rather suggest a range of effects due to Magel2 variants as in human SYS patients.
Schaaf-Yang 综合征（SYS）是一种神经发育障碍，由位于 Prader-Willi 关键区域 15q11-q13 的 MAGEL2 父本等位基因截断变异引起。尽管 SYS 的表型与 Prader-Willi 综合征（PWS）重叠，包括新生儿低张力、喂养问题和发育迟缓/智力残疾，但 SYS 患者表现出自闭症谱系障碍和关节挛缩，这是 PWS 的非典型表型。因此，我们假设截断的 Magel2 蛋白可能产生功能获得性毒性作用。为了验证这一假设，我们生成了两种工程小鼠模型；一种是过表达模型，该模型表达了用强泛在启动子标记的 FLAG 标签的 Magel2 的 N 端区域，另一种是基因组编辑模型，该模型使用 CRISPR/Cas9 系统产生了 Magel2 的截断变体。在过表达模型中，所有转基因小鼠都在胎儿或新生儿期死亡，表明转基因的胚胎或新生儿致死性。因此，截断的 Magel2 的过表达可能显示出毒性作用。在基因组编辑模型中，我们生成了一种携带 Magel2 中的移码变异（c.1690_1924del;p(Glu564Serfs*130)）的小鼠模型。携带 Magel2 父本或母本等位基因中移码变异的模型小鼠分别称为 Magel2P:fs 和 Magel2M:fs。截断的 Magel2 转录物在大脑中的印记表达和空间分布得以维持。尽管新生的 Magel2P:fs 小鼠比野生型同窝仔轻，但 Magel2P:fs 雄性和雌性在八周和四周龄时的体重与野生型同窝仔相同。总的来说，过表达小鼠模型可能再现 SYS 最严重的表型，即胎儿或新生儿死亡。相比之下，基因组编辑模型维持了大脑中截断的 Magel2 转录物的基因组印记和分布，但仅部分再现了 SYS 表型。因此，我们的结果表明，简单的功能获得性毒性作用可能无法解释 SYS 的发病机制，而是暗示由于人类 SYS 患者中的 Magel2 变异而产生的一系列影响。
