The major spliceosome mediates pre-mRNA splicing by recognizing the highly conserved sequences at the 5’ and 3’ splice sites and the branch point. More than 150 proteins participate in the splicing process and are organized in the spliceosomal A, B, and C complexes. FRA10AC1 is a peripheral protein of the spliceosomal C complex and its ortholog in the green alga facilitates recognition or interaction with splice sites. We identified biallelic pathogenic variants in FRA10AC1 in five individuals from three consanguineous families. The two unrelated patients 1 and 2 with loss-of-function variants showed developmental delay, intellectual disability, and no speech, while three siblings with the c.494_496delAAG (p.Glu165del) variant had borderline to mild intellectual disability. All patients had microcephaly, hypoplasia or agenesis of the corpus callosum, growth retardation, and craniofacial dysmorphism. FRA10AC1 transcripts and proteins were drastically reduced or absent in fibroblasts of patients 1 and 2. In a heterologous expression system, the p. Glu165del variant impacts intrinsic stability of FRA10AC1 but does not affect its nuclear localization. By co-immunoprecipitation, we found ectopically expressed HA-FRA10AC1 in complex with endogenous DGCR14, another component of the spliceosomal C complex, while the splice factors CHERP, NKAP, RED, and SF3B2 could not be co-immunoprecipitated. Using an in vitro splicing reporter assay, we did not obtain evidence for FRA10AC1 deficiency to suppress missplicing events caused by mutations in the highly conserved dinucleotides of 5’ and 3’ splice sites in an in vitro splicing assay in patient-derived fibroblasts. Our data highlight the importance of specific peripheral spliceosomal C complex proteins for neurodevelopment. It remains possible that FRA10AC1 may have other and/or additional cellular functions, such as coupling of transcription and splicing reactions.

中文翻译：

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双等位基因 FRA10AC1 变体导致生长迟缓的神经发育障碍

主要剪接体通过识别 5' 和 3' 剪接位点和分支点的高度保守序列来介导前 mRNA 剪接。超过 150 种蛋白质参与剪接过程，并组织在剪接体 A、B 和 C 复合物中。FRA10AC1 是剪接体 C 复合体的外周蛋白，其在绿藻中的直系同源物有助于识别或与剪接位点相互作用。我们在来自三个近亲家族的五个个体中鉴定了 FRA10AC1 中的双等位基因致病变异。具有功能丧失变异的两名不相关的患者 1 和 2 表现出发育迟缓、智力障碍和无言语，而具有 c.494_496delAAG (p.Glu165del) 变异的三个兄弟姐妹则具有轻度智力障碍的边缘。所有患者都有小头畸形，胼胝体发育不全或发育不全、生长迟缓和颅面畸形。FRA10AC1 转录物和蛋白质在患者 1 和 2 的成纤维细胞中急剧减少或缺失。在异源表达系统中，p。Glu165del 变体影响 FRA10AC1 的内在稳定性，但不影响其核定位。通过免疫共沉淀，我们发现异位表达的 HA-FRA10AC1 与内源性 DGCR14（剪接体 C 复合体的另一个组成部分）复合，而剪接因子 CHERP、NKAP、RED 和 SF3B2 不能共免疫沉淀。使用体外剪接报告基因测定，在患者来源的成纤维细胞的体外剪接试验中，我们没有获得 FRA10AC1 缺乏抑制由 5' 和 3' 剪接位点高度保守的二核苷酸突变引起的错误剪接事件的证据。我们的数据强调了特定的外周剪接体 C 复合物蛋白对神经发育的重要性。FRA10AC1 仍有可能具有其他和/或额外的细胞功能，例如转录和剪接反应的偶联。