Concepcion Dorothy, Liang Catherine, Kim Daniel, Hamilton Bruce A
Department of Cellular and Molecular Medicine, Department of Medicine, Moores UC San Diego Cancer Center, Institute for Genomic Medicine, University of California San Diego School of Medicine, University of California San Diego, 3147 Biomedical Sciences Way, La Jolla, CA 92093.
Genetics. 2025 Aug 18. doi: 10.1093/genetics/iyaf164.
Genetic variants that introduce a premature termination codon (PTC) are often assumed equivalent and functionally null. Exceptions depend on the specific architectures of the affected mRNA and protein. Here we address phenotypic differences among early truncating variants of mouse Zfp423, whose phenotypes resemble Joubert Syndrome and Related Disorders (JSRD). We replicate quantitative differences previously seen between presumptive null PTC variants based on their position in the coding sequence. We show with reciprocal congenic strains that large phenotype differences between two PTC variants with the same predicted stop and reinitiation codons is due to the specific allele rather than different strain backgrounds, with no evidence for induced exon skipping. Differences in RNA structure, however, could influence translation rate across the affected exon. Using a reporter assay, we find differences in translational reinitiation between two deletion variants that correlate with predicted RNA structure rather than distance from the canonical initiation codon. These results confirm and extend earlier evidence for differences among Zfp423 PTC variants, identify parameters for translational reinitiation after an early termination codon, and reinforce caution in the null interpretation of early PTC variants.
引入过早终止密码子（PTC）的基因变异通常被认为是等效的且功能缺失。例外情况取决于受影响的mRNA和蛋白质的具体结构。在这里，我们研究了小鼠Zfp423早期截短变异体之间的表型差异，其表型类似于乔伯特综合征及相关疾病（JSRD）。我们重现了先前在假定的无效PTC变异体之间基于其在编码序列中的位置所观察到的定量差异。我们通过相互同源近交系表明，具有相同预测终止和重新起始密码子的两个PTC变异体之间的巨大表型差异是由于特定等位基因而非不同的品系背景，且没有证据表明存在诱导外显子跳跃。然而，RNA结构的差异可能会影响受影响外显子的翻译速率。使用报告基因测定法，我们发现两个缺失变异体之间的翻译重新起始存在差异，这与预测的RNA结构相关，而非与距经典起始密码子的距离相关。这些结果证实并扩展了早期关于Zfp423 PTC变异体之间差异的证据，确定了早期终止密码子后翻译重新起始的参数，并强调了在对早期PTC变异体进行无效解释时需谨慎。
