Missense mutations of the RET gene have been identified in both multiple endocrine neoplasia (MEN) type 2A/B and Hirschsprung disease (HSCR: congenital absence of the enteric nervous system, ENS). Current consensus holds that MEN2A/B and HSCR are caused by activating and inactivating RET mutations, respectively. However, the biological significance of RET missense mutations in vivo has not been fully elucidated. In the present study, we introduced one MEN2B-associated (M918T) and two HSCR-associated (N394K and Y791F) RET missense mutations into the corresponding regions of the mouse Ret gene by genome editing (RetM919T , RetN396K and RetY792F ) and performed histological examinations of Ret-expressing tissues to understand the pathogenetic impact of each mutant in vivo. RetM919T/+ mice displayed MEN2B-related phenotypes, including C-cell hyperplasia and abnormal enlargement of the primary sympathetic ganglia. Similar sympathetic phenotype was observed in RetM919T/- mice, demonstrating a strong pathogenetic effect of the Ret M918T by a single-allele expression. In contrast, no abnormality was found in the ENS of mice harboring the Ret N394K or Y791F mutation. Most surprisingly, single-allele expression of RET N394K or Y791F was sufficient for normal ENS development, indicating that these RET mutants exert largely physiological function in vivo. This study reveals contrasting pathogenetic effects between MEN2B- and HSCR-associated RET missense mutations, and suggests that some of HSCR-associated RET missense mutations are by themselves neither inactivating nor pathogenetic and require involvement of other gene mutations for disease expressivity.

中文翻译：

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小鼠中的点诱变揭示了MEN2B-和Hirschsprung疾病相关的RET基因错义突变之间的致病作用的对比。

在多发性内分泌肿瘤（MEN）2A / B型和Hirschsprung病（HSCR：先天性肠神经系统缺失，ENS）中都发现了RET基因的错义突变。目前的共识认为，MEN2A / B和HSCR分别是由激活和失活RET突变引起的。但是，尚未完全阐明体内RET错义突变的生物学意义。在本研究中，我们通过基因组编辑（RetM919T，RetN396K和RetY792F）将一个MEN2B相关（M918T）和两个HSCR相关（N394K和Y791F）RET错义突变引入到小鼠Ret基因的相应区域，并进行了组织学检查表达Ret的组织以了解每种突变体在体内的致病作用。RetM919T / +小鼠表现出MEN2B相关表型，包括C细胞增生和原发性交感神经节异常扩大。在RetM919T /-小鼠中观察到类似的交感型，通过单等位基因表达证明Ret M918T具有很强的致病作用。相反，在带有Ret N394K或Y791F突变的小鼠的ENS中未发现异常。最令人惊讶的是，RET N394K或Y791F的单等位基因表达足以正常ENS发育，表明这些RET突变体在体内发挥了很大的生理功能。这项研究揭示了MEN2B和HSCR相关的RET错义突变之间的致病作用的对比，并表明一些HSCR相关的RET错义突变本身既不失活也不致病，并且需要其他基因突变参与疾病表达。