Combined methylmalonic acidemia and homocystinuria, cblC type, is the most common inherited disorder of cobalamin metabolism and is characterized by severe fetal developmental defects primarily impacting the central nervous system, hematopoietic system, and heart. CblC was previously shown to be due to mutations in the MMACHC gene, which encodes a protein thought to function in intracellular cobalamin trafficking and biosynthesis of adenosylcobalamin (AdoCbl) and methylcobalamin (MeCbl). These coenzymes are required for the production of succinyl-CoA and methionine, respectively. However, it is currently unclear whether additional roles for MMACHC exist outside of cobalamin metabolism. Furthermore, due to a lack of sufficient animal models, the exact pathophysiology of cblC remains unknown. Here, we report the generation and characterization of two new mouse models to study the role of MMACHC in vivo. CRISPR/Cas9 genome editing was used to develop a Mmachc floxed allele (Mmachc^flox/flox), which we validated as a conditional null. For a gain-of-function approach, we generated a transgenic mouse line that over-expresses functional Mmachc (Mmachc-OE^+/tg) capable of rescuing Mmachc homozygous mutant lethality. Surprisingly, our data also suggest that these mice may exhibit a partially penetrant maternal-effect rescue, which might have implications for in utero therapeutic interventions to treat cblC. Both the Mmachc^flox/flox and Mmachc-OE^+/tg mouse models will be valuable resources for understanding the biological roles of MMACHC in a variety of tissue contexts and allow for deeper understanding of the pathophysiology of cblC.

甲基丙二酸血症和高胱氨酸尿症合并症，cblC 型，是钴胺素代谢最常见的遗传性疾病，其特征是严重的胎儿发育缺陷，主要影响中枢神经系统、造血系统和心脏。CblC 以前被证明是由于MMACHC 中的突变基因，其编码的蛋白质被认为在细胞内钴胺素运输和腺苷钴胺素 (AdoCbl) 和甲基钴胺素 (MeCbl) 的生物合成中起作用。这些辅酶分别是生产琥珀酰辅酶 A 和甲硫氨酸所必需的。然而，目前尚不清楚在钴胺素代谢之外是否存在 MMACHC 的其他作用。此外，由于缺乏足够的动物模型，cblC 的确切病理生理学仍然未知。在这里，我们报告了两种新小鼠模型的生成和表征，以研究 MMACHC在体内的作用。CRISPR/Cas9 基因组编辑用于开发Mmachc floxed 等位基因(Mmachc ^flox/flox )，我们将其验证为条件空值。对于功能获得方法，我们生成了一种转基因小鼠品系，该品系过表达功能性Mmachc (Mmachc-OE ^+/tg )，能够挽救Mmachc纯合突变体的致死率。令人惊讶的是，我们的数据还表明，这些小鼠可能表现出部分渗透性的母体效应拯救，这可能对子宫内治疗 cblC 的干预措施产生影响。无论是Mmachc ^{FLOX / FLOX}和Mmachc-OE ^{+ / TG}小鼠模型将是宝贵的资源，了解在各种组织中的上下文MMACHC的生物学作用，并允许cblC的病理生理的更深入的了解。