Heterozygous loss-of-function mutation in Delta-like ligand-4 (Dll4) is an important cause of Adams-Oliver syndrome (AOS). Cardiac defects, in particular outflow tract (OFT) alignment defects, are observed in about one-fourth of patients with this syndrome. The mechanism underlying this genotype-phenotype correlation has not yet been established. Dll4-mediated Notch signaling is known to play a crucial role in second heart field (SHF) progenitor cell proliferation. We hypothesized that the depletion of the SHF progenitor pool of cells due to partial loss of Dll4 is responsible for the OFT alignment defects seen in AOS. To demonstrate this, we studied Dll4 expression by murine SHF progenitor cells around E9.5, a crucial time-point in SHF biology. We used SHF-specific (Islet1-Cre) conditional knockout of Dll4 to bypass the early embryonic lethality seen in global Dll4 heterozygotes. Dll4-mediated Notch signaling is critically required for SHF proliferation such that Dll4 knockout results in a 33% reduction in proliferation and a fourfold increase in apoptosis in SHF cells, leading to a 56% decline in the size of the SHF progenitor pool. A reduction in SHF cells available for incorporation into the developing heart leads to underdevelopment of the SHF-derived right ventricle and OFT. Similar to the clinical syndrome, 32% of SHF-specific Dll4 heterozygotes demonstrate foreshortened and misaligned OFT, resulting in a double outlet right ventricle. Our murine model provides a molecular mechanism to explain the cardiac defects observed in AOS and establishes a novel clinical role for Dll4-mediated Notch signaling in SHF progenitor biology.

中文翻译：

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在 Delta-Like Ligand-4 Haploinsufficiency 驱动的 Adams-Oliver 综合征中观察到的小鼠心脏缺陷模型

Delta 样配体 4 ( Dll4 ) 中的杂合功能丧失突变是 Adams-Oliver 综合征 (AOS) 的重要原因。在大约四分之一的患有这种综合征的患者中观察到心脏缺陷，特别是流出道 (OFT) 排列缺陷。这种基因型-表型相关性的机制尚未确定。已知 Dll4 介导的 Notch 信号传导在第二心场 (SHF) 祖细胞增殖中起关键作用。我们假设由于DLL4的部分丢失导致SHF祖细胞池的消耗是AOS中出现的OFT对齐缺陷的原因。为了证明这一点，我们研究了 E9.5 附近鼠 SHF 祖细胞的 Dll4 表达，这是 SHF 生物学中的一个关键时间点。我们使用 SHF 特定 (Islet1-Cre) 条件性敲除Dll4绕过在全球 Dll4 杂合子中看到的早期胚胎致死率。Dll4 介导的 Notch 信号是 SHF 增殖的关键，因此Dll4敲除导致 SHF 细胞的增殖减少 33% 和细胞凋亡增加四倍，导致 SHF 祖细胞池的大小下降 56%。可用于掺入发育中的心脏的 SHF 细胞减少导致 SHF 衍生的右心室和 OFT 发育不全。与临床综合征相似，32% 的 SHF 特异性Dll4杂合子表现出缩短和错位的OFT，导致右心室双出口。我们的小鼠模型提供了一种分子机制来解释 AOS 中观察到的心脏缺陷，并为 Dll4 介导的 Notch 信号在 SHF 祖细胞生物学中建立了新的临床作用。