Division of Developmental Biology, Cincinnati Children's Hospital Medical Center, 3333 Burnet Avenue, Cincinnati, OH 45229, USA.
Dis Model Mech. 2014 Apr;7(4):483-93. doi: 10.1242/dmm.014530. Epub 2014 Feb 13.
Anorectal malformations are congenital anomalies that form a spectrum of disorders, from the most benign type with excellent functional prognosis, to very complex, such as cloaca malformation in females in which the rectum, vagina and urethra fail to develop separately and instead drain via a single common channel into the perineum. The severity of this phenotype suggests that the defect occurs in the early stages of embryonic development of the organs derived from the cloaca. Owing to the inability to directly investigate human embryonic cloaca development, current research has relied on the use of mouse models of anorectal malformations. However, even studies of mouse embryos lack analysis of the earliest stages of cloaca patterning and morphogenesis. Here we compared human and mouse cloaca development and retrospectively identified that early mis-patterning of the embryonic cloaca might underlie the most severe forms of anorectal malformation in humans. In mouse, we identified that defective sonic hedgehog (Shh) signaling results in early dorsal-ventral epithelial abnormalities prior to the reported defects in septation. This is manifested by the absence of Sox2 and aberrant expression of keratins in the embryonic cloaca of Shh knockout mice. Shh knockout embryos additionally develop a hypervascular stroma, which is defective in BMP signaling. These epithelial and stromal defects persist later, creating an indeterminate epithelium with molecular alterations in the common channel. We then used these animals to perform a broad comparison with patients with mild-to-severe forms of anorectal malformations including cloaca malformation. We found striking parallels with the Shh mouse model, including nearly identical defective molecular identity of the epithelium and surrounding stroma. Our work strongly suggests that early embryonic cloacal epithelial differentiation defects might be the underlying cause of severe forms of anorectal malformations in humans. Moreover, deranged Shh and BMP signaling is correlated with severe anorectal malformations in both mouse and humans.
肛门直肠畸形是一种先天性异常，其表现为一系列疾病，从预后良好的最良性类型到非常复杂的类型，如女性的泄殖腔畸形，其中直肠、阴道和尿道未能分别发育，而是通过单一的共同通道排入会阴。这种表型的严重程度表明，缺陷发生在源自泄殖腔的器官的胚胎发育早期。由于无法直接研究人类胚胎泄殖腔的发育，目前的研究依赖于使用肛门直肠畸形的小鼠模型。然而，即使是对小鼠胚胎的研究也缺乏对泄殖腔模式形成和形态发生的最早阶段的分析。在这里，我们比较了人和小鼠的泄殖腔发育，并回顾性地发现，胚胎泄殖腔的早期模式形成错误可能是导致人类最严重肛门直肠畸形的基础。在小鼠中，我们发现，缺陷性 sonic hedgehog（Shh）信号导致早期背腹上皮异常，早于报道的分隔缺陷。这表现为 Shh 敲除小鼠胚胎泄殖腔 Sox2 和角蛋白表达异常缺失。Shh 敲除胚胎还会发展出一种富含血管的基质，其 BMP 信号传导缺陷。这些上皮和基质缺陷持续存在，导致共同通道中的上皮不确定，并出现分子改变。然后，我们使用这些动物与轻度至重度肛门直肠畸形（包括泄殖腔畸形）患者进行了广泛比较。我们发现与 Shh 小鼠模型存在惊人的相似之处，包括上皮和周围基质的几乎相同的缺陷分子特征。我们的工作强烈表明，早期胚胎泄殖腔上皮分化缺陷可能是人类严重肛门直肠畸形的根本原因。此外，Shh 和 BMP 信号传导紊乱与小鼠和人类的严重肛门直肠畸形相关。
