EMBRYOLOGICAL STUDY OF RETINOIC ACID RECEPTORS IN ANIMAL MODEL FOR ANORECTAL MALFORMATION

维甲酸介导的信号转导在各种器官的发生中起着至关重要的作用。为探讨肛门直肠畸形（ARM）的发病机制，研究了全反式维甲酸（ATRA）诱导的ARM小鼠胚胎中维甲酸受体（RAR）的分布。方法：孕鼠于妊娠第9天（E9.0）灌胃给予ATRA 100 mg/kg。在E11.0和E14.0之间获得胚胎，并立即在4%多聚甲醛溶液中固定。使用针对RAR-α、RAR-β和RAR-γ特异性产生的抗体制备冷冻切片用于免疫组织化学。结果：超过98%的胚胎给予ATRA ARM，直肠前列腺尿道和直肠泄殖腔瘘是最常见的异常。在E11.5正常胚胎的后肠-尾肠上皮中同样发现了RAR-α的免疫反应性。然而，在处理的胚胎中，后肠中不存在。RAR-β和RAR-γ的免疫反应性在后肠远端没有差异。结论：E11.5时后肠-尾肠中RAR-α分布受损导致E14.0时泄殖腔和直肠尿道或直肠泄殖腔瘘的不完全分隔。这些结果表明，过量的全反式维甲酸影响远端后肠发育直接破坏类维生素A介导的信号通路。

Retinoid-mediated signal transduction plays a crucial role in the organogenesis of various organs. To investigate the pathogenesis of anorectal malformations (ARM), the authors studied the distribution pattern of retinoic acid receptors (RARs) in ARM murine embryos induced by overdose of all-trans retinoic acid (ATRA). METHODS : Pregnant mice were gavage-fed 100 mg/kg of ATRA on the ninth gestational day (E9.0). Embryos were obtained between E11.0 and E14.0 and were fixed immediately in a 4% paraformaldehyde solution. Frozen sections were prepared for immunohistochemistry using antibodies specifically raised against RAR-alpha, RAR-beta, and RAR-gamma. RESULTS : Over 98% of the embryos administered ATRA had ARM ; rectoprostatic urethral and rectocloacal fistulas were the most frequent anomalies. The immunoreactivity of RAR-alpha was found equally in the epithelium of hindgut-tailgut in normal embryos on E11.5. However, it was absent in the hindgut in the treated embryos. The immunoreactivities of RAR-beta and RAR-gamma showed no difference in the distal hindgut. CONCLUSIONS : Impaired distribution of RAR-alpha in the hindgut-tailgut on E11.5 resulted in the incomplete partitioning of the cloaca and the rectourethral or rectocloacal fistula on E14.0. These results suggest mat overdose of ATRA affects the distal hindgut development by directly disrupting the retinoid-mediated signalling pathway.