Spatiotemporal expression of BMP7 in the development of anorectal malformations in fetal rats

The aim of this study was to determine the expression patterns of bone morphogenetic protein 7 (BMP7) during anorectal development in normal rat embryos and in embryos with anorectal malformations (ARM), and to investigate the possible role of BMP7 in the pathogenesis of ARM. ARM was induced by treating rat embryos with ethylenethiourea on the 10th gestational day (GD10). Embryos were harvested by Cesarean delivery and the spatiotemporal expression of BMP7 was evaluated in normal (n= 168) and ARM embryos (n= 171) from GD13 to GD16 using immunohistochemistry staining and western blot analysis. Immunohistochemical staining in normal embryos revealed that BMP7 was abundantly expressed on the epithelium of the urorectal septum (URS) and the hindgut on GD13, and BMP7-immunopositive cells were extensively detected in the URS, hindgut, and cloacal membrane by GD14. Increased positive tissue staining was noted on the fused tissue of the URS and the thin anal membrane on GD15. In ARM embryos, the epithelium of the cloaca, URS, and anorectum were negatively or only faintly immunostained for BMP7. BMP7 protein expression showed time-dependent changes in the developing hindgut according to western blotting, and reached a peak on GD15 during anus formation. BMP7 expression levels from GD14 to GD15 were significantly lower in the ARM group compared with the normal group (P< 0.05). Spatiotemporal expression of BMP7 was disrupted in ARM embryos during anorectal morphogenesis from GD13 to GD16. These results suggest that downregulation of BMP7 at the time of cloacal separation into the primitive rectum and UGS might be related to the development of ARM.