Spatiotemporal distribution of caudal-type homeobox proteins during development of the hindgut and anorectum in human embryos.

Background. The objectives of this study were to determine the spatiotemporal distribution of human caudal-type homeobox proteins CDX1, CDX2 and CDX4 during development of the hindgut and anorectum in the embryo and to explore the possible roles of CDX genes during morphogenesis of the hindgut and anorectum. Methods. Embryos (89) were cut into sections serially and sagittally. From gestation weeks 4-9, CDX1, CDX2 and CDX4 proteins were detected on the caudal midline by immunohistochemical staining. Results. During week 4, extensive immunoreactivity of CDX1, CDX2 and CDX4 was detected in the dorsal urorectal septum, urogenital sinus and hindgut. From weeks 5-7, CDX1-, CDX2- and CDX4- positive cells were detected mainly in the mesenchyme of the urorectal septum and hindgut. The levels of CDX2 and CDX4 immunoreactivity were lower compared to CDX1. During weeks 8 and 9, the anorectal epithelium stained positive for CDX1 and CDX4, and the anal epithelium was positive for CDX2. Conclusions. The CDX proteins are constantly distributed during development of the hindgut and anorectum and exhibit overlapping distribution patterns in the cloaca/hindgut, suggesting they are important in the morphogenesis of the human hindgut and anorectum. CDX genes might be involved in development of the anorectal epithelium after the rectum has separated from the urorectal septum.