20 / 492
14:12 - 14:15
S1-15
(PP)
CLARIFICATION OF MAMMALIAN CLOACA MORPHOGENESIS USING HIGH-
RESOLUTION EPISCOPIC MICROSCOPY
Sean LI and Yichen HUANG
Boston Children's Hospital, Urology, Boston, USA
PURPOSE
The cloaca of placental mammals is divided during embryogenesis but the underlying mechanism remains obscure.
Furthermore, growing evidence suggests that the incompatibility exists between experimental findings and the
anticipated outcomes of the classical septation models.
MATERIAL AND METHODS
We use high-resolution episcopic microscopy to examine a series of normal and mutant mouse embryos in which the
detailed 3-dimentional morphological features are illuminated and "time-lapse" imaged. A total of nine stages of wild
type embryos from day 9.5 to 13.5, 4 stages of Dkk1 mutants with imperforate anus phenotype and 2 stages of Shh
mutants with persistent cloaca phenotype were analyzed. Virtual sections and 3-D video were generated. Relative
position of each involved structures were examined using the standard point of reference along the rostrocaudal axis.
RESULTS
The dorsal peri-cloacal mesenchyme (dPCM) marks the caudal boundary of the cloaca and unexpectedly, the dPCM
remains at a fixed position while other surrounding mesenchymal tissues grow and shift caudally. Stationariness of the
dPCM is likely important for narrowing and eventual occlusion of the cloaca. Indeed, Shh mutants exhibit a hypoplastic
defect of the dPCM. Conversely, Dkk1 mutants have hyperplasitic dPCM.
CONCLUSIONS
We show that dPCM is critical for cloaca septation. The presumptive urorectal septum is not observed. Together, these
findings provide supporting evidence of an occlusion model and offer a new framework to investigate molecular basis of
urogenital and anorectal development and birth defects.