An investigation of the proctodeal region with respect to development and breakdown of the cloacal membrane in Xenopus laevis
Date
2009-05-29T05:48:28Z
Authors
Jones, Deborah Marie
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Abstract
Anorectal malformations are common congenital anomalies which disable the
newborn. In order to gain insight into the development and causes of these
anomalies, the normal development of the hindgut requires elucidation at the
structural and molecular level. During normal embryonic development of the
alimentary canal, the proctodeum develops at the posterior end of the embryo and
together with the stomodeum, is the only region where the ectoderm and endoderm
are directly juxtaposed. The juxtaposed ectoderm and endoderm go on to form the
cloacal membrane, which eventually perforates to allow continuity to the exterior.
This study investigated morphological features and mechanisms involved in
proctodeal development and cloacal membrane dissolution in Xenopus laevis
embryos. Embryos were collected, staged and processed for various techniques.
Analysis using time course, confocal, scanning electron microscopy and histology
revealed the presence of a proctodeal depression by stage 21. This is earlier in
development than the initial appearance of the stomodeum. Prominent morphological
features found in the proctodeal region included cilia and vacuolated cells.
Immunolocalization of the basement membrane between the proctodeal ectoderm and
hindgut endoderm, and apoptosis detection proved inconclusive, but the results
suggest that they may play a role in hindgut development. BMP-4 expression, often
associated with apoptosis and thought to be involved in anorectal malformations, decreased in the proctodeal region as the embryos developed. The combination of
morphological and molecular evidence as found in Xenopus laevis provides a greater
understanding of hindgut development. These results may stimulate further research
into anorectal malformations in an attempt to provide a more comprehensive
understanding of the mechanisms involved in the occurrence of these anomalies.