Year: 2013
Type: dissertation
Abstract: The pylorus is the junction between the stomach and the small intestine. It regulates food movement between the two organs and prevents the regurgitation of duodenal contents into the stomach. An evolutionarily conserved network of gene expression has been documented at the pylorus: Nkx2-5, Sox9, and Grem1 show pyloric-specific expression domains and are functionally involved in pyloric development. However, the expression domains of these genes had not been determined on a cellular basis. Nkx2-5 was of particular interest since human genomic studies indicate that polymorphisms near this locus are associated with the pyloric pathology Infantile Hypertrophic Pyloric Stenosis. Work in this thesis shows that these three genes are expressed in the pyloric musculature with Nkx2-5 and Grem1 expressed in both the inner circular (ICM) and outer longitudinal (OLM) layers of muscle. In contrast, Sox9 expression is largely limited to the OLM. Gata3, another transcription factor that we identified as a pyloric specific gene in earlier studies, is also OLM specific. Using genetic mouse models, we demonstrate that Nkx2-5 and Gata3 are independently required for the formation of a specific fascicle of OLM at the pylorus, while loss of Grem1 appears to have no effect on pyloric development. After loss of either Nkx2-5 or Gata3, smooth muscle cell differentiation is compromised and apoptosis is increased. Sox9 is downstream of both Gata3 and Nkx2-5, but the latter two factors appear to act independently. Together, these data lead us to posit that some cases of IHPS might be caused by activating mutations in Nxk2-5 (or Gata3 or Sox9). Three dimensional reconstruction of the expression domains of Gata3, Nkx2-5 and the smooth muscle marker, aSMA, reveal that the pyloric OLM fascicle is continuous with cord-like structures on the ventral surface of the stomach, previously called gastric ligaments. These structures are composed of smooth muscle and, like the OLM, are dependent upon Gata3 and Nkx2-5 for proper maturation. Since these ligaments may be necessary for maintenance of the proper pyloro-duodenal angle, we have re-named them as the pyloric ligaments.
Author: Ajay Prakash
Language: English
Subfield: Molecular Biology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W945693841