Grants and Contributions:

Grant or Award spanning more than one fiscal year. (2017-2018 to 2018-2019)

The definitive endoderm (DE), one of the primary germ layers in the embryo, gives rise to the organs of the respiratory and gastrointestinal tracts, including the epithelial cells of the lungs, stomach, colon, intestine, liver, and pancreas. Considering that these tissues are major sites of health problems, including congenital defects, cancers, and organ malfunctions, we know surprisingly little about the early embryonic development of the DE. This is primarily due to a lack of specific regionally expressed genes that can be used to evaluate DE patterning in the embryo. In screen for novel DE markers, we identified the gene Nephrocan (Nepn) that is exclusively expressed in the midgut of the mouse embryo beginning at gastrulation This genes is the earliest known marker of the midgut endoderm. We are using this gene as a window to understand gut formation and patterning. To that end, we have generated a mouse line in which an inducible version of CRE is under the control of the Nepn promoter. We will use this mouse line to identify the decedents of the midgut lineage and determine the plasticity of the gut endoderm. Moreover, we will probe the role of SOX transcription factors in midgut development.

The hypothesis guiding this project is that midgut endoderm is a distinct lineage from foregut and hindgut, and that it is essential for posterior stomach, dorsal pancreas and duodenal development. Three specific aims will address midgut development.
Aim 1. Determination of the developmental fate of midgut endoderm progenitors . By using genetic lineage tracing, we will examine the fate of the Nepn expressing cells in the mouse embryo.
Aim 2. Assessment of midgut ablation in embryogenesis . By using Diphtheria Toxin Fragment A (DTA) to ablate cells expressing Nepn, we will delete midgut endoderm.
Aim 3. Delineation of the roles of SOX transcription factors in the midgut endoderm . We will examine the role of Sox17 and Sox9 in midgut endoderm.

Through these experiments we will gain insight into how and where midgut DE progenitor cells are determined, the fate of these cells in the mouse embryo and the molecular mechanisms controlling midgut formation. Knowledge of the mechanisms through which tissues develop in the embryo will provide insight into the properties of potential stem cells of the gastrointestinal tract. Together, the experiments presented here will begin to address the mechanisms involved in the development of the midgut in the mouse.