Single-cell murine genetic fate mapping reveals bipotential hepatoblasts and novel multi-organ endoderm progenitors.

The definitive endoderm (DE) is the embryonic germ layer that forms the gut tube and associated organs, including thymus, lungs, liver and pancreas. To understand how individual DE cells furnish gut organs, genetic fate mapping was performed using the Cre-reporter paired with a tamoxifen-inducible DE-specific Cre-expressing transgene. We established a low tamoxifen dose that infrequently induced heritable expression in a single cell of individual E8.

Identification and fate mapping of the pancreatic mesenchyme.

The murine pancreas buds from the ventral embryonic endoderm at approximately 8.75 dpc and a second pancreas bud emerges from the dorsal endoderm by 9.0 dpc.

Patterning of the hepato-pancreatobiliary boundary by BMP reveals heterogeneity within the murine liver bud.

Unlabelled: During development, the endoderm initiates organ-restricted gene expression patterns in a spatiotemporally controlled manner. This process, termed induction, requires signals from adjacent mesodermal derivatives. Fibroblast growth factor (FGF) and bone morphogenetic protein (BMP) emanating from the cardiac mesoderm and the septum transversum mesenchyme (STM), respectively, are believed to be simultaneously and uniformly required to directly induce hepatic gene expression from the murine endoderm.

Laser-mediated cell ablation during post-implantation mouse development.

Background: Laser-mediated cell ablation is a powerful tool that has been used to understand cell fate in a variety of externally developing organisms but has not been used during mammalian post-implantation development.

Results: We describe a method pairing laser ablation with murine embryo culture and establish parameters that can be used to precisely ablate cells in the selected field with minimal disruption to adjacent cells or the underlying cell matrix. Ablation of a large domain of endoderm, followed by ~1 day of culture results in a phenotypically normal embryo and gut tube, indicating that laser ablation is compatible with normal development.

Morphogenetic analysis of peri-implantation development.

Background: Although successful implantation is required for development in placental mammals, the molecular and morphogenetic events that define peri-implantation remain largely unexplored.

Results: Here we present detailed morphological and immunohistochemical analysis of mouse embryos between embryonic day 3.75 and 5.

A fate map of the murine pancreas buds reveals a multipotent ventral foregut organ progenitor.

The definitive endoderm is the embryonic germ layer that gives rise to the budding endodermal organs including the thyroid, lung, liver and pancreas as well as the remainder of the gut tube. DiI fate mapping and whole embryo culture were used to determine the endodermal origin of the 9.5 days post coitum (dpc) dorsal and ventral pancreas buds.