Tools and Techniques for Wt1-Based Lineage Tracing.

The spatiotemporal expression pattern of Wt1 has been extensively studied in a number of animal models to establish its function and the developmental fate of the cells expressing this gene. In this chapter, we review the available animal models for Wt1-expressing cell lineage analysis, including direct Wt1 expression reporters and systems for permanent Wt1 lineage tracing. We describe the presently used constitutive or inducible genetic lineage tracing approaches based on the Cre/loxP system utilizing Cre recombinase expression under control of a Wt1 promoter.To make these systems accessible, we provide laboratory protocols that include dissection and processing of the tissues for immunofluorescence and histopathological analysis of the lineage-labeled Wt1-derived cells within the embryo/tissue context

Visceral and subcutaneous fat have different origins and evidence supports a mesothelial source

International audience: Fuelled by the obesity epidemic, there is considerable interest in the developmental origins of white adipose tissue (WAT) and the stem and progenitor cells from which it arises. Whereas increased visceral fat mass is associated with metabolic dysfunction, increased subcutaneous WAT is protective. There are six visceral fat depots: perirenal, gonadal, epicardial, retroperitoneal, omental and mesenteric, and it is a subject of much debate whether these have a common developmental origin and whether this differs from that for subcutaneous WAT. Here we show that all six visceral WAT depots receive a significant contribution from cells expressing Wt1 late in gestation. Conversely, no subcutaneous WAT or brown adipose tissue arises from Wt1-expressing cells. Postnatally, a subset of visceral WAT continues to arise from Wt1-expressing cells, consistent with the finding that Wt1 marks a proportion of cell populations enriched in WAT progenitors. We show that all visceral fat depots have a mesothelial layer like the visceral organs with which they are associated, and provide several lines of evidence that Wt1-expressing mesothelium can produce adipocytes. These results reveal a major ontogenetic difference between visceral and subcutaneous WAT, and pinpoint the lateral plate mesoderm as a major source of visceral WAT. They also support the notion that visceral WAT progenitors are heterogeneous, and suggest that mesothelium is a source of adipocytes