Id2 controls specification of Lgr5 ⁺ intestinal stem cell progenitors during gut development

Abstract

The adult intestinal stem cells (ISCs), their hierarchies, mechanisms of maintenance and differentiation have been extensively studied. However, when and how ISCs are established during embryogenesis remains unknown. We show here that the transcription regulator Id2 controls the specification of embryonic Lgr5 progenitors in the developing murine small intestine. Cell fate mapping analysis revealed that Lgr5 progenitors emerge at E13.5 in wild-type embryos and differ from the rest on the intestinal epithelium by a characteristic ISC signature. In the absence of Id2, the intestinal epithelium differentiates into Lgr5 cells already at E9.5. Furthermore, the size of the Lgr5 cell pool is significantly increased. We show that Id2 restricts the activity of the Wnt signalling pathway at early stages and prevents precocious differentiation of the embryonic intestinal epithelium. Id2-deficient embryonic epithelial cells cultured strongly activate Wnt target genes as well as markers of neoplastic transformation and form fast growing undifferentiated spheroids. Furthermore, adult ISCs from Id2-deficient mice display a distinct transcriptional signature, supporting an essential role for Id2 in the correct specification of ISCs.

Morphogenesis and maturation of the embryonic and postnatal intestine

“…Collectively, these studies suggest that Wnt/β-catenin signaling is dispensable for proliferation during pseudostratified intestinal development. In this context, it is interesting to note that several separate studies have shown that the Wnt/β-catenin target gene, and well described adult intestinal stem cell marker, Lgr5 [13], is expressed during this time of low Wnt activity [109–111]. Recent lineage tracing experiments in Lgr5-creER mice have shown that lineage tracing can occur as early as E12.5 [109].…”

“…Recent lineage tracing experiments in Lgr5-creER mice have shown that lineage tracing can occur as early as E12.5 [109]. Mechanistically, it appears that the transcription factor Id2, restricts Wnt activity during this window of development and Id2-deficient intestinal epithelial tissue had more Lgr5+ cells starting at E9.5 compared to controls [111]. Evidence also suggested that Id2 deletion increased Wnt/β-catenin signaling activity in these animals.…”

“…Collectively, these studies point to an interesting and unexplained paradox. While Lgr5 is considered a sensitive Wnt/β-catenin target gene in the adult intestine, it appears that it is already expressed during a time when Wnt/β-catenin signaling is very low in the fetal gut (E12.5–E13.5) [108–111]. On the other hand, removing Id2, which presumably lead to an increase in Wnt/β-catenin signaling, increased the number of cells expressing Lgr5 [111].…”

“…While Lgr5 is considered a sensitive Wnt/β-catenin target gene in the adult intestine, it appears that it is already expressed during a time when Wnt/β-catenin signaling is very low in the fetal gut (E12.5–E13.5) [108–111]. On the other hand, removing Id2, which presumably lead to an increase in Wnt/β-catenin signaling, increased the number of cells expressing Lgr5 [111]. Thus, it is unresolved if, how and why Lgr5 is present when Wnt-signaling is very low but still seems to respond as a target gene when Wnt-signaling is activated in Id2-null epithelium.…”

Everything has its time: Id2 clocks embryonic specification of Lgr5 + gut stem cells

“…In this issue of The EMBO Journal, Nigmatullina et al (2017) show that maturation of Lgr5 + progenitors in the small intestinal epithelium during murine embryonic development is controlled by the transcription factor Id2. In this issue of The EMBO Journal, Nigmatullina et al (2017) show that maturation of Lgr5 + progenitors in the small intestinal epithelium during murine embryonic development is controlled by the transcription factor Id2.…”