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The intestine‐specific caudal‐related homeobox gene‐2 (CDX2) homeobox gene, while being a tumor suppressor in the gut, is ectopically expressed in a large proportion of acute leukemia and is associated with poor prognosis. Here, we report that turning on human CDX2 expression in the hematopoietic lineage of mice induces acute monoblastic leukemia, characterized by the decrease in erythroid and lymphoid cells at the benefit of immature monocytic and granulocytic cells. One of the highly stimulated genes in leukemic bone marrow cells was BMP and activin membrane‐bound inhibitor (Bambi), an inhibitor of transforming growth factor‐β (TGF‐β) signaling. The CDX2 protein was shown to bind to and activate the transcription of the human BAMBI promoter. Moreover, in a leukemic cell line established from CDX2‐expressing mice, reducing the levels of CDX2 or Bambi stimulated the TGF‐β‐dependent expression of Cd11b, a marker of monocyte maturation. Taken together, this work demonstrates the strong oncogenic potential of the homeobox gene CDX2 in the hematopoietic lineage, in contrast with its physiological tumor suppressor activity exerted in the gut. It also reveals, through BAMBI and TGF‐β signaling, the involvement of CDX2 in the perturbation of the interactions between leukemia cells and their microenvironment.

Whether a gene involved in distinct tissue or cell functions exerts a core of common molecular activities is a relevant topic in evolutionary, developmental, and pathological perspectives. Here, we addressed this question by focusing on the transcription factor and regulator of chromatin accessibility encoded by the Cdx2 homeobox gene that plays important functions during embryonic development and in adult diseases. By integrating RNAseq data in mouse embryogenesis, we unveiled a core set of common genes whose expression is responsive to the CDX2 homeoprotein during trophectoderm formation, posterior body elongation and intestinal specification. ChIPseq data analysis also identified a set of common chromosomal regions targeted by CDX2 at these three developmental steps. The transcriptional core set of genes was then validated with transgenic mouse models of loss or gain of function of Cdx2. Finally, based on human cancer data, we highlight the relevance of these results by displaying a significant number of human orthologous genes to the core set of mouse CDX2-responsive genes exhibiting an altered expression along with CDX2 in human malignancies.

Collagen 6A3 (Col6a3), a component of extracellular matrix, is often up-regulated in tumours and is believed to play a pro-oncogenic role. However the mechanisms of its tumorigenic activity are poorly understood. We show here that Col6a3 is highly expressed in densely growing mouse embryonic fibroblasts (MEFs). In MEFs where the TAF4 subunit of general transcription factor IID (TFIID) has been inactivated, elevated Col6a3 expression prevents contact inhibition promoting their 3 dimensional growth as foci and fibrospheres. Analyses of gene expression in densely growing Taf4(-/-) MEFs revealed repression of the Hippo pathway and activation of Wnt signalling. The Hippo activator Kibra/Wwc1 is repressed under dense conditions in Taf4(-/-) MEFs, leading to nuclear accumulation of the proliferation factor YAP1 in the cells forming 3D foci. At the same time, Wnt9a is activated and the Sfrp2 antagonist of Wnt signalling is repressed. Surprisingly, treatment of Taf4(-/-) MEFs with all-trans retinoic acid (ATRA) restores contact inhibition suppressing 3D growth. ATRA represses Col6a3 expression independently of TAF4 expression and Col6a3 silencing is sufficient to restore contact inhibition in Taf4(-/-) MEFs and to suppress 3D growth by reactivating Kibra expression to induce Hippo signalling and by inducing Sfrp2 expression to antagonize Wnt signalling. All together, these results reveal a critical role for Col6a3 in regulating both Hippo and Wnt signalling to promote 3D growth, and show that the TFIID subunit TAF4 is essential to restrain the growth promoting properties of Col6a3. Our data provide new insight into the role of extra cellular matrix components in regulating cell growth.

This protocol describes a method for efficient immunolabelling of thin tissue slices containing a few rows of intact intestinal crypts, which yields large numbers of them being oriented favorably for recording stacks of optical sections aligned with the crypt long axis (Bellis et al., 2012). The latter can then be used for cell positional analysis, 3D-reconstruction and -analysis. The simple epithelium lining the small intestine is organized into contiguous crypts of Lieberkühn (Potten, 1998; Barker et al., 2012; De Mey and Freund, 2013) several of which making up a crypt/villus unit. Each crypt is a multicellular proliferation unit with a tight hierarchical organization. Under steady state conditions, the epithelium is continuously and rapidly renewed, driven by divisions of multipotent intestinal SCs near the crypt base and cell removal from the villus tip. Techniques for analyzing the organization of the crypts play an important role in the field. Maximal efficiency is obtained by using optical sections obtained from confocal scanning and/or Nomarski optics passing through the center of the longitudinal crypt axis to view the crypt as two cell columns of hierarchical lineage starting from cells positioned at or near the crypt base. This enables positional analysis of certain cellular capacities like performing DNA synthesis, undergoing mitosis and apoptosis (Caldwell et al., 2007; Fleming et al., 2007; Quyn et al., 2010), responding to injury (Potten et al., 1997), or expressing genes (Barker et al., 2012; Bjerknes et al., 2012; Itzkovitz et al., 2012). Our protocol has allowed us to demonstrate that some divisions are asymmetric with respect to cell fate and the occurrence of oriented cell division (OCD) in 80% of the proliferating cells in the upper stem cell and transit amplifying zones. It has further revealed planar cell polarities which are important for crypt homeostasis and stem cell biology and alterations in apparently normal crypts and microadenomas of mice carrying germline Apc mutations shedding new light on the first stages of progression towards colorectal cancer.