Essential roles for Cdx in murine primitive hematopoiesis

Abstract

The Cdx transcription factors play essential roles in primitive hematopoiesis in the zebrafish where they exert their effects, in part, through regulation of hox genes. Defects in hematopoiesis have also been reported in Cdx mutant murine embryonic stem cell models, however, to date no mouse model reflecting the zebrafish Cdx mutant hematopoietic phenotype has been described. This is likely due, in part, to functional redundancy among Cdx members and the early lethality of Cdx2 null mutants. To circumvent these limitations, we used Cre-mediated conditional deletion to assess the impact of concomitant loss of Cdx1 and Cdx2 on murine primitive hematopoiesis. We found that Cdx1/Cdx2 double mutants exhibited defects in primitive hematopoiesis and yolk sac vasculature concomitant with reduced expression of several genes encoding hematopoietic transcription factors including Scl/Tal1. Chromatin immunoprecipitation analysis revealed that Scl was occupied by Cdx2 in vivo, and Cdx mutant hematopoietic yolk sac differentiation defects could be rescued by expression of exogenous Scl. These findings demonstrate critical roles for Cdx members in murine primitive hematopoiesis upstream of Scl.

Role of Cdx factors in early mesodermal fate decisions

“…As previously described (Wang et al, 2008;Brooke-Bisschop et al, 2017), ChIP-seq identified Scl (Tal1), which encodes a master regulator of hematopoiesis, as a Cdx2 target ( Fig. 2A; Shivdasani et al, 1995;van Handel et al, 2012;Org et al, 2015).…”

“…Moreover, Brg1 binding and chromatin structure was altered at these genes in Cdx mutants. As Cdx is essential for yolk sac hematopoiesis (Davidson and Zon, 2006;Davidson et al, 2003;Lengerke et al, 2007;Wang et al, 2008;Brooke-Bisschop et al, 2017), these findings suggest that Cdx function regulates chromatin remodeling events necessary for the coordinated expression of transcription factors that direct hematopoietic versus cardiac fates from a common progenitor population.…”

“…Dll1; Grainger et al, 2012) to 3100 (e.g. Scl;Savory et al, 2011;Brooke-Bisschop et al, 2017). Gene ontology (GO) term enrichment analysis was conducted using the 441 peaks annotated to a reference gene that met this threshold.…”

“…Analysis of these mutants also revealed a requirement for Cdx genes in diverse processes in development and in the adult intestinal track. These include, for example, roles for Cdx proteins in specification and development of the intestine and its homeostasis in the adult (Beck et al, 1999(Beck et al, , 2003Chawengsaksophak et al, 1997;Gao et al, 2009;Grainger et al, 2010;Stringer et al, 2012;Hryniuk et al, 2012), yolk sac hematopoiesis (Lengerke et al, 2007;Wang et al, 2008;Brooke-Bisschop et al, 2017;Davidson and Zon, 2006;Davidson et al, 2003), neural tube closure, and elaboration of the post-otic embryo (Savory et al, 2009a(Savory et al, , 2011van Rooijen et al, 2012).…”

“…In agreement with their functional overlap (van den Akker et al, 2002;Davidson and Zon, 2006;van Nes et al, 2006;Faas and Isaacs, 2009), Cdx family members appear comparable in their ability to occupy, and regulate, target genes (Charité et al, 1998;Savory et al, 2009a). Targets identified to date include a number of Hox genes, implicated in Cdx-dependent vertebral patterning (Shashikant et al, 1995;Charité et al, 1998;Subramanian et al, 1995;Pownall et al, 1996;Isaacs et al, 1998;van den Akker et al, 2002;Gaunt et al, 2003Gaunt et al, , 2008, Cyp26A1, which is essential for catabolism of retinoic acid (RA) and crucial for the maintenance of a caudal progenitor population driving axial elongation (Wingert et al, 2007;Savory et al, 2009a;Young et al, 2009;Martin and Kimelman, 2010), genes encoding products involved in intestinal differentiation and homeostasis (Beck et al, 1999(Beck et al, , 2003Chawengsaksophak et al, 1997;Gao et al, 2009;Grainger et al, 2010;Hryniuk et al, 2012), and targets necessary for yolk sac hematopoiesis (Davidson et al, 2003;Davidson and Zon, 2006;Lengerke et al, 2007;Wang et al, 2008;Brooke-Bisschop et al, 2017).…”