The HMG-box transcription factor Sox2 plays a role throughout neurogenesis and also acts at other stages of development, as illustrated by the multiple organs affected in the anophthalmia syndrome caused by SOX2 mutations. Here we combined proteomic and genomic approaches to characterize gene regulation by Sox2 in neural stem cells. Chd7, a chromatin remodeling ATPase associated with CHARGE syndrome, was identified as a Sox2 transcriptional cofactor. Sox2 and Chd7 physically interact, have overlapping genome-wide binding sites and regulate a set of common target genes including Jag1, Gli3 and Mycn, genes mutated in Alagille, Pallister-Hall and Feingold syndromes, which show malformations also associated with SOX2 anophthalmia syndrome or CHARGE syndrome. Regulation of disease-associated genes by a Sox2-Chd7 complex provides a plausible explanation for several malformations associated with SOX2 anophthalmia syndrome or CHARGE syndrome. Indeed, we found that Chd7-haploinsufficient embryos showed severely reduced expression of Jag1 in the developing inner ear.

Glucocorticoids are vital for the structural and functional maturation of foetal organs, yet excessive foetal exposure is detrimental to adult cardiovascular health. To elucidate the role of glucocorticoid signalling in late-gestation cardiovascular maturation, we have generated mice with conditional disruption of glucocorticoid receptor (GR) in cardiomyocytes and vascular smooth muscle cells using smooth muscle protein 22-driven Cre recombinase (SMGRKO mice) and compared them with mice with global deficiency in GR (GR(-/-)). Echocardiography shows impaired heart function in both SMGRKO and GR(-/-) mice at embryonic day (E)17.5, associated with generalized oedema. Cardiac ultrastructure is markedly disrupted in both SMGRKO and GR(-/-) mice at E17.5, with short, disorganized myofibrils and cardiomyocytes that fail to align in the compact myocardium. Failure to induce critical genes involved in contractile function, calcium handling and energy metabolism underpins this common phenotype. However, although hearts of GR(-/-) mice are smaller, with 22% reduced ventricular volume at E17.5, SMGRKO hearts are normally sized. Moreover, while levels of mRNA encoding atrial natriuretic peptide are reduced in E17.5 GR(-/-) hearts, they are normal in foetal SMGRKO hearts. These data demonstrate that structural, functional and biochemical maturation of the foetal heart is dependent on glucocorticoid signalling within cardiomyocytes and vascular smooth muscle, though some aspects of heart maturation (size, ANP expression) are independent of GR at these key sites.

We have identified an ethylnitrosourea (ENU)-induced recessive mouse mutation (Vcc) with a pleiotropic phenotype that includes cardiac, tracheoesophageal, anorectal, anteroposterior patterning defects, exomphalos, hindlimb hypoplasia, a presacral mass, renal and palatal agenesis, and pulmonary hypoplasia. It results from a C470R mutation in the proprotein convertase PCSK5 (PC5/6). Compound mutants (Pcsk5 Vcc/null ) completely recapitulate the Pcsk5Vcc/Vcc phenotype, as does an epiblast-specific conditional deletion of Pcsk5. The C470R mutation ablates a disulfide bond in the P domain, and blocks export from the endoplasmic reticulum and proprotein convertase activity. We show that GDF11 is cleaved and activated by PCSK5A, but not by PCSK5A-C470R, and that Gdf11-deficient embryos, in addition to having anteroposterior patterning defects and renal and palatal agenesis, also have a presacral mass, anorectal malformation, and exomphalos. Pcsk5 mutation results in abnormal expression of several paralogous Hox genes (Hoxa, Hoxc, and Hoxd), and of Mnx1 (Hlxb9). These include known Gdf11 targets, and are necessary for caudal embryo development. We identified nonsynonymous mutations in PCSK5 in patients with VACTERL (vertebral, anorectal, cardiac, tracheoesophageal, renal, limb malformation OMIM 192350) and caudal regression syndrome, the phenotypic features of which resemble the mouse mutation. We propose that Pcsk5, at least in part via GDF11, coordinately regulates caudal Hox paralogs, to control anteroposterior patterning, nephrogenesis, skeletal, and anorectal development.[Keywords: Mouse; proprotein convertase; Gdf11; Hox; VACTERL] Supplemental material is available at http://www.genesdev.org.

The Polycomb repressive complexes PRC1 and PRC2 are key mediators of heritable gene silencing in multicellular organisms. Here, we characterise AEBP2, a known PRC2 co-factor which, in vitro, has been shown to stimulate PRC2 activity. We show that AEBP2 localises specifically to PRC2 target loci, including the inactive X chromosome. Proteomic analysis confirms that AEBP2 associates exclusively with PRC2 complexes. However, analysis of embryos homozygous for a targeted mutation of Aebp2 unexpectedly revealed a Trithorax phenotype, normally linked to antagonism of Polycomb function. Consistent with this, we observe elevated levels of PRC2-mediated histone H3K27 methylation at target loci in Aebp2 mutant embryonic stem cells (ESCs). We further demonstrate that mutant ESCs assemble atypical hybrid PRC2 subcomplexes, potentially accounting for enhancement of Polycomb activity, and suggesting that AEBP2 normally plays a role in defining the mutually exclusive composition of PRC2 subcomplexes.