Dgcr8 functions in the secondary heart field for outflow tract and right ventricle development in mammals

The DGCR8 gene, encoding a critical miRNA processing protein, maps within the hemizygous region in patients with 22q11.2 deletion syndrome. Most patients have malformations of the cardiac outflow tract that is derived in part from the anterior second heart field (aSHF) mesoderm. To understand the function of Dgcr8 in the aSHF, we inactivated it in mice using Mef2c-AHF-Cre. Inactivation resulted in a fully penetrant persistent truncus arteriosus and a hypoplastic right ventricle leading to lethality by E14.5. To understand the molecular mechanism for this phenotype, we performed gene expression profiling of the aSHF and the cardiac outflow tract with right ventricle in conditional null versus normal mouse littermates at stage E9.5 prior to morphology changes. We identified dysregulation of mRNA gene expression, of which some are relevant to cardiogenesis. Many pri-miRNA genes were strongly increased in expression in mutant embryos along with reduced expression of mature miRNA genes. We further examined the individual, mature miRNAs that were decreased in expression along with pri-miRNAs that were accumulated that could be direct effects due to loss of Dgcr8. Among these genes, were miR-1a, miR-133a, miR-134, miR143 and miR145a, which have known functions in heart development. These early mRNA and miRNA changes may in part, explain the first steps that lead to the resulting phenotype in Dgcr8 aSHF conditional mutant embryos.

Crk and Crkl have shared functions in neural crest cells for cardiac outflow tract septation and vascular smooth muscle differentiation

CRK and CRKL encode cytoplasmic adaptors that contribute to the etiology of congenital heart disease. Neural crest cells (NCCs) are required for cardiac outflow tract (OFT) septation and aortic arch formation. The roles of Crk/Crkl in NCCs during mouse cardiovascular development remains unknown. To test this, we inactivated Crk and/or Crkl in NCCs. We found that the loss of Crk, rather than Crkl, in NCCs resulted in double outlet right ventricle, while loss of both Crk/Crkl in NCCs resulted in severe defects with earlier lethality due to failed OFT septation and severe dilation of the pharyngeal arch arteries (PAAs). We found that these defects are due to altered cell morphology resulting in reduced localization of NCCs to the OFT and failed integrity of the PAAs, along with reduced expression of Integrin signaling genes. Further, molecular studies identified reduced differentiation of vascular smooth muscle cells that may in part be due to altered Notch signaling. Additionally, there is increased cellular stress that leads to modest increase in apoptosis. Overall, this explains the mechanism for the Crk/Crkl phenotype.

Dysregulation of TBX1 dosage in the anterior heart field results in congenital heart disease resembling the 22q11.2 duplication syndrome

Non-allelic homologous recombination events on chromosome 22q11.2 during meiosis can result in either the deletion (22q11.2DS) or duplication (22q11.2DupS) syndrome. Although the spectrum and frequency of congenital heart disease (CHD) are known for 22q11.2DS, there is less known for 22q11.2DupS. We now evaluated cardiac phenotypes in 235 subjects with 22q11.2DupS including 102 subjects we collected and 133 subjects that were previously reported as a confirmation and found 25% have CHD, mostly affecting the cardiac outflow tract (OFT). Previous studies have shown that global loss or gain of function (LOF; GOF) of mouse Tbx1, encoding a T-box transcription factor mapping to the region of synteny to 22q11.2, results in similar OFT defects. To further evaluate Tbx1 function in the progenitor cells forming the cardiac OFT, termed the anterior heart field, Tbx1 was overexpressed using the Mef2c-AHF-Cre driver (Tbx1 GOF). Here we found that all resulting conditional GOF embryos had a persistent truncus arteriosus (PTA), similar to what was previously reported for conditional Tbx1 LOF mutant embryos. To understand the basis for the PTA in the conditional GOF embryos, we found that proliferation in the Mef2c-AHF-Cre lineage cells before migrating to the heart, was reduced and critical genes were oppositely changed in this tissue in Tbx1 GOF embryos versus conditional LOF embryos. These results suggest that a major function of TBX1 in the AHF is to maintain the normal balance of expression of key cardiac developmental genes required to form the aorta and pulmonary trunk, which is disrupted in 22q11.2DS and 22q11.2DupS.

Genetic Drivers of Kidney Defects in the DiGeorge Syndrome

BACKGROUND

The DiGeorge syndrome, the most common of the microdeletion syndromes, affects multiple organs, including the heart, the nervous system, and the kidney. It is caused by deletions on chromosome 22q11.2; the genetic driver of the kidney defects is unknown.

METHODS

We conducted a genomewide search for structural variants in two cohorts: 2080 patients with congenital kidney and urinary tract anomalies and 22,094 controls. We performed exome and targeted resequencing in samples obtained from 586 additional patients with congenital kidney anomalies. We also carried out functional studies using zebrafish and mice.

RESULTS

We identified heterozygous deletions of 22q11.2 in 1.1% of the patients with congenital kidney anomalies and in 0.01% of population controls (odds ratio, 81.5; P=4.5×10^-14). We localized the main drivers of renal disease in the DiGeorge syndrome to a 370-kb region containing nine genes. In zebrafish embryos, an induced loss of function in snap29, aifm3, and crkl resulted in renal defects; the loss of crkl alone was sufficient to induce defects. Five of 586 patients with congenital urinary anomalies had newly identified, heterozygous protein-altering variants, including a premature termination codon, in CRKL. The inactivation of Crkl in the mouse model induced developmental defects similar to those observed in patients with congenital urinary anomalies.

CONCLUSIONS

We identified a recurrent 370-kb deletion at the 22q11.2 locus as a driver of kidney defects in the DiGeorge syndrome and in sporadic congenital kidney and urinary tract anomalies. Of the nine genes at this locus, SNAP29, AIFM3, and CRKL appear to be critical to the phenotype, with haploinsufficiency of CRKL emerging as the main genetic driver. (Funded by the National Institutes of Health and others.).

Rare copy number variants and congenital heart defects in the 22q11.2 deletion syndrome

The 22q11.2 deletion syndrome (22q11DS; velocardiofacial/DiGeorge syndrome; VCFS/DGS; MIM #192430; 188400) is the most common microdeletion syndrome. The phenotypic presentation of 22q11DS is highly variable; approximately 60-75 % of 22q11DS patients have been reported to have a congenital heart defect (CHD), mostly of the conotruncal type, and/or aortic arch defect. The etiology of the cardiac phenotypic variability is not currently known for the majority of patients. We hypothesized that rare copy number variants (CNVs) outside the 22q11.2 deleted region may modify the risk of being born with a CHD in this sensitized population. Rare CNV analysis was performed using Affymetrix SNP Array 6.0 data from 946 22q11DS subjects with CHDs (n = 607) or with normal cardiac anatomy (n = 339). Although there was no significant difference in the overall burden of rare CNVs, an overabundance of CNVs affecting cardiac-related genes was detected in 22q11DS individuals with CHDs. When the rare CNVs were examined with regard to gene interactions, specific cardiac networks, such as Wnt signaling, appear to be overrepresented in 22q11DS CHD cases but not 22q11DS controls with a normal heart. Collectively, these data suggest that CNVs outside the 22q11.2 region may contain genes that modify risk for CHDs in some 22q11DS patients.

Tbx1 is required autonomously for cell survival and fate in the pharyngeal core mesoderm to form the muscles of mastication

Velo-cardio-facial/DiGeorge syndrome, also known as 22q11.2 deletion syndrome, is a congenital anomaly disorder characterized by craniofacial anomalies including velo-pharyngeal insufficiency, facial muscle hypotonia and feeding difficulties, in part due to hypoplasia of the branchiomeric muscles. Inactivation of both alleles of mouse Tbx1, encoding a T-box transcription factor, deleted on chromosome 22q11.2, results in reduction or loss of branchiomeric muscles. To identify downstream pathways, we performed gene profiling of microdissected pharyngeal arch one (PA1) from Tbx1(+/+) and Tbx1(-/-) embryos at stages E9.5 (somites 20-25) and E10.5 (somites 30-35). Basic helix-loop-helix (bHLH) transcription factors were reduced, while secondary heart field genes were increased in expression early and were replaced by an increase in expression of cellular stress response genes later, suggesting a change in gene expression patterns or cell populations. Lineage tracing studies using Mesp1(Cre) and T-Cre drivers showed that core mesoderm cells within PA1 were present at E9.5 but were greatly reduced by E10.5 in Tbx1(-/-) embryos. Using Tbx1(Cre) knock-in mice, we found that cells are lost due to apoptosis, consistent with increase in expression of cellular stress response genes at E10.5. To determine whether Tbx1 is required autonomously in the core mesoderm, we used Mesp1(Cre) and T-Cre mesodermal drivers in combination with inactivate Tbx1 and found reduction or loss of branchiomeric muscles from PA1. These mechanistic studies inform us that Tbx1 is required upstream of key myogenic genes needed for core mesoderm cell survival and fate, between E9.5 and E10.5, resulting in formation of the branchiomeric muscles.

Dynamic changes of the Golgi apparatus during bovine in vitro oocyte maturation

For successful fertilization by the male gamete, oocyte cytoplasmic organelles such as the Golgi apparatus have to undergo specific changes: the entire process is known as cytoplasmic maturation. The goal of this study was to unravel the dynamics of the Golgi apparatus in bovine oocytes at critical stages ofin vitromaturation, i.e. germinal vesicle (GV), GV breakdown (GVBD), metaphase I (MI) and metaphase II, and to investigate the role of various molecules critically involved therein. The cytoplasmic distribution of proteins was assessed by immunocytochemistry and laser confocal microscopy. We applied specific inhibitors, including nocodazole to unravel the functional role of the microtubular elements; sodium orthovanadate, which primarily inhibits cytoplasmic dynein ATPase activity; monastrol which inhibits the kinesin EG5; and roscovitine to inhibit the kinase cyclin-dependent kinase 2A (CDC2A). Prior to GVBD, the Golgi apparatus was translocated from the centre of the cytoplasm to the cortical area in the periphery, where it underwent fragmentation. A second translocation was observed between GVBD and MI stages, when the Golgi apparatus was moved from the cortex to the centre of the cytoplasm. Incubation with the specific inhibitors revealed that microtubules played an active role in the final localization at GVBD, while CDC2A was essential for Golgi fragmentation at GVBD stage. This partitioning was a precondition for the second movement. In conclusion, for the first time we show basic mechanisms critically involved in the regulation of the dynamic changes of Golgi apparatus during meiosis of the bovine oocyte.

Effects of follicle size and stages of maturation on mRNA expression in bovine in vitro matured oocytes

Transcription in bovine oocytes: The goal of this study was to unravel the dynamics of transcripts thought to be critically involved in oocyte maturation. The relative abundance (RA) of DYNLL1 (cytoplasmic dynein light chain LC8), DYNC1I1 (cytoplasmic dynein 1 intermediate chain), DCTN1 (dynactin 1; pGlued homolog, the activator of the cytoplasmic dynein complex 1), PMSB1 (proteasome beta subunit 1), PMSA4 (proteasome alfa subunit 4), PAP (poly-A polymerase) and Cx43 (connexin 43) were determined by semi-quantitative endpoint RT-PCR at different stages of IVM, that is, GV, GVBD, MI and MII in oocytes collected from follicles of two different size categories, that is, <2 mm and 2-8 mm. The RA of DYNLL1 and DYNC1I1 were significantly higher in immature oocytes from bigger follicles than in oocytes from small follicles. Messenger RNA expression levels were similar for DCTN1, PMSB1, PMSA4, PAP, and Cx43 in the two groups during the maturation process. RA of DYNLL1, DYNC1I1 and PMSB1 decreased significantly during IVM in oocytes from follicles 2 to 8 mm. The RA for DYNLL1 was significantly higher in GVBD and MI in the oocytes from follicles 2 to 8 mm in size compared to the other group. The higher mRNA expression of DYNLL1 and DYNC1I1 and the diverging dynamics of DYNLL1, DYNC1I1, and PMSB1 mRNA expression during IVM in oocytes from the different follicle categories could be related to the developmental capacity, that is, development to blastocysts after IVF. The differences found between groups of oocytes could serve as a marker to assess the developmental capacity of bovine oocytes.