Collagen type VI expression during cardiac development and in human fetuses with trisomy 21

The role played by specific extracellular matrix molecules in normal endocardial cushion differentiation into valves and septa remains to be established. In this respect, type collagen VI is of particular interest because genes encoding the alpha1 and alpha2 chains are located on chromosome 21, and defects involving the atrioventricular (AV) cushions are frequent in trisomy 21. Collagen VI expression was studied in normal human embryonic and fetal hearts (5-18 weeks of development) and compared by immunohistochemistry with results from fetuses (10-16 weeks of development) with trisomy 21. During normal endocardial cushion differentiation (5-8 weeks) there was marked collagen VI expression in the AV cushions, whereas only minor expression was seen in the outflow tract cushions. In the normal fetuses (10-18 weeks), collagen VI in the AV cushions had condensed into a marked zone on the atrial side of the leaflets, as well as subendocardially in other regions of high shear stress. Morphological defects involving the endocardial cushion-derived structures were present in all trisomy 21 cases. An abnormally large membranous septum was observed in three cases. An AV septal defect (AVSD) was present in two, while one had a ventricular septal defect (VSD). Two cases presented with a secondary atrial septal defect (ASDII), and one had an AVSD. Mild to moderate valve dysmorphia was found in all cases. Collagen VI staining in trisomy 21 was more intense than in the normal subjects; however, there were no differences in the spatial expression patterns. We conclude that collagen VI is expressed in the AV cushions and persists during valve differentiation. Collagen VI is more prominent in fetal trisomy 21 hearts than in normal hearts. We hypothesise that collagen VI has a role in the development of heart defects involving endocardial cushion differentiation-specifically in the AV canal, the most common site of malformations affecting children with trisomy 21.

Targeted inactivation of serum response factor in the developing heart results in myocardial defects and embryonic lethality

Serum response factor (SRF) is at the confluence of multiple signaling pathways controlling the transcription of immediate-early response genes and muscle-specific genes. There are active SRF target sequences in more than 50 genes expressed in the three muscle lineages including normal and diseased hearts. However, the role of SRF in heart formation has not been addressed in vivo thus far due to the early requirement of SRF for mesoderm formation. We have generated a conditional mutant of SRF by using Cre-LoxP strategy that will be extremely useful to study the role of SRF in embryonic and postnatal cardiac functions, as well as in other tissues. This report shows that heart-specific deletion of SRF in the embryo by using a new beta MHC-Cre transgenic mouse line results in lethal cardiac defects between embryonic day 10.5 (E10.5) and E13.5, as evidenced by abnormally thin myocardium, dilated cardiac chambers, poor trabeculation, and a disorganized interventricular septum. At E9.5, we found a marked reduction in the expression of essential regulators of heart development, including Nkx2.5, GATA4, myocardin, and the SRF target gene c-fos prior to overt maldevelopment. We conclude that SRF is crucial for cardiac differentiation and maturation, acting as a global regulator of multiple developmental genes.

Embryonic Conduction Tissue:

INTRODUCTION

The occurrence of arrhythmias in adult patients may arise preferentially in anatomic regions derived from the specialized cardiac conduction system. To examine this hypothesis, we performed a detailed analysis of the developing cardiac conduction system using the recently described CCS-lacZ transgenic mouse strain.

METHODS AND RESULTS

Transgenic embryos (E9.5-15.5) were stained for beta-galactosidase activity and co-stained with the myocardial marker HHF35. Results were reconstructed three dimensionally. CCS-lacZ expression was observed in the sinoatrial node, left and right venous valves, septum spurium, right and left atrioventricular ring, His bundle, bundle branches, and right ventricular moderator band. Furthermore, lacZ-positive cells could be demonstrated for the first time in the left atrium, in the posterior wall surrounding the pulmonary venous orifice. and, in later stages, surrounding the pulmonary venous wall. These cells were continuous with the left venous valve in the right atrium. LacZ-positive tissue also could be identified in Bachmann's bundle, running retro-aortically between the right atrium and left atrium.

CONCLUSION

Known arrhythmogenic areas including Bachmann's bundle, the pulmonary veins, and sinus venosus derived internodal structures, demonstrate lacZ expression. These data support the hypothesis that areas derived from the developing cardiac conduction system may contribute to the arrhythmogenic substrate in adult hearts.

Developmental Control of Titin Isoform Expression and Passive Stiffness in Fetal and Neonatal Myocardium

Developmental changes in contractile behavior are known to occur during fetal and postnatal heart development. In this study, we examined whether adaptations take place in titin. A range of species was used to evaluate titin isoform expression and altered function during cardiac muscle development. A novel titin exon microarray that allows all 363 titin exons to be monitored simultaneously was used for transcript studies. Results reveal expression of fetal titin isoforms, characterized by additional spring elements both in the tandem Ig and PEVK region of the molecule. At the protein level, the fetal cardiac isoform predominates in fetal and neonatal myocardium and gradually disappears during postnatal development with a time course that varies in different species. Passive myocardium, contrary to previous reports, was found to be less stiff in the neonate than in the adult. This can be explained by the unique spring composition of fetal cardiac titin expressed by the neonate. Changes in titin expression are likely to impact functional transitions and diastolic filling behavior during development of the heart.

Developmentally regulated switching of titin size alters myofibrillar stiffness in the perinatal heart

Before birth, the compliance of the heart is limited predominantly by extracardiac constraint. Reduction of this constraint at birth requires that myocardial compliance be determined mainly by the heart's own constituents. Because titin is a principal contributor to ventricular passive tension (PT), we studied the expression and mechanics of cardiac-titin isoforms during perinatal rat heart development. Gel electrophoresis and immunoblotting revealed a single, 3.7-MDa, N2BA isoform present 6 days before birth and an additional, also previously unknown, N2BA isoform of 3.5 to 3.6 MDa expressed in the near-term fetus. These large isoforms rapidly disappear after birth and are replaced by a small N2B isoform (3.0 MDa) predominating in 1-week-old and adult rats. In addition, neonatal pig hearts showed large N2BA-titin isoforms distinct from those present in the adult porcine myocardium. By quantitative reverse transcriptase-polymerase chain reaction, developmentally expressed titin-mRNA species were detected in rat heart. Titin-based PT was much lower (approximately 15 times) in fetal than adult rat cardiomyocytes, and measured PT levels were readily predictable with a model of worm-like chain titin elasticity. Immunofluorescence microscopy showed the extensibility of the differentially spliced molecular spring regions of fetal/neonatal titin isoforms in isolated rat cardiomyofibrils. Whereas the titin-isoform shift by 700 kDa ensures high passive stiffness of the postnatal cardiac myofibrils, the expression of specific fetal/neonatal cardiac-titin isoforms may also have important functions for contractile properties, myofibril assembly or turnover, and myocardial signaling during perinatal heart development.

Notch activation results in phenotypic and functional changes consistent with endothelial-to-mesenchymal transformation

Various studies have identified a critical role for Notch signaling in cardiovascular development. In this and other systems, Notch receptors and ligands are expressed in regions that undergo epithelial-to-mesenchymal transformation. However, there is no direct evidence that Notch activation can induce mesenchymal transdifferentiation. In this study we show that Notch activation in endothelial cells results in morphological, phenotypic, and functional changes consistent with mesenchymal transformation. These changes include downregulation of endothelial markers (vascular endothelial [VE]-cadherin, Tie1, Tie2, platelet-endothelial cell adhesion molecule-1, and endothelial NO synthase), upregulation of mesenchymal markers (alpha-smooth muscle actin, fibronectin, and platelet-derived growth factor receptors), and migration toward platelet-derived growth factor-BB. Notch-induced endothelial-to-mesenchymal transformation does not seem to require external regulation and is restricted to cells expressing activated Notch. Jagged1 stimulation of endothelial cells induces a similar mesenchymal transformation, and Jagged1, Notch1, and Notch4 are expressed in the ventricular outflow tract during stages of endocardial cushion formation. This is the first evidence that Jagged1-Notch interactions induce endothelial-to-mesenchymal transformation, and our findings suggest that Notch signaling may be required for proper endocardial cushion differentiation and/or vascular smooth muscle cell development.

A trisomic transmission disequilibrium test

Certain congenital disorders that are rare in the general population are quite common in individuals with trisomic conditions. For example, complete atrioventricular septal defect occurs in about 20% of individuals with Down syndrome, an approximately 500-fold increase in risk as compared to individuals without Down syndrome. Genetic variation on the chromosome involved in the trisomy may affect susceptibility to these trisomy-specific disorders. That is, increased dosage of a variant may be directly involved in increasing the risk of a disorder, or it may be indirectly involved by causing up- or downregulation of other genes. As in standard disomic gene-mapping, one can search for genes using linkage or association methods. Within association methods, one can consider case-control methods or family-based control methods such as the transmission disequilibrium test (TDT). Most gene-mapping methods need to be substantially redesigned for use with trisomic data. In this paper, we present a "trisomic TDT", a statistical method of testing for nonrandom transmission of alleles from parents to trisomic children. We demonstrate the method on a dataset of parent-child trios in which the child has Down syndrome.

[The 5-HT2B receptor: a main cardio-pulmonary target of serotonin]

In agreement with previous data in the literature, our results indicate that serotonin, a monoamine neurotransmitter, can also regulate cell proliferation, cell movements and cell differentiation. We have recently shown that serotonin is required for embryonic heart development. Genetic ablation of the 5-HT2B receptor leads to partial embryonic and postnatal lethality with abnormal heart development. Similar molecular mechanisms seem to be involved in adult cardiomyocytes since mutant mice surviving to adulthood display a dilated cardiomyopathy. Furthermore this receptor appears to be involved in survival of cardiomyocytes. The 5-HT2B receptor is also implicated in systemic hypertension. Furthermore, mice with pharmacological or genetic ablation of 5-HT2B receptor are totally resistant to hypoxia-induced pulmonary hypertension, indicating that this receptor is regulating the pathologic vascular proliferation leading to this disease. Underlying mechanisms are still to be discovered.

Ectopic expression of an embryonic skeletal myosin heavy chain in human fetal and Syrian hamster hearts

The mammalian heart is known to contain only two isoformic myosin heavy chain (MHC) genes, alpha and beta. A previously uncharacterized MHC gene was isolated in Syrian hamster hearts (McCully et al., JMol Biol 1991). We identified the novel MHC gene as a hamster embryonic skeletal MHC gene based on the developmental stage- and tissue-specific expression pattern: the restricted expression ofmRNA to striated muscles was highest in embryonic skeletal muscle and was developmentally down-regulated. We confirmed that the embryonic skeletal MHC gene exhibited higher expression in cardiomyopathic than in normal hamster hearts, and was up-regulated during the development of cardiomyopathy. The sporadic expression was highly localized in the endocardium. The present study identified that a very small number of undifferentiated myogenic cells existed in adult hamster endocardium. Moreover, using RT-PCR, a homologue of embryonic skeletal MHC mRNA was also expressed in human embryonic, but not adult ventricles. Our data provide a new insight into the regulatory mechanisms of MHCs in the cardiomyopathic hamster heart.

Myocardin expression is regulated by Nkx2.5, and its function is required for cardiomyogenesis

Nkx2.5 (also known as Csx) is an evolutionarily conserved cardiac transcription factor of the homeobox gene family. Nkx2.5 is required for early heart development, since Nkx2.5-null mice die before completion of cardiac looping. To identify genes regulated by Nkx2.5 in the developing heart, we performed subtractive hybridization by using RNA isolated from wild-type and Nkx2.5-null hearts at embryonic day 8.5. We isolated a mouse cDNA encoding myocardin A, which is an alternative spliced isoform of myocardin and the most abundant isoform in the heart from embryo to adult. The expression of myocardin A and myocardin was markedly downregulated in Nkx2.5-null mouse hearts. Transient-cotransfection analysis showed that Nkx2.5 transactivates the myocardin promoter. Inhibition of myocardin function in the teratocarcinoma cell line P19CL6 prevented differentiation into cardiac myocytes after dimethyl sulfoxide treatment. Myocardin A transactivated the promoter of the atrial natriuretic factor gene through the serum response element, which was augmented by bone morphogenetic protein 2 and transforming growth factor beta-activated kinase 1. These results suggest that myocardin expression is regulated by Nkx2.5 and that its function is required for cardiomyogenesis.

Serotonin and its transporter on proliferation of fetal heart cells

Besides neuronal transmission, serotonin (5-HT) also acts as a trophic signal during the development of the central nervous and neural crest systems. In this study, we report that in addition to trophic effect, 5-HT increases the proliferation of fetal heart cells. We showed for the first time that the cultured heart cells, express serotonin transporter (5-HTT), which confirmed the previously observed accumulation of 5-HT in developing heart. The influence of 5-HT on developing heart cells is studied throughout the dosage. We found that 5-HT concentration at physiological level, 4 microM, permits an optimal proliferation of heart cells as indicated by the number of 5-bromo-deoxyuridine immunoreactive (BrdU-im) cells and myosin heavy chain immunoreactive cells (MF20-im); fluctuation towards either concentrations reduce the proliferation. We hypothesized that 5-HTT plays a role in the heart development. Our study indicated that the blockade of 5-HT uptake by paroxetine decreased the number of BrdU-im cells and MF20-im cells. These data indicate a role of 5-HT and 5-HTT on heart development. Abnormal 5-HT level or misuse of 5-HT uptake blocker may alter the heart development.

Endothelial lineage-mediated loss of the GATA cofactor Friend of GATA 1 impairs cardiac development

GATA transcription factors, together with Friend of GATA (FOG) cofactors, are required for the differentiation of diverse cell types. Multiple aspects of hematopoiesis are controlled by the interaction of FOG-1 with the GATA-1/2/3 subfamily. Likewise, FOG-2 is coexpressed with the GATA-4/5/6 subfamily at other sites, including the heart and gonads. FOG-2 and GATA-4 are required for cardiac development. Through transgenic rescue of hematopoietic defects of FOG-1-/- embryos we define an unsuspected role for FOG-1 in heart development. In particular, rescued FOG-1-/- mice die at embryonic day (E) 14.5 with cardiac defects that include double outlet right ventricle and a common atrioventricular valve. Using conditional inactivation of Fog-1 we assign the cell of origin in which FOG-1 function is required. Neural crest cells migrate properly into FOG-1-/- hearts and mice with FOG-1 conditionally excised from neural crest derivatives fail to develop cardiac abnormalities. In contrast, conditional inactivation of FOG-1 in endothelial-derived tissues by means of Tie-2-expressed Cre recapitulates the rescue-knockout defects. These findings establish a nonredundant requirement for FOG-1 in the outlet tract and atrioventricular valves of the heart that depend on expression in endothelial-derived tissue and presumably reflect cooperation with the GATA-4/5/6 subfamily.

NFATc3 and NFATc4 are required for cardiac development and mitochondrial function

Activation of the nuclear factor of activated T-cell (NFAT) family of transcription factors is associated with changes in gene expression and myocyte function in adult cardiac and skeletal muscle. However, the role of NFATs in normal embryonic heart development is not well characterized. In this report, the function of NFATc3 and NFATc4 in embryonic heart development was examined in mice with targeted disruption of both nfatc3 and nfatc4 genes. The nfatc3-/-nfatc4-/- mice demonstrate embryonic lethality after embryonic day 10.5 and have thin ventricles, pericardial effusion, and a reduction in ventricular myocyte proliferation. Cardiac mitochondria are swollen with abnormal cristae, indicative of metabolic failure, but hallmarks of apoptosis are not evident. Furthermore, enzymatic activity of complex II and IV of the respiratory chain and mitochondrial oxidative activity are reduced in nfatc3-/-nfatc4-/- cardiomyocytes. Cardiac-specific expression of constitutively active NFATc4 in nfatc3-/-nfatc4-/- embryos prolongs embryonic viability to embryonic day 12 and preserves ventricular myocyte proliferation, compact zone density, and trabecular formation. The rescued embryos also maintain cardiac mitochondrial ultrastructure and complex II enzyme activity. Together, these data support the hypothesis that loss of NFAT activity in the heart results in a deficiency in mitochondrial energy metabolism required for cardiac morphogenesis and function.

Comparison of connexin expression patterns in the developing mouse heart and human foetal heart

Heart muscle cells are electrically coupled by gap junctions, clusters of low-resistance transmembrane channels composed of connexins (Cx). The expression of the three major connexins (Cx43, Cx40 and Cx45) present in cardiac myocytes is known to be developmentally regulated but it is not clear how the patterns in the human heart compare with those found in the mouse. This issue is of importance given the wide use of transgenic mice to investigate gene function with the aim of extrapolating the results to human. In the present study we applied immunoconfocal microscopy to investigate the spatial distribution of the three connexins in the developing mouse heart and foetal human heart. Although Cx45 labelling was present at low levels throughout the developing mouse heart and human foetal (9-week) heart, it was most prominent in the conduction tissues. In the developing mouse heart, Cx40 was widely expressed at embryonic day 12.5 (E12.5) but at E17.5 expression was restricted to the conduction tissues and atria. In the 9-week human foetal heart, the Cx40 labelling pattern was similar to the E15 mouse heart, being far more abundant in conduction tissues (bundle branches to Purkinje fibres) and atria than in the ventricular muscle. Cx43 labelling became more apparent in the ventricular myocardium as development of the mouse heart progressed but was virtually undetectable in the central conduction system. In the human foetal heart Cx43 was virtually undetectable in the atria but was the predominant connexin in the ventricles. We conclude that, at least in some key aspects, the pattern of connexin expression in the developing mouse heart parallels that found in the human embryonic heart.

Expression of a novel Krüpple-like zinc-finger gene, ZNF382, in human heart

With the aim of identifying genes involved in human heart development and disease, we have isolated a novel KRAB-related zinc-finger gene named ZNF382 from heart cDNA library. The ZNF382 gene has a predicted 548-amino acid open reading frame, encoding a putative 64kDa zinc-finger protein. The N-terminus of the ZNF382 coding region has a well-conserved Krüpple-associated box domain that consists of KRAB boxes A and B, whereas the C-terminus contains a Krüpple-type zinc-finger domain possessing nine C(2)H(2) zinc-finger motifs in tandem arrays. The ZNF382 gene is mapped to chromosome 19q13.13. Northern blot analysis indicates that a 2.9-kb transcript specific for ZNF382 is expressed at very early embryonic stage of human (at least earlier than gestation 34 day) and widely in human embryo tissues. At the adult stage, ZNF382 expression is restricted largely to heart tissue suggesting a potential role in heart development and function.

Expression of endothelins in human cardiogenesis

Genetic disruption of endothelin (ET) 1, endothelin-converting enzyme (ECE) 1, and endothelin receptor A (ET(A)) in "knockout" or mutant mouse models result in defects in branchial arch derived craniofacial tissues and in cardiac outflow and great vessel structures. Interestingly, certain types of human congenital cardiovascular malformations such as Catch 22 syndrome and type B interruption of the aortic arch strongly resemble defects seen in knockout animal models. To better address the exact involvement of the ET system in heart formation we explored the spatiotemporal pattern of expression of the components of the ET system during critical phases of cardiogenesis in the human embryo (3-6 weeks of development; Carnegie stages 10-17) by in situ hybridization. We detected high ET-1 mRNA expression in endocardial cells lining the heart outflow tract in the region where the future aortic valves will form. No hybridization signal corresponding to pre-pro-ET-3 was observed in the heart. At the same location, the underlying myocytes express ET(A) mRNA. Whereas a functional role of ET in the valve formation can be proposed because of the simultaneous presence of all the components of the endothelin system (ET-1/ECE-1/ET(A)), this seems not to be the case for the formation of the ventricular septum where endocardial cells do not express ET-1, and only a weak ET(A) hybridization signal was detected in the surrounding myocardium. An abnormal hemodynamism indirectly due to valve malformation may be the indirect cause of this septal defect. The results of this study suggest an important role for the ET system in the formation of certain anatomical structures of the developing human heart.

SAGE identification of differentiation responsive genes in P19 embryonic cells induced to form cardiomyocytes in vitro

Transcriptome profiling facilitates the identification of developmentally regulated genes. To quantify the functionally active genome of P19 embryonic carcinoma (EC) cells induced to form cardiomyocytes, we employed serial analysis of gene expression (SAGE) to sequence and compare a total of 171,735 SAGE tags from three libraries (undifferentiated P19 EC cells, differentiation days 3 + 0.5 and 3 + 3.0). After in vitro differentiation, only 3.1% of the gene products demonstrated significant (P < 0.05) changes in expression. The most highly significant changes (P < 0.01) involved altered expression of 410 genes encoding predominantly transcription factors, differentiation factors and growth regulators. Quantitative polymerase chain reaction analysis and in situ hybridization revealed five growth regulators (Dlk1, Igfbp5, Hmga2, Podxl and Ptn) and two unknown ESTs with expression profiles similar to known cardiac transcription factors, implicating these growth regulators in cardiac differentiation. These SAGE libraries thus serve as a reference resource for understanding the role of differentiation-dependent genes in embryonic stem cell models induced to form cardiomyocytes in vitro.

Normal fate and altered function of the cardiac neural crest cell lineage in retinoic acid receptor mutant embryos

Mouse embryos lacking the retinoic acid (RA) receptors RARalpha1 and RARbeta suffer from a failure to properly septate (divide) the early outflow tract of the heart into distinct aortic and pulmonary channels, a phenotype termed persistent truncus arteriosus. This phenotype is associated with a failure in the development of the cardiac neural crest cell lineage, which normally forms the aorticopulmonary septum. In this study, we examined the fate of the neural crest lineage in RARalpha1/RARbeta mutant embryos by crossing with the Wnt1-cre and conditional R26R alleles, which together constitute a genetic lineage marker for the neural crest. We find that the number, migration, and terminal fate of the cardiac neural crest is normal in mutant embryos; however, the specific function of these cells in forming the aorticopulmonary septum is impaired. We furthermore show that the neural crest cells themselves do not utilize retinoid receptors and do not respond to RA during this process, but rather that the phenotype is cell non-autonomous for the neural crest cell lineage. This suggests that an alternative tissue in the vicinity of the outflow tract of the heart responds directly to RA, and thereby induces or permits the neural crest cell lineage to initiate aorticopulmonary septation.

The heart LIM protein gene (Hlp), expressed in the developing and adult heart, defines a new tissue-specific LIM-only protein family

In a subtraction designed to identify transcripts accompanying mesodermal lineage specification in mouse ES differentiation cultures, we identified a gene encoding a two LIM-domain protein which we named heart LIM protein (Hlp). Hlp is most closely related to thymus LIM protein, and these two genes comprise a new gene family related to the cysteine-rich protein (CRP) gene family. In the embryo, Hlp expression is primarily restricted to the developing heart. In situ hybridization showed expression at E7.75 in the paired heart-forming primordia prior to linear heart-tube formation. At E8.5, strong expression is detected in the heart, with equal expression in both heart chambers. Hlp expression is detected in both myocardium and endocardium, and in vascular endothelium. Later in fetal development low levels of Hlp expression are detected outside the heart, including dorsal root ganglia and the spinal cord. In the adult, Hlp is expressed at highest levels in the heart, and at lower levels in the brain, skeletal muscle and aorta. Hlp expression is unchanged in hypertrophic hearts induced by aortic constriction. These data suggest a role for the two LIM-domain gene Hlp in the very earliest stages of heart differentiation and development.

Microarray gene expression profiles in dilated and hypertrophic cardiomyopathic end-stage heart failure

Despite similar clinical endpoints, heart failure resulting from dilated cardiomyopathy (DCM) or hypertrophic cardiomyopathy (HCM) appears to develop through different remodeling and molecular pathways. Current understanding of heart failure has been facilitated by microarray technology. We constructed an in-house spotted cDNA microarray using 10,272 unique clones from various cardiovascular cDNA libraries sequenced and annotated in our laboratory. RNA samples were obtained from left ventricular tissues of precardiac transplantation DCM and HCM patients and were hybridized against normal adult heart reference RNA. After filtering, differentially expressed genes were determined using novel analyzing software. We demonstrated that normalization for cDNA microarray data is slide-dependent and nonlinear. The feasibility of this model was validated by quantitative real-time reverse transcription-PCR, and the accuracy rate depended on the fold change and statistical significance level. Our results showed that 192 genes were highly expressed in both DCM and HCM (e.g., atrial natriuretic peptide, CD59, decorin, elongation factor 2, and heat shock protein 90), and 51 genes were downregulated in both conditions (e.g., elastin, sarcoplasmic/endoplasmic reticulum Ca2+-ATPase). We also identified several genes differentially expressed between DCM and HCM (e.g., alphaB-crystallin, antagonizer of myc transcriptional activity, beta-dystrobrevin, calsequestrin, lipocortin, and lumican). Microarray technology provides us with a genomic approach to explore the genetic markers and molecular mechanisms leading to heart failure.

The effect of a chronic maternal cortisol infusion on the late-gestation fetal sheep

Exposure of the fetus to excess maternal glucocorticoids has been postulated to alter fetal growth and development, and thus provide a possible mechanism for the link between impaired fetal growth and altered postnatal physiology. However, the effects of exposure to excess maternal glucocorticoids on fetal physiology and metabolism in utero have not been described. We therefore studied the effects of chronic maternal cortisol infusion on fetal growth, blood pressure, metabolism and endocrine status in chronically catheterised fetal sheep. We infused hydrocortisone (80 mg/day, n=6) or saline (n=8) for 10 days into the pregnant ewes beginning at 119 days of gestation. Maternal cortisol infusion reduced fetal growth rate by 30% (girth increment 2.9+/-0.3 vs 1.8+/-0.4 mm/day, P=0.03). Maternal cortisol infusion increased fetal heart weight by 15% relative to body weight and increased ventricular wall thickness by 30% in the left and 50% in the right ventricle. The weight of the spleen was reduced by 30% and placental weight reduced by 25%. Fetal blood pressure increased by approximately 10 mmHg (20%) during maternal cortisol infusion. Maternal cortisol infusion did not alter amino-nitrogen concentrations. However, maternal lactate concentrations increased by 80% and fetal lactate concentrations increased by 74% with maternal cortisol infusion, and both maternal and fetal urea concentrations increased by 40%. Circulating maternal IGF-binding protein (IGFBP)-3 levels had increased by 20% by the end of the maternal cortisol infusion. Fetal IGF-I concentrations decreased during cortisol infusion and fetal IGFBP-1 concentrations were negatively correlated with fetal weight (r=-0.76, P=0.02). We conclude that even a modest elevation of maternal cortisol levels affects fetal growth, cardiovascular function, metabolism and endocrine status which may have long-term consequences.

Expression and mutation analysis of BRUNOL3, a candidate gene for heart and thymus developmental defects associated with partial monosomy 10p

Partial monosomy 10p is a rare chromosomal aberration. Patients often show symptoms of the DiGeorge/velocardiofacial syndrome spectrum. The phenotype is the result of haploinsufficiency of at least two regions on 10p, the HDR1 region associated with hypoparathyroidism, sensorineural deafness, and renal defects (HDR syndrome) and the more proximal region DGCR2 responsible for heart defects and thymus hypoplasia/aplasia. While GATA3 was identified as the disease causing gene for HDR syndrome, no genes have been identified thus far for the symptoms associated with DGCR2 haploinsufficiency. We constructed a deletion map of partial monosomy 10p patients and narrowed the critical region DGCR2 to about 300 kb. The genomic draft sequence of this region contains only one known gene, BRUNOL3 ( NAPOR, CUGBP2, ETR3). In situ hybridization of human embryos and fetuses revealed as well as in other tissues a strong expression of BRUNOL3 in thymus during different developmental stages. BRUNOL3 appears to be an important factor for thymus development and is therefore a candidate gene for the thymus hypoplasia/aplasia seen in partial monosomy 10p patients. We did not find BRUNOL3 mutations in 92 DiGeorge syndrome-like patients without chromosomal deletions and in 8 parents with congenital heart defect children.

Natriuretic peptide system in fetal heart and circulation

Atrial natriuretic peptide, brain natriuretic peptide and C-type natriuretic peptide belong to a family of hormones that have diuretic, natriuretic and vasodepressor activity and play a part in pressure and volume homeostasis in adults. As little is known about the natriuretic peptides during cardiac maturation, this review summarizes current knowledge about the early expression of components of the natriuretic peptide system in the heart during embryonic and fetal development. The data indicate a functional importance of the fetal natriuretic peptide system, especially under pathophysiological conditions. Thus, in the fetus, the system fulfils important beneficial compensatory roles in cardiovascular disease, rather than in day-to-day pressure and volume homeostasis. In comparison with data on the relevance of natriuretic peptides in adults, those summarized here indicate a functional maturation of the natriuretic peptide system during ontogeny in mammals.