Cardioinductive network guiding stem cell differentiation revealed by proteomic cartography of tumor necrosis factor alpha-primed endodermal secretome

In the developing embryo, instructive guidance from the ventral endoderm secures cardiac program induction within the anterolateral mesoderm. Endoderm-guided cardiogenesis, however, has yet to be resolved at the proteome level. Here, through cardiopoietic priming of the endoderm with the reprogramming cytokine tumor necrosis factor alpha (TNFalpha), candidate effectors of embryonic stem cell cardiac differentiation were delineated by comparative proteomics. Differential two-dimensional gel electrophoretic mapping revealed that more than 75% of protein species increased >1.5-fold in the TNFalpha-primed versus unprimed endodermal secretome. Protein spot identification by linear ion trap quadrupole (LTQ) tandem mass spectrometry (MS/MS) and validation by shotgun LTQ-Fourier transform MS/MS following multidimensional chromatography mapped 99 unique proteins from 153 spot assignments. A definitive set of 48 secretome proteins was deduced by iterative bioinformatic screening using algorithms for detection of canonical and noncanonical indices of secretion. Protein-protein interaction analysis, in conjunction with respective expression level changes, revealed a nonstochastic TNFalpha-centric secretome network with a scale-free hierarchical architecture. Cardiovascular development was the primary developmental function of the resolved TNFalpha-anchored network. Functional cooperativity of the derived cardioinductive network was validated through direct application of the TNFalpha-primed secretome on embryonic stem cells, potentiating cardiac commitment and sarcomerogenesis. Conversely, inhibition of primary network hubs negated the procardiogenic effects of TNFalpha priming. Thus, proteomic cartography establishes a systems biology framework for the endodermal secretome network guiding stem cell cardiopoiesis.

PRL-3 initiates tumor angiogenesis by recruiting endothelial cells in vitro and in vivo

We show here that PRL-3 protein is expressed in fetal heart, developing blood vessels, and pre-erythrocytes but not in their mature counterparts. These observations imply that PRL-3 may be involved in the early development of the circulatory system. Because PRL-3 mRNA had been reported to be consistently elevated in metastatic samples derived from colorectal cancers, we attempted to investigate if PRL-3 might be involved in tumor angiogenesis and if PRL-3-expressing cells could cross-talk to human umbilical vascular endothelial cells (HUVEC) by using an in vitro coculture system. HUVECs were grown with fibroblasts, which were later overlaid with PRL-3-expressing cells. We observed that both PRL-3-expressing Chinese hamster ovary (CHO) cells and PRL-3-expressing DLD-1 human colon cancer cells could redirect the migration of HUVECs toward them; in addition, PRL-3-expressing DLD-1 cells could enhance HUVEC vascular formation. In vivo injection of PRL-3-expressing CHO cells into nude mice to form local tumors resulted in the recruitment of host endothelial cells into the tumors and initiation of angiogenesis. We further showed that PRL-3-expressing cells reduced interleukin-4 (IL-4) expression levels and thus attenuated IL-4 inhibitory effects on the HUVEC vasculature. Our findings provide direct evidence that PRL-3 may be involved in triggering angiogenesis and establishing microvasculature and it may serve as an attractive therapeutic target with respect to both angiogenesis and cancer metastasis.

TGF-beta 1 and fibroblast growth factors selectively up-regulate tissue-specific fetal genes in cardiac muscle cells

TGF-beta 1, like basic and acidic fibroblast growth factor (FGF), inhibits differentiated gene expression in skeletal myoblasts. It potentiates FGF-beta 1 down-regulated expression of the alpha-myosin heavy chain gene and the sarcoplasmic reticulum calcium ATPase gene, yet up-regulated expression of the genes for beta-myosin heavy chain, atrial natriuretic factor, and both skeletal and smooth muscle alpha-actin-four transcripts associated with the embryonic heart. TGF-beta 1 did not affect cardiac alpha-actin gene expression. These responses resemble the generalized 'fetal' phenotype seen during hypertrophy triggered by a haemodynamic load. Chick skeletal and cardiac alpha-actin promoter-driven reported genes were transfected into neonatal rat cardiac myocytes. TGF-beta 1 stimulated skeletal alpha-actin transcription, but not transcription from the cardiac alpha-actin promoter. Basic FGF produced the same results as TGF-beta 1, but acidic FGF suppressed expression of both alpha-actin genes; these results were true for purified and recombinant FGFs. Modulation of alpha-actin transcription by growth factors corresponded accurately to control of the endogenous genes. Three positive cis-acting elements were critical for skeletal alpha-actin transcription in cardiac, as well as skeletal, myocytes, particularly the downstream CCAAT box-associated repeat. Thus, TGF-beta 1 and FGFs selectively induce an ensemble of 'fetal' genes and differentially regulate alpha-actin transcription in cardiac muscle cells.

Knockout mice lacking cPGES/p23, a constitutively expressed PGE2 synthetic enzyme, are peri-natally lethal

Cytosolic prostaglandin (PG) E synthase (cPGES) is constitutively expressed in various cells and regulates cyclooxygenase (COX)-1-dependent immediate PGE(2) generation. Its primary structure is identical to co-chaperone p23, a heat shock protein 90 (Hsp90)-binding protein. We have revealed that Hsp90 regulated both cPGES/p23 and its client protein kinase CK2. In this study, in order to examine the role of cPGES/p23 in vivo, we generated mice deficient in cPGES/p23 by a targeted disruption of exons 2 and 3, containing Tyr9, which is essential for catalytic activity. Heterozygotes are viable, fertile, and appear normal, despite a decrease in cPGES/p23 protein level. A generation of offsprings derived from intercrosses of cPGES/p23 homozygous mice revealed that 109, 247, and 10 pups were wild type, heterozygous, and homozygous, respectively; however, all homozygotes died at birth. The absence of viable null mutants, with heterozygotes and wild-type offspring obtained at a ratio of approximately 2:1, indicated that homozygosity for the cPGES/p23 null mutant leads to peri-natal lethality. Embryos homozygous for cPGES/p23-null had lower body weights than wild-type embryos, and abnormal morphology of skin and lungs. Moreover, the PGE(2) content in the lungs of cPGES/p23-null embryos was lower than that of the wild type. These results indicate that cPGES-derived PGES is involved in the normal development of mouse embryonic lung.

Msx1 and Msx2 regulate survival of secondary heart field precursors and post-migratory proliferation of cardiac neural crest in the outflow tract

Msx1 and Msx2 are highly conserved, Nk-related homeodomain transcription factors that are essential for a variety of tissue-tissue interactions during vertebrate organogenesis. Here we show that combined deficiencies of Msx1 and Msx2 cause conotruncal anomalies associated with malalignment of the cardiac outflow tract (OFT). Msx1 and Msx2 play dual roles in outflow tract morphogenesis by both protecting secondary heart field (SHF) precursors against apoptosis and inhibiting excessive proliferation of cardiac neural crest, endothelial and myocardial cells in the conotruncal cushions. During incorporation of SHF precursors into the OFT myocardium, ectopic apoptosis in the Msx1-/-; Msx2-/- mutant SHF is associated with reduced expression of Hand1 and Hand2, which from work on Hand1 and Hand2 mutants may be functionally important in the inhibition of apoptosis in Msx1/2 mutants. Later during aorticopulmonary septation, excessive proliferation in the OFT cushion mesenchyme and myocardium of Msx1-/-; Msx2-/- mutants is associated with premature down-regulation of p27(KIP1), an inhibitor of cyclin-dependent kinases. Diminished accretion of SHF precursors to the elongating OFT myocardium and excessive accumulation of mesenchymal cells in the conotruncal cushions may work together to perturb the rotation of the truncus arteriosus, leading to OFT malalignment defects including double-outlet right ventricle, overriding aorta and pulmonary stenosis.

MicroRNAs in the human heart: a clue to fetal gene reprogramming in heart failure

BACKGROUND

Chronic heart failure is characterized by left ventricular remodeling and reactivation of a fetal gene program; the underlying mechanisms are only partly understood. Here we provide evidence that cardiac microRNAs, recently discovered key regulators of gene expression, contribute to the transcriptional changes observed in heart failure.

METHODS AND RESULTS

Cardiac transcriptome analyses revealed striking similarities between fetal and failing human heart tissue. Using microRNA arrays, we discovered profound alterations of microRNA expression in failing hearts. These changes closely mimicked the microRNA expression pattern observed in fetal cardiac tissue. Bioinformatic analysis demonstrated a striking concordance between regulated messenger RNA expression in heart failure and the presence of microRNA binding sites in the respective 3' untranslated regions. Messenger RNAs upregulated in the failing heart contained preferentially binding sites for downregulated microRNAs and vice versa. Mechanistically, transfection of cardiomyocytes with a set of fetal microRNAs induced cellular hypertrophy as well as changes in gene expression comparable to the failing heart.

CONCLUSIONS

Our data support a novel mode of regulation for the transcriptional changes in cardiac failure. Reactivation of a fetal microRNA program substantially contributes to alterations of gene expression in the failing human heart.

[Differentially expressed transcription factors in the cardiac outflow tract tissue of connexin43 knockout mice]

OBJECTIVE

To investigate the changes in the expression of cardiac transcription factors in the cardiac outflow tract (OFT) tissues in the connexin43 knockout homozygotes (Cx43 KO), connexin43 heterozygotes, and connexin43 wild-type mice (Cx43 WT).

METHODS

The cDNA was retrotranscribed from the RNA extracted from the OFT tissues of 6 Cx43 KO, 6 Cx43 WT, and 6 Cx43 heterozygotes genotyped by PCR method on the embryonic day (ED) 13.5 and ED 14.5. The biotin-labeled cRNA derived from the transcription of cDNA was fragmented as probes. The probes were hybridized with Affymetrix Mouse Genome 430 2.0 Array. Gene Array Scanner was used to screen the signals of hybridization and detect the expression of genes. The mRNA expression levels of 3 cardiac transcription factors: Sox11, Foxp1, and Tbx20 were measured by real time quantitative RT-PCR.

RESULTS

The ratios of the expression of the 6 genes, all cardiac transcription factors: Gata4, Mef2C, Sox4, Sox11, Foxp1, and Tbx20 between the Cx43 KO and Cx43 WT groups were 1:1.41, 1:2.30, 1:3.25, 1:0.71, 1:0.66, and 1:0.54. The expression levels of Sox11 and Foxp1 on ED13.5 in the Cx43 K group were 4.76 +/- 0.19 and 5.08 +/- 0.28 respectively, both significantly lower than those of the Cx43 WT group (5.34 +/- 0.25 and 5.64 +/- 0.15 respectively, both P < 0.01), and expression level of Tbx20 on ED 13.5 in the Cx43 K group was 7.18 +/- 0.16, not significantly different from that of the Cx43 WT group (7.47 +/- 0.27, P > 0.05). The expression levels of the genes Sox11, Foxp1, Tbx20 on ED 14,5 were 4.71 +/- 0.27, 5.25 +/- 0.31, and 7.05 +/- 0.17 respectively, all significantly lower than those of the Cx43 WT group (5.00 +/- 0.19, 5.77 +/- 0.16,) and 7.43 +/- 0.25, all P < 0.05). The results of the expression of these genes by real time PCR analysis showed an excellent concordance with those indicated by the microarray analysis.

CONCLUSION

The cardiac transcription factors such as Sox11, Foxp1, and Tbx20 that are differently expressed in the Cx43 KO OFT tissue may be involved in the pathogenesis of the OFT defects.

Return to the fetal gene program protects the stressed heart: a strong hypothesis

A common feature of the hemodynamically or metabolically stressed heart is the return to a pattern of fetal metabolism. A hallmark of fetal metabolism is the predominance of carbohydrates as substrates for energy provision in a relatively hypoxic environment. When the normal heart is exposed to an oxygen rich environment after birth, energy substrate metabolism is rapidly switched to oxidation of fatty acids. This switch goes along with the expression of "adult" isoforms of metabolic enzymes and other proteins. However, the heart retains the ability to return to the "fetal" gene program. Specifically, the fetal gene program is predominant in a variety of pathophysiologic conditions including hypoxia, ischemia, hypertrophy, and atrophy. A common feature of all of these conditions is extensive remodeling, a decrease in the rate of aerobic metabolism in the cardiomyocyte, and an increase in cardiac efficiency. The adaptation is associated with a whole program of cell survival under stress. The adaptive mechanisms are prominently developed in hibernating myocardium, but they are also a feature of the failing heart muscle. We propose that in failing heart muscle at a certain point the fetal gene program is no longer sufficient to support cardiac structure and function. The exact mechanisms underlying the transition from adaptation to cardiomyocyte dysfunction are still not completely understood.

SJ. Identification and characterization of a novel Schwann and outflow tract endocardial cushion lineage-restricted periostin enhancer

Periostin is a fasciclin-containing adhesive glycoprotein that facilitates the migration and differentiation of cells that have undergone epithelial-mesenchymal transformation during embryogenesis and in pathological conditions. Despite the importance of post-transformational differentiation as a general developmental mechanism, little is known how periostin's embryonic expression is regulated. To help resolve this deficiency, a 3.9-kb periostin proximal promoter was isolated and shown to drive tissue-specific expression in the neural crest-derived Schwann cell lineage and in a subpopulation of periostin-expressing cells in the cardiac outflow tract endocardial cushions. In order to identify the enhancer and associated DNA binding factor(s) responsible, in vitro promoter dissection was undertaken in a Schwannoma line. Ultimately a 304-bp(peri) enhancer was identified and shown to be capable of recapitulating 3.9 kb(peri-lacZ)in vivo spatiotemporal patterns. Further mutational and EMSA analysis helped identify a minimal 37-bp region that is bound by the YY1 transcription factor. The 37-bp enhancer was subsequently shown to be essential for in vivo 3.9 kb(peri-lacZ) promoter activity. Taken together, these studies identify an evolutionary-conserved YY1-binding 37-bp region within a 304-bp periostin core enhancer that is capable of regulating simultaneous novel tissue-specific periostin expression in the cardiac outflow-tract cushion mesenchyme and Schwann cell lineages.

Mapping the consequence of Notch1 proteolysis in vivo with NIP-CRE

The four highly conserved Notch receptors receive short-range signals that control many biological processes during development and in adult vertebrate tissues. The involvement of Notch1 signaling in tissue self-renewal is less clear, however. We developed a novel genetic approach N(1)IP-CRE (Notch1 Intramembrane Proteolysis) to follow, at high resolution, the descendents of cells experiencing Notch1 activation in the mouse. By combining N(1)IP-CRE with loss-of-function analysis, Notch activation patterns were correlated with function during development, self-renewal and malignancy in selected tissues. Identification of many known functions of Notch1 throughout development validated the utility of this approach. Importantly, novel roles for Notch1 signaling were identified in heart, vasculature, retina and in the stem cell compartments of self-renewing epithelia. We find that the probability of Notch1 activation in different tissues does not always indicate a requirement for this receptor and that gradients of Notch1 activation are evident within one organ. These findings highlight an underappreciated layer of complexity of Notch signaling in vivo. Moreover, NIP-CRE represents a general strategy applicable for monitoring proteolysis-dependent signaling in vivo.

ColVa1 and ColXIa1 are required for myocardial morphogenesis and heart valve development

Genetic mutations in minor fibrillar collagen types Va1 (ColVa1) and XIa1 (ColXI) have been identified in connective tissue disorders including Ehlers-Danlos syndrome and chondrodysplasias. ColVa1+/- and ColXIa1-/- mutant mice recapitulate these human disorders and show aberrations in collagen fiber organization in connective tissue of the skin, cornea, cartilage, and tendon. In the heart, fibrous networks of collagen fibers form throughout the ventricular myocardium and heart valves, and alterations in collagen fiber homeostasis are apparent in many forms of cardiac disease associated with myocardial dysfunction and valvular insufficiency. There is increasing evidence for cardiac dysfunction in connective tissue disorders, but the mechanisms have not been addressed. ColVa1+/- and ColXIa1-/- mutant mice were used to identify roles for ColVa1 and ColXIa1 in ventricular myocardial morphogenesis and heart valve development. These affected cardiac structures show a compensatory increase in type I collagen deposition, similar to that previously described in valvular and cardiomyopathic disease. Morphological cardiac defects associated with changes in collagen fiber homeostasis identified in ColVa1+/- and ColXIa1-/- mice provide an insight into previously unappreciated forms of cardiac dysfunction associated with connective tissue disorders.

Expression of Liver X Receptor α in Rat Fetal Tissues at Different Developmental Stages

The liver X receptor (LXR) is a nuclear receptor that acts as a sterol sensor and metabolic regulator of cholesterol and lipid homeostasis. Using a novel LXRα-specific antibody for immunohistochemistry, we evaluated cellular expression of LXRα in fetal rat tissues. In the fetal liver, LXRα-positive macrophages appeared at 12 days and their number peaked at 18 days of gestation. In contrast, hepatocytes expressed LXRα during the later stage of gestation, suggesting the functional development of the liver during ontogeny. Later, macrophages in spleen and thymus expressed LXRα, and some mononuclear cells in the vascular lumen compatible to primitive/fetal macrophages in the fetal circulation were found to express LXRα. In vitro, rat monocytes did not express LXRα, but monocyte-derived macrophages cultured in the presence of macrophage-colony stimulating factor revealed the distinct expression of LXRα in nucleoli. These findings suggest that LXRα plays a role in the differentiation of fetal macrophages, particularly hepatic macrophages, in rat development.

Developmental changes in rat cardiac titin/connectin: transitions in normal animals and in mutants with a delayed pattern of isoform transition

Rat cardiac titin undergoes developmental changes in isoform expression during the period from late embryonic through the first 20-25 days of life. At least five size classes of titin isoforms have been identified using SDS agarose gel electrophoresis. The longest normal isoform is expressed in the embryonic stages, and it is progressively replaced with increasingly smaller versions. The isoform switching is consistent with changes in resting tension from lower values in one-day neonates to higher levels in adult myocytes. Considerable micro-heterogeneity in alternative splicing patterns also was found, particularly in the N2BA PEVK region of human, rat, and dog ventricle. A rat mutation has been identified in which the embryonic-neonatal titin isoform transitions are markedly delayed. These mutant animals may prove useful for examining the role of titin in stretch-activated signal transduction and in the Frank-Starling relationship.

Dosage-dependent transcriptional regulation by the calcineurin/NFAT signaling in developing myocardium transition

Thin spongy myocardium is critical at early embryonic stage [before embryonic day (E) 13.5 in mice] to allow diffusion of oxygen and nutrients to the developing cardiomyocytes. However, establishment of compact myocardium at later stage ( approximately E16.5) during development is necessary to prepare for the increase in demand for blood circulation. Elucidating molecular targets of the spongy-compact myocardium transition between E13.5 and E16.5 in heart development is thus important. Previous studies demonstrated that multiple transcription factors and signaling pathways are involved in the regulation and function of the myocardium in heart development. Disruption of certain transcription factors or critical components of signaling pathways frequently causes structural malformation in heart and persistence of "thin spongy myocardium". We have recently demonstrated activation of the calcineurin/NFAT signaling pathway at E14.5 in developing myocardium. Constitutive inhibition of the calcineurin/NFAT signaling pathway caused embryonic lethality. Molecular targets downstream of the calcineurin/NFAT signaling pathway, however, remains elusive. Here, we report transcription targets, independently and dependently, regulated by the calcineurin/NFAT signaling during the E13.5-E16.5 myocardium transition. We have uncovered that expression of one-third of the induced genes during myocardium transition is calcineurin/NFAT-dependent. Among these calcineurin/NFAT-dependent transcription targets, there is a dosage-dependent regulation. Molecular studies indicate that formation of distinct NFAT:DNA complex, in part, accounts for the dosage-dependent regulation. Thus, in addition to temporal and spatial regulation, dosage-dependent threshold requirement provides another mechanism to modulate transcription response mediated by the calcineurin/NFAT signaling during heart development.

Cardiomyocyte-restricted deletion of connexin43 during mouse development

Although the gap junction protein Connexin43 (Cx43) is expressed in various cell types during embryonic development, mice with a global inactivation of Cx43 survive until birth but die perinatally due to an obstruction of the right ventricular outflow tract of the heart. To analyze the functional role of Cx43 gap junction channels in cardiomyocytes of the developing and early postnatal heart, we used alphaMyHC-Cre mice to ablate Cx43 expression selectively in cardiomyocytes during development. We found efficient ablation of Cx43 in cardiomyocytes during embryonic development starting at embryonic day (ED) 9.5 in the ventricular wall. Analyses of cardiac Cx43 protein at birth indicated complete loss of Cx43 expression in cardiomyocytes. All mice homozygously deficient for Cx43 in cardiomyocytes died until postnatal day (PD) 16. Heterozygous inactivation of Cx43 in cardiomyocytes neither altered atrial nor ventricular activation, but homozygous ablation led to changes in ventricular activation, i.e. significant decrease of the QRS-amplitude and prolonged QRS-duration already at PD 4. Cardiac morphology was similar to controls until PD 1, but subtle morphological changes were found in a subgroup of mutant mice at later stages. Besides narrowing of the ventricular outlet region at PD 6, hypertrophy of ventricular myocardium was found at PD 12. Our data indicate that complete inactivation of cardiac Cx43 during development predisposes hearts to develop postnatal morphological alterations, which differ from outflow tract obstructions described for Cx43 null mice. In addition, complete loss of cardiac Cx43 protein during development correlates with slowed ventricular activation at PD 4, impairs viability during development, and leads to death of all mutant mice until PD 16.

Apoptosis in the developing mouse heart

Apoptosis occurs at high frequency in the myocardium of the developing avian cardiac outflow tract (OFT). Up- or down-regulating apoptosis results in defects resembling human conotruncal heart anomalies. This finding suggested that regulated levels of apoptosis are critical for normal morphogenesis of the four-chambered heart. Recent evidence supports an important role for hypoxia of the OFT myocardium in regulating cell death and vasculogenesis. The purpose of this study was to determine whether apoptosis in the outflow tract myocardium occurs in the mouse heart during developmental stages comparable to the avian heart and to determine whether differential hypoxia is also present at this site in the murine heart. Apoptosis was detected using a fluorescent vital dye, Lysotracker Red (LTR), in the OFT myocardium of the mouse starting at embryonic day (E) 12.5, peaking at E13.5-14.5, and declining thereafter to low or background levels by E18.5. In addition, high levels of apoptosis were detected in other cardiac regions, including the apices of the ventricles and along the interventricular sulcus. Apoptosis in the myocardium was detected by double-labeling with LTR and cardiomyocyte markers. Terminal deoxynucleotidyl transferase-mediated deoxyuridinetriphosphate nick end-labeling (TUNEL) and immunostaining for cleaved Caspase-3 were used to confirm the LTR results. At the peak of OFT apoptosis in the mouse, the OFT myocardium was relatively hypoxic, as indicated by specific and intense EF5 staining and HIF1alpha nuclear localization, and was surrounded by the developing vasculature as in the chicken embryo. These findings suggest that cardiomyocyte apoptosis is an evolutionarily conserved mechanism for normal morphogenesis of the outflow tract myocardium in avian and mammalian species.

Igf-2r expression regulated by epigenetic modification and the locus of gene imprinting disrupted in cloned cattle

Epigenetic reprogramming has a crucial role in establishing nuclear totipotency in normal development and in cloned animals. Insulin-like growth factor-2 receptor (Igf-2r) is a tissue-specifically and species-dependently imprinted gene, regulated by epigenetic modifications. The diversity of Igf-2r imprinting suggests that the success of animal cloning may be species-dependent. To determine the relation between epigenetic modifications and Igf-2r expression in cattle, and explore whether this gene was correctly imprinted and reprogrammed after nuclear transfer, we quantified Igf-2r mRNA in a cattle cell line after treated with an inhibitor of DNA methylation transferase or an inhibitor of histone deacetylase, and confirmed that DNA methylation and histone acetylation could regulate this gene expression. CpG island searching showed that there is a conservative imprinting control region (ICR) within the second intron of Igf-2r in cattle, analogous to mice and sheep, regulating this gene imprinting. DNA methylation analysis in sperm and blood cells showed that DNA methylation at Igf-2r ICR2 was reprogrammed in normal cattle. The methylation at Igf-2r ICR2 showed significant variation in tissues, such as blood, liver, brain, heart and heart. It suggested that Igf-2r imprinting was tissue-specifically regulated. In cloned cattle, DNA methylation at Igf-2r ICR2 was markedly altered in comparison with normal fetus, while patterns of DNA methylation at Igf-2r 3'-UTR (3-terminal untranslated region) were similar to normal fetus, it indicated that 3'-UTR was not significantly altered by cloning procedures, but DNA methylation at the locus of gene imprinting was disrupted and not completely reprogrammed after nuclear transfer.

The immediate upstream sequence of the mouse Ret gene controls tissue-specific expression in transgenic mice

The RET gene is tightly regulated at the transcriptional level during embryo development, however in vitro experiments in cultured cells have failed to clarify the molecular mechanism of cell-type specificity of RET promoter activity. Therefore, we have generated transgenic mice in which the LacZ reporter gene is controlled by murine Ret promoter sequences to clarify in an in vivo model how this transcriptional regulation is achieved. We describe here the results of reporter gene expression in mice in which the transgene contained 380- and 1962-bp sequence upstream of the ATG start codon, derived from the mouse Ret promoter region, fused to the beta-galactosidase coding sequence. Transgenic mice showed well-defined patterns of beta-galactosidase staining obtained with both transgenes, suggesting that they were able per se to direct the reporter gene expression in specific districts, such as cranial ganglia, dorsal root ganglia, the heart and the kidney, partially recapitulating the profile of the endogenous Ret gene. In particular, proper expression in the developing excretory system seemed quite significant when considering that the appropriate regulation was obtained with a very short, 380 bp, fragment of Ret 5' flanking sequence.

N-cadherin is required for neural crest remodeling of the cardiac outflow tract

Cardiac neural crest cells undergo extensive cell rearrangements during the formation of the aorticopulmonary septum in the outflow tract. However, the morphogenetic mechanisms involved in this fundamental process remain poorly understood. To determine the function of the Ca2+-dependent cell adhesion molecule, N-cadherin, in murine neural crest, we applied the Cre/loxP system and created mouse embryos genetically mosaic for N-cadherin. Specifically, deletion of N-cadherin in neural crest cells led to embryonic lethality with distinct cardiovascular defects. Neural crest cell migration and homing to the cardiac outflow tract niche were unaffected by loss of N-cadherin. However, N-cadherin-deficient neural crest cells were unable to undergo the normal morphogenetic changes associated with outflow tract remodeling, resulting in persistent truncus arteriosus in the majority of mutant embryos. Other mutant embryos initiated aorticopulmonary septum formation; however, the neural crest cells were unable to elongate and align properly along the midline and remained rounded with limited contact with their neighbors. Interestingly, rotation of the outflow tract was incomplete in these mutants suggesting that alignment of the channels is dependent on N-cadherin-generated cytoskeletal forces. A second cardiac phenotype was observed where loss of N-cadherin in the epicardium led to disruption of heterotypic cell interactions between the epicardium and myocardium resulting in a thinned ventricular myocardium. Thus, we conclude that in addition to its role in myocardial cell adhesion, N-cadherin is required for neural crest cell rearrangements critical for patterning of the cardiac outflow tract and in the maintenance of epicardial-myocardial cell interactions.

Uptake and distribution of catechins in fetal organs following in utero exposure in rats

BACKGROUND

Although catechins are known to be powerful antioxidants, no reports have shown their transport to fetal organs. We investigated the distribution of catechins in fetal rat organs after maternal exposure to green tea extract (GTE).

METHODS

GTE (550 mg/kg) or water was fed orally to pregnant dams at 15.5 days of gestation, the dams were sacrificed and fetal organs were dissected 0, 0.5, 1, 2, 3, 5, and 8 h later. Catechins and catechin gallates were determined by high-performance liquid chromatography (HPLC) after solid-phase extraction.

RESULTS

In the GTE-treated group, catechins were detected in most of the fetal organs studied, including the brain, eyes, heart, lungs, kidneys and liver but not in the control group. The first peak times (T(max)) were about 0.5-1 h. The maximum concentrations (C(max)) of catechins in the fetal eye were about 2-10 times higher than in the other organs, ranging from 249 pmol/g for epicatechin (EC) to 831 pmol/g for epigallocatechin gallate (EGCG). Catechin gallates were generally more readily taken up by fetal organs than catechins. EGCG had the highest level of uptake according to area under the curve (AUC) plots and the highest C(max) in all organs.

CONCLUSIONS

Various fetal organs had low but significant levels of catechins after GTE intake by the dams, and organ levels were found to be related to catechin structure. EGCG could be a potential candidate for antioxidant supplementation of the fetus in utero.

Isolation of Bovine Cardiomyocytes for Reprogramming Studies Based on Nuclear Transfer

The goal of this study was to establish and validate a protocol for preparing bovine cardiomyocytes from slaughterhouse material for nuclear transfer experiments. The cardiomyocyte was selected because it is a terminally differentiated cell and strongly expresses a unique subset of genes which can be monitored during the reprogramming period. A total of 39 trials were conducted, and an optimized protocol was developed yielding individual contractile cardiomyocytes from 3-5-month-old bovine fetuses The basic protocol involves stabilization of bovine heart tissue for transportation from the slaughterhouse to the laboratory by perfusion with Custodiol. This was followed by an enzymatic dissociation with collagenase in calcium-free medium and yielded individual contractile rod-shaped cardiomyocytes. Subsequent addition of Ca2+ caused the cardiomyocytes to round up which was an essential pre-condition for drawing them into glass transfer pipettes for delivery into the perivitelline space and for efficient electrofusion with cytoplasts derived from in vitro matured bovine oocytes. The use of cardiomyocytes maintained at 37 degrees C in nuclear transfer, resulted in a significantly reduced proportion of blastocysts compared to adult fibroblasts (14.0% versus 32.7%). Storage of cardiomyocytes at 4 degrees C prior to nuclear transfer was not compatible with blastocyst development. It is expected that this system will be valuable for investigating the reprogramming of gene expression which occurs after somatic cell nuclear transfer.

Co-activation of Atrial Natriuretic Factor Promoter by Tip60 and Serum Response Factor

Tat-interactive protein 60 (Tip60) is a member of the MYST family of histone acetyltransferases (HATs). In addition to its HAT domain, Tip contains a heterochromatin-associated protein 1-like chromodomain and a zinc finger-like domain. Several alternative splice variants of Tip60 have been characterized, including full-length Tip60alpha, Tip60beta (which lacks exon V encoded by the Tip60 gene), and Tip55 (which encodes a novel 103-amino-acid C terminus). We report here that isoproteins recognized by a pan-Tip60 antibody are strongly and transiently expressed between embryonic days 8 and 11 in the embryonic mouse myocardium. A functional role for Tip60 isoproteins in cardiac myocyte differentiation is suggested by immunoprecipitation experiments showing that Tip60alpha, Tip60beta, and Tip55 can bind serum response factor (SRF) and by transient transfection assessments showing that Tip60 and SRF cooperatively activate the atrial natriuretic factor promoter. Although this combinatorial activity is inhibited by histone deacetylase 7, it was unexpectedly enhanced by point mutation of the HAT domain. Ablation of the chromodomain from Tip60beta caused derepression. These findings suggest that Tip60 modulates expression of SRF-dependent cardiac genes.

Genes encoding bile acid, phospholipid and anion transporters are expressed in a human fetal cardiomyocyte culture

OBJECTIVES

To establish a human fetal cardiomyocyte culture and to investigate whether the genes that encode transporters that may influence influx or efflux of bile acids are expressed in human fetal cardiomyocytes.

DESIGN

Laboratory study.

SETTING

Imperial College London.

SAMPLE

Six fetal hearts were obtained at the time of termination of pregnancy at 12-13 weeks of gestation and used to generate primary human cardiomyocyte cultures.

METHODS

To confirm the presence of cardiomyocytes, the cells were incubated with monoclonal antibodies to sarcomeric alpha-actinin and anticardiac myosin heavy chain. Real-time reverse transcription polymerase chain reaction was used to establish whether transcripts of genes that may influence bile acid transport are present in the culture (NTCP, BSEP, MDR3, FIC1, MRP2, MRP3, OATP-A, OATP-C, OATP-D, OATP-E) and whether taurocholate administration alters messenger RNA (mRNA) expression.

MAIN OUTCOME MEASURES

Relative mRNA expression of genes of interest.

RESULTS

Real-time polymerase chain reaction demonstrated the presence of mRNA for BSEP, MDR3, FIC1, OATP-C, OATP-D and OATP-E in fetal heart. Four transcripts remained in the cardiomyocyte culture (BSEP, MDR3, FIC1 and OATP-D), and we demonstrated the influence of taurocholate on gene expression.

CONCLUSIONS

We have developed an in vitro model of the fetal heart that may be used for studies of the cardiac effect of endobiotics, e.g. bile acids, or of specific agents that may be used to treat the mother or fetus in pregnancy.

Left-right lineage analysis of the embryonic Xenopus heart reveals a novel framework linking congenital cardiac defects and laterality disease

The significant morbidity and mortality associated with laterality disease almost always are attributed to complex congenital heart defects (CHDs), reflecting the extreme susceptibility of the developing heart to disturbances in the left-right (LR) body plan. To determine how LR positional information becomes ;translated' into anatomical asymmetry, left versus right side cardiomyocyte cell lineages were traced in normal and laterality defective embryos of the frog, Xenopus laevis. In normal embryos, myocytes in some regions of the heart were derived consistently from a unilateral lineage, whereas other regions were derived consistently from both left and right side lineages. However, in heterotaxic embryos experimentally induced by ectopic activation or attenuation of ALK4 signaling, hearts contained variable LR cell composition, not only compared with controls but also compared with hearts from other heterotaxic embryos. In most cases, LR cell lineage defects were associated with abnormal cardiac morphology and were preceded by abnormal Pitx2c expression in the lateral plate mesoderm. In situs inversus embryos there was a mirror image reversal in Pitx2c expression and LR lineage composition. Surprisingly, most of the embryos that failed to develop heterotaxy or situs inversus in response to misregulated ALK4 signaling nevertheless had altered Pitx2c expression, abnormal cardiomyocyte LR lineage composition and abnormal heart structure, demonstrating that cardiac laterality defects can occur even in instances of otherwise normal body situs. These results indicate that: (1) different regions of the heart contain distinct LR myocyte compositions; (2) LR cardiomyocyte lineages and Pitx2c expression are altered in laterality defective embryos; and (3) abnormal LR cardiac lineage composition frequently is associated with cardiac malformations. We propose that proper LR cell composition is necessary for normal morphogenesis, and that misallocated LR cell lineages may be causatively linked with CHDs that are present in heterotaxic individuals, as well as some 'isolated' CHDs that are found in individuals lacking overt features of laterality disease.

Maternal diabetes and the fetal heart

Maternal diabetes mellitus significantly affects the fetal heart and fetal-placental circulation in both structure and function. The influence of pre-conceptional diabetes begins during embryonic development in the first trimester, with altered cardiac morphogenesis and placental development. It continues to have an influence on the fetal circulation through the second and third trimesters and into the perinatal and neonatal period.